Ultra-high Performance Concrete Slabs Research Articles

Pull-out behavior of cluster stud-post pouring UHPC connectors in prefabricated steel-concrete composite beam

The use of ultra-high performance concrete (UHPC) as a connection material for cluster studs of prefabricated steel-concrete composite beams can achieve higher connection strength and less space for reserved holes. However, in addition to bearing the shear force, the studs need to bear the pull-out force to counteract the vertical relative separation between the steel and concrete. The pull-out behavior for cluster stud-post pouring UHPC connectors is complex and has not been clarified completely. Thus, a total of 30 cluster stud pull-out tests in 10 groups were carried out in this study, and the interface type, length-to-diameter ratio of the stud, transverse spacing of stud group, dimensions of the reserved holes, and type of post pouring concrete were considered. The results showed that the pull-out behavior of the cluster studs was different from that of studs embedded in cast-in-place intact UHPC slabs due to the UHPC conical integrity having been reduced significantly by the old-to-new concrete interface. The rough groove interface and UHPC as a post pouring material significantly improved the pull-out capacity and stiffness of the cluster studs. The stud fracture belongs to ductile failure, whereas UHPC and normal concrete (NC) cone failures are brittle. The bearing capacity of the UHPC cone is observed to increase with the effective embedment depth of the stud, the transverse spacing, and the dimensions of the reserved holes. The angle of the UHPC conical failure surface is 70° based on 3D laser scanning. Finally, the theoretical equations for predicting the pull-out capacity of stud-post pouring UHPC connectors with a rough groove interface were proposed, and the critical length-to-diameter ratio of the stud was calculated for different combinations of stud and UHPC strength.

Shear performance of headless studs in ultra-high performance concrete bridge deck

Conventional stud connectors were proved to be inconvenient for the later disassembly and replacement in ultra-high performance concrete (UHPC) bridge decks. In this study, the headless studs which is a type of studs with their heads removed were employed as a substitute for conventional stud connectors, aiming to enhance the detachability of the bridge decks on the premise of ensuring the anti-lift bearing capacity of the decks. Three push-out specimens containing the headless studs with a diameter of 13 mm were carried out to study the mechanical properties of headless studs. In addition, the finite element model was developed to reveal the failure mechanism of headless studs in UHPC. Results indicated that the load-slip curve of headless stud connector can be divided into elastic stage, plastic stage and failure stage. The failure mode of headless studs was the shear fracture at the root of stud shank. Headless stud connections under cyclic loading can produce greater plastic deformation. The ultimate shear capacity and shear stiffness of headless studs were lower than those of conventional studs. Additionally, the UHPC slabs configured with headless studs have a small quantity of separation at the steel-UHPC interface, so it is suggested to use headless studs and conventional studs together in UHPC slabs to ensure the necessary anti-lift bearing capacity. Finite element analysis indicated that in the elastic stage, the bearing capacity of the push-specimen was dominated by the material properties of the headless stud. After entering the plastic stage, the bearing capacity of the push-specimen was mainly controlled by the UHPC below the headless stud.

Investigation on shear behavior of large diameter short stud connectors in steel- thin UHPC bridge deck

Ultra-high performance concrete (UHPC) is a promising alternative for improving the mechanical performance of the steel and reinforced concrete composite bridge deck. Because of the excellent compression and tensile strength as well as the superior durability, the thickness of the UHPC slab can be effectively reduced. Therefore, large diameter short headed stud connector was proposed in this study to match the thin UHPC slab. To investigate the shear behavior of the large diameter headed studs in steel-thin UHPC composite bridges, 6 groups of 12 push-out specimens were designed and tested under the static loading. During the test, the failure mode, load-slip curves, the ductility, shear stiffness and shear strength of the specimens were emphatically focused. Besides, the influences of the aspect ratio of the stud, the thickness of the UHPC slab and the number of the stud in one position on shear behavior of the specimens were evaluated. Furthermore, the ABAQUS software has been used to analyse the large diameter short stud. A proposed modelling strategy used for further parametric analysis was validated with the test results. For the parametric research, different aspect ratio of stud and ultimate strength of stud were evaluated. Test and FEM results showed that the specimens failed in the failure of the root of the stud and the crushing of the concrete. With the increasing of the diameter of the stud, the thickness of the UHPC slab and the ultimate strength of stud, the shear strength and the shear stiffness of the specimens increased. Under the same cross-sectional area of the stud, the shear behavior of a single large diameter short stud connector could be comparable to that of two conventional stud connectors. Finally, after evaluating the results obtained from existing formulas, a predictive equation for the shear bearing capacity of large diameter short studs was proposed, and the accuracy of the calculated results was verified.

