Ultra-high Performance Concrete Slabs Research Articles

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.

Self-heating ultra-high performance concrete with stainless steel wires for active deicing and snow-melting of transportation infrastructures

The development of self-heating concrete composites with stable electrical conductivity and strong heating capability as well as high mechanical properties is the key for achieving active deicing and snow-melting of transportation infrastructures. Due to their microscale diameter and high aspect ratio, stainless steel wires (SSWs) can form an extensive electrically and thermally conductive as well as reinforcing network inside concrete at a low content. Together with the stainless feature of SSWs as well as high structural compactness and durability of ultra-high performance concrete (UHPC), SSWs reinforced UHPC is expected to be developed into self-heating composites with strong and stable heating capability as well as ultra-high mechanical performance and durability. Therefore, this study evaluated the self-heating capability as well as active deicing and snow-melting performances of such composites. The developed SSWs reinforced UHPC slab demonstrates stable electrical conductivity and strong self-heating capability in cycle uses as well as efficient active deicing and snow-melting properties under different environmental conditions. The electrical resistivity of SSWs reinforced UHPC is only 2.58 Ω cm and it is hardly affected by the change in temperatures, numbers of cyclic self-heating, and numbers of deicing and snow-melting. The SSWs reinforced UHPC slab can be heated from 21.4 °C to 82.4 °C in 16.18 min under the voltages of 30 V in an indoor environment at a temperature of 21.2 °C. The slab only needs 28.98 min, 15.20 min, and 27.31 min to completely melt 9 mm of ice in a freezer at a temperature of −25.6 °C, 5 cm of naturally accumulated snow and 2 cm of artificially compacted snow in an outdoor environment at a temperature of about −5 °C with the wind speed up to 5.36 m s−1. Furthermore, thanks to their characteristics of no adverse effect on vehicle tires and excellent fatigue resistance, self-heating SSWs reinforced UHPC shows promising application prospects in active deicing and snow-melting of transportation infrastructures (e.g., airport runway, pavement and bridge deck) suffering from frigid weather.

Effects of stud aspect ratio and cover thickness on push-out performance of thin full-depth precast UHPC slabs with grouped short studs: Experimental evaluation and design considerations

Steel-precast ultra-high-performance concrete (UHPC) composite beams containing grouped short studs in thin full-depth slabs are an economical and eco-friendly alternative for accelerated bridge construction (ABC). Nevertheless, there is limited information on the push-out performance of thin full-depth precast UHPC slabs with grouped short studs. To this end, this study examined the impacts of stud heights disturbing from 35 mm to 85 mm, stud diameters ranging from 16 mm to 22 mm, and cover thicknesses varying from 15 mm to 65 mm on the push-out performances of such members. The test results indicated that increases in stud height yielded insignificant enhancements in the shear stiffness, strength, and ductility of grouped short studs embedded in thin full-depth precast UHPC slabs. Similarly, variations in the stud height and cover thickness exerted negligible influence on the structural performance. Notwithstanding, larger cover thicknesses or larger stud diameters allow the stud to exhibit attractive shear behaviors. Based on these results, a lower limit of 1.84 for stud aspect ratios (i.e. the ratio of stud height to stud diameter) and 15 mm for cover thickness were recommended. Finally, more accurate formulas were developed to predict the shear capacity of studs by capturing weld collar contributions and to simulate the load-slip relationship of grouped short studs embedded in thin full-depth precast UHPC slabs by considering the effects of slab thickness.

Avaliação de danos e inovação de solução eficiente de reabilitação de lajes de concreto armado expostas a explosão de contato

abstract: Under contact explosions, the reinforced concrete structures can behave in a brittle manner with highly localized damage like concrete cratering, spalling, and reinforcement rupturing. High-speed fragmentation resulting from concrete spall may cause severe casualties and injuries. It is therefore important to restrained concrete fragments and improve collapse resistance of the slab. A new retrofitting technique is proposed in this paper which completely prevents fragmentation. To mitigate blast effects on civil structures, a new kind of concrete material named Ultra-High-Performance-Concrete (UHPC) is now widely studied and applied. UHPC material is known for its high compressive and tensile strength, large energy absorption capacity as well as good workability and anti-abrasion ability compared to normal strength concrete(NRC). All of recent experimental published work concerning blast performance of UHPC slabs under far or near explosion effect, on the other side, the contact explosion tests are relatively limited experimentally and nearly impossible because of security restrictions and costly in terms of both preparation and measurements. So, the real and accurate finite element models are needed to address this gap and understanding the real contact-explosion behavior of both NRC and UHPC slabs. The numerical analyses allow gaining insight into the complex failure mechanisms occurring in the slab and not directly observable. In this study, coupled smoothed particle hydrodynamics (SPH) method and finite element method is utilized to simulate the contact blast tests. Numerical results are compared with the experimental observations, and the feasibility and accuracy of the numerical model are validated. The validated numerical model provided a useful tool for designing potential blast-retrofitting solutions which can prevent the local material damage and fragmentations in both NRC & UHPC slabs subjected to contact explosion. This study introduced adequate and very efficient protection solution for both NRC & UHPC slabs exposed to contact explosion (1 kg of TNT) by utilizing the composite action generated between slabs & bonded steel plates. The 2 mm and 1 mm bonded steel plates at both faces of the NRC and UHPC slabs respectively attained a superior resistance to contact explosion.

