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Predicting the shear strength of composite girders is critical in improving the efficiency of bridge engineering. To investigate the shear behavior of slender continuous steel–concrete composite girders commonly employed in bridge structures in hogging moment regions, experiments were conducted on three slender two-span continuous composite girders with the moment/shear ratio of the section at the interior support as the test parameter. The test results showed that all three continuous girders experienced web shear buckling and shear failure of the concrete slabs. As the moment/shear ratio increased from 0.59 to 0.89, the shear strength decreased by 12.5%. The shear strengths of the specimens were evaluated using the design methods in the existing AASHTO and Eurocode 4 codes, as well as the one proposed by Liang et al. They were 21%–38% and 33%–50% higher than those calculated by the existing AASHTO and EC4 codes, respectively, indicating that the two codes yielded very conservative results. A numerical study was conducted using the nonlinear finite element model validated by the test results. The results showed that the moment/shear ratio, concrete slab thickness, and web height-to-thickness ratio all significantly influence the shear strength; the codes will yield increasingly conservative predictions with the increase of concrete slab thickness or web height-to-thickness ratio. Both test and numerical results revealed that the design method proposed by Liang et al. can better predict the shear strength of continuous composite girders in hogging moment regions. [ABSTRACT FROM AUTHOR]

Composite columns of concrete-filled steel tubes (CFSTs) are very efficient in providing large structural resistances and rigidities. However, high strength S690 steel tubes are not covered in current design codes. Therefore, a series of experimental investigations into stocky composite columns with circular CFSTs under compression were conducted. A total of 21 stocky composite columns with different tube diameters and thicknesses made of Grades S355, S460 and S690 steel and Grade C60/75 concrete were tested under different loading conditions. Moreover, extensive measurements on the surface strains of the steel tubes were made during tests. Data analyses on the test results reveal that all composite columns exhibit enhanced section resistances and ductility at large deformations, indicating that the use of S690 steel and C60/75 concrete in these composite columns are highly efficient. A simple method for determining confining pressures provided by the steel tubes to the concrete cores in these composite columns is proposed, which involves a systematic analysis on the measured data and the use of von Mises yielding criterion without any complicated plasticity formulation. Based on the proposed method, the resistance contributions of both the steel tubes and the concrete cores are successfully quantified. Comparison between the measured and the predicted resistances using EN 1994–1-1 of these composite columns reveals that while the section resistances of these composite columns are safely predicted, the resistances of the steel tubes are underpredicted while those of the concrete cores are overpredicted correspondingly. The findings highlight the need to improve the predictability of the current design rules, and to give increased resistances of the steel tubes when high strength S690 steel tubes are used. [Display omitted] • Compression tests on composite columns of concrete-filled circular S690 steel tubes. • The use of S690 steel and C60/75 concrete in circular CFSTs are highly efficient. • A simple method for determining confining pressures is proposed. • Resistance contributions of the steel tubes and the concrete cores are quantified. • EC4 safely estimated section resistances but underestimated steel tube resistances. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation on the stability behaviour of cold-formed thick-walled steel tubes. Axial compression tests were conducted on 15 steel tubes with square and rectangle cross-sections to investigate their structural behaviours. The primary test parameters were slenderness and width-to-thickness ratios. Material properties, failure modes, load-deflection curves, and load-strain curves of the specimens are discussed. Furthermore, a numerical simulation was conducted to further investigate the effects of the slenderness ratio, width-to-thickness ratio, and initial geometric imperfection on the axial compression behaviour of cold-formed thick-walled tubes. Based on the experimental and numerical results, the applicability of the design codes, GB50018–2002, AISI S100–16, and EN 1993-1-1 was assessed. Results revealed that all three codes predicted the yield strength well after considering the cold-formed effect. With an increase in the slenderness ratio, GB50018–2002 and AISI S100–16 yielded increasingly unsafe predictions for overall stability, whereas EN 1993-1-1 yielded safe predictions. Finally, a modified design method for the overall buckling resistance of cold-formed thick-walled rectangular tubes under axial compression was proposed based on EN 1993-1-1 and verified using test and FEM results. • Axial compression behaviour of cold-formed thick-walled steel tubes is studied. • Cold-formed thick-walled steel tubes with square and rectangle sections were tested. • A nonlinear finite element model was developed and verified using tests results. • Eurocode 3 well predicted axial resistances of cold-formed thick-walled steel tubes. • A modified method for predicting axial overall buckling resistances was proposed. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) fiber is widely used in high strength engineered cementitious composites (ECC) due to its exceptional mechanical properties. However, the strong hydrophobicity of PE fibers hinders the bonding between fibers and matrix. To enhance the interfacial bond and fully utilize the reinforcing effect of PE fiber, this study employed polyvinylpyrrolidone (PVP) to modify the surface of PE fiber. The improvement effect of various PVP solution concentrations on ECC behavior was investigated. The microscopic characterization tests revealed that the surface of PE fibers was effectively coated by PVP, and the hydrophilicity of PE fibers was significantly improved after modification. Uniaxial tensile tests demonstrated that after PVP modification, the tensile strength and ultimate tensile strain of ECC increased by 20.7–27.2% and 87.3–109.3%, respectively. Furthermore, the ECC with modified PE fibers exhibited a decrease of 10–20% in the average crack width, coupled with a nearly twofold increase in the number of cracks, compared to the pristine ECC specimens. At microscale, the single fiber pull-out tests demonstrated that the interfacial frictional bond between fiber and matrix was effectively enhanced after PVP modification. The proposed method of modifying PE fibers surface with PVP offered a simple and environmentally friendly approach to enhance the strain hardening behavior of ECC, which provided valuable insights for optimizing the design of high strength ECC. • The PE fiber was modified by using polyvinylpyrrolidone (PVP) solutions. • The tensile properties of high strength ECC were improved upon fiber modifications. • The fiber/matrix interfacial bond was enhanced after PVP modification to PE fiber. [ABSTRACT FROM AUTHOR]