Cracking performance in the hogging moment region of HSS-UHPC continuous composite girder bridges

To elucidate the cracking performance of concrete slabs at the negative bending moment region of high strength steel (HSS)-ultra high performance concrete (UHPC) continuous composite girder bridges, eight scale-reduced steel-concrete composite beams, constructed using HSS and UHPC that varying parameters of UHPC slab thickness and width and shear connection degree at the steel-concrete interface were prepared and tested. The composite beams' cracking pattern, bending stiffness, load-deflection curve, steel-concrete interfacial slippage, and strain history were presented and discussed. The test results show that the HSS-UHPC composite beams subjected to negative bending moments exhibited favorable cracking performance. With the UHPC slab width increasing from 450 mm to 550 mm, the composite beams' initial cracking moment, bending stiffness, and flexural ductility increased by 33.4%, 20.5%, and 39.8%, respectively. The utilization of a thick UHPC slab benefited the performance of the composite beams under negative bending moments. Replacing the 80 mm-thick slab with a 110 mm-thick slab improved the structure’s cracking moment and bending stiffness by 15.0% and 21.4%, respectively. Additionally, as the shear connection degree increases from 0.64 to 1.02, the initial cracking and ultimate failure moments of the composite beam were improved by 7.2% and 1.6%, respectively. In contrast, the bending stiffness of the beams with a shear connection degree of 1.02 was 12.4% smaller than those of 0.64. A comprehensive comparison between the formula-predicted cracking performance and current experimental results was performed to examine the capability of existing design approaches in calculating the HSS-UHPC composite beams. The flexural resistance algorithm proffered by Xu exhibits favorable alignment with test results, thereby providing a compelling methodology for designing HSS-UHPC continuous composite girder bridges.

Experimental and numerical analyses on the shear behavior of grouped single-embedded-nut high-strength bolts in steel–ultra-high-performance concrete composite slabs

Incorporating utilization of ultra-high-performance concrete (UHPC) slabs and single-embedded-nut high-strength bolts (SENHSBs) can optimize the structural performance and construction efficiency of steel–concrete composite slabs. Typically, SENHSBs are required to be densely arranged in groups to transfer sufficient interfacial shear forces in complex stress regions. However, the investigations focused on the performance of grouped SENHSBs embedded in UHPC slabs is limited. Against this background, 15 push-out tests were conducted, accompanied by comprehensive numerical analyses, to study the shear behaviors of grouped SENHSBs in steel–UHPC composite slabs. The test results demonstrated that the failure model was governed by SENHSB fracture. Specimens with the longitudinal spacing of twice the bolt diameter exhibited overlapping crushing areas in the UHPC slabs. The longitudinal spacing significantly influenced both the ultimate shear and ultimate slip capacities of the grouped SENHSBs, whereas the transverse spacing significantly affected both the shear stiffness and maximum slip of grouped SENHSBs. Additionally, the per bolt ultimate shear capacities of the specimens with multi-layer SENHSBs were significantly lower than those with single-layer SENHSBs. The SENHSBs located at various positions experienced different shear stresses, and the deviations became more significant as the longitudinal spacing decreased. Consequently, a formula was proposed to evaluate the strength reduction factor of the grouped SENHSBs. Furthermore, accurate models were developed for determining the ultimate shear capacity and load–slip relationship of grouped SENHSBs in steel–UHPC composite slabs.

