In steel-concrete multi-girder composite bridges, transverse connections and load transfer between girders result in distinct structural behavior compared to conventional single-girder composite beams. To explore the structural response of each girder and the load transfer path, a model test with a scale of 1: 3.33 for multi-girder composite bridge consisting of cross beams, steel plate girders, and a concrete deck was conducted. Subsequently, static loading tests were carried out on two single composite girders obtained by cutting and separating the original bridge. Structural response of each girder in the multi-girder composite bridge under different load configurations, quantity of cross beams, single-girder and multi-girder systems are presented and discussed, including load-deflection curves, flexural stiffness, strain history, shear lag effect and transverse moment distribution. Experimental results indicated that cross beams and concrete deck are the key components for load transfer. The maximum flexural stiffness of the girder was exhibited under between girders loading, while the concrete deck under middle girder loading demonstrated severe shear lag effect. The cross beam arrangement has significant impact on the performance of composite bridge, and the flexural stiffness and transverse moment were reduced by 30.2% and 35.1%, respectively, by decreasing the number of cross beams from 6 to 0. Experimental results also highlighted the discrepancy of mechanical performance for main girders in multi-girder and single-girder systems. As compared to girder in multi-girder systems, the flexural stiffness and shear lag effect of the girder after separation were reduced by 18.9% and 65.9%, respectively. Finally, the applicability of existing standards for predicting effective width and transverse moment of multi-girder composite bridges were performed.

In this paper, a novel U-shaped steel-concrete composite bent cap (USCBC) is introduced, and numerical models of the USCBC are established to investigate their failure mechanism. Parametric analyses use parameters such as steel plate thickness, material strength, cross-sectional dimensions, and shear connector capacity. Formulas are derived to calculate the cracking and peak load applicable to the USCBC. The research findings indicate that under a four-point loading condition at mid-span, the USCBC exhibits flexural behavior prior to yielding and then shear behavior post-yielding, ultimately failing when the concrete in the shear span region reaches its tensile ultimate strength. During the loading process, a positive shear lag effect is observed along the transverse direction of the cross-section. The most significant factors affecting the flexural performance of the USCBC are the cross-sectional height and concrete strength, while the cross-sectional width and steel strength have less notable impacts. The shear connector capacity considerably influences the structure's post-cracking behavior. The calculated results from the proposed formulas for cracking load and peak load of the USCBC align well with the finite element simulation results, thereby providing theoretical support for the flexural calculations of the USCBC. The proposed design formulas are applicable to USCBCs with conventional materials (e.g., steel grades Q235-Q460 and concrete grades C30-C80) and within the studied geometric parameter ranges.

Staggered widening refers to a rehabilitation scheme in which new bridge piers are not aligned with existing ones due to constraints from current river embankments or road boundaries. To date, research on staggered widening bridges remains limited. Owing to the staggered span layout, girders are supported by piers of adjacent bridges at the mid-span region, leading to a vehicular load distribution mechanism distinct from that of conventional widening bridges, especially for interior girders near the closure slab. This study investigates the load distribution factor (LDF) for bending moment in staggered widening bridges. First, a simplified analytical model is developed using the rigid-jointed girder (RJG) method to derive transverse influence lines. The boundary conditions in the conventional RJG method are modified to capture the mid-span supporting effects provided by adjacent piers. The governing equation of the analytical model is derived based on the updated model configuration. The accuracy of the simplified model is then verified against finite element analysis results. Transverse load distribution characteristics of staggered widening bridges are compared with those of conventional widening schemes. On this basis, a parametric study is performed to examine the effects of key parameters, including diaphragm rigidity, flange rigidity, girder rotational stiffness, closure slab width, girder width, and the number of girders, on the LDF. Finally, based on the parametric analysis results, a generalized formula is proposed for predicting the girder LDF of staggered widening bridges.

