Use of shear nails connector to improve UHPC-NC interface bonding performance of functional graded concrete components in offshore structure

Use of shear nails connector to improve UHPC-NC interface bonding performance of functional graded concrete components in offshore structure | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Use of shear nails connector to improve UHPC-NC interface bonding performance of functional graded concrete components in offshore structure Jianmin HE, Xiaodong WEN, Wenbo GONG This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4954119/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This paper designed functional graded concrete components to meet the bearing and durability improvement subjected to marine environment, where the normal concrete (NC) core was used to bear loads and was protected by the ultra-high-performance concrete (UHPC) permanent formwork from chloride ion permeability. By inspiring of transfer printing technology and controlled permeability formwork, a new simple shear nails construction treatment on UHPC formwork was proposed for establishing a connection between UHPC formwork and NC core. In order to study shear nails construction measures on the interface bonding performance between UHPC and NC, UHPC-NC bonding specimens were subjected to double-sided shear tests using the density and distribution spacing of shear nails on the surface of UHPC formwork as experimental parameters. The results showed when the shear nail density ρ ≥ 6.4, the specimen failure transformed into axial compression failure of NC core. The shear stress on the bonding surface increases approximately parabolic with the density of shear nails. Under the same density, the shear stress on the bonding surface of specimens with larger nail spacing was enhanced by 19.04%-41.74% compared to specimens with smaller spacing. The results show that the density and the distribution spacing of shear nails have a significant impact on the shear strength of the UHPC-NC surface. The influence of shear nail density on the shear strength of UHPC-NC interface is greater than that of the distribution spacing of shear nails. Based on comparing and analyzing the existing shear strength models of UHPC-NC bonding surfaces, fully considering the failure mode of bonding surfaces, a calculation formula for the shear strength of prefabricated UHPC-NC bonding surfaces was established. The calculation results have a high degree of agreement with experimental values, which can provide reference for the interface design of UHPC-NC composite specimens. UHPC Permanent formwork Shear resistance performance Interfacial bond performance Shear nail connector numerical formula Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction Along with urban sprawl and a severe shortage of land resources, marine resources have become an inevitable trend in the development. As this trend continues, there are an increasing number of coastal engineering. However, ocean engineering usually shows durability issues in harsh marine environments where dry-wet cycles, corrosive substances such as SO 4 2− and Cl − result in the corrosion of steel bars. Recently, functionally graded concrete (FGC) has been adopted to improve the durability of these structures. FGC is a cementitious composite that the material compositions are spatially varied by two or more mixes [ 1 – 2 ] , and material properties are engineered to change locally in a controlled way to meet the actual need. Wen et al. [ 2 ] investigated the possibility of protecting steel reinforcement through an external layer of low-permeability concrete. FGC can be divided into layered or continuously graded concrete. The former, the layered graded concrete is further classified as fresh-on-hardened and fresh-on-fresh layered graded concrete according to the sequence of casting operations. In fresh-on-hardened layered graded concrete, new layers of fresh concrete are added when previous layers have set and hardened, while different concretes are mixed and cast simultaneously in fresh-on-fresh layered graded concrete. Fresh-on-hardened layered graded concrete is more widely adopted than fresh-on-fresh layered graded concrete to achieve functional gradation due that the production process of latter is more complicate by requiring multiple concrete mixes to be mixed at the same time [ 3 ] . In recent years, many scholars have proposed permanent formworks [ 4 – 7 ] . These formworks are specially designed to contain the fresh concrete, mold it to the required dimensions and remain in site throughout the service life of structures. Using permanent formworks can simplify construction processes, save the construction time, and reduce the engineering cost [ 4 ] . Therefore, replacing traditional construction formworks with permanent formworks is gaining its significance. If permanent formworks techniques could be utilized in graded concrete element, it allows the geometry of the layers and the location of each interface to be accurately monitored during production. Ultra-high-performance concrete (UHPC), as a new type of cement-based composite material developed in recent years, has high strength, high density, high toughness, high durability, and good ductility [ 8 – 9 ] . At the same time, it also has good bonding performance with steel bars [ 10 ] . UHPC, as a permanent template material, can improve the load-bearing capacity of the template, reduce the thickness and weight of the template, and has received widespread attention. In the UHPC permanent formwork structure system, the bonding interface between the formwork and cast-in-place ordinary concrete is the weakest link in the composite structure. Therefore, domestic and foreign scholars have conducted experimental research on the interface shear performance of UHPC-NC composite components. For example, Munoz et al. [ 11 ] conducted oblique shear and splitting experiments, and studied the bonding performance between the two materials under different conditions such as concrete wetness and surface roughness. The experimental results show that regardless of the exposure degree of freeze-thaw cycles, the age of composite specimens, the roughness of concrete substrates, and different loading schemes, the bonding performance between UHPC and NC is sufficient for the requirements of bridge cover layer. Bassam et al. [ 12 ] conducted oblique shear and splitting experiments to study the adhesive strength and permeability between the two materials. The experimental results show that the bonding strength between the UHPC layer and the NC matrix is high, and the impermeability of the UHPC-NC interface are good, which can significantly improve the impermeability of the concrete matrix. Wang Xingwang [ 13 ] conducted interface shear tests on UHPC-NC structures and studied the stress and failure modes of the reinforcement model using ANSYS numerical analysis method. Husam et al. [ 14 ] conducted interface direct tensile experiments and determined the cohesion between UHPC and high-strength concrete using the roughness of the material surface as a variable, and deduced the friction coefficient between the materials. Due to the smooth surface of the UHPC template, Zhang Rui et al. [ 15 ] uniformly distributed pits on UHPC templates and improved interface adhesion by embedding shear keys into the pits with post poured concrete. Wang Dehong et al. [ 16 ] set grooves on the surface of the template to improve its roughness, and established a calculation formula between keyway density and bonding surface shear stress through double-sided shear tests. However, these processing methods form ordinary concrete shear keys, exhibiting NC shear failure [ 17 ] , and therefore the improvement is limited. In summary, this article proposes to set up UHPC shear stubs for prefabricated templates, which can shift from NC failure to UHPC shear when subjected to loads, further improving the interfacial bonding performance of UHPC template NC core composite specimens. However, there is little research in this area. Therefore, this article conducts double-sided shear tests on UHPC-NC to study the influence of shear nail density and distribution spacing on interface failure modes and shear bonding performance, and establishes a formula for calculating the shear strength of interface bonding, in order to provide useful reference for the design and construction of UHPC-NC composite specimens. 2. Experiment Overview 2.1 Design and Fabrication of Specimen To study the impacts of shear nails on interface bonding performance, density and distribution spacing of shear nails on the surface of UHPC formwork to be more specific, double-sided shear tests have been carried out, design parameters can be found in Table 1 . Each specimen consists of UHPC formwork and normal concrete inner core. Table 1 Specimen design No. Outer diameter of shear nail Height of shear nail Number of shear nail Density of shear nail N0 0 0 0 0 N1 50 30 1 0.533 N2 50 30 2 1.067 N3 50 30 3 1.6 N4K 50 30 4 2.133 N6K 50 30 6 3.2 N8K 50 30 8 4.267 N12K 50 30 12 6.4 N18H 50 30 18 9.6 N4M 50 30 4 2.133 N4K 50 30 4 2.133 N8M 50 30 8 4.267 N8K N12M 50 50 30 30 8 12 4.267 6.4 N: Sticking; number: number of nails applied; K: wide distance between nails; M: narrow distance between nails UHPC was made up of Grade 52.5 ordinary Portland cement, I grade fly ash, silica fume, quartz powder, quartz sand, steel fiber, polycarboxylate superplasticizer and water. Mixture proportion of the UHPC is shown in Table 2 . The volume ration of steel fibers to UHPC is 2.5%. According to GB/T 50081 − 2019, the slump-flow of UHPC was tested, and the result was 720mm. In accordance with GB/T 31387 − 2015, the compressive strength of UHPC was measured using cube specimens with 100 mm×100 mm × 100 mm size, and the result was 142.3MPa. According to GB/T 50081 − 2019, the tensile properties of UHPC were tested using dog bone-shaped specimens with a cross-section of 100 mm × 50 mm size, and the result was 8.3MPa. Table 2 Mix proportion of UHPC P.O 52.5 cement Silica fume Fly ash Quartz sand Quartz powder water Superplasticizer Steel fiber/% 1 0.23 0.15 1.0 0.08 0.25 0.025 0.228 Table 3 Mix proportion of C30 concrete P.O 42.5 cement II-Fly ash Coarse aggregate Fine aggregate water 1 0.43 4.92 3.14 0.71 Normal concrete with a designed compressive strength grade of C30 was used for this study. The mixture was mainly consisted of ordinary Portland cement, river sand with a fineness modulus of 2.3, II grade fly ash, gravel with maximum size of 31.5mm, naphthalene superplasticizer and water. Table 3 list the mix proportion of normal concrete in this study. The measured compressive strength of the concrete standard cubic specimen was 38.5MPa. The computational formula for the density of shear nails \(\:\:\) is as follows [ 18 ] : $$\:\begin{array}{c}\rho\:=\:\frac{n{V}_{u}}{S}\left(1\right)\end{array}$$ Where \(\:\rho\:\) is the density of shear nails; \(\:n\) is number of shear nails; \(\:{V}_{u}\) is volume of single shear nail; \(\:S\) is area of bonding surface. 1) Casting of UHPC formwork By inspiring of transfer printing technology, a new simple shear nails processing method on UHPC formwork inner surface was proposed for establishing a connection between UHPC formwork shell and NC core. Moreover, in order to identify the impact of UHPC formwork's shear nails structural measures on interface bonding performance between UHPC and post-poured NC, formworks were treated in different ways at the time of UHPC pouring, as well as no treatment. Formworks were treated as follows: the wooden mold lined with silicone sheet (there are 30mm-deep holes distributed in different positions on the sheet) were adopted to make UHPC formworks with different numbers of shear nails and placed in different positions; for specifics, see Fig. 1 . By changing the surface of silicone sheet, different shear nails structure of UHPC formwork could be realized, as shown in Fig. 2 . Afterwards, fresh UHPC was stirred and poured into a prepared mold. The poured UHPC formwork was rested quietly and demolded after 24 hours, and then placed to a standard curbing box for 28 days. 2) Casting of specimen The prefabricated UHPC formwork was installed in the prepared mold, with the UHPC formwork on both sides clinging to the inner walls of mold, and then normal concrete was poured in the middle. In order to ensure the quality of pouring, when each 1/3 concrete was poured, it was vibrated by a vibrating rod. After settling for 24h, the mold was removed, and specimen was cured in standard curing box for 28d. Process flow is shown in Fig. 2 . 2.2 Test Loading Device and Measuring Point Arrangement The testing device consists of 200t POPWIL static pressure tester, 60L concrete mixer, Donghua static collector, industrial camera, digital collector, electro-hydraulic loading system and displacement meter, as shown in Fig. 3 . The strain distribution law of UHPC formwork and concrete core can be obtained by strain sensors on the surfaces of prefabricated UHPC and concrete. The arrangement scheme for such strain gauges is as follows: ten strain sensors are separately attached to UHPC and NC near interface to obtain the strain values of UHPC slab and concrete length-wise. four sensors are arranged at each cross section, as shown in Fig. 4(a) ; the average value of sensors at the same cross section is taken as the strain values of UHPC and NC near interface; for instance, the strain values of UHPC and NC at 1–1 cross section near interface are denoted as U1 and C1, respectively. Moreover, displacement meters are separately inserted on UHPC and NC to obtain the slip values of UHPC formwork and concrete core. 4 and 6 displacement meters are inserted on UHPC formwork and NC core, respectively, including 2 displacement meters on NC at opposite angles of A-A cross-section and 2 displacement meters on UHPC and NC in the centers of B-B cross-section and C-C cross-section, as shown in Fig. 4(b) . Worth noticing is that the average value of displacement meters at the same cross-section is taken as the displacement values of UHPC, NC at such cross-section; for instance, the displacement values of UHPC and NC at B-B cross-section are denoted as UB and C B , respectively. Preloading is conducted before test; loading rate is controlled at 5KN/min; preloading ends at 5KN, while in the test round, the loading rate is controlled at 5KN/min until specimen fails. 