Slender steel-concrete composite girders are commonly used in bridge structures; however, the influences of web shear-buckling and concrete slabs on the shear strength of these girders have rarely been investigated thus far. In this study, an experimental and numerical investigation was condcuted to determine the ultimate shear strength of slender composite girders in hogging moment regions. Six simply-supported composite girders and a bare-steel girder were experimentally subjected to combined negative moment and shear. In addition, the influences of the moment/shear ratio, web height–thickness ratio, concrete slab thickness, and web aspect ratio on the failure modes, web elastic buckling loads, ultimate loads, and web out-of-plane deformations of composite girders were investigated. Moreover, a nonlinear finite element (FE) model was developed and verified using the experimental results, and the verified FE model was used to conduct the parametric analysis. The results revealed that the shear strength of the composite girders in hogging moment regions increased linearly with the thickness, longitudinal reinforcement ratio, and width of the concrete slab, among which the slab thickness posed the greatest effect, followed by the reinforcement ratio, and lastly, the slab width. Furthermore, an equation was proposed based on the web shear-buckling and the concrete slab shear contribution to express the shear strength of composite girders in hogging moment regions. Conclusively, the proposed equation was validated with the experimental and numerical results. • Shear strength of slender composite girders in hogging moment regions is studied. • A 3D nonlinear finite element model is developed and validated using tests results. • Shear strength increases linearly with thickness, width, and rebar ratio of slab. • A new equation for shear strength of slender composite girders is proposed. • Effects of web shear-buckling and the concrete slab are considered in the equation. [ABSTRACT FROM AUTHOR]

• Web shear buckling of composite girders in negative-moment regions is studied. • A 3D nonlinear finite element prediction model is developed and validated. • Top flange and slab together provide fixed boundary condition on one edge for web. • A new formula for web shear-buckling coefficients of composite girders is proposed. Steel–concrete composite girder webs used to connect flanges in bridges are generally slender, which introduces stability problems. The assumption in existing codes that the web is simply supported on four sides is excessively conservative and unreasonable. In this study, web shear buckling of steel–concrete composite girders in negative-moment regions were experimentally and numerically investigated. The failure modes, shear-buckling loads, and ultimate loads of the specimens were analysed. Based on the surface strain and out-of-plane deflection of the web, the web shear-buckling load was determined and compared with the theoretical results. A three-dimensional non-linear finite element model is developed and validated based on the experimental results. Using the validated numerical model, the elastic shear-buckling behaviour of the webs of composite girders under actual boundary conditions were investigated. The numerical results showed that the boundary conditions of the composite girder web can be regarded as simply supported on two opposite edges, fixed on one edge, and restrained by the bottom flange on one edge. A formula for calculating the web shear-buckling coefficient of composite girders was proposed based on the numerical results. [ABSTRACT FROM AUTHOR]