Numerical and theoretical research on flexural behaviour of steel-precast UHPC composite beams

In order to promote the utilization of high strength materials and application of prefabricated structures, flexural behaviour of section steel-precast UHPC (Ultra-High performance concrete) slab composite beams prefabricated with bolt shear connectors are numerically simulated by the finite element (FE) software ABAQUS. The model is verified by three prefabricated steel-concrete composite beams tested. Numerical analysis results are in good accordance with experimental results. Furthermore, parametric studies are conducted to investigate the effects of strength of section steel and concrete of precast slab, thickness of section steel, width and height of precast concrete slab, diameters of steel bars and bolt shear connectors. The flexural behaviour of composite beams, in terms of bearing capacity, deflection, ductility and energy dissipation, are compared. The numerical results indicate that the improvement of strength of section steel results in a decrease of ductility, but a significant increase of the ultimate load and energy dissipation. Compared with composite beam made of section steel with thickness of 10 mm, the ultimate load of beams made of section steel with thickness of 14 and 18 mm improve by 29.0% and 58.8%, respectively, the ductility enhance by 2.8% and 8.3%, respectively, and the energy dissipation improve by 8.0% and 12.3%, respectively. With the increase of concrete strength, the ultimate load, deflection and energy dissipation gradually increase. The ductility of steel-UHPC composite beam is the highest, that of steel-HSC composite beam is the lowest. The effect of reinforcement ratio of concrete slab and diameter of shear bolts on the ultimate load of composite beam is limited. Simplified formulae for two different sectional types of proper-reinforced section steel-precast UHPC slab composite beams occurred bending failure are proposed, and the predicted results fit well with the simulated results. The results can be taken as a reference for the design and construction of section steel-precast UHPC slab composite beams.

An experimental study of FRP truss side plate joint

Ultra-high performance concrete (UHPC) slab - fiber reinforced polymer (FRP) truss hybrid beam has been proved as an effective and advanced bridge system. However, the limited shear strength and the significantly lower transverse properties compared with its longitudinal counterparts result in low rigidity and load carrying capacity of bolted FRP truss joints, which governs the overall performance of the UHPC slab- FRP truss hybrid beam. A FRP truss side plate joint was proposed which integrates a steel U-shaped gusset plate (SUGP) to reinforce the traditional bolted joint. The proposed joint outperformed the conventional bolted joints in terms of the failure mode, load carrying capacity, and stiffness. The load carrying capacity of the proposed joint can be improved by up to 63% and the ultimate deflection was reduced by up to 33%. The effects of a variety of key design parameters, including adhesive, bolt diameter, pre-torque, and length and thickness of the gusset plate, on the performance of the SUGP joint were evaluated. Test results showed that: (i) the adhesive between the pultruded FRP profiles and the steel gusset plate could increase both the initial stiffness and ultimate load carrying capacity of the steel SUGP joint; (ii) length and thickness of the steel gusset plate did not result in notable difference in the behavior of the steel SUGP joint for the range of parameters investigated herein; and (iii) application of pre-tightening torque within the thread of the bolts slightly improved the load carrying capacity but significantly improved the ductility of the steel SUGP joint.

Effect of Spraying Polyurea on the Anti-Blast Performance of the Ultra-High Performance Concrete Slab.

Recently, polyurea has been applied to improve the anti-blast performance of metal plates, masonry walls, and concrete structures. However, the strengthening effectiveness of polyurea on ultra-high performance concrete (UHPC) slabs with an overall response is still unclear. Hence, this paper examined the strengthening effectiveness of polyurea on the anti-blast performance of UHPC slabs under near-field explosion by the finite element (FE) method. First, a benchmark finite element model for UHPC and polyurea-UHPC (PUHPC) slabs under blast loading was established and validated by field blast tests, with scaled distances ranging from 0.4 m/kg1/3 to 0.8 m/kg1/3. After that, parametric analysis was conducted to fully understand the strengthening effectiveness of polyurea on the anti-blast performance of the UHPC slab. Factors including the scaled distance, polyurea thickness, span-to-depth ratio of the slab, and longitudinal reinforcement ratio were considered. The results showed that (1) spraying polyurea on the rear face of the UHPC slab can reduce the width of cracks and mitigate the damage of specimens; (2) the strengthening effectiveness of polyurea on the UHPC slab became prominent when the UHPC slab suffered a larger maximum deflection; (3) in terms of the deflection and energy absorption capacity of PUHPC slabs, the optimum thickness of sprayed polyurea was determined to be 8 mm to 12 mm; and (4) by adopting the multiple nonlinear regression method, a prediction formula was developed to quickly obtain the end rotation of the UHPC slab strengthened with polyurea under near-field explosions.