3. Experiment Result and Its Analysis 3.1 Failure Mode Table 4 presents the test results of the ultimate bearing capacity, interface shear stress, and failure mode of the specimens. When the UHPC template is not equipped with nails, the interface of the UHPC-NC composite specimen experiences shear failure of the bonding surface after being sheared, and the cross-section is smooth and flat. After the shear nail construction is set on the surface of the template, its failure mode presents three types: Table 4 Experimental results Serial number ultimate bearing capacity (P u /KN) interfacial shear stress (MPa) failure mode N0 100.2 1.67 Shear failure between UHPC and NC N1 130.2 2.17 A N2 149.4 2.49 A N3 185.8 3.10 A N4K 205.99 3.43 B N6K 273.2 4.55 B N8K 288 4.8 B N12K 356.53 5.94 C N18K 393.6 6.56 C N4M 145.1 2.42 B N4K 205.99 3.43 B N8M 206 3.43 B N8K 288 4.8 B N12M 299.6 4.99 B A type: UHPC-NC bonds and nails shear failure. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Small shear cracks first appear on the bonding surface near the free end and propagate along the bonding surface until encounters shear nails. Afterwards, the interface shear performance of composite specimens is mainly provided by shear nails. Due to insufficient density of shear nails on the template, UHPC shear nails were cut along the root. Finally, shear failure occurred on the bonding surface and shear nails of the composite specimen. B type: UHPC-NC bonding surface shear failure, UHPC shear nail shear failure or peeling off. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Shear failure first occurs in the free end, and as the load increases, the force continues to propagate along the bonding surface until it encounters a group of shear nails. Afterwards, the interface shear performance of the composite specimen is mainly provided by the shear nail group. Under the action of the shear nail group, the force continues to propagate along the bonding surface until the UHPC shear nail is sheared, especially near the free end. In addition, some force develops obliquely to the NC near the shear nail and micro cracks appear. Finally, the NC adhered to the UHPC shear nail is peeled off together. C type: Shear failure of UHPC-NC bonding surface and axial compression failure of NC cores. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Shear failure first occurs near the free end, and as the load increases, the force continues to propagate along the bonding surface until it encounters the shear nail group. If the density of shear nails is large enough, under the action of shear nail group, cracks will develop diagonally to the loading point at NC, and finally exhibit NC axial compression failure. These three typical failure modes are shown in Fig. 5 , when 2.133 ≤ shear nail density ρ<6.4, the specimen undergoes a transition from A type failure to B type failure. When the shear nail density ρ ≥ 6.4, the specimen failure transformed into C type failure. 3.2 Load-strain relation curve Figure 6 shows specimen's load-strain relation curves under different parameters. According to Fig. 6 , the development and distribution of strain on interface under different treatments are quite similar. In the initial stage of loading, only the sensors near the free end had data changes, in which case, the interfacial chemical action of UHPC formwork and NC core served to bear load, whose load-strain relation curve appeared to be linear. As load gradually increased, shear nails and aggregate on the UHPC-NC bonding surface started to act, so the difference between the free end's strain and the loading end's strain gradually increased until failure. In the whole process of loading, strain increased linearly with load. As shown by the linearity stages on the load-strain curve of UHPC-NC specimens, the slope of curve from the free end to the loading end increased, suggesting that strain was gradually delivered from the free end to the loading end; as it reached the ultimate load, specimen failure quickly occurred. 3.3 Load-slip relation curve With displacement meters on UHPC and NC, the load-slip curve at A, B and C cross-sections in UHPC and NC's effective bonding sections are recorded as shown in Fig. 7 . After it reached the peak load, shear specimen was quickly separated, so there was no descent part of the curve. The load-slip curves for various specimens prepared with different construction measures showed a same pattern. In the initial stage of loading, UHPC and NC at interface deformed synergistically, in which case, the shear force at the prefabricated UHPC-NC interface was borne by the chemical action. As load continued to increase, the mechanical meshing force between shear nails and aggregate started to play a role, so shear strength increased and slip increased with load linearly. As the mechanical meshing force between shear nails and aggregate continued playing a role until cracked, slip increased nonlinearly with load. When it reached the ultimate load, interfacial bonding failed quickly. As shown in Fig. 7 , subject to the same load, compared with curves C B and U B , the difference in slippage of curves C C and U C were large, so failure at specimen interface should occur at the free end first. The difference in slippage between UHPC and NC at cross-section C# can be used to derive the relative displacement of C# cross-section. Figure 8 showed the load-relative displacement curve of composite specimen under different constructions. As indicated by Fig. 8(a) , the ultimate bearing capacity of specimen N8K was larger than that of N4K, but smaller than that of N12K. Subjected to the same load, relative displacement on the bonding surface of N8K was larger than that of N12K, but smaller than that of N4K. This showed that as the density of shear nails increased ( \(\:\rho\:\le\:9.6\) ), the bond performance at specimen's bonding surface became better. The impact of shear nail interval on the load-slip curve was shown in Fig. 8(b) . As shown in the figure, when \(\:\rho\:=4.267\) , the ultimate bearing capacity of N8K is higher than that of N8M. N8K's relative displacement was smaller subject to the same load, so N8K had better bond performance. Likewise, specimen with density \(\:(\rho\:=6.4)\) showed same pattern. The ultimate bearing capacity of N12K was larger than N12M. N12K's relative displacement was smaller subject to the same load, so N12K had better bond performance. This suggested that with same density of shear nails, increasing shear nail interval can further improve the interfacial bond performance. 3.4 Interfacial bonding shear strength The bonding shear strength of the prefabricated UHPC-NC specimen is calculated according to Equ. (2). $$\:\begin{array}{c}{\tau\:}_{u}=\frac{P}{2A}\left(2\right)\end{array}$$ Where, \(\:{\tau\:}_{u}\) is the bonding shear strength; \(\:P\) is the shear peak load; \(\:A\) is the area of the bonding surface, A = 60000 mm 2 . The bonding shear strength of the prefabricated UHPC-NC is calculated according to Equ.(2), as shown in Fig. 9 . From Fig. 9 , under the same condition, the bonding shear strength of UHPC-NC composite specimen increased with the density of shear nails, and the bonding shear strength features parabolic relation with the density of shear nails. Because as the density of shear nails at prefabricated UHPC increased, the mechanical meshing force at the bonding surface increased, thus increasing the bonding shear strength. With the same grooving density, the bonding shear strength of prefabricated UHPC-NC and the impact of shear nail interval were further studied, with its result shown in Fig. 10 . According to Fig. 10 , the bonding shear strength of prefabricated UHPC-NC increased with shear nail interval. The bonding shear strength of specimen N4K was 41.74% higher than that of N4M, and the bonding shear strength of N8K was 39.94% higher than that of N8M, and the bonding shear strength of N12K was 19.04% higher than N12M. This is because as shear nail interval increased, the interlocking mechanism of shear nails and aggregate increased and the interfacial bonding shear strength increased. 3.5 shear strength of single shear nail Furthermore, as indicated by the results of shear strength tests of single shear nail, with different shear nail densities, the relation between the shear strength of the bonding surface and the shear nail density of prefabricated UHPC was parabolic. The bonding strength of superposed concrete structure comes from the mechanical meshing force of the bonding surface, its chemical action force and Van der Waals force [ 19 – 20 ] . The mechanical meshing force is generated by the interfacial interaction on uneven bonding surface; generally, the mechanical meshing force is the main part of interfacial bonding force. Chemical action force is generated by chemical reaction between two materials on the bonding surface. Van der Waals force is caused by the mutual attraction of molecules between crystals; crystal's intermolecular distance in concrete is so large that Van der Waals force is negligible [ 16 ] . Therefore, this paper assumes that the bonding force fully comes from mechanical meshing force and chemical action force. When there was no shear nail on UHPC ( \(\:\rho\:=0\) ), its formwork surface was smooth, and upon subjected to load, interface encountered shear failure. Failure surface was relatively flat, whose interfacial bond strength fully came from chemical action. After shear nails were placed on formwork surface ( \(\:\rho\:＞0\) ), the interfacial bonding strength of specimen came from mechanical meshing and chemical action. Compared with the specimen with smooth formwork, the composite specimen with shear nail also encountered the mechanical meshing force. So, the specimen's mechanical meshing force [ 16 ] can be derived by discounting the corresponding shear capacity of the corresponding smooth interface from that of composite specimen’s shear capacity. The mechanical meshing force of single shear nail can be obtained by dividing the obtained mechanical meshing force by the number of shear nails, with its result shown in Table 5 . According to Table 5 , as the density of shear nails increased, the shear strength of single nail gradually decreased. The causes may be as follows, (1) when the density of shear nail was excessively large, the bonding interface was dispersed, interfacial chemical bonding actions can't develop concurrently, resulting in decreasing effective bonding area, and (2) when the density of shear nails was excessively large, the interlocking mechanism between shear nails and aggregate failed to fully develop. Both causes led to a decrease in both the number of effective shear nails within interface and mechanical meshing force. Therefore, the density of shear nails on UHPC formworks shall be controlled to a reasonable level in real practice. Table 5 The shear strength of a single shear nail Serial number Nail Density Shear strength /MPa Discounted shear strength /MPa Shear strength of one single nail /MPa N0 0 1.67 1.67 / N1 0.533 2.17 0.72 0.72 N2 1.067 2.49 1.26 0.63 N3 1.6 3.10 2.09 0.70 N4K 2.133 3.43 2.63 0.66 N6K 3.2 4.55 4.19 0.70 N8K 4.267 4.8 4.88 0.61 N12K 6.4 5.94 6.89 0.57 N18K 9.6 6.56 8.82 0.49 4. Calculation of interface shear strength With respect to calculation of shear strength of the bonding surface of superposed member, domestic and foreign scholars have conducted extensive research and analysis, and figured out the corresponding calculation method. As specified in the Code for Design of Concrete Structures (GB50010-2010), regarding non-reinforced superposed slab, if there is compliance with the provision relating to construction in subparagraph 10.6.15 (Roughness of Superposed Cross-section) of the Code, the shear strength of its superposed surface shall be not higher than 0.4 N/mm 2[ 21 ] . Foreign codes such as Eurocode 2, ACI 318 [ 22 – 23 ] consider the bonding force, aggregate interlocking effect and the role of anti-shear pins, it is stipulated as follows: 1) In Eurocode 2 (1992), the shear strength \(\:{{\tau\:}}_{\text{u}}\) of concrete bonding surface can be calculated according to Equ. (3): $$\:\begin{array}{c}{\tau\:}_{u}=c{f}_{t}+\mu\:{\sigma\:}_{n}+\rho\:{f}_{yd}\left(\mu\:sin\alpha\:+cos\alpha\:\right)\le\:0.5v{f}_{cd}\left(3\right)\end{array}$$ Where, \(\:c\) and \(\:\mu\:\) represent cohesion coefficient and friction coefficient relating to the superposed surface construction mode, 0.35 and 0.6 are taken for the natural bonding surface without special treatment, 0.45 and 0.7 are taken for rough bonding surface; \(\:{f}_{t}\) is the lowest tensile strength of two materials; \(\:\rho\:\) is reinforcement ratio of shear reinforcement on superposed surface; \(\:{f}_{yd}\) is the design value of yield strength of shear reinforcement on superposed surface; \(\:{\sigma\:}_{n}\) is the minimum value of normal positive pressure to which interface is subject; \(\:{f}_{cd}\) is the design value of concrete compressive strength; \(\:v\) is strength reduction factor, for which 0.6 is taken, if \(\:{f}_{ck}\le\:60\) MPa, the requirement \(\:0.9-{f}_{ck}/200\ge\:0.5\) shall be satisfied, \(\:{f}_{ck}\) is the standard value of compressive strength of concrete's axial compressive strength. 2) In the Code ACI 318M-05 (2005), when the bonding surface is a natural rough surface and there is no or little shear reinforcement, the shear capacity of superposed surface is as follows: $$\:\begin{array}{c}{V}_{nh}=0.55{b}_{v}d\left(4\right)\end{array}$$ Where, \(\:{V}_{nh}\) is the shear capacity of superposed surface, \(\:{b}_{v}\) , \(\:d\) represent the width and length of superposed surface, separately. 