Ballistic impact resistance of ultra-high-performance concrete (UHPC): A comprehensive experimental investigation and parametric analysis

This study explores the ballistic impact resistance of Ultra-High Performance Concrete (UHPC) through an extensive and detailed experimental investigation. This study will address various gaps related to the impact performance of UHPC. This investigation focused on understanding the ballistic resistance performance of UHPC based on (a) the influence of projectile/bullet parameters (hardness, velocity/energy, diameter, and nose shape), (b) the effect of hybrid fibers, (c) comparative analysis of the use of steel mesh and reinforcement bars and (d) effect of sub-zero temperature. In this parametric investigation, different types and shapes (flat, conical, and ogive) of hardened steel projectiles (diameter 12 and 18 mm) with impact velocities ranging from 103 to 182 m/s or impact energy ranging from 674 to 2103 J and UHPC slabs with thickness ranging from 36 to 100 mm was considered. Steel mesh and reinforcement bars at different spacing (with and without fiber UHPC) were also assessed, along with the effect of sub-zero temperature of −30 °C. The impact energy of the projectile and thickness of UHPC targets were statistically significant parameters affecting penetration depth in UHPC compared to other parameters with a p-value much less than 0.001. The Artificial Neural Network (ANN) model developed in the study could predict the penetration depth with reasonable accuracy (MAPE and RMSE were observed to be 7.69 and 12.12, respectively). The experimental results of this study will provide insights into the development of guidelines for using UHPC as a protective material, which can help ensure the safety and resilience of infrastructures in the face of potential threats.

Experimental study on thermal behaviors of two-layered functionally graded concrete slabs subjected to fire

In order to improve structural thermal performances, this paper designed a two-layered functionally graded concrete (FGC) slab composed of an ultra-high performance concrete (UHPC) layer and a lightweight aggregate concrete (LWAC) layer. UHPC layers are used as structural layers to bear loads while LWAC layers are used for thermal insulation. Fire tests were conducted to investigate the fire resistance behaviors of the FGC slabs with different LWAC thicknesses under the ISO834 heating regime while homogeneous UHPC and normal concrete (NC) slabs were prepared as a contrast. The experimental results revealed that the LWAC could significantly reduce the temperature transferred to UHPC layers, where the interfacial temperatures of FGC slabs with 40 mm and 30 mm thick LWAC layers were 197 °C and 325 °C respectively. Meanwhile, the maximal mid-span deflections ranged from 26.1 mm to 31.5 mm respectively, approximately 55%-65% lower than those of homogeneous material specimens. Besides, FGC slabs presented good explosive spalling resistance, no delamination or debonding occurred at interfacial regions, and LWAC layers adhered to UHPC layers in the form of “multi-point attachment”. The studies provided a solution to the fire resistance design of reinforced concrete structures under high temperature based on the structural level, and the thickness of LWAC layers was optimized by finite element analyses.

Efficient numerical simulation of steel-UHPC composite structures based on a fiber beam-column model

To satisfy the demands of different engineering scenarios, ultra-high performance concrete (UHPC) is usually combined with steel to form various steel-UHPC composite structures. This study proposes an efficient numerical method for simulating steel-UHPC composite structures. A finite element analysis program, SU-COMPONA, is developed, which combines the fiber beam-column model and the concept of smeared cracks. Rational material constitutive laws are proposed and integrated into the program to describe the uniaxial behavior of UHPC and steel fibers. The proposed numerical method is validated against sufficient experimental data for various steel-UHPC composite structures, including reinforced UHPC beams and slabs, steel-UHPC composite beams and slabs and steel-UHPC-steel sandwich beams. In addition, the simulation performance is evaluated quantitatively. The results show that the proposed method can predict the ultimate capacity, the load-deflection curve and the development of crack widths with satisfactory accuracy and stability. Compared with the elaborate three-dimensional finite element method, the proposed method based on the fiber beam-column model is a competitive numerical approach that can achieve higher efficiency with slightly less accuracy.