This study presents a semi-precast U-shaped steel-concrete composite cap beam (USCCB), in which the steel shell serves as both permanent formwork and a structural load-bearing component. The design uses Perfobond Leiste (PBL) connectors and longitudinal reinforcement in the bottom plate to reduce longitudinal slip. PBL connectors, combined with shear studs on the web, enable effective shear transfer and enhance composite action with the concrete, while also acting as stiffening ribs. Two 1:2-scale specimens were fabricated and subjected to four-point bending tests. Steel-concrete interface debonding was simulated by applying a release agent to investigate its effects on the mechanical performance of the USCCB. Experimental observations showed that, compared to the debonded specimens, the USCCB with intact bonding exhibited stronger composite action and negligible interfacial slip. Under ultimate load, both specimens exhibited crushing of the concrete at midspan first, followed by varying degrees of local buckling in the flange plates. The test results revealed a 5.9% reduction in the ultimate bearing capacity for the debonded specimens, while the maximum interface relative slip reached 3.5 mm. A finite element (FE) model was developed and validated through comparison with experimental results and digital image correlation (DIC) data. Furthermore, a theoretical model for flexure-dominated failure was established, including a discussion on the coefficient for the equivalent rectangular stress block depth. Based on comparisons between the FE results and shear-dominated failure predictions under different shear-span ratios, web thicknesses, and concrete strengths, recommendations were proposed regarding the necessity of iterative analysis. These findings provide a theoretical foundation for the structural design of the USCCBs.

In the seismically active zone stretching from Nyingchi to Chamdo in Tibet, China, talus slopes are widely distributed. To investigate their seismic stability and failure mechanism, three models, mixed, pure gravel, and pure sand models were constructed for shaking table tests and DEM simulations. The results indicate that seismic loading significantly impairs the stability of talus slopes, leading to two distinct failure modes: shallow failure and large-scale failure. For large-scale failure, three models exhibited a consistent failure process consisting of initial triggering, subsequent sliding, and final spreading stages. Grading fundamentally controls sliding through its influence on mesostructural evolution. The particle sorting in the mixed model was notably pronounced, generating a stratified three-layer structure comprising a low-resistance intermediate finer layer, along with the large voids and wheel structures in the shear zone, resulting in the longest sliding. For the pure gravel model, shear resistance weakened progressively along with significant dilation, resulting in the longest triggering stage but the shortest sliding distance. The pure sand model developed distinct wheel structures with negligible large voids inside the shear zone, exhibiting intermediate sliding distance. Furthermore, an assessment method for seismic damage regarding the actual seismic loading, slope scale, and material composition was proposed for dry talus slopes in the studied region.

Debonded link slabs are commonly adopted to replace the expansion joints of existing simply supported bridges, thereby protecting the girders and piers underneath them from exposure to water and deleterious agents. The primary challenges for the accurate simulation of link slab bridges are the modeling of slab-girder interaction as well as cracking and plastic behavior in both girders and link slabs. However, these nonlinear effects are not fully captured by the current analysis methods, leading to inconsistent research findings. In this study, a refined finite element model (FEM) was established in ABAQUS to simulate the behavior of link slab bridges, and its accuracy was validated by comparison with existing test data. The simulation results indicated that: (1) the inconsistent findings in previous studies are partly attributed to the neglect of cracking and plastic behavior in girders, and (2) debonded link slabs are separated from girders under vertical loads. A novel macroscopic mechanical model was developed based on a "two-point contact" deformation pattern to simplify the complex interaction between the link slabs and girders. Moreover, both the tensile force and bending moment in the link slab were incorporated into the macroscopic model to improve simulation accuracy. The model formulations were derived based on different support conditions. This macroscopic model can be naturally integrated with existing general numerical approaches, such as the finite element method, discrete element method, and applied element method, allowing cracking and plastic behavior in girders to be incorporated into the numerical formulation. The accuracy of the developed macroscopic model was validated by comparison with the simulation results of the refined FEM. Finally, an influence analysis was performed using a macroscopic model to investigate the behavior of the link slab bridges.