3) In the Code AASHTO LRFD (2005), the nominal shear capacity of superposed surface is as follows: $$\:\begin{array}{c}{V}_{u}=c{A}_{cv}+\mu\:\left({A}_{vf}{f}_{y}+{P}_{c}\right)\le\:\text{min}\left(0.2{f}_{c}^{{\prime\:}}{A}_{cv}，5.5{A}_{cv}\right)\left(5\right)\end{array}$$ Where, when concrete is later poured onto the hardened rough concrete surface, \(\:c\) =0.7, \(\:\mu\:=1\) ; \(\:{A}_{cv}\) is the area of superposed surface; \(\:{A}_{vf}\) is the area of shear reinforcement; \(\:{f}_{y}\) is the yield strength of shear reinforcement; \(\:{P}_{c}\) is the pressure perpendicular to superposed surface; \(\:{f}_{c}^{{\prime\:}}\) is concrete's compressive strength, whichever is lower. The interfacial bonding shear strength of fabricated UHPC-NC specimen in this test was calculated according to the above codes. The tensile strength \(\:{f}_{t}\) of C30 was 2.348 MPa, which was calculated according to the relationship [ 24 ] between compressive strength and tensile strength. NC compressive strength \(\:{f}_{cu}\) in this study was the measured value of 150mm×150mm×150mm cubic specimen, which was different from the Formula's compressive strength \(\:{f}_{c}^{{\prime\:}}\) , \(\:{f}_{c}^{{\prime\:}}=0.79{f}_{cu}\) [ 24 ] .C30's compressive strength \(\:{f}_{c}^{{\prime\:}}\) was taken as 30.42MPa. Comparison between the normalized value of prefabricated UHPC-NC's bonding shear strength and experimental value were shown in Table 6 . Table 6 Experimental results No Measured value \(\:{\tau\:}_{u}\) /MPa Eurocode 2 \(\:{\tau\:}_{1}\) /MPa ACI 318M-05 \(\:{\tau\:}_{2}\) /MPa AASHTO LRFD \(\:{\tau\:}_{3}\) /MPa GB 50010 − 2010 \(\:{\tau\:}_{4}\) /MPa \(\:{\tau\:}_{u}/{\tau\:}_{1}\) \(\:{\tau\:}_{u}/{\tau\:}_{2}\) \(\:{\tau\:}_{u}/{\tau\:}_{3}\) \(\:{\tau\:}_{u}/{\tau\:}_{4}\) N0 1.67 0.822 0.55 0.7 0.4 2.032 3.306 2.385 4.175 N1 2.17 1.057 0.55 0.7 0.4 2.053 3.945 3.1 5.425 N2 2.49 1.057 0.55 0.7 0.4 2.356 4.527 3.557 6.225 N3 3.10 1.057 0.55 0.7 0.4 2.933 5.636 4.429 7.75 N4K 3.43 1.057 0.55 0.7 0.4 3.245 6.236 4.9 8.575 N6K 4.55 1.057 0.55 0.7 0.4 4.305 8.273 6.5 11.375 N8K 4.8 1.057 0.55 0.7 0.4 4.541 8.727 6.857 12 N12K 5.94 1.057 0.55 0.7 0.4 5.620 10.8 8.486 14.85 N18K 6.56 1.057 0.55 0.7 0.4 6.206 11.927 9.371 16.4 N4M 2.42 1.057 0.55 0.7 0.4 2.289 4.4 3.457 6.05 N4K 3.43 1.057 0.55 0.7 0.4 3.245 6.236 4.9 8.575 N8M 3.43 1.057 0.55 0.7 0.4 3.245 6.236 4.9 8.575 N8K N12M N12K 4.8 4.99 5.94 1.057 1.057 1.057 0.55 0.55 0.55 0.7 0.7 0.7 0.4 0.4 0.4 4.541 4.721 5.620 8.727 9.073 10.8 6.857 7.129 8.486 12 12.475 14.85 According to data in the table, the result of Eurocode 2 formula is closest to experimental value, while results from the other three formulas greatly differ from experimental value. However, Eurocode 2 formula does not consider the impact from the density of shear nails on interfacial shear stress. When the density of shear nails is excessively high, such formula is no longer applicable. Thus, this paper puts forward a new parameter \(\:\gamma\:\) , which relates to UHPC's density of shear nails, and develops the following proposed formula. This equation does not consider the interfacial normal pressure and shear reinforcement. $$\:\begin{array}{c}{\tau\:}_{u}=\gamma\:{f}_{t}\left(6\right)\end{array}$$ Where, \(\:{\tau\:}_{u}\) = interface shear strength between UHPC formwork and NC core; \(\:\gamma\:\) = parameter relating to UHPC's density of shear nails; \(\:{f}_{t}\) = NC's tensile strength. In real practice, Eq. (6) can be expressed in the following way based on the conversion relation between concrete's axial tension strength \(\:{f}_{t}\) and cube compressive strength \(\:{f}_{cu}\) : $$\:\begin{array}{c}{\tau\:}_{u}=0.395\gamma\:{f}_{cu}^{0.55}\left(7\right)\end{array}$$ According to experimental result, the relationship between \(\:\gamma\:\) , from Eq. (7), and the density of shear nails \(\:\rho\:\) can be written as \(\:\gamma\:=-0.0174{\rho\:}^{2}+0.3425\rho\:+0.5402,\rho\:\le\:9.6\) , Correlation index \(\:\:{R}^{2}=0.9935\) , suggesting that the such formula is reliable. Combining the above equation with Eq. (7), correlation-ship between interfacial shear stress of prefabricated UHPC-NC and the density of shear nails can be arrived, as shown in Eq. (8). $$\:\begin{array}{c}{\tau\:}_{u}=（-0.006873{\rho\:}^{2}+0.135288\rho\:+0.213379）{f}_{cu}^{0.55}\left(8\right)\end{array}$$ Where, \(\:\rho\:\) is density of shear nails; \(\:{f}_{cu}\) is cube compressive strength. According to Table 7 , the model built in this paper was used to calculate the interface shear strength in references [16] and references [25]. Results showed that the ratio of experimental value to calculated value was smaller than 1, but discreteness was low, for instance, experimental value/calculated value in references [16] fluctuate around 0.548, while that in references [25] it fluctuated around 0.771, correlation index R 2 = 0.9935. Table 7 Calculated values of corrected model and experimental values for interface shear strength Specimens in this paper Calculated values (experimental value / calculated value)/MPa Specimens in references [16] Calculated values (experimental value / calculated value) /MPa Specimens in references [25] Calculated values (experimental value / calculated value) /MPa N0 1.589(0.951) SB3 2.911(0.436) ZJ-Z-1-1 2.830(0.735) N1 2.112(0.973) SB4 3.622(0.513) ZJ-Z-1-2 3.935(0.788) N2 2.606(1.047) SB5 3.988(0.512) ZJ-Z-1-3 4.823(0.647) N3 3.071(0.991) SC3 4.014(0.605) ZJ-Z-2-2 3.935(0.795) N4K 3.506(1.022) SC4 4.990(0.573) ZJ-Z-2-3 4.823(0.889) N6K 4.289(0.943) SC5 5.499(0.556) / / N8K 4.957(1.033) SD3 5.152(0.595) / / N12K 5.940(1.000) SD4 6.124(0.581) / / N18K 6.542(0.997) SD5 6.740(0.558) / / The cause for the fact that the calculated values were higher than the experimental results in references [16] and references [25] is as follows. The model built in this paper is based on the case where UHPC's shear nails on the bonding surface are sheared, while the interfacial failure mode in references [16] is that NC is sheared, and the failure mode in references [25] is UHPC-NC's composite failure (bonding interface and NC failure), thus the errors in theoretical calculation. Therefore, it is necessary to consider the failure mode on the bonding surface of UHPC-NC's composite members, and introduce correction factor a to Eq. (8). When failure mode appears to be the case where NC is sheard, the average value is 0.584, which is the experimental value/calculated value in references [16]. When failure mode is bonding surface failure, the average value is 0.832, which is the experimental value/calculated value in references [25]. When failure mode appears to be the case where UHPC is sheard, a = 1. Therefore, based on Eq. (8), considering different bonding surface failure modes, and the calculation formula for shear strength of the bonding surface of UHPC-NC's composite specimen is developed: $$\:\begin{array}{c}{\tau\:}_{u}=（-0.006873{\rho\:}^{2}+0.135288\rho\:+0.213379）a{f}_{cu}^{0.55}\left(8\right)\end{array}$$ Where, \(\:\rho\:\) =density of shear nails; \(\:{f}_{cu}\) =cube compressive strength; a = the parameter of bonding surface failure mode; when interface is the case where NC is sheared, a = 0.584; when interface is bonding surface and NC failure, a = 0.832; when interface is the case where UHPC's shear nails are sheared, a = 1. Equation (8) was used to calculate shear strength in references [16] and references [20], the results and experimental value / calculated value ratio are listed in Table 8 . From Table 8 , experimental-to-calculated ratio for references [16] was 1.0040, mean square error and coefficient of variation were 0.0936 and 0.0932 respectively, while experimental-to-calculated ratio for references [25] = 1.0002, mean square error and coefficient of variation were 0.1032 and 0.1032 respectively. Calculation agreed well with experiment, which suggest the theoretic model can be used to predict and evaluate the bonding shear stress of UHPC-NC interface. Table 8 Calculated and experimental values of the modified model of shear strength of bonded surface of UHPC-NC specimens after the introduction of parameters Specimens in this paper Calculated values (experimental value / calculated value)/MPa Specimens in references [11] Calculated values (experimental value / calculated value)/MPa Specimens in references [20] Calculated values (experimental value / calculated value)/MPa N0 1.589(1.051) SB3 1.648(0.781) ZJ-Z-1-1 2.181(0.954) N1 2.111(1.028) SB4 1.959(0.948) ZJ-Z-1-2 3.033(1.022) N2 2.606(0.955) SB5 2.157(0.946) ZJ-Z-1-3 3.717(0.839) N3 3.070(1.010) SC3 2.273(1.068) ZJ-Z-2-2 3.033(1.032) N4K 3.505(0.979) SC4 2.702(1.058) ZJ-Z-2-3 3.717(1.154) N6K 4.289(1.061) SC5 2.975(1.028) / / N8K 4.956(0.969) SD3 2.787(1.100) / / N12K 5.940(1.000) SD4 3.313(1.074) / / N18K 6.544(1.002) SD5 3.648(1.033) / / 5. Conclusion (1) When the UHPC template is not equipped with studs, the interface of the UHPC-NC composite specimen experiences shear failure of the bonding surface after being sheared, and the cross-section is smooth and flat. After the shear nail construction is set on the surface of the template, its failure mode presents three situations. Namely, A type failure: shear failure of UHPC-NC bonds and nails; B type failure: UHPC-NC bonding surface shear failure, UHPC shear nail shear failure or peeling off; C type failure: Shear failure of UHPC-NC bonding surface and axial compression failure of NC core. when 2.133 ≤ shear nail density ρ<6.4, the specimen undergoes a transition from A type failure to B type failure. When the shear nail density ρ ≥ 6.4, the specimen failure transformed into C type failure. (2) The interface shear strength between UHPC formwork and NC core is 1.67-6.56MPa. The shear stress between the bonding surfaces mainly comes from mechanical biting force and chemical bonding effect. Reasonably setting shear forces between precast UHPC-NC bonding surfaces can fully utilize the strength of precast UHPC and significantly increase the shear stress between bonding surfaces. (3) The density and distribution spacing of prefabricated UHPC shear nails have a significant impact on the shear strength of prefabricated UHPC-NC bonding surface, and the influence of nail density on the shear strength of the bonding surface is greater than that of the distribution spacing. Under the same conditions, when the shear nail density is between 0 and 9.6, and the higher the shear nail density, the greater the shear strength of the prefabricated UHPC-NC bonding surface. Under the same density of shear nails, compared to specimens with smaller spacing of shear nails, the shear stress with larger spacing of shear nails can be increased by 19.04–41.74%. (4) After comparing and analyzing the existing shear strength models of UHPC-NC bonding surfaces and the failure modes of bonding surfaces during testing, the failure mode parameters of bonding surfaces are introduced to establish a new rule to calculate the shear strength of prefabricated UHPC-NC bonding surfaces. The calculation results have a high degree of agreement with the experimental values, which can provide reference for the interface design of UHPC-NC composite specimens. Declarations Acknowledgements The study was supported by National Natural Science Foundation of China (No.51569305) and Ningbo Scientific and Technological Innovation Major Project in 2035 (No.2023Z148, No.2023Z017). References Wen XD, Ma BG, Gan WZ, Xian ZW (2010) Design and research on gradient structure concrete based on volumetric stabilization. ACI Mater J 107:611–616 Wen XD, Tu JL, Gan WZ (2013) Durability protection of the functionally graded structure concrete in the splash zone. Constr Build Mater 41:246–251 Giacomo T, Fernández MG, Janet ML (2020) Functionally graded concrete: Design objectives, production techniques and analysis methods for layered and continuously graded elements. Constr Build Mater 242:118040 Zhang R, Hu P, Zheng XH, Cai LH, Guo R, Wei DB (2020) Shear behavior of RC slender beams without stirrups by using precast U-shaped ECC permanent formwork. Constr Build Mater 260:120430 Kim GB, Pilakoutas K, Waldron P (2008) Development of thin FRP reinforced GFRC permanent formwork systems. Constr Build Mater 22(11):2250–2259 Peng-gang WANG, Ming-hai ZHAO, Tian LI et al (2024) Shear performance of interface bonding between prefabricated keyway UHPC and post-cast concrete. China J Compos Mater 41(5):2633–2644 Xu-dong SHAO, Ming-hong QIU, Ban-fu YAN et al (2017) A Review on the Research and Application of Ultra-High-Performance Concrete in Bridge Engineering an Around the World. Mater Rep 31(23):33–43 LI, Qing-hua (2009) XU Shi-lang. Performance and application of ultra-high toughness cementitious composite. Eng Mech 26(Suppl2):23–67 Ming-ke DENG, Xin-xing BU, Jiao-jiao PAN et al (2017) Experimental study on seismic behavior of steel reinforced high ductile concrete short columns. Eng Mech 34(1):163–170 Hung CC, Sherif ET, Chao SH (2021) A review of developments and challenges for UHPC in structural engineering: Behavior, analysis, and design. J Struct Eng 147(9):03121001 MUÑOZ M A C, DEVIN A M A, THERESA P M A et al (2014) Bond performance between ultrahigh-performance concrete and normal-strength concrete. J Mater Civ Eng 26(8):04014031 BASSAM AT, ABU B.H.B, MEGAT MA et al (2014) Microstructural analysis of the adhesion mechanism between old concrete substrate and UHPFC. J Adhes Sci Technol 28(18):1846–1864 WANG Xing-wang (2016) Study on interfacial shear resistance between UHPC and ordinary reinforced concrete structures. Hunan University, Changsha HUSAM HH, KENNETH K.W SHADMS et al (2016) Interfacial properties of ultrahigh-performance concrete and high-strength concrete bridge connections. J Mater Civ Eng 28(5):04015208 Rui ZHANG, Peng HU, Xi LI et al (2021) Shear behavior of reinforced concrete composite beams without stirrups using U-shaped UHPC permanent formwork. China J Highway Transp 34(08):145–156 De-hong WANG, Tong SHEN, Yan-zhong J et al (2020) Study on bonding shear properties of post-poured ordinary concrete and prefabricated UHPC. J Building Struct 41(S2):411–419 Jun YANG, Jian-ting ZHOU, Zhong-ya ZHANG et al (2021) China J Highway Transp 34(08):132–144 Min CHAI, Su-rong LUO (2013) Experimental study on shear performance of self-compacting concrete and old concrete. J Fuzhou Univ (Natural Sci Edition) 41(05):922–927 LI Ping-xian ZHAO, Guo-fan ZHANG, Lei-shun (2005) Experimental study on epoxy sand to improve the bond strength of new and old concrete. J Dalian Univ Technol, (02): 255–259 LIU Chuan-qi Experimental study of old and new concrete interface mechanism of paste. Xi'an: Chang-an University (2014) : 45–47 Code for design of concrete structures (2010) GB 50010 – 2010. China Architecture & Building, Beijing British Standards Institution (2004) Eurocode 2: design of concrete structures: part 1: general rules and rules for buildings: BS EN 1992-1-1. British Standards Institution, London ACI 318 Committee (2005) Building code requirements for structural concrete and commentary: ACI 318M-05. American Concrete Institute, Farmington Hills, MI Southeast University (2015) Concrete structure, the first volume, Design theory for concrete structure. China Architecture & Building, Beijing Jianting ZHOU, Tianxiang HU, Jun YANG et al (2021) Experimental study on adhesion properties of UHPC-NC interface of keyway structure. Mater Rep 35(16):16050–16057 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4954119","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":348562486,"identity":"526f68d3-621d-4ccb-9a53-cb9ab47940cd","order_by":0,"name":"Jianmin HE","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIiWNgGAWjYBACxvbmgw8//LCR4ydaC3PPsWRjyZ40Y8kGYrWwz8hRk+BhO5S44QCxWngbchgkJHgOMG4+nryB4UfFNsJaJBvOHjAosLjDbHbmWQFjz5nbhLUYNvYlJEjwPGMzu5FjwMzYRoQW+8M8Bgd42A7zGM8gVgtjG49hA1CLhIEE0Vp62JKZgYFsIAH0y0Gi/MI4//Hxn8CorO9vT9744EcFEVqQQILBAZLUg7WQqmMUjIJRMApGCAAAJTZAgnad4DYAAAAASUVORK5CYII=","orcid":"","institution":"Zhejiang Guangtian Component Group Co.