Behavior of Reinforced Ultra-High Performance Concrete Slabs Under Impact Loading After Exposure to Elevated Temperatures

Steel fiber-reinforced ultra-high performance concrete (UHPC) material is prone to explosive spalling under elevated temperatures. With the addition of polypropylene (PP) fiber, thermal spalling of UHPC can be mitigated and its fire resistance can be improved. This research investigates the impact resistance of steel and PP fiber-reinforced UHPC slabs after exposure to elevated temperatures, and the structural behavior and damage were compared against normal strength concrete (NSC) slabs. Karagozian & Case concrete (KCC) model was adopted to simulate both NSC and UHPC materials. With consideration of thermal hazards, the material damage, equation of state and strain rate sensitivity were adapted. The validity of this numerical model was evaluated against available experimental results. The numerical model was used to investigate the impact resistance of the reinforced UHPC slabs after exposure to fire hazards. The effect of fire exposure time, impact velocity and impact mass on the resistance of the reinforced NSC and UHPC slabs were analyzed. The simulation results revealed that punching shear failure areas in the NSC slabs were 2.5 times, 3.4 times, 3.0 times and 1.2 times larger than the UHPC slabs after exposure to international standardization ISO-834 standard fire for 1[Formula: see text]h, 2[Formula: see text]h, 3[Formula: see text]h and 4[Formula: see text]h, respectively. After exposure to the standard fire ISO-834 for 2 h, the punching shear failure on the bottom side of NSC increased 90.9% with the increase in falling height from 1[Formula: see text]m to 7[Formula: see text]m, while for the UHPC slabs, the increment was around 67.9%. After exposure to the standard fire ISO-834 for 2[Formula: see text]h, the punching shear damage of the NSC slabs increased by 72.9% with the punch weight increased from 100[Formula: see text]kg to 700[Formula: see text]kg, whereas the damage in the UHPC slabs increased by 53.8%.

Parametric Study on Contact Explosion Resistance of Steel Wire Mesh Reinforced Geopolymer Based Ultra-High Performance Concrete Slabs Using Calibrated Continuous Surface Cap Model

This paper conducts a parametric analysis on the response of geopolymer-based ultra-high-performance concrete (G-UHPC) slabs reinforced with steel wire mesh (SWM) subjected to contact explosions using the validated Continuous Surface Cap (CSC) model. Firstly, based on the available experimental data, the CSC model parameters, which account for the yield surface, damage formulation, kinematic hardening, and strain rate effect, were comprehensively developed for G-UHPC. The modified CSC model was initially assessed by comparing the quasi-static test results of G-UHPC. Then, the numerical modeling was performed on 200 mm thick SWM-reinforced G-UHPC slabs against 0.4 kg and 1.0 kg TNT contact explosions. The fair agreement between the numerical and experimental data concerning the local damage of the slabs was reported to demonstrate the applicability of the material and structural models. With the validated numerical models, a parametric study was further acted upon to explore the contribution of the variables of SWM, slab thickness, and TNT equivalence on the local damage and energy evolution of G-UHPC slabs subjected to contact blasts. Moreover, based on simulation results from the parametric study, an updated empirical model was derived to evaluate the local damage pattern and internal energy absorption rate of SWM-reinforced G-UHPC slabs.

Experiment and finite element analysis of bending behavior of high strength steel-UHPC composite beams