In order to determine the pull-out capacity and failure mechanisms of headed stud connectors under freeze-thaw cycles (FTCs), freeze-thaw and pull-out tests were performed on thirty-six pull-out specimens with varying effective embedment depths (60 mm, 90 mm, and 110 mm) subjected to 0, 50, 75, and 100 FTCs. Failure modes, concrete strength, dynamic elastic modulus, mass loss rate, and load-displacement behavior of the specimens after different FTCs were presented and discussed. Experimental results indicated that the degradation of pull-out capacity (Pu) is significantly affected by freeze-thaw damage, particularly after 50 FTCs. Increasing the number of FTCs from 0 to 50 and 100 times, the Pu decreased by 14.9 % and 38.7 %, respectively. Results also indicated that the Pu was enlarged by the magnification of the embedment depth. Increasing the embedment depth from 60 to 90 and 110 mm, the Pu magnified by 65.0 % and 171.1 %, respectively. A finite element (FE) model was further established to gain insight into the effects of concrete strength, effective embedment depth, and stud head diameter on the Pu after FTCs. Numerical results indicated that smaller embedment depths and stud head diameters reduced freeze-thaw resistance, while freeze-thaw damage was minimally influenced by concrete strength. Increasing embedment depth and stud head diameter is recommended to improve the freeze-thaw resistance of pull-out capacity. Furthermore, an analytical model that considers the number of freeze-thaw cycles that is capable of predicting the pull-out capacity of headed studs after freeze-thaw damage was proposed.

In steel-concrete composite structures, in addition to shear, tension, and combined shear and tension loads, stud connectors also are subjected to combined shear and compression loads. This study is the first to systematically investigate mechanical performance of stud connectors under combined shear and compression loads through experiments and finite element (FE) stimulations. Nine specimens of push-out test are conducted with varying parameters, including axial compressive stress and the friction coefficient at the interface between the steel girder and concrete. Additionally, the finite element simulation and parametric analyses are conducted to further study the influence of the stud length, the stud diameter, the concrete strength, the axial compressive stress and the friction coefficient on the mechanical performance of stud connectors. Based on the experiments and finite element analysis, the calculation equation for predicting the shear capacity of stud connector subjected to combined shear and compression loads in steel-concrete composite structures are proposed and validated by experimental results. The results indicate that at low friction coefficients, increasing axial compressive stress has a negligible effect on the shear capacity of stud connectors. Moreover, specimens with higher friction coefficients exhibit reduced ductility compared to those with lower friction coefficients. The presence of axial compressive stress also alters the influence of stud diameter, stud length, and concrete strength on the mechanical performance of the stud connectors, leading to deviations from the trends typically observed under conventional loading conditions. Furthermore, increasing the friction coefficient proves more effective in improving the shear capacity than merely increasing the axial compressive stress. The proposed shear capacity equation for stud connectors under combined shear and compression loads offers improved accuracy in evaluating connection performance, thereby contributing to the optimized design of steel-concrete composite structures.

Basalt fiber reinforced recycled aggregate concrete is a sustainable and environmentally friendly concrete material with great high temperature resistance. Mechanical properties can be enhanced after filling concrete into steel tubes to form concrete-filled steel tubes. Post-fire behavior is critical in structural design, as high temperature severely deteriorate the capacity and deformation characteristics of concrete and steel structures. This study established finite element models to assess the post-fire axial compressive behavior of basalt fiber reinforced recycled aggregate concrete-filled steel tube based on 20 short columns axial compressive tests after natural-cooling from 20, 300, 500, and 800 ℃. The findings revealed that recycled aggregate decreased post-fire capacity and stiffness, while basalt fiber reduced post-fire capacity but increased the compressive stiffness of the short columns. Based on test results and existing formulas, a novel constitutive relationship for basalt fiber reinforced recycled aggregate core concrete was formulated, accounting for the impact of basalt fiber content, recycled aggregate replacement ratio, and temperature. The finite element model aligns well with test results and can be used in sustainable basalt fiber reinforced recycled aggregate concrete-filled steel tube design and repair. Five design standards were evaluated to calculate the post-fire load capacity. The assessment shows EN 1994-1-1 performs the best in design standards, followed by AS/NZS 2327, AIJ 1997, and GB 50936-2014. ANSI/AISC 360-16 is the worst which seriously underestimated the load capacity.