，Ltd","correspondingAuthor":true,"prefix":"","firstName":"Jianmin","middleName":"","lastName":"HE","suffix":""},{"id":348562487,"identity":"cce5404b-24db-4903-a09c-788ecfe9e02b","order_by":1,"name":"Xiaodong WEN","email":"","orcid":"","institution":"Ningbo University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xiaodong","middleName":"","lastName":"WEN","suffix":""},{"id":348562488,"identity":"92149642-4a9f-49b6-9a45-aed0f134a25d","order_by":2,"name":"Wenbo 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formwork\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/cbc541aadbd8852c83d0a9ab.jpg"},{"id":65851275,"identity":"3d01929a-6610-4e29-8a37-884a871f4743","added_by":"auto","created_at":"2024-10-03 14:20:14","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82113,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFlow chart of specimen preparation\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/e6945ae4e8aa445e3d402b7b.jpg"},{"id":65849542,"identity":"9c11d4fd-ce60-4297-8c98-77bbe6c46d41","added_by":"auto","created_at":"2024-10-03 14:04:14","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":43400,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTest loading device\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/44f18b6865e6f6ed35e2dfdb.jpg"},{"id":65850811,"identity":"6eb27ca0-488e-40b9-9ea8-dc343b249316","added_by":"auto","created_at":"2024-10-03 14:12:15","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":76178,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic diagram of the arrangement of strain gauges and displacement measurement points on the specimen\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/ffdd20769e3cd3eb356fe2db.jpg"},{"id":65849538,"identity":"5d1f3a22-ef9e-4347-8a95-3d27acd1cf99","added_by":"auto","created_at":"2024-10-03 14:04:14","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":54078,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTypical failure mode of specimens\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/7ed1e75cf9e6448919d62795.jpg"},{"id":65851276,"identity":"35ae30c4-712c-4cdc-a6cd-685c8c877069","added_by":"auto","created_at":"2024-10-03 14:20:14","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":111960,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStrain distribution of specimens under various loads\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/cb9cfd7ca214186cbea7522c.jpg"},{"id":65849543,"identity":"6654ba67-5ab5-42c9-87ed-800585569038","added_by":"auto","created_at":"2024-10-03 14:04:15","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":22744,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eslip curve of mode\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/c4160df2e5f7a4a494c79139.jpg"},{"id":65849545,"identity":"48199a35-c2ba-4213-892b-75cfee062e42","added_by":"auto","created_at":"2024-10-03 14:04:15","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":43822,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLoad-slip evolution rule under the different parameters\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/cabba0523c612e63eaf48c0b.jpg"},{"id":65850809,"identity":"77e4e46c-d973-40ec-a181-49904e474783","added_by":"auto","created_at":"2024-10-03 14:12:15","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":10672,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between shear strength and shear nails density (ρ)\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/96d349abd404b1c259f77941.jpg"},{"id":65849544,"identity":"bd3db50c-8663-441b-ab41-5fa99e0132a0","added_by":"auto","created_at":"2024-10-03 14:04:15","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":13278,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between shear strength shear nails distribution spacing\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/e834b47be450951953add242.jpg"},{"id":68588077,"identity":"7a6cd454-c321-49ec-9a39-957e65c9c339","added_by":"auto","created_at":"2024-11-08 22:07:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1604829,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4954119/v1/d07e578c-3670-482a-98fc-f44ea7065728.pdf"}],"financialInterests":"","formattedTitle":"Use of shear nails connector to improve UHPC-NC interface bonding performance of functional graded concrete components in offshore structure","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAlong with urban sprawl and a severe shortage of land resources, marine resources have become an inevitable trend in the development. As this trend continues, there are an increasing number of coastal engineering. However, ocean engineering usually shows durability issues in harsh marine environments where dry-wet cycles, corrosive substances such as SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e result in the corrosion of steel bars.\u003c/p\u003e \u003cp\u003eRecently, functionally graded concrete (FGC) has been adopted to improve the durability of these structures. FGC is a cementitious composite that the material compositions are spatially varied by two or more mixes \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e, and material properties are engineered to change locally in a controlled way to meet the actual need. Wen et al. \u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e investigated the possibility of protecting steel reinforcement through an external layer of low-permeability concrete. FGC can be divided into layered or continuously graded concrete. The former, the layered graded concrete is further classified as fresh-on-hardened and fresh-on-fresh layered graded concrete according to the sequence of casting operations. In fresh-on-hardened layered graded concrete, new layers of fresh concrete are added when previous layers have set and hardened, while different concretes are mixed and cast simultaneously in fresh-on-fresh layered graded concrete. Fresh-on-hardened layered graded concrete is more widely adopted than fresh-on-fresh layered graded concrete to achieve functional gradation due that the production process of latter is more complicate by requiring multiple concrete mixes to be mixed at the same time \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn recent years, many scholars have proposed permanent formworks \u003csup\u003e[\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. These formworks are specially designed to contain the fresh concrete, mold it to the required dimensions and remain in site throughout the service life of structures. Using permanent formworks can simplify construction processes, save the construction time, and reduce the engineering cost \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. Therefore, replacing traditional construction formworks with permanent formworks is gaining its significance. If permanent formworks techniques could be utilized in graded concrete element, it allows the geometry of the layers and the location of each interface to be accurately monitored during production. Ultra-high-performance concrete (UHPC), as a new type of cement-based composite material developed in recent years, has high strength, high density, high toughness, high durability, and good ductility \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. At the same time, it also has good bonding performance with steel bars \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e. UHPC, as a permanent template material, can improve the load-bearing capacity of the template, reduce the thickness and weight of the template, and has received widespread attention.\u003c/p\u003e \u003cp\u003eIn the UHPC permanent formwork structure system, the bonding interface between the formwork and cast-in-place ordinary concrete is the weakest link in the composite structure. Therefore, domestic and foreign scholars have conducted experimental research on the interface shear performance of UHPC-NC composite components. For example, Munoz et al. \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e conducted oblique shear and splitting experiments, and studied the bonding performance between the two materials under different conditions such as concrete wetness and surface roughness. The experimental results show that regardless of the exposure degree of freeze-thaw cycles, the age of composite specimens, the roughness of concrete substrates, and different loading schemes, the bonding performance between UHPC and NC is sufficient for the requirements of bridge cover layer. Bassam et al. \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e conducted oblique shear and splitting experiments to study the adhesive strength and permeability between the two materials. The experimental results show that the bonding strength between the UHPC layer and the NC matrix is high, and the impermeability of the UHPC-NC interface are good, which can significantly improve the impermeability of the concrete matrix. Wang Xingwang\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e conducted interface shear tests on UHPC-NC structures and studied the stress and failure modes of the reinforcement model using ANSYS numerical analysis method. Husam et al. \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e conducted interface direct tensile experiments and determined the cohesion between UHPC and high-strength concrete using the roughness of the material surface as a variable, and deduced the friction coefficient between the materials. Due to the smooth surface of the UHPC template, Zhang Rui et al. \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e uniformly distributed pits on UHPC templates and improved interface adhesion by embedding shear keys into the pits with post poured concrete. Wang Dehong et al. \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e set grooves on the surface of the template to improve its roughness, and established a calculation formula between keyway density and bonding surface shear stress through double-sided shear tests. However, these processing methods form ordinary concrete shear keys, exhibiting NC shear failure \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e, and therefore the improvement is limited.\u003c/p\u003e \u003cp\u003eIn summary, this article proposes to set up UHPC shear stubs for prefabricated templates, which can shift from NC failure to UHPC shear when subjected to loads, further improving the interfacial bonding performance of UHPC template NC core composite specimens. However, there is little research in this area. Therefore, this article conducts double-sided shear tests on UHPC-NC to study the influence of shear nail density and distribution spacing on interface failure modes and shear bonding performance, and establishes a formula for calculating the shear strength of interface bonding, in order to provide useful reference for the design and construction of UHPC-NC composite specimens.\u003c/p\u003e"},{"header":"2. Experiment Overview","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Design and Fabrication of Specimen\u003c/h2\u003e \u003cp\u003eTo study the impacts of shear nails on interface bonding performance, density and distribution spacing of shear nails on the surface of UHPC formwork to be more specific, double-sided shear tests have been carried out, design parameters can be found in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Each specimen consists of UHPC formwork and normal concrete inner core.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSpecimen design\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOuter diameter of shear nail\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHeight of shear nail\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNumber of shear nail\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDensity of shear nail\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.533\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.067\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.133\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN6K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.267\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN12K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN18H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.133\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.133\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.267\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003cp\u003eN12M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.267\u003c/p\u003e \u003cp\u003e6.