Behavior and design of steel-UHPC composite beams subjected to negative moment

To improve the crack resistance of concrete deck slabs of steel–concrete composite beams in the negative moment regions, Normal Concrete (NC) and Ultra-high Performance Concrete (UHPC) were respectively used to cast the deck slab to investigate the effects of different slab materials on the failure modes, crack characteristics and flexural performance. The flexural performance tests under negative bending moment were conducted, and the impact of different slab materials on the mechanical performance of the composite beams were analyzed using the numerical simulation method verified by the tests. The method of calculating the ultimate flexural capacity of steel-UHPC composite beam, which considered the material micromechanics mechanism such as fiber distribution, orientation, burial depth and interfacial bond strength, was proposed based on the simplified plasticity theory and were verified with existing method by the test results of related literature. The results show that the force characteristics of the two composite beams were similar, and the failure modes were both flexural failures. Compared with the steel–concrete composite beam, the cracks of the steel-UHPC composite beam were more evenly distributed and narrower, with larger crack distribution spacing and fewer secondary cracks. The cracking resistance of composite beam can be effectively improved by using UHPC slab, and the flexural capacity improved slightly. The cracking load of the deck slab of the steel-UHPC composite beam was improved by 500%, the corresponding load when the crack width reached 0.2 mm was improved by 37.5%, and the ductility and ultimate flexural capacity were improved by 30% and 5 %. In addition, the ultimate flexural capacity of steel-UHPC composite beam should consider the tensile contribution of UHPC, and the proposed calculation method is suitable for steel-UHPC composite beam with different UHPC mix ratios.

Flexural behavior and crack width prediction of UHPC slabs reinforced with FRP bars

This paper aims to investigate the effects of FRP-bar configurations on the flexural behavior of the FRP-reinforced ultra-high-performance concrete (UHPC) deck slab and to propose the calculation method of crack width. Firstly, flexural tests were performed on six FRP-reinforced UHPC slab specimens with varying bar diameters, reinforcement ratios, cover thickness, and slab thicknesses. The load-deflection responses, load-FRP strain relations, and cracking behavior are measured and discussed. The results show that under service loads, the maximum crack widths of all specimens are around 0.03 mm–0.04 mm, which is significantly less than the permitted 0.5 mm in international codes for FRP-reinforced structures. At similar reinforcement ratios, a small FRP-bar diameter with a corresponding reduced bar spacing increases the ultimate capacity and energy dissipation ability. The effects of FRP-bar configurations are minor under service loads, while beyond these loads decreasing the bar diameter is beneficial for reducing the bar strain and crack width. Subsequently, by developing a practical calculation method of the stress of FRP bar embedded in UHPC slab and calibrating the bond coefficient between FRP bar and UHPC against test data, an engineer-friendly calculation method of crack width is proposed. Comparisons between predicted and experimental results indicate the proposed method is capable of producing accurate and safe predictions. The results may give guidance to designers on the appropriate FRP-bar configurations and the control of crack width for the FRP-reinforced UHPC deck slab.

Assessment of impact resistance recovery in Ultra High-Performance Concrete through stimulated autogenous self-healing in various healing environments

Ultra High-Performance Concrete (UHPC) is widely acknowledged for its remarkable mechanical properties, owing to its compact microstructure. The response of UHPC to impact forces plays a vital role in ensuring the safety and longevity of structures, specifically in protective buildings, high-performance pavements and offshore concrete structures. In this context, this paper reports on an experimental investigation aimed at assessing the effects of stimulated autogenous self-healing of UHPC on the recovery of its performance under impact loadings. Drop weight tests were performed on UHPC slabs, with a 10 kg heavy impactor dropped from the height of 1 m on the centre of the specimens. Specimens were pre-cracked by repeated impacts up to 40% of their predetermined capacity. Pre-cracked specimens were exposed to different healing conditions, water submersion, 95% ± 5% RH, and wet/dry cycling (12/12 h) either in water or in a NaCl solution. Self-healing was evaluated through rebound height, elastic stiffness recovery, natural frequency, and laser displacement measurements. High-speed cameras and Digital Image Correlation were used to capture rebound height and crack formation. Performance was assessed at time 0, pre-damaging, 1, 2, and 4 months. After the healing period, all specimens were tested to failure. Specimens exhibited an increasing healing efficiency when moving from 95% ± 5% RH, over wet/dry cycling, to submerged conditions. Specimens healed continuously under submerged conditions exhibited a complete closure of surface cracks (50–150 μm) and an 80% recovery in natural frequency. Furthermore, they showed a more than 10% increase in stiffness and energy dissipation capacity after four months of healing.

