Search Results (32)

Shear connections between concrete structural elements play a vital role in defining performance and overall stability. However, limitations in traditional methods for predicting the shear capacity (Vu) of stud connectors in concrete have been highlighted. Developing strategies that precisely describe the performance of stud-headed connectors requires insight into their failure mechanisms and the corresponding shear transmission. Therefore, leveraging advancements in machine learning, this study aims to predict the Vu of the headed stud connector in concrete structures using various input parameters. A database (1121) of the shear strength collected from the literature was trained using six machine learning (ML) algorithms: extreme learning machine (ELM), decision tree (DT), artificial neural network (ANN), multi-linear regression (MLR), support vector machine (SVM), and hybrid ANN–particle swarm optimization (ANN-PSO). Feature selection methods and system identification were applied to explore the optimal or most relevant input parameters. The feature selection techniques indicated that the geometric properties of the stud connector (diameter and cross-sectional area), the concrete modulus of elasticity (Ec), and the height of the weld collar (h_w) are the most relevant input variables. The ANN-PSO model outperformed the other classical models in estimating the shear capacity at two modeling stages. The hybrid ANN-PSO achieved R² = 0.976, MAE = 7.61 kN, RMSE = 10.8 kN, and MAPE = 8.04%, demonstrating the best predictive accuracy among the classical models. On the other hand, DT is the second-best model, with an R² of 0.958, MAE of 10.27 kN, RMSE of 14.43 kN, and MAPE of 8.53 kN for forecasting the shear capacity of stud connectors in concrete. Full article

This study experimentally evaluates the structural performance of Concrete-Filled Double-Skin (CFDS) hybrid connections that are intended as key components of large-scale floating offshore wind substructures. The innovative aspect of this work lies in the direct experimental comparison of five representative connection details—Headed Stud (HS), Perfobond (PB), L-beam-joint (LJ), L-beam-spacing (LS), and Angle (AN)—with respect to multiple performance indices that are critical under harsh offshore environments. First, full-scale CFDS specimens were fabricated with identical global dimensions while varying only the connection details. The hybrid behavior of the CFDS system arises from the complementary actions of the outer steel tube, which primarily resists tensile forces, and the infilled concrete, which provides dominant compressive resistance and confinement. This composite interaction enhances the stiffness, ductility, and energy absorption capacity of the member under flexural demands, which are essential for floating offshore structures operating under complex marine loading. Second, monotonic bending tests were conducted using a 2000 kN actuator under a cantilever-type configuration, and load–displacement responses were recorded at three locations. Third, the stiffness, ductility, and energy absorption capacity (toughness) were quantified from the measured curves to clarify the deformation and failure characteristics of each connection type. The results show that the PB connection achieved the highest maximum load and exhibited stable ductile behavior with plastic energy dominating the total toughness. The LJ connection provided well-balanced stiffness and deformation capacity with low sensitivity to measurement locations, indicating high reliability for design applications. In contrast, the HS and LS connections experienced localized slip and position-dependent stiffness, while the AN connection showed the lowest load-carrying efficiency. Overall, the findings highlight that connection-level detailing has a decisive influence on the global performance of CFDS hybrid members and provide fundamental data for developing design guidelines for floating offshore structures operating under complex marine loading conditions. Full article

This study adopts the east approach bridge of the Section II extra-long-span bridge on the Urumqi Ring Expressway (West Line) as an engineering prototype. A three-dimensional nonlinear finite element push-out model of headed stud connectors was developed in ABAQUS/Explicit and validated against existing test data. On this basis, parametric analyses were carried out to investigate the effects of material and geometric parameters on the shear performance of the studs. The results indicate that the load–slip response can be divided into four stages: elastic, plastic-damage development, plateau, and softening. Compared with C50 concrete, UHPC markedly increases the initial stiffness of the connectors and raises the peak shear resistance by approximately 30–40%. For the smallest stud diameter, the ductility decreases by up to about 10% and the post-peak degradation becomes more rapid, i.e., ductility deterioration is more pronounced; this unfavorable effect is particularly significant when small stud diameter is combined with shallow embedment depth. Increasing the stud diameter enhances both stiffness and peak shear resistance, whereas increasing the embedment depth delays post-peak degradation, improves residual capacity and energy dissipation, and promotes a transition in failure mode from concrete-governed failure to ductile bending–shear failure of the stud. Based on these parametric results, a larger stud height-to-diameter ratio is recommended for UHPC composite structures to achieve coordinated optimization of connection stiffness, load-carrying capacity, and ductility performance. Full article

Increasing the shear reinforcement ratio (ρ_w) can help meet architectural and structural requirements but often results in less reliable punching strength estimates from design codes. Nonlinear finite element analysis (NLFEA) has the potential to support a thorough assessment of the punching strength of slabs with shear studs, yet accurately modelling the interaction between concrete and transverse steel to capture the strength provided by shear rebars is challenging while using user-friendly software. This paper explores methodologies to assess the punching strength of slabs with double-headed studs with a commercial NLFEA program. Experimental tests were used to define the input parameters for the concrete’s nonlinear behaviour and to evaluate modelling approaches for shear studs, resulting in two strategies applied to slabs with varying ρ_w. NLFEA provided accurate punching strength estimates, consistently reproducing slabs’ rotations, crack patterns, and flexural strains. However, discrepancies in shear rebar strains highlight the challenges of using NLFEA to assess the response of slabs with shear reinforcement. Moreover, NLFE and experimental strengths were compared to estimates using the fib Model Code 2010 with levels of approximation (LoA) II, III, and IV, showing that, for the selected tests, increasing complexity in LoA IV did not consistently improve strength estimate accuracy. Full article