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eN: Sticking; number: number of nails applied; K: wide distance between nails; M: narrow distance between nails\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eUHPC was made up of Grade 52.5 ordinary Portland cement, I grade fly ash, silica fume, quartz powder, quartz sand, steel fiber, polycarboxylate superplasticizer and water. Mixture proportion of the UHPC is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The volume ration of steel fibers to UHPC is 2.5%. According to GB/T 50081\u0026thinsp;\u0026minus;\u0026thinsp;2019, the slump-flow of UHPC was tested, and the result was 720mm. In accordance with GB/T 31387\u0026thinsp;\u0026minus;\u0026thinsp;2015, the compressive strength of UHPC was measured using cube specimens with 100 mm\u0026times;100 mm \u0026times; 100 mm size, and the result was 142.3MPa. According to GB/T 50081\u0026thinsp;\u0026minus;\u0026thinsp;2019, the tensile properties of UHPC were tested using dog bone-shaped specimens with a cross-section of 100 mm \u0026times; 50 mm size, and the result was 8.3MPa.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMix proportion of UHPC\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP.O 52.5 cement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSilica fume\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFly ash\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQuartz sand\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eQuartz powder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ewater\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSuperplasticizer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSteel fiber/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.228\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMix proportion of C30 concrete\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP.O 42.5 cement\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eII-Fly ash\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCoarse aggregate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFine aggregate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ewater\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNormal concrete with a designed compressive strength grade of C30 was used for this study. The mixture was mainly consisted of ordinary Portland cement, river sand with a fineness modulus of 2.3, II grade fly ash, gravel with maximum size of 31.5mm, naphthalene superplasticizer and water. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e list the mix proportion of normal concrete in this study. The measured compressive strength of the concrete standard cubic specimen was 38.5MPa.\u003c/p\u003e \u003cp\u003eThe computational formula for the density of shear nails\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:\\)\u003c/span\u003e\u003c/span\u003eis as follows \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\rho\\:=\\:\\frac{n{V}_{u}}{S}\\left(1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e is the density of shear nails; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:n\\)\u003c/span\u003e\u003c/span\u003e is number of shear nails; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{u}\\)\u003c/span\u003e\u003c/span\u003e is volume of single shear nail; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:S\\)\u003c/span\u003e\u003c/span\u003e is area of bonding surface.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e1) Casting of UHPC formwork\u003c/h3\u003e\n\u003cp\u003eBy inspiring of transfer printing technology, a new simple shear nails processing method on UHPC formwork inner surface was proposed for establishing a connection between UHPC formwork shell and NC core. Moreover, in order to identify the impact of UHPC formwork's shear nails structural measures on interface bonding performance between UHPC and post-poured NC, formworks were treated in different ways at the time of UHPC pouring, as well as no treatment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFormworks were treated as follows: the wooden mold lined with silicone sheet (there are 30mm-deep holes distributed in different positions on the sheet) were adopted to make UHPC formworks with different numbers of shear nails and placed in different positions; for specifics, see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eBy changing the surface of silicone sheet, different shear nails structure of UHPC formwork could be realized, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Afterwards, fresh UHPC was stirred and poured into a prepared mold. The poured UHPC formwork was rested quietly and demolded after 24 hours, and then placed to a standard curbing box for 28 days.\u003c/p\u003e\n\u003ch3\u003e2) Casting of specimen\u003c/h3\u003e\n\u003cp\u003eThe prefabricated UHPC formwork was installed in the prepared mold, with the UHPC formwork on both sides clinging to the inner walls of mold, and then normal concrete was poured in the middle. In order to ensure the quality of pouring, when each 1/3 concrete was poured, it was vibrated by a vibrating rod. After settling for 24h, the mold was removed, and specimen was cured in standard curing box for 28d. Process flow is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Test Loading Device and Measuring Point Arrangement\u003c/h2\u003e \u003cp\u003eThe testing device consists of 200t POPWIL static pressure tester, 60L concrete mixer, Donghua static collector, industrial camera, digital collector, electro-hydraulic loading system and displacement meter, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe strain distribution law of UHPC formwork and concrete core can be obtained by strain sensors on the surfaces of prefabricated UHPC and concrete. The arrangement scheme for such strain gauges is as follows: ten strain sensors are separately attached to UHPC and NC near interface to obtain the strain values of UHPC slab and concrete length-wise. four sensors are arranged at each cross section, as shown in \u003cem\u003eFig.\u0026nbsp;4(a)\u003c/em\u003e; the average value of sensors at the same cross section is taken as the strain values of UHPC and NC near interface; for instance, the strain values of UHPC and NC at 1\u0026ndash;1 cross section near interface are denoted as U1 and C1, respectively.\u003c/p\u003e \u003cp\u003eMoreover, displacement meters are separately inserted on UHPC and NC to obtain the slip values of UHPC formwork and concrete core. 4 and 6 displacement meters are inserted on UHPC formwork and NC core, respectively, including 2 displacement meters on NC at opposite angles of A-A cross-section and 2 displacement meters on UHPC and NC in the centers of B-B cross-section and C-C cross-section, as shown in \u003cem\u003eFig.\u0026nbsp;4(b)\u003c/em\u003e. Worth noticing is that the average value of displacement meters at the same cross-section is taken as the displacement values of UHPC, NC at such cross-section; for instance, the displacement values of UHPC and NC at B-B cross-section are denoted as UB and C\u003csub\u003eB\u003c/sub\u003e, respectively.\u003c/p\u003e \u003cp\u003ePreloading is conducted before test; loading rate is controlled at 5KN/min; preloading ends at 5KN, while in the test round, the loading rate is controlled at 5KN/min until specimen fails.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Experiment Result and Its Analysis","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Failure Mode\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e presents the test results of the ultimate bearing capacity, interface shear stress, and failure mode of the specimens.\u003c/p\u003e\n \u003cp\u003eWhen the UHPC template is not equipped with nails, the interface of the UHPC-NC composite specimen experiences shear failure of the bonding surface after being sheared, and the cross-section is smooth and flat. After the shear nail construction is set on the surface of the template, its failure mode presents three types:\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eExperimental results\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSerial number\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eultimate bearing capacity (P\u003csub\u003eu\u003c/sub\u003e/KN)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003einterfacial shear stress (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003efailure mode\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eShear failure between UHPC and NC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e130.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e149.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e185.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN4K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e205.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN6K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e273.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN8K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e288\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN12K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e356.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN18K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e393.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN4M\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e145.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN4K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e205.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN8M\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e206\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN8K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e288\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN12M\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e299.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eA type: UHPC-NC bonds and nails shear failure. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Small shear cracks first appear on the bonding surface near the free end and propagate along the bonding surface until encounters shear nails. Afterwards, the interface shear performance of composite specimens is mainly provided by shear nails. Due to insufficient density of shear nails on the template, UHPC shear nails were cut along the root. Finally, shear failure occurred on the bonding surface and shear nails of the composite specimen.\u003c/p\u003e\n \u003cp\u003eB type: UHPC-NC bonding surface shear failure, UHPC shear nail shear failure or peeling off. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Shear failure first occurs in the free end, and as the load increases, the force continues to propagate along the bonding surface until it encounters a group of shear nails. Afterwards, the interface shear performance of the composite specimen is mainly provided by the shear nail group. Under the action of the shear nail group, the force continues to propagate along the bonding surface until the UHPC shear nail is sheared, especially near the free end. In addition, some force develops obliquely to the NC near the shear nail and micro cracks appear. Finally, the NC adhered to the UHPC shear nail is peeled off together.\u003c/p\u003e\n \u003cp\u003eC type: Shear failure of UHPC-NC bonding surface and axial compression failure of NC cores. In the early stage of loading, the shear performance of the composite specimen interface is mainly borne by the bonding force between UHPC-NC. Shear failure first occurs near the free end, and as the load increases, the force continues to propagate along the bonding surface until it encounters the shear nail group. If the density of shear nails is large enough, under the action of shear nail group, cracks will develop diagonally to the loading point at NC, and finally exhibit NC axial compression failure.\u003c/p\u003e\n \u003cp\u003eThese three typical failure modes are shown in \u003cem\u003eFig.\u0026nbsp;5\u003c/em\u003e, when 2.133\u0026thinsp;\u0026le;\u0026thinsp;shear nail density \u0026rho;\u0026lt;6.4, the specimen undergoes a transition from A type failure to B type failure. When the shear nail density \u0026rho;\u0026thinsp;\u0026ge;\u0026thinsp;6.4, the specimen failure transformed into C type failure.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Load-strain relation curve\u003c/h2\u003e\n \u003cp\u003e\u003cem\u003eFigure\u0026nbsp;6\u003c/em\u003e shows specimen\u0026apos;s load-strain relation curves under different parameters.\u003c/p\u003e\n \u003cp\u003eAccording to \u003cem\u003eFig.\u0026nbsp;6\u003c/em\u003e, the development and distribution of strain on interface under different treatments are quite similar. In the initial stage of loading, only the sensors near the free end had data changes, in which case, the interfacial chemical action of UHPC formwork and NC core served to bear load, whose load-strain relation curve appeared to be linear. As load gradually increased, shear nails and aggregate on the UHPC-NC bonding surface started to act, so the difference between the free end\u0026apos;s strain and the loading end\u0026apos;s strain gradually increased until failure. In the whole process of loading, strain increased linearly with load. As shown by the linearity stages on the load-strain curve of UHPC-NC specimens, the slope of curve from the free end to the loading end increased, suggesting that strain was gradually delivered from the free end to the loading end; as it reached the ultimate load, specimen failure quickly occurred.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Load-slip relation curve\u003c/h2\u003e\n \u003cp\u003eWith displacement meters on UHPC and NC, the load-slip curve at A, B and C cross-sections in UHPC and NC\u0026apos;s effective bonding sections are recorded as shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. After it reached the peak load, shear specimen was quickly separated, so there was no descent part of the curve. The load-slip curves for various specimens prepared with different construction measures showed a same pattern. In the initial stage of loading, UHPC and NC at interface deformed synergistically, in which case, the shear force at the prefabricated UHPC-NC interface was borne by the chemical action. As load continued to increase, the mechanical meshing force between shear nails and aggregate started to play a role, so shear strength increased and slip increased with load linearly. As the mechanical meshing force between shear nails and aggregate continued playing a role until cracked, slip increased nonlinearly with load. When it reached the ultimate load, interfacial bonding failed quickly. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, subject to the same load, compared with curves C\u003csub\u003eB\u003c/sub\u003e and U\u003csub\u003eB\u003c/sub\u003e, the difference in slippage of curves C\u003csub\u003eC\u003c/sub\u003e and U\u003csub\u003eC\u003c/sub\u003e were large, so failure at specimen interface should occur at the free end first.\u003c/p\u003e\n \u003cp\u003eThe difference in slippage between UHPC and NC at cross-section C# can be used to derive the relative displacement of C# cross-section. Figure 8 showed the load-relative displacement curve of composite specimen under different constructions. As indicated by \u003cem\u003eFig.\u0026nbsp;8(a)\u003c/em\u003e, the ultimate bearing capacity of specimen N8K was larger than that of N4K, but smaller than that of N12K. Subjected to the same load, relative displacement on the bonding surface of N8K was larger than that of N12K, but smaller than that of N4K. This showed that as the density of shear nails increased (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\le\\:9.6\\)\u003c/span\u003e\u003c/span\u003e), the bond performance at specimen\u0026apos;s bonding surface became better. The impact of shear nail interval on the load-slip curve was shown in \u003cem\u003eFig.\u0026nbsp;8(b)\u003c/em\u003e. As shown in the figure, when \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:=4.267\\)\u003c/span\u003e\u003c/span\u003e, the ultimate bearing capacity of N8K is higher than that of N8M. N8K\u0026apos;s relative displacement was smaller subject to the same load, so N8K had better bond performance. Likewise, specimen with density \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:(\\rho\\:=6.4)\\)\u003c/span\u003e\u003c/span\u003e showed same pattern. The ultimate bearing capacity of N12K was larger than N12M. N12K\u0026apos;s relative displacement was smaller subject to the same load, so N12K had better bond performance. This suggested that with same density of shear nails, increasing shear nail interval can further improve the interfacial bond performance.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Interfacial bonding shear strength\u003c/h2\u003e\n \u003cp\u003eThe bonding shear strength of the prefabricated UHPC-NC specimen is calculated according to Equ. (2).\u003c/p\u003e\n \u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e$$\\:\\begin{array}{c}{\\tau\\:}_{u}=\\frac{P}{2A}\\left(2\\right)\\end{array}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}\\)\u003c/span\u003e\u003c/span\u003e is the bonding shear strength; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:P\\)\u003c/span\u003e\u003c/span\u003e is the shear peak load; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:A\\)\u003c/span\u003e\u003c/span\u003e is the area of the bonding surface, A\u0026thinsp;=\u0026thinsp;60000 mm\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eThe bonding shear strength of the prefabricated UHPC-NC is calculated according to Equ.(2), as shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eFrom Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, under the same condition, the bonding shear strength of UHPC-NC composite specimen increased with the density of shear nails, and the bonding shear strength features parabolic relation with the density of shear nails. Because as the density of shear nails at prefabricated UHPC increased, the mechanical meshing force at the bonding surface increased, thus increasing the bonding shear strength.\u003c/p\u003e\n \u003cp\u003eWith the same grooving density, the bonding shear strength of prefabricated UHPC-NC and the impact of shear nail interval were further studied, with its result shown in \u003cem\u003eFig.\u0026nbsp;10\u003c/em\u003e.\u003c/p\u003e\n \u003cp\u003eAccording to \u003cem\u003eFig.\u0026nbsp;10\u003c/em\u003e, the bonding shear strength of prefabricated UHPC-NC increased with shear nail interval. The bonding shear strength of specimen N4K was 41.74% higher than that of N4M, and the bonding shear strength of N8K was 39.94% higher than that of N8M, and the bonding shear strength of N12K was 19.04% higher than N12M. This is because as shear nail interval increased, the interlocking mechanism of shear nails and aggregate increased and the interfacial bonding shear strength increased.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 shear strength of single shear nail\u003c/h2\u003e\n \u003cp\u003eFurthermore, as indicated by the results of shear strength tests of single shear nail, with different shear nail densities, the relation between the shear strength of the bonding surface and the shear nail density of prefabricated UHPC was parabolic. The bonding strength of superposed concrete structure comes from the mechanical meshing force of the bonding surface, its chemical action force and Van der Waals force \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. The mechanical meshing force is generated by the interfacial interaction on uneven bonding surface; generally, the mechanical meshing force is the main part of interfacial bonding force. Chemical action force is generated by chemical reaction between two materials on the bonding surface. Van der Waals force is caused by the mutual attraction of molecules between crystals; crystal\u0026apos;s intermolecular distance in concrete is so large that Van der Waals force is negligible \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. Therefore, this paper assumes that the bonding force fully comes from mechanical meshing force and chemical action force.\u003c/p\u003e\n \u003cp\u003eWhen there was no shear nail on UHPC (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:=0\\)\u003c/span\u003e\u003c/span\u003e), its formwork surface was smooth, and upon subjected to load, interface encountered shear failure. Failure surface was relatively flat, whose interfacial bond strength fully came from chemical action. After shear nails were placed on formwork surface (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:＞0\\)\u003c/span\u003e\u003c/span\u003e), the interfacial bonding strength of specimen came from mechanical meshing and chemical action. Compared with the specimen with smooth formwork, the composite specimen with shear nail also encountered the mechanical meshing force. So, the specimen\u0026apos;s mechanical meshing force \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e can be derived by discounting the corresponding shear capacity of the corresponding smooth interface from that of composite specimen\u0026rsquo;s shear capacity. The mechanical meshing force of single shear nail can be obtained by dividing the obtained mechanical meshing force by the number of shear nails, with its result shown in Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eAccording to Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, as the density of shear nails increased, the shear strength of single nail gradually decreased. The causes may be as follows, (1) when the density of shear nail was excessively large, the bonding interface was dispersed, interfacial chemical bonding actions can\u0026apos;t develop concurrently, resulting in decreasing effective bonding area, and (2) when the density of shear nails was excessively large, the interlocking mechanism between shear nails and aggregate failed to fully develop. Both causes led to a decrease in both the number of effective shear nails within interface and mechanical meshing force. Therefore, the density of shear nails on UHPC formworks shall be controlled to a reasonable level in real practice.\u003c/p\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe shear strength of a single shear nail\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSerial number\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNail Density\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eShear strength\u003c/p\u003e\n \u003cp\u003e/MPa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDiscounted shear strength /MPa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eShear strength of one single nail /MPa\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.533\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.067\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN4K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.133\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN6K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN8K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.267\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN12K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eN18K\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Calculation of interface shear strength","content":"\u003cp\u003eWith respect to calculation of shear strength of the bonding surface of superposed member, domestic and foreign scholars have conducted extensive research and analysis, and figured out the corresponding calculation method. As specified in the Code for Design of Concrete Structures (GB50010-2010), regarding non-reinforced superposed slab, if there is compliance with the provision relating to construction in subparagraph 10.6.15 (Roughness of Superposed Cross-section) of the Code, the shear strength of its superposed surface shall be not higher than 0.4 N/mm\u003csup\u003e2[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. Foreign codes such as Eurocode 2, ACI 318\u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e consider the bonding force, aggregate interlocking effect and the role of anti-shear pins, it is stipulated as follows:\u003c/p\u003e \u003cp\u003e1) In Eurocode 2 (1992), the shear strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\tau\\:}}_{\\text{u}}\\)\u003c/span\u003e\u003c/span\u003e of concrete bonding surface can be calculated according to Equ. (3):\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\tau\\:}_{u}=c{f}_{t}+\\mu\\:{\\sigma\\:}_{n}+\\rho\\:{f}_{yd}\\left(\\mu\\:sin\\alpha\\:+cos\\alpha\\:\\right)\\le\\:0.5v{f}_{cd}\\left(3\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:c\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:\\)\u003c/span\u003e\u003c/span\u003e represent cohesion coefficient and friction coefficient relating to the superposed surface construction mode, 0.35 and 0.6 are taken for the natural bonding surface without special treatment, 0.45 and 0.7 are taken for rough bonding surface; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{t}\\)\u003c/span\u003e\u003c/span\u003e is the lowest tensile strength of two materials; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e is reinforcement ratio of shear reinforcement on superposed surface; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{yd}\\)\u003c/span\u003e\u003c/span\u003e is the design value of yield strength of shear reinforcement on superposed surface; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\sigma\\:}_{n}\\)\u003c/span\u003e\u003c/span\u003e is the minimum value of normal positive pressure to which interface is subject; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{cd}\\)\u003c/span\u003e\u003c/span\u003e is the design value of concrete compressive strength; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:v\\)\u003c/span\u003e\u003c/span\u003e is strength reduction factor, for which 0.6 is taken, if \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{ck}\\le\\:60\\)\u003c/span\u003e\u003c/span\u003e MPa, the requirement \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:0.9-{f}_{ck}/200\\ge\\:0.5\\)\u003c/span\u003e\u003c/span\u003e shall be satisfied, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{ck}\\)\u003c/span\u003e\u003c/span\u003e is the standard value of compressive strength of concrete's axial compressive strength.\u003c/p\u003e \u003cp\u003e2) In the Code ACI 318M-05 (2005), when the bonding surface is a natural rough surface and there is no or little shear reinforcement, the shear capacity of superposed surface is as follows:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{V}_{nh}=0.55{b}_{v}d\\left(4\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{V}_{nh}\\)\u003c/span\u003e\u003c/span\u003e is the shear capacity of superposed surface, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{b}_{v}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:d\\)\u003c/span\u003e\u003c/span\u003e represent the width and length of superposed surface, separately.\u003c/p\u003e \u003cp\u003e3) In the Code AASHTO LRFD (2005), the nominal shear capacity of superposed surface is as follows:\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{V}_{u}=c{A}_{cv}+\\mu\\:\\left({A}_{vf}{f}_{y}+{P}_{c}\\right)\\le\\:\\text{min}\\left(0.2{f}_{c}^{{\\prime\\:}}{A}_{cv}，5.5{A}_{cv}\\right)\\left(5\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, when concrete is later poured onto the hardened rough concrete surface, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:c\\)\u003c/span\u003e\u003c/span\u003e =0.7, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\mu\\:=1\\)\u003c/span\u003e\u003c/span\u003e; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{cv}\\)\u003c/span\u003e\u003c/span\u003e is the area of superposed surface; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{vf}\\)\u003c/span\u003e\u003c/span\u003e is the area of shear reinforcement; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{y}\\)\u003c/span\u003e\u003c/span\u003e is the yield strength of shear reinforcement; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{c}\\)\u003c/span\u003e\u003c/span\u003e is the pressure perpendicular to superposed surface; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{c}^{{\\prime\\:}}\\)\u003c/span\u003e\u003c/span\u003e is concrete's compressive strength, whichever is lower.