Punching Shear Behavior of FRP Grid-Reinforced Ultra-High Performance Concrete Slabs

Fiber-reinforced polymer (FRP) grid-reinforced ultra-high performance concrete (UHPC) slabs are new structural solutions that take advantage of the mechanical properties of FRP and UHPC. However, the punching shear behavior of this new slab type has not been characterized. Therefore, punching shear tests were conducted to eight carbon fiber-reinforced polymer (CFRP) bars or grid-reinforced UHPC square slabs (600 mm side width × 40 mm thick). Several influential factors [e.g., use of CFRP bars or grids as flexural reinforcements, type of strengthening short fiber, steel fiber (SF) content, and presence of shear reinforcements] were investigated. The test results showed that FRP grids and short fibers helped to distribute the applied loads and dissipate the input energy; therefore, more cracks were observed, and higher punching shear capacities were achieved. Furthermore, increasing the reinforcement ratio in the FRP grids led to a more significant postcrack ductility response, which increased the punching shear capacity by 17%. In addition, SF addition could enhance the initial cracking load of the slab (Vcr), and polyethylene (PE) fiber addition could intensify the postcrack ductility response, both enhanced the punching shear capacity. The installation of shear reinforcements (eight pieces of 80 mm long CFRP grid strips) appeared to be more cost-effective than increasing SF content. Finally, compared with the current design provisions for conventional reinforced concrete slabs, a more accurate (average error of 8%) punching shear model was proposed for FRP grid-reinforced UHPC slabs with or without SF additions. However, the robustness of the proposed model will be assessed with more test data in the future.

Experimental study on the performance of shear connections between local UHPC slabs and GFRP girders

This paper proposes a novel fiber-reinforced polymer (FRP)-concrete hybrid system with local ultrahigh-performance concrete (UHPC) in key parts to accelerate construction and reduce the cost of UHPC. Fifteen push-out specimens were tested to investigate the shear behavior of the UHPC-FRP hybrid interface embedded with bolts in a local UHPC slab. The parameters varied were the local UHPC width, types of concrete slabs, bolt diameter, bolt number and bolt embedding length in concrete. Push-out test results showed that (1) the increase in bolt embedding length substantially reduced the bearing capacity, with a maximum reduction of 25.8%; (2) the interfacial bearing capacity and rigidity increased significantly with increasing bolt diameter, while the excessive diameter may cause the failure of GFRP flange shear-out; (3) the increase of the number of bolts improved the interface performance, but decreased the efficiency of a single bolt utilization; (4) the employment of local UHPC increased the slip stiffness by 16.9%, which had similar shear performance to that of the whole UHPC slab; (5) further changing the local UHPC width had little effect on the shear performance of the push-out specimens. Finally, the calculation method of the bolt shear bearing capacity considering the influence of the embedded length was proposed by modifying the existing formula.

Strength, Ductility, and Collapse Response of UHPC Waffle Slabs

Waffle slabs made of ultra-high performance concrete (UHPC) are now being widely used in bridge deck construction. However, to date, no research has been conducted to study their failure behavior. Two one-way waffle slab strips made of UHPC were load-tested under four-point bending to investigate their strength, ductility, and failure patterns. An identical set made of high strength concrete (HSC) was also tested to provide a comparison to specimens made with traditional construction materials. The UHPC specimens exhibited multiple fine cracks prior to rebar yielding and failed by steel rebar rupture after a single crack localized. In contrast, the HSC slab strips exhibited several large cracks and substantially larger ductility than the UHPC slab strips, although their strength was about 40% less than the corresponding UHPC specimens. The experimental results were used to validate a three-dimensional finite element model, which was then employed to investigate the two-way response of UHPC waffle slabs. The simulation study revealed that the yield line design method is applicable to UHPC waffle slabs despite their markedly different behavior compared to concrete slabs. Like the HSC slabs, the UHPC slabs also exhibited displacements and load carrying capacities well in excess of those predicted by flexural theories, due to formation of membrane action.