Fatigue cumulative damage of stud connectors critically affects the safety and durability of steel-concrete composite beams, particularly under corrosive environments. To address this issue, ten push-out tests are conducted in this study, including three under static loading and seven under cyclic loading, to investigate the fatigue cumulative damage of stud connectors under non-corroded, pre-corroded, and coupled corrosion conditions. The experimental results are analyzed to compare fatigue performance and reveal the corresponding fatigue cumulative damage mechanisms. Two types of fatigue cumulative damage processes are identified: critically triggered and continuously accumulated. Based on these findings, fatigue cumulative damage evolution models for both types are developed and experimentally validated. The results indicate that fatigue load and corrosion conditions have significant effects on the fatigue life and interfacial cumulative slip growth rate of stud connectors. However, corrosion has a relatively less impact on shear stiffness degradation laws during cyclic loading. All fatigue specimens ultimately fail due to fracture of the stud connectors. The stud connectors exhibit the largest bending deformation under the coupled corrosion-fatigue condition, followed by the pre-corrosion fatigue condition and no-corrosion fatigue condition. Despite differences in fatigue load and corrosion conditions, all specimens follow a similar fatigue cumulative damage process, which can be divided into three stages: bonding failure at the steel-concrete interface, degradation of the concrete anchorage effect, and bending and failure of the stud connectors. These three stages approximately account for 10 %, 80 %, and 10 % of the total fatigue life, respectively. Additionally, the two proposed fatigue cumulative damage evolution models are validated and demonstrated good reliability, showing potential for accurately predicting the remaining fatigue life of stud connectors in steel-concrete composite structures.

This study introduced a new type of welded joint called the non-planar oblique butt-welded joint. This joint conceptualized from cable-stayed bridge anchor plate involves mother plates with both out-of-plane and in-plane angles, leading to a complex stress concentration phenomenon. A dataset of equivalent structural stress concentration factors (ESCF) which was effective in evaluating complex welded structures fatigue was extracted from the test-validated finite element models. Five machine learning models were trained. The best-performing Support Vector Regression (SVR) was selected to build an ESCF prediction model based on the parameters (out-of-plane angle, in-plane angles, length-to-thickness ratio, and stress amplitude ratio), and then subjected to a SHapley Additive exPlanations (SHAP) analysis. Results showed that the ESCF on the concave side increased with the out-of-plane angle and decreased on the convex side, similar to the influence of the length-to-thickness ratio and the stress amplitude ratio. The increase of the in-plane angles led to the redistribution of ESCF value due to the change in structural stiffness. As a result of the analysis, an anti-fatigue design framework was developed. This framework assists designers in optimizing the parameters and predicting fatigue behavior of non-planar oblique butt-welded joints.

The chopped basalt fiber reinforced concrete (BFRC) exhibits excellent tensile, flexural, crack resistance, and durability properties, but the factors influencing BFRC compressive strength have not been fully discussed. There are contradictory reports in some studies on the effect of basalt fiber (BF) on the concrete compressive strength. This study investigated the coupling influence of plain concrete and BF on BFRC compressive strength. Firstly, 328 data points from 22 literatures were collected, then a statistical analysis was conducted, indicating that when the water-binder ratio < 0.45, 0.4 < sand rate < 0.55, fly ash – binder ratio > 0.15, binder – aggregate ratio > 0.24, and recycled aggregate replacement ratio was low, adding appropriate BF tended to improve the compressive strength. To effectively evaluate BFRC compressive strength, XGBoost regression model and seven classification models were trained to predict the effect of BF on compressive strength. It is found that classification models have more practical values. Random Forest and XGBoost classification model exhibit well, with accuracy over 93

This paper investigates the mechanical behavior of PBL shear connectors in UHPC during the elastic stage, utilizing push-out experiments and numerical simulation. This study simplifies the mechanical behavior of PBL shear connectors in UHPC under normal service conditions as a plane strain problem for the UHPC dowel and a Winkler’s Elastic foundation beam theory for the transverse reinforcement. The UHPC dowel is a thick-walled cylindrical shell subjected to non-axisymmetric loads inside and outside simultaneously in the plane-strain state. The stress solution is derived by assuming the contact stress distribution function and using the Airy stress function. The displacement solution is subsequently determined from the stresses by differentiating between elastic and rigid body displacements. By modeling the transverse reinforcement as an infinitely long elastic foundation beam, its displacement solution and stress solution are obtained. We obtain the load–slip curve calculation method by superimposing the displacement of UHPC with the transverse reinforcement in the direction of shear action. The proposed analytical solutions for stress and slip, as well as the method for calculating load–slip, are shown to be reliable by comparing them to the numerical simulation analysis results.