High-strength steel (HSS) members with welded sections exhibit a notably lower residual compressive stress ratio compared with common mild steel (CMS) members. Despite this difference, current codes often generalize the findings from CMS members to HSS members, and the previous unified residual stress models are generally conservative. This study focuses on the membrane residual stress distribution in Q690 steel welded box sections. By leveraging experimental results, the influence of section sizes and welding parameters on membrane residual stress was delved into. A larger plate size correlates with a decrease in the residual compressive stress across the section, with a more pronounced reduction observed in adjacent plates. Additionally, augmenting the number of welding passes tends to diminish residual stresses across the section. Results showed that membrane residual stress adhered to the section's self-equilibrium, while the self-equilibrium in the plates was not a uniform pattern. A reliable residual stress simulation method for Q690 steel welded box sections was established using a three-dimensional thermal–elastic–plastic finite element model (3DTEFEM) grounded in experimental data. This method served as the cornerstone for parameter analysis in this study and set the stage for subsequent research. As a result, an accurate unified residual stress model for Q690 steel welded box sections was derived. [ABSTRACT FROM AUTHOR]

Existing studies on the behaviour of steel–concrete composite girders under combined bending and shear are mainly focused only on composite beams with compact sections; very few studies have investigated slender composite girders, which are commonly used in bridge engineering. Therefore, the behaviour of slender steel–concrete composite girders under combined negative moment and shear were investigated experimentally and numerically in this paper. With the moment/shear ratio, reinforcement ratio, connection type, and web thickness as the experimental parameters, experiments were conducted on seven simply supported composite girders subjected to negative moment and shear. The test results showed that reinforcement ratio, concrete slab thickness, and web thickness significantly influence the ultimate load and failure modes of composite girders; the connection type only slightly influences the behaviour of full-shear-connection composite girders under combined negative moment–shear interaction. All the test data were outside the moment–shear interaction curve of Eurocode 4, i.e. Eurocode 4 tended to produce safer results. Then, a nonlinear finite element model was developed and validated using the experimental results. The factors affecting the moment–shear interaction of composite girders in negative-moment zones were studied through numerical simulation. The numerical results showed that the negative moment–shear interaction law changes little with the change of reinforcement ratio or slab thickness. The web depth-to-thickness ratio significantly influences the negative moment–shear interaction law, and the higher the web depth-to-thickness ratio, the earlier the composite girder begin experiencing moment–shear interaction. Unlabelled Image • Behaviour of slender steel-concrete composite girders under moment–shear is studied. • Composite girders with different experimental parameters were tested • A finite element (FE) prediction model is developed and validated. • Slab & web thicknesses greatly affect composite girder capacity and failure mode. • Web depth–thickness ratio greatly affects composite girder moment–shear interaction. [ABSTRACT FROM AUTHOR]

• Vertical shear behaviour of steel–concrete composite girders under negative moment. • Non-compact sections are considered. • A nonlinear finite element model was developed and verified using tests results. • The shear distribution of the cross-section in the load process was investigated. • Concrete slab contributes greatly to the shear capacity of non-compact girders. To investigate the vertical shear performance of steel–concrete composite girders commonly used in bridge engineering, experimental tests were conducted on five simply supported composite girders and one bare steel girder under negative moments. The main test parameters were depth and reinforcement ratio of concrete slab, connection type, and web thickness. The test results showed that the ultimate load of the composite girder increased by 10–20% compared with that of the bare steel girder. When the concrete slab thickness increased from 115 mm to 180 mm, the reinforcement ratio was doubled, web thickness increased from 6 mm to 8 mm, the shear capacity of the composite girders increased by 9.1%, 4.4%, and 49%, respectively. The specimen with Perfobond rib connectors exhibited comparatively better ductility. Compared with the results obtained with the current AASHTO and EC4 codes, the shear capacity increased by 8–16% and 5.8% for composite girders with web thicknesses of 6 mm and 8 mm, respectively. A nonlinear finite element model was developed and verified using the test results. Using the validated numerical model, the shear distribution of the cross-section was investigated and parametric analyses were conducted. The shear distribution of the section was divided into four stages, namely elastic, slab cracking, steady, and web buckling stages, during the entire loading procedure. Parameter analysis showed that the slab thickness significantly influences the shear capacity of the composite girder. With increasing web depth–thickness ratio, the contribution of the concrete slab to the shear capacity increases. [ABSTRACT FROM AUTHOR]