Impact Test of Ultra-High Performance Concrete Slab with Basalt Fiber

In order to study the impact resistance performance of ultra-high performance concrete (UHPC) slab with basalt fiber, the experiment of six concrete slabs was conducted. The following factors were considered in this study: different basalt fiber types, steel mesh, and water-based epoxy mixture. The drop weight method was used, and the effect of various factors on the impact resistance performance of ultra-high performance concrete slab with basalt fiber were investigated in details. The test results showed that the basalt fiber could significantly increase the impact resistance of UHPC slab. The basalt fiber with a long length after cracking was more significant to improve the impact resistance performance of UHPC slab. The basalt fiber, steel mesh, and water-based epoxy can significantly improve the impact resistance and energy absorption capacity of UHPC slab. The ductility coefficient of UHPC slabs are less than 0.6.

Experimental Study on Flexural Behavior of RC–UHPC Slabs with EPS Lightweight Concrete Core

This paper presents an experimental investigation that focuses on the flexural behavior of an innovative reinforced concrete–ultra-high performance concrete slab with an expanded polystyrene lightweight concrete core. This type of slab is proposed to serve the semi-precast solution, in which the bottom layer is ultra-high performance concrete working as a formwork during the construction of semi-precast slab, the expanded polystyrene lightweight concrete layer is used for the reduction of structure self-weight, and the top layer is normal concrete designed to withstand compressive stress when the slab is loaded. Two similar large-scale specimens with dimensions of 6200 mm × 1000 mm × 210 mm were fabricated and tested under four-point bending conditions to investigate the flexural behavior of composite slab. Test results indicated that three different layers of materials can work effectively together without separation. The bottom ultra-high performance concrete layer leads to the high ductility of the slab and has a good effect in limiting the widening of the crack width by forming other cracks. According to design code ACI 544.4R, a modified distribution stress diagram on the composite section was proposed and proven to be suitable for the prediction of flexural strength of the composite section with an error of 3.4% compared to the experimental result. The effect of the ultra-high performance concrete layer on the flexural strength of the composite slab was clearly demonstrated, and for the case in this study, the ultra-high performance concrete layer improves the flexural strength of the slab by about 11.5%.

Full-Scale Experimental Study on Flexural Performance of the New Precast UHPC Diaphragm Slab in Utility Tunnels

In this paper, a bending test of a precast ultra-high-performance concrete (UHPC) diaphragm slab was carried out. The test revealed that the flexural failure process of specimens under the action of a positive bending moment can be divided into three stages: the elastic, crack-propagation, and yield stages. The first stiffness reduction of the structure was caused by cracks at the bottom of the diaphragm slab, while the second stiffness drop resulted from the yielding of the bottom longitudinal rebars. During the loading process, the ultimate bearing capacity was 3.75 times higher than the design load value (150 kN vs. 40 kN). Additionally, a nonlinear finite element model was established using Abaqus software validated by the test and exploiting parameter analysis. Based on this model, the initial crack stress of the actual slab was determined to be 5.12 MPa. Parameter analysis indicated that the shear strength of the diaphragm slab was stronger than the flexural strength, and the diaphragm slab’s bearing capacity could be improved by increasing the ratio of bottom longitudinal reinforcement. This research confirmed that the new UHPC diaphragm slab used in Guangzhou Smart City is safe, and it also helped the design of similar UHPC slabs for utility tunnels.