\u003c/p\u003e \u003cp\u003eThe interfacial bonding shear strength of fabricated UHPC-NC specimen in this test was calculated according to the above codes. The tensile strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{t}\\)\u003c/span\u003e\u003c/span\u003e of C30 was 2.348 MPa, which was calculated according to the relationship \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e between compressive strength and tensile strength. NC compressive strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{cu}\\)\u003c/span\u003e\u003c/span\u003e in this study was the measured value of 150mm\u0026times;150mm\u0026times;150mm cubic specimen, which was different from the Formula's compressive strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{c}^{{\\prime\\:}}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{c}^{{\\prime\\:}}=0.79{f}_{cu}\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e.C30's compressive strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{c}^{{\\prime\\:}}\\)\u003c/span\u003e\u003c/span\u003e was taken as 30.42MPa.\u003c/p\u003e \u003cp\u003eComparison between the normalized value of prefabricated UHPC-NC's bonding shear strength and experimental value were shown in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental results\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMeasured value \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}\\)\u003c/span\u003e\u003c/span\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEurocode 2\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eACI 318M-05\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{2}\\)\u003c/span\u003e\u003c/span\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAASHTO LRFD\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{3}\\)\u003c/span\u003e\u003c/span\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGB 50010\u0026thinsp;\u0026minus;\u0026thinsp;2010\u003c/p\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{4}\\)\u003c/span\u003e\u003c/span\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}/{\\tau\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}/{\\tau\\:}_{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}/{\\tau\\:}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}/{\\tau\\:}_{4}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.822\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.032\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.306\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.175\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.053\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.945\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.425\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.527\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.557\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.225\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.933\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.636\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.429\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.245\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e6.236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.575\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN6K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.305\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e8.273\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e11.375\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.541\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e8.727\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6.857\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN12K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e5.620\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e10.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.486\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e14.85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN18K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.206\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e11.927\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e9.371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e16.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.289\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e3.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.245\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e6.236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.575\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e3.245\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e6.236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.575\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003cp\u003eN12M\u003c/p\u003e \u003cp\u003eN12K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003cp\u003e4.99\u003c/p\u003e \u003cp\u003e5.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.057\u003c/p\u003e \u003cp\u003e1.057\u003c/p\u003e \u003cp\u003e1.057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003cp\u003e0.55\u003c/p\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003cp\u003e0.7\u003c/p\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003cp\u003e0.4\u003c/p\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e4.541\u003c/p\u003e \u003cp\u003e4.721\u003c/p\u003e \u003cp\u003e5.620\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e8.727\u003c/p\u003e \u003cp\u003e9.073\u003c/p\u003e \u003cp\u003e10.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6.857\u003c/p\u003e \u003cp\u003e7.129\u003c/p\u003e \u003cp\u003e8.486\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e12\u003c/p\u003e \u003cp\u003e12.475\u003c/p\u003e \u003cp\u003e14.85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to data in the table, the result of Eurocode 2 formula is closest to experimental value, while results from the other three formulas greatly differ from experimental value. However, Eurocode 2 formula does not consider the impact from the density of shear nails on interfacial shear stress. When the density of shear nails is excessively high, such formula is no longer applicable.\u003c/p\u003e \u003cp\u003eThus, this paper puts forward a new parameter \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\gamma\\:\\)\u003c/span\u003e\u003c/span\u003e, which relates to UHPC's density of shear nails, and develops the following proposed formula. This equation does not consider the interfacial normal pressure and shear reinforcement.\u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equf\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\tau\\:}_{u}=\\gamma\\:{f}_{t}\\left(6\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere,\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{u}\\)\u003c/span\u003e \u003c/span\u003e = interface shear strength between UHPC formwork and NC core;\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\gamma\\:\\)\u003c/span\u003e \u003c/span\u003e = parameter relating to UHPC's density of shear nails;\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{t}\\)\u003c/span\u003e \u003c/span\u003e = NC's tensile strength.\u003c/p\u003e \u003cp\u003eIn real practice, Eq.\u0026nbsp;(6) can be expressed in the following way based on the conversion relation between concrete's axial tension strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{t}\\)\u003c/span\u003e\u003c/span\u003e and cube compressive strength \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{cu}\\)\u003c/span\u003e\u003c/span\u003e:\u003cdiv id=\"Equg\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equg\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\tau\\:}_{u}=0.395\\gamma\\:{f}_{cu}^{0.55}\\left(7\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAccording to experimental result, the relationship between \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\gamma\\:\\)\u003c/span\u003e\u003c/span\u003e, from Eq.\u0026nbsp;(7), and the density of shear nails \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e can be written as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\gamma\\:=-0.0174{\\rho\\:}^{2}+0.3425\\rho\\:+0.5402,\\rho\\:\\le\\:9.6\\)\u003c/span\u003e\u003c/span\u003e, Correlation index\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:{R}^{2}=0.9935\\)\u003c/span\u003e\u003c/span\u003e, suggesting that the such formula is reliable. Combining the above equation with Eq.\u0026nbsp;(7), correlation-ship between interfacial shear stress of prefabricated UHPC-NC and the density of shear nails can be arrived, as shown in Eq.\u0026nbsp;(8).\u003cdiv id=\"Equh\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equh\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\tau\\:}_{u}=（-0.006873{\\rho\\:}^{2}+0.135288\\rho\\:+0.213379）{f}_{cu}^{0.55}\\left(8\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e is density of shear nails; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{cu}\\)\u003c/span\u003e\u003c/span\u003e is cube compressive strength.\u003c/p\u003e \u003cp\u003eAccording to Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the model built in this paper was used to calculate the interface shear strength in references [16] and references [25]. Results showed that the ratio of experimental value to calculated value was smaller than 1, but discreteness was low, for instance, experimental value/calculated value in references [16] fluctuate around 0.548, while that in references [25] it fluctuated around 0.771, correlation index R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9935.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated values of corrected model and experimental values for interface shear strength\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimens in this paper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value)/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpecimens in references [16]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value) /MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSpecimens in references [25]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value) /MPa\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.589(0.951)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.911(0.436)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.830(0.735)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.112(0.973)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.622(0.513)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.935(0.788)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.606(1.047)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.988(0.512)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.823(0.647)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.071(0.991)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.014(0.605)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-2-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.935(0.795)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.506(1.022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.990(0.573)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-2-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.823(0.889)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN6K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.289(0.943)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.499(0.556)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.957(1.033)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.152(0.595)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN12K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.940(1.000)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.124(0.581)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN18K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.542(0.997)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.740(0.558)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eThe cause for the fact that the calculated values were higher than the experimental results in references [16] and references [25] is as follows. The model built in this paper is based on the case where UHPC's shear nails on the bonding surface are sheared, while the interfacial failure mode in references [16] is that NC is sheared, and the failure mode in references [25] is UHPC-NC's composite failure (bonding interface and NC failure), thus the errors in theoretical calculation. Therefore, it is necessary to consider the failure mode on the bonding surface of UHPC-NC's composite members, and introduce correction factor \u003cem\u003ea\u003c/em\u003e to Eq.\u0026nbsp;(8). When failure mode appears to be the case where NC is sheard, the average value is 0.584, which is the experimental value/calculated value in references [16]. When failure mode is bonding surface failure, the average value is 0.832, which is the experimental value/calculated value in references [25]. When failure mode appears to be the case where UHPC is sheard, a\u0026thinsp;=\u0026thinsp;1. Therefore, based on Eq.\u0026nbsp;(8), considering different bonding surface failure modes, and the calculation formula for shear strength of the bonding surface of UHPC-NC's composite specimen is developed:\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003cdiv id=\"Equi\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equi\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\tau\\:}_{u}=（-0.006873{\\rho\\:}^{2}+0.135288\\rho\\:+0.213379）a{f}_{cu}^{0.55}\\left(8\\right)\\end{array}$$\u003c/div\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eWhere,\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e \u003c/span\u003e =density of shear nails;\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{f}_{cu}\\)\u003c/span\u003e \u003c/span\u003e =cube compressive strength;\u003c/p\u003e \u003cp\u003ea\u0026thinsp;=\u0026thinsp;the parameter of bonding surface failure mode; when interface is the case where NC is sheared, a\u0026thinsp;=\u0026thinsp;0.584; when interface is bonding surface and NC failure, a\u0026thinsp;=\u0026thinsp;0.832; when interface is the case where UHPC's shear nails are sheared, a\u0026thinsp;=\u0026thinsp;1.