The behavior of steel–concrete composite structures is significantly influenced by the efficiency of the shear connections that link the two materials. This research examines the performance of stud shear connectors, with an emphasis on analyzing the effect of different geometric design parameters. A computational model was created utilizing Python 3.13 to enable thorough digital monitoring of the influence of these parameters on the structural performance of composite connections. Developed within the ABAQUS framework, the model integrates geometric nonlinearity and the Concrete Damage Plasticity (CDP) approach to achieve detailed simulation of structural behavior. Essential design aspects, including stud diameter, stud height, head dimensions, and spacing in both longitudinal and transverse directions, were analyzed. The Python-based parametric model allows for easy modification of design parameters, ensuring efficiency and minimizing modeling errors. The significance of stud diameter changes was analyzed in accordance with Eurocode standards and previous studies. It was found that stud length has a reduced effect on structural performance, particularly when considering the concrete properties used in bridge construction, where compressive failure of the concrete zone is more critical at lower concrete strengths. Additional factors, such as stud head dimensions, were investigated but were found to have minimal effect on the behavior of steel–concrete composite connections. Longitudinal stud spacing emerged as a critical factor influencing structural performance, with optimal results achieved at a spacing of 13d. Spacings of 2d, 3d, and 4d demonstrated overlapping effects, leading to significant performance reductions, as indicated by comparisons of ultimate load and force–displacement responses. For transverse spacing, closer stud arrangements proved effective in reducing the likelihood of slip at the steel–concrete interface, enhancing composite action, and lowering stress concentrations. Additionally, reducing the transverse distance between studs allowed for the use of more shear connectors, increasing redundancy and enhancing performance, especially with grouped-stud connectors (GSCs). Full article

Recent research indicates that high-strength bolts could be more effectively and efficiently used to connect steel girders and fabricated decks or retrofit existing composite girders than headed studs. To reduce the number of bolt shear connectors and, thus, further accelerate the construction of composite girders, high-strength large bolts could be an excellent alternative, resulting in greater concrete stress below the bolt. Also, hybrid fiber-reinforced concrete (HFRC) has better tensile ductility and strength than that of ordinary concrete (OC). Therefore, this study tried to design eighteen push-out test specimens, including different configurations of bolt shear connectors, to investigate the static properties of post-installed, high-strength, large-bolt shear connectors with fabricated HFRC/OC slabs. The experimental results indicated that the capacity and initial stiffness of a high-strength large through-bolt shear connector was the smallest. The fiber might enhance the capacity and initial stiffness of bolt shear connectors. Increasing the bolt diameter can significantly enhance the initial stiffness and load-bearing capacity, while the clearance of the bolt hole had a great influence on the capacity, initial stiffness, and slippage of the post-installed high-strength large-bolt shear connector. Finally, the capacity equation and slip behavior of post-installed, high-strength, large-bolt shear connector with fabricated HFRC deck were obtained using the regression method, which could provide the reference for their design. Full article

Ultra-high performance concrete (UHPC) combined with shorter stud shear connectors (h/d < 4) presents challenges that existing analytical models for stud connectors cannot adequately address. This study enhances the elastic foundation beam model to better accommodate these material and dimensional changes. Key improvements include the analytical calculation of equivalent foundation stiffness, which incorporates the rotation of the stud head—an aspect often neglected in previous research—and considers the post-yield plastic hinge at the stud weld. The proposed analytical model effectively captures variations in stud diameter and concrete elastic modulus, providing a load–slip curve with broader applicability than traditional empirical formulas. Validation against experimental data from 21 push-out specimens of varying diameters shows strong agreement, confirming the accuracy of the method. Moreover, a parametric study based on the analytical model reveals the sequential relationship between the formation of plastic hinges at the stud weld and the development of plastic regions in the concrete. This relationship is influenced by factors such as stud diameter, yield strength, and concrete strength. Notably, an increase in concrete strength significantly enhances the shear force at the stud root at the point when the concrete reaches its compressive strength. This explains why high-strength concrete specimens exhibit lower ultimate slip. These findings provide a crucial basis for understanding the behavior of stud shear connectors in composite structures. Full article

For continuous steel–concrete composite girder bridges based on the post-combined method, the conventional rectangular group studs contribute to the isolation of the steel girder and the concrete slab before prestressing, leading to the majority of prestress forces being introduced to the concrete slab. However, rectangular-group stud holes cause the prestress forces to be unevenly distributed. In this study, a new type of bellow-sleeved stud (BSS) was developed to mitigate the weakening effects of rectangular group stud holes on the slab. A steel corrugated sleeve with a diameter of 60 mm was employed to cover the stud, which served as an internal formwork to prevent the concrete from bonding with the root of the stud. After prestressing was complete, the steel sleeve was filled with ultra-high-