This paper presents an investigation into the fatigue performance and life prediction of perfobond strip connectors (PBLs) in steel-ultra-high performance concrete (UHPC) composite structure, based on three static push-out tests and nine fatigue tests. From the three static push-out tests results, the fatigue load and load amplitude for fatigue tests are determined. A comparative analysis is then conducted on the fatigue life, failure modes, slip curves, shear stiffness degradation laws and failure mechanisms of PBL connectors under static and fatigue loading conditions. Two-stage fatigue cumulative damage mode applicable to PBL connectors in UHPC is then proposed. Finally, based on above analysis, the fatigue life prediction model of the PBL connectors in UHPC is proposed and validated by experimental results. The results indicate that the load amplitude remains the primary factor affecting the fatigue life of PBL connectors. The fatigue cumulative damage of PBL connectors in UHPC is more unstable compared to that of PBL connectors in normal concrete, showing three-stage fatigue cumulative damage under small load amplitude and five-stage fatigue cumulative damage under large load amplitude. The final failure mode of PBL connectors in UHPC under static and fatigue test is characterized by the fracture of the transverse rebar, whereas in normal concrete, the failure mode primarily involves the crushing and splitting of the concrete slab at the PBL connectors. The fatigue damage of PBL connectors in UHPC more accurately is divided into two stages: the UHPC-dominated damage stage and the transverse rebar-dominated damage stage. The fatigue life prediction model of PBL connectors is proposed and validated by experimental results.

This study reports the results of post-fire axial compressive tests on 87 basalt fiber recycled aggregate concrete (BFRAC) cubes and 25 basalt fiber recycled aggregate concrete filled steel tube (BF-RACFST) short columns. The variables were temperature (20, 300, 500, and 800 degrees C), recycled aggregate replacement ratio (0, 50, and 100 %), basalt fiber content (0, 4, and 8 kg/m3), and cooling method. The specimens were firstly heated at constant high temperatures. After cooling to room temperature, the axial compression tests were conducted. The findings revealed that recycled aggregate prevented explosive spalling of BFRAC but reduced the post-fire capacity and stiffness of BF-RACFST. Adding basalt fiber increased the compressive strength of BFRAC cubes, decreased BFRACFST post-fire capacity, and slightly increased the post-fire compressive stiffness of the short columns. After cooling in water, the load and failure capacity of BF-RACFST were lower than those of natural cooling. Since structures are employed in the elastic phase under normal working conditions, adding basalt fiber can compensate for the compressive stiffness loss caused by recycled aggregate in concrete filled steel tubes after high temperatures. However, the reduction in capacity safety reserves should be considered when designing and post-fire repairing. If circumstances allow, rapid cooling methods, such as water cooling, should be avoided during fire extinguishing to reduce structural strength loss. Eventually, a design model was built to calculate the residual strength, compressive stiffness, and peak strain of the post-fire BF-RACFST short columns.

Deformation behaviors and soil-pile interaction are complex for the pile-supported embankment over soft clay, which may result in tension cracks between piles and soils and provide infiltration paths for rainwater. On-site investigation and numerical simulations were conducted in the study of a pile-supported embankment on soft clay with tension crack appeared. The investigation revealed the distribution and formation process of the tension cracks and structural cracks. The numerical simulation reproduced the observations of on-site investigation with a simplified width-related permeability model of tension crack and a simplified model for the distribution of crack hydrostatic pressure. The following conclusions are drawn from the study. The tension cracks appeared in the early stages of consolidation at the soil-pile interface, which mainly caused by the shearing of the soils, the earth pressure on the piles, and the soil-pile interaction under embankment loading and other surcharges. Subsequently, the structural crack appeared on the attachment structures supported by shallow foundations. When entering the rainy season, hydrostatic pressure in the tension cracks was generated under heavy rainfall which could push the piles and surrounding soils to move horizontally and cause large lateral deformations. Large lateral deformations caused structural cracks in main structures supported by pile foundation consequently. Reducing the permeability of tension cracks can avoid the generation of the hydrostatic pressure and decrease lateral deformations of the embankment significantly.