Shear performance of the epoxy-bolt interface between UHPC slabs and GFRP girder

The shear performance of the epoxy-bolt interface between ultrahigh-performance concrete (UHPC) slabs and glass fibre-reinforced polymer (GFRP) girder was evaluated via push-out tests. A total of thirteen GFRP-concrete push-out specimens, including eleven GFRP-UHPC specimens with an epoxy-bolt interface, one GFRP-UHPC specimen with a bolt interface and one GFRP-normal-strength concrete (NSC) specimen with a bolt interface, were compared. Experimental parameters included the concrete strength, interface type, bolt spacing (sbolt), bolt-embedding length (hbolt), bolt number (nbolt), bolt diameter (dbolt) and bolt strength (σbolt). The test results revealed four failure modes, i.e., debonding of the epoxy layer, bolt shank shear failure, GFRP flange shear-out failure and concrete failure. Compared to the GFRP-UHPC specimen with a bolt interface, the bearing capacity and shear stiffness of the GFRP-UHPC specimen with an epoxy-bolt interface were approximately 10% and 40% higher, respectively, and the ultimate slip was approximately 3.5% lower. The employment of the UHPC slab substantially improved the shear stiffness by 19% compared with the GFRP-NSC push-out specimen. The nbolt, dbolt and σbolt showed a positive influence on the bearing capacity, whereas the hbolt showed a negative influence. The epoxy-bolt interface was recommended in the GFRP-UHPC hybrid beams to improve the composite action. Finally, the bearing capacities of the GFRP-UHPC push-out specimens with the epoxy-bolt interface were predicted.

Theoretical calculation of bending capacity of a steel beam - ultra high performance concrete slab composite girder

The composite girder, which combines a steel beam with an ultra-high-performance concrete (UHPC) slab, has gained significant attention in recent years as a new type of bridge structure. However, accurately estimating the bending capacity of such girders remains a challenge, as practical methods are limited. In this article, the authors propose a theoretical approach based on the Euler-Bernoulli beam theory to determine the bending capacity of composite girders. This approach considers the assumptions of plane sections remaining plane and infinitesimal strains during bending. By applying this theoretical approach, the authors derive a formula that allows engineers to calculate the bending capacity of the composite girder. The formula takes into account the dimensions and properties of both the steel beam and the UHPC slab. The derived formula serves as a valuable tool for evaluating the structural behavior and performance of composite girders. To validate its accuracy, the authors compare the results obtained from their calculations with numerical simulations of composite girder failures caused by bending. The close agreement between the theoretical calculations and the numerical simulation results confirms the reliability and applicability of the proposed formula. This research significantly contributes to the field of composite girder design by providing a practical and reliable method for estimating the bending capacity of steel beam-UHPC slab composite girders. The proposed theoretical approach, validated through numerical simulations, offers valuable insights for the design and optimization of these composite girders in various engineering applications.

Shear performance and failure process of perfobond connector in steel-UHPC composite structures

Nowadays, the application of Ultra-High Performance Concrete (UHPC) provides innovative concepts for structural designs of composite structures. Perfobond connectors (PBLs) with excellent shear capacity and fatigue performance may fully use the superiority of UHPC and thus are increasingly adopted in various novel steel-UHPC composite structures. However, the shear behavior and failure modes of PBLs embedded in UHPC slabs still need to be clarified. Therefore, this paper aims to evaluate the shear performance and further propose an equation for the shear capacity of UHPC PBLs. Firstly, six standard push-out tests taking the hole diameter, hole height, and whether perforated rebar was used as the parameters were performed. Subsequently, a detailed finite element (FE) model for the push-out test was established and validated by the test results, which took the fracture of perforated rebars into account by introducing the LW fracture criterion. Further, a parametric study was carried out to clarify the effects of dowel area, rebar sectional area, and hole shape. The results showed that benefiting from the high rigidity of UHPC, the PBLs with perforated rebars presented a slip-hardening behavior and excellent ductility. The slip corresponding to the rebar fracture grew with the rebar and hole diameter. Besides, the shear stiffness markedly rose with the hole diameter and height, while the effect of perforated rebars on shear stiffness was relatively small. Finally, the shear capacity equations for long-hole PBLs embedded in UHPC were proposed. The calculated results matched well with the 80 numerical and 21 collected experimental results.