High-strength structural steel (HSS) and ultra-high-performance concrete (UHPC) are materials countries hope to use in civil engineering construction. This study investigated the static bending performance of HSS-UHPC composite beams through experiment and finite element analysis. First, four static bending tests were conducted. The test parameters included the degree of shear connection and the arrangement of studs (single-stud and group-stud arrangement). The group-stud arrangement was applicable for the assembly construction, which developed increasing fast in civil engineering. The experimental results showed that the failure mode of the composite beam with partial shear connection was stud fracture caused by an insufficient number of studs to withstand the shear force on the steel–concrete interface; for the composite beam with full shear connection, the failure mode was the crushing of the UHPC slab at the loading point. The deflections at mid-span for both the single-stud and group-stud specimens were the same in the elastic stage. However, the deflection of the group-stud specimen was greater than that of the single-stud specimen in the plastic stage. The results showed that the bending stiffness of the composite beam with studs arranged in a group decreased faster. Under the same load, the steel–concrete interfacial slip of the group-stud specimen was also greater than that of the single-stud specimen. Finally, this study compared the mechanical properties of the Q690-UHPC and Q690-normal strength concrete C60 (NSC60) composite beams through finite element analysis. It was found that under the same deflection, the damage of the normal strength concrete slab was more substantial than that of the UHPC slab. The bending stiffness and ultimate bending capacity of the Q690-UHPC composite beam were greater. Q690 HSS had better material strength matching with UHPC than that of normal strength concrete C60.

Experimental study of damage to ultra-high performance concrete slabs subjected to partially embedded cylindrical explosive charges

In this study, long and thin cylindrical charges were partially embedded in ultra-high-performance concrete (UHPC) and normal-strength concrete (NSC) slabs to investigate the damage characteristics of UHPC slabs subjected to explosions by conventional weaponry. The sizes of ejection and spalling craters were recorded after the experiment to compare the obtained data with the concrete slab damage characteristics predicted by current damage forecasting methods. The current damage forecasting methods were found to be unsuitable for the conditions considered in this study as they do not account for the effects of the explosive shape and depth of embedment (DOE) simultaneously. The results of the experiment using partially embedded charges indicated that the damage on the sides of the slabs decreased with decreasing slab thickness; the use of UHPC without fiber reinforcement instead of using NSC significantly increased the compressive strength but decreased the ability of the concrete structure to resist spalling damage; furthermore, a suggested estimation of the cone slope angle is 60° for theoretical analyses and the design of numerical simulation or field experiments.

Interfacial shear and flexural performances of steel–precast UHPC composite beams: Full-depth slabs with studs vs. demountable slabs with bolts

Two types of steel–precast ultra-high-performance concrete (UHPC) composite beams were investigated in this study, which can be vastly used in accelerated bridge construction (ABC). One of them contains full-depth slabs with stud shear connectors embedded in shear pockets, while the remaining one adopts demountable slabs with high-strength friction-grip bolts (HSFGBs). Four-point bending tests were conducted on six large-scale composite beams to investigate the interfacial shear and flexural performance of such innovative types of steel–precast UHPC composite structures. The failure modes, vertical deflection, horizontal interfacial slip and the stain distribution at mid-span cross-section were investigated. The experimental results indicated that the cracking patterns and failure modes of the composite beams were highly dependent on the slab concrete types and the degrees of shear connection. The composite beams adopting UHPC slabs achieved larger cracking resistance and higher ultimate strength than those containing normal-strength concrete slabs and favorable ductility. Similar trends were also presented by the composite beams with large degrees of shear connection. The composite beams with HSFGBs showed enhanced load capacities and larger vertical deflections and horizontal interface slips at peak load than those adopting stud shear connectors. Additionally, the composite beams that failed in shear connector fractures presented shear resistance–interface slip relationships comparable to their push-out counterparts. Finally, theoretical formulas based on rigid plastic analysis were proposed for predicting the flexural capacity of both types of composite beams.

Experimental and Numerical Study on the Shear Performance of Short Stud Shear Connectors in Steel–UHPC Composite Beams

Steel–ultra-high-performance concrete (UHPC) composite beams offer numerous advantages, such as structural self-weight reduction, bending stiffness improvement, and tensile cracking limitation in slabs. However, few studies have focused on the shear performance of short stud shear connectors in steel–UHPC composite structures. To this end, push-out tests were carried out to evaluate the effect of slab thickness, stud diameter, and casting method on the failure mode, load–slip relationship, ultimate shear strength, shear stiffness, and ductility. The test results indicate that by increasing the slab thickness from 50 to 75 mm, the stud shear capacity and initial shear stiffness were improved by 11.38% and 23.28%, respectively. The stud shear capacity and initial shear stiffness for specimens with stud diameters of 25 mm were 1.29 and 1.23 times that of their 22-mm-diameter counterparts. In addition, adopting precast UHPC slabs could achieve comparative shear resistance (94.91%) but a better slip capacity (108.94%) than those containing conventional monolithic cast slabs. Based on the experimental results, a finite element (FE) model was established to reflect the plastic behavior of the tests and the damage process in the short stud shear connectors. Based on the validated FE model, a parameter study was then performed to further explore the influence of the stud diameter, stud tensile strength, steel beam tensile strength, monolithic slab concrete strength, precast slab concrete strength, and shear pocket concrete strength on the shear performance of short studs in steel–UHPC composite structures.