To study the local stress distributions and fatigue performance of load-carrying 60° oblique cruciform full-penetration welded joints (OCFWJs), three test specimens were designed for fatigue tests under three nominal stress amplitude levels, and the numbers of loading cycles until fatigue failure of the specimens were obtained. Using ABAQUS finite element software, the finite element models of 60°OCFWJs were established, and the hot spot normal stress, hot spot shear stress, and equivalent hot spot stress at the weld toe were calculated. Based on the nominal stress S-N curves and the hot spot stress S-N curves defined in the specifications, the fatigue life of 60° OCWJs under the combined action of tensile and shear stress were evaluated by using the nominal principal stress method, the equivalent hot spot stress method, and the interaction equation method, respectively. The results showed that whether the nominal stress range, the nominal tensile stress range, or the nominal shear stress range were used, the fatigue life of 60° OCWJs couldn't reliably evaluated. According to the International Institute of Welding specification, whether the hot spot tensile stress ranges or the hot spot shear stress ranges couldn't be used to evaluate the fatigue life of 60° OCFWJs reliably. The fatigue lives predicted by the interaction equation method in Eurocode 3:Design of Steel Structures were much lower than the experimental values , and the fatigue lives predicted by the equivalent hot spot stress method were in good agreement with the experimental values .

Carbonate gravelly soils are widely distributed in sub-tropical marine areas. During construction and engineering operations, carbonate gravel undergoes considerable particle crushing, which has remarkable effects on their engineering properties. A series of large-diameter oedometer tests, large-diameter drained and undrained triaxial shear tests were conducted on carbonate gravel specimens taken from the South China Sea. The carbonate gravel specimens exhibit significant particle crushing at common engineering pressure levels, and the particle crushing highly depends on the initial density, loading history and stress path. Three fragmentation modes, fracture, attrition, and abrasion, are notable in carbonate gravel specimens, which induces significant variations of PSD curves and greatly effects the mechanical properties. Particle crushing in carbonate gravel specimens increases the compressibility resulting in the compression index increases with the increase of surcharge pressure; decreases the pressure-hardening resulting in the initial Young's and secant moduli slightly increase with the increase of initial confining pressure; and decreases the dilatancy resulting in the peak and critical state friction angles significantly deceases with the increase of initial confining pressure. Particle crushing also shows great effect on the CSL of the carbonate gravel specimens in both p & PRIME;- q space and e - p & PRIME; space.

Expansive soil is prevalent in the Chengdu area, and rainfall is a significant factor triggering deep foundation pit engineering accidents. Through the investigation of engineering cases, the typical deformation and failure processes of deep foundation pits in the Chengdu area, supported by piles under rainfall infiltration, were analyzed and summarized. The measured horizontal deformation curves of supporting piles in foundation pit engineering were categorized into three types: steep, gradual, and stable types. The early risk prevention of deep foundation pits in Chengdu's expansive soil area can be based on the horizontal deformation of supporting structures, as indicated by the deformation developments of unstable pits and the three types of measured deformation curves during early rainfall after excavation. Using wavelet analysis, artificial neural networks, and Copula random variable correlation analysis, a prediction model for the horizontal deformation of supporting structures in foundation pits, considering rainfall influence, was established. The actual deformation curves of deep foundation pits were predicted based on this model. Finally, the prediction results enable early risk warnings based on deformation predictions. The predicted deformation results align well with the measured data, preliminarily confirming the validity of the proposed model. Using the same deformation warning index, the risk warning based on predicted deformation can significantly advance the warning time, providing a basis for optimizing the treatment scheme.