There is a lack of reliable research regarding the current engineering specifications considering the broad applications of high-strength steel (HSS) in civil engineering. Axial compression tests were performed on 12 HSS welded H-section stub columns using Q420–Q960 grade steels to study their local buckling behavior. In addition, we performed a parametric analysis using a finite-element model (FEM). Prior to the tests, the initial geometric imperfections and material properties of the specimens were measured to ensure that they satisfy the relevant engineering specifications. Twelve specimens exhibited typical local buckling. The axial deformation and axial strain were analyzed, and the utilization rate of the steel strength decreases with an increase in the yield strength and width–thickness ratio. Furthermore, a close relationship was observed between the occurrence of local buckling in the flange and the web. The results also indicate that the postbuckling strength of the axially compressed HSS welded H-section stub columns with slender sections cannot be ignored. The test results were used to verify the accuracy of the FEM, which considers the initial geometric imperfections and welding residual stress. For the Q420–Q960 steel welded H-section stub columns, parametric analysis was performed using the verified FEM to evaluate the limits of the width–thickness ratio and ultimate axially compressed bearing capacity. To apply current European, American, and Chinese codes, the modification factors for the width-thickness ratio limit and ultimate bearing capacity are given. [ABSTRACT FROM AUTHOR]

The static mechanical properties of grouped-stud shear connectors in steel–ultra-high-performance concrete (UHPC) composite beams are rarely investigated. In this study, the static mechanical properties of grouped-stud shear connectors in steel–UHPC composite beams are investigated via experiments and numerical simulations. Seven sets (14 specimens) of push-out tests are conducted by varying the parameters, including the concrete type, stud diameter, stud vertical spacing, and number of stud rows. The test results show that the shear bearing capacity of grouped-stud shear connectors increases by 27.5% as the stud diameter increases from 19 to 22 mm, by 13.2% compared with that of grouped-stud shear connectors in steel–UHPC and steel–normal concrete (NC), and by 5.8% when the stud vertical spacing increases from 125 mm (5.68 d) to 200 mm (9.09 d). However, the shear bearing capacity of the grouped-stud shear connectors remain almost unchanged when the number of stud rows is changed from two to four. The effects of stud diameter, stud tensile strength, stud vertical spacing, stud length, the cover thickness of the stud head, and stud transverse spacing on the shear bearing capacity of the grouped-stud shear connectors are investigated via numerical simulations. The results show that the stud diameter, stud tensile strength, and stud vertical spacing significantly affect the shear bearing capacity of the grouped-stud shear connectors, whereas the stud length, the cover thickness of the stud head, and stud transverse spacing exert almost no effect. Based on experimental and numerical analyses, an equation for predicting the shear bearing capacity of grouped-stud shear connectors in steel–UHPC is proposed and validated based on experimental and numerical results. • The static mechanical properties of grouped-stud shear connectors in steel–UHPC composite beams are investigated. • A nonlinear finite element model was developed and verified using tests results. • The Shear carrying capacity of the grouped-stud shear connectors in steel–UHPC is evaluated using current codes. • A formula for predicting the shear bearing capacity of grouped-stud shear connectors in steel–UHPC is proposed and validated based on experimental and numerical results. [ABSTRACT FROM AUTHOR]

Considering the broad applications of high-strength steel (HSS) in civil engineering and addressing the dearth of reliable research on current engineering specifications, axial compression tests were conducted on 12 HSS welded box-section stub columns made of Q420–Q960 grade steels; moreover, their local buckling behaviour was studied. In addition, a parametric analysis was performed using a finite element model (FEM). Prior to the tests, the initial geometric imperfections and material properties of the specimens were measured to ensure their adherence to relevant engineering specifications. The local buckling process, axial deformation, and strain of the specimens were analysed. As observed, the utilisation rate of steel strength decreased as the width–thickness ratio and yield strength increased. More importantly, the results revealed that the post-buckling strength of the axially compressed HSS welded box-section stub columns with slender sections cannot be neglected. Accordingly, a finite element analysis was conducted to verify the accuracy of the FEM that considered the initial geometric imperfections and welding residual stress. For the Q420–Q960 steel welded box-section stub columns, a parametric analysis was performed using the verified FEM to evaluate the limits of the width–thickness ratio and the ultimate bearing capacity. A new formula for the limit of the plate width–thickness ratio is proposed. To enable the application of the EN 1993-1-5 and ANSI/AISC 360–16 guidelines as well as the Chinese codes GB 50017–2017 and JGJ/T 483–2020, the modification factors are also provided for the ultimate bearing capacity. • Local buckling of Q420–Q960 steel welded box-section stub columns is studied. • Steel strength utilisation rate reduced as yield strength increased. • Post-buckling strength of axially compressed stub columns is not negligible. • A new formula for the limit of the plate width–thickness ratio is proposed. • The modification factors are also provided for the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]