\u003c/p\u003e \u003cp\u003eEquation (8) was used to calculate shear strength in references [16] and references [20], the results and experimental value / calculated value ratio are listed in Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFrom Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, experimental-to-calculated ratio for references [16] was 1.0040, mean square error and coefficient of variation were 0.0936 and 0.0932 respectively, while experimental-to-calculated ratio for references [25]\u0026thinsp;=\u0026thinsp;1.0002, mean square error and coefficient of variation were 0.1032 and 0.1032 respectively. Calculation agreed well with experiment, which suggest the theoretic model can be used to predict and evaluate the bonding shear stress of UHPC-NC interface.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab8\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated and experimental values of the modified model of shear strength of bonded surface of UHPC-NC specimens after the introduction of parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecimens in this paper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value)/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpecimens in references [11]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value)/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSpecimens in references [20]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCalculated values (experimental value / calculated value)/MPa\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.589(1.051)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.648(0.781)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.181(0.954)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.111(1.028)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.959(0.948)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.033(1.022)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.606(0.955)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSB5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.157(0.946)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-1-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.717(0.839)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.070(1.010)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.273(1.068)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-2-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.033(1.032)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN4K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.505(0.979)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.702(1.058)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eZJ-Z-2-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.717(1.154)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN6K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.289(1.061)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.975(1.028)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN8K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.956(0.969)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.787(1.100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN12K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.940(1.000)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.313(1.074)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eN18K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.544(1.002)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSD5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.648(1.033)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003e(1) When the UHPC template is not equipped with studs, the interface of the UHPC-NC composite specimen experiences shear failure of the bonding surface after being sheared, and the cross-section is smooth and flat. After the shear nail construction is set on the surface of the template, its failure mode presents three situations. Namely, A type failure: shear failure of UHPC-NC bonds and nails; B type failure: UHPC-NC bonding surface shear failure, UHPC shear nail shear failure or peeling off; C type failure: Shear failure of UHPC-NC bonding surface and axial compression failure of NC core. when 2.133\u0026thinsp;\u0026le;\u0026thinsp;shear nail density ρ\u0026lt;6.4, the specimen undergoes a transition from A type failure to B type failure. When the shear nail density ρ\u0026thinsp;\u0026ge;\u0026thinsp;6.4, the specimen failure transformed into C type failure.\u003c/p\u003e \u003cp\u003e(2) The interface shear strength between UHPC formwork and NC core is 1.67-6.56MPa. The shear stress between the bonding surfaces mainly comes from mechanical biting force and chemical bonding effect. Reasonably setting shear forces between precast UHPC-NC bonding surfaces can fully utilize the strength of precast UHPC and significantly increase the shear stress between bonding surfaces.\u003c/p\u003e \u003cp\u003e(3) The density and distribution spacing of prefabricated UHPC shear nails have a significant impact on the shear strength of prefabricated UHPC-NC bonding surface, and the influence of nail density on the shear strength of the bonding surface is greater than that of the distribution spacing. Under the same conditions, when the shear nail density is between 0 and 9.6, and the higher the shear nail density, the greater the shear strength of the prefabricated UHPC-NC bonding surface. Under the same density of shear nails, compared to specimens with smaller spacing of shear nails, the shear stress with larger spacing of shear nails can be increased by 19.04\u0026ndash;41.74%.\u003c/p\u003e \u003cp\u003e(4) After comparing and analyzing the existing shear strength models of UHPC-NC bonding surfaces and the failure modes of bonding surfaces during testing, the failure mode parameters of bonding surfaces are introduced to establish a new rule to calculate the shear strength of prefabricated UHPC-NC bonding surfaces. The calculation results have a high degree of agreement with the experimental values, which can provide reference for the interface design of UHPC-NC composite specimens.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe study was supported by National Natural Science Foundation of China (No.51569305) and Ningbo Scientific and Technological Innovation Major Project in 2035 (No.2023Z148, No.2023Z017).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWen XD, Ma BG, Gan WZ, Xian ZW (2010) Design and research on gradient structure concrete based on volumetric stabilization. ACI Mater J 107:611\u0026ndash;616\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen XD, Tu JL, Gan WZ (2013) Durability protection of the functionally graded structure concrete in the splash zone. Constr Build Mater 41:246\u0026ndash;251\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGiacomo T, Fern\u0026aacute;ndez MG, Janet ML (2020) Functionally graded concrete: Design objectives, production techniques and analysis methods for layered and continuously graded elements. Constr Build Mater 242:118040\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang R, Hu P, Zheng XH, Cai LH, Guo R, Wei DB (2020) Shear behavior of RC slender beams without stirrups by using precast U-shaped ECC permanent formwork. Constr Build Mater 260:120430\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim GB, Pilakoutas K, Waldron P (2008) Development of thin FRP reinforced GFRC permanent formwork systems. Constr Build Mater 22(11):2250\u0026ndash;2259\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeng-gang WANG, Ming-hai ZHAO, Tian LI et al (2024) Shear performance of interface bonding between prefabricated keyway UHPC and post-cast concrete. China J Compos Mater 41(5):2633\u0026ndash;2644\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu-dong SHAO, Ming-hong QIU, Ban-fu YAN et al (2017) A Review on the Research and Application of Ultra-High-Performance Concrete in Bridge Engineering an Around the World. Mater Rep 31(23):33\u0026ndash;43\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLI, Qing-hua (2009) XU Shi-lang. Performance and application of ultra-high toughness cementitious composite. Eng Mech 26(Suppl2):23\u0026ndash;67\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMing-ke DENG, Xin-xing BU, Jiao-jiao PAN et al (2017) Experimental study on seismic behavior of steel reinforced high ductile concrete short columns. Eng Mech 34(1):163\u0026ndash;170\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHung CC, Sherif ET, Chao SH (2021) A review of developments and challenges for UHPC in structural engineering: Behavior, analysis, and design. J Struct Eng 147(9):03121001\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMU\u0026Ntilde;OZ M A C, DEVIN A M A, THERESA P M A et al (2014) Bond performance between ultrahigh-performance concrete and normal-strength concrete. J Mater Civ Eng 26(8):04014031\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBASSAM AT, ABU B.H.B, MEGAT MA et al (2014) Microstructural analysis of the adhesion mechanism between old concrete substrate and UHPFC. J Adhes Sci Technol 28(18):1846\u0026ndash;1864\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWANG Xing-wang (2016) Study on interfacial shear resistance between UHPC and ordinary reinforced concrete structures. Hunan University, Changsha\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHUSAM HH, KENNETH K.W SHADMS et al (2016) Interfacial properties of ultrahigh-performance concrete and high-strength concrete bridge connections. 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J Fuzhou Univ (Natural Sci Edition) 41(05):922\u0026ndash;927\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLI Ping-xian ZHAO, Guo-fan ZHANG, Lei-shun (2005) Experimental study on epoxy sand to improve the bond strength of new and old concrete. J Dalian Univ Technol, (02): 255\u0026ndash;259\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLIU Chuan-qi Experimental study of old and new concrete interface mechanism of paste. Xi'an: Chang-an University (2014) : 45\u0026ndash;47\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCode for design of concrete structures (2010) GB 50010\u0026thinsp;\u0026ndash;\u0026thinsp;2010. China Architecture \u0026amp; Building, Beijing\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBritish Standards Institution (2004) Eurocode 2: design of concrete structures: part 1: general rules and rules for buildings: BS EN 1992-1-1. British Standards Institution, London\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eACI 318 Committee (2005) Building code requirements for structural concrete and commentary: ACI 318M-05. American Concrete Institute, Farmington Hills, MI\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSoutheast University (2015) Concrete structure, the first volume, Design theory for concrete structure. China Architecture \u0026amp; Building, Beijing\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJianting ZHOU, Tianxiang HU, Jun YANG et al (2021) Experimental study on adhesion properties of UHPC-NC interface of keyway structure. Mater Rep 35(16):16050\u0026ndash;16057\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"UHPC Permanent formwork, Shear resistance performance, Interfacial bond performance, Shear nail connector, numerical formula","lastPublishedDoi":"10.21203/rs.3.rs-4954119/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4954119/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper designed functional graded concrete components to meet the bearing and durability improvement subjected to marine environment, where the normal concrete (NC) core was used to bear loads and was protected by the ultra-high-performance concrete (UHPC) permanent formwork from chloride ion permeability. By inspiring of transfer printing technology and controlled permeability formwork, a new simple shear nails construction treatment on UHPC formwork was proposed for establishing a connection between UHPC formwork and NC core. In order to study shear nails construction measures on the interface bonding performance between UHPC and NC, UHPC-NC bonding specimens were subjected to double-sided shear tests using the density and distribution spacing of shear nails on the surface of UHPC formwork as experimental parameters. The results showed when the shear nail density ρ\u0026thinsp;\u0026ge;\u0026thinsp;6.4, the specimen failure transformed into axial compression failure of NC core. The shear stress on the bonding surface increases approximately parabolic with the density of shear nails. Under the same density, the shear stress on the bonding surface of specimens with larger nail spacing was enhanced by 19.04%-41.74% compared to specimens with smaller spacing. The results show that the density and the distribution spacing of shear nails have a significant impact on the shear strength of the UHPC-NC surface. The influence of shear nail density on the shear strength of UHPC-NC interface is greater than that of the distribution spacing of shear nails. Based on comparing and analyzing the existing shear strength models of UHPC-NC bonding surfaces, fully considering the failure mode of bonding surfaces, a calculation formula for the shear strength of prefabricated UHPC-NC bonding surfaces was established. The calculation results have a high degree of agreement with experimental values, which can provide reference for the interface design of UHPC-NC composite specimens.\u003c/p\u003e","manuscriptTitle":"Use of shear nails connector to improve UHPC-NC interface bonding performance of functional graded concrete components in offshore structure","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-03 14:04:10","doi":"10.21203/rs.3.rs-4954119/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"593a5967-776d-4668-b13c-a779be454601","owner":[],"postedDate":"October 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-11-08T21:59:47+00:00","versionOfRecord":[],"versionCreatedAt":"2024-10-03 14:04:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4954119","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4954119","identity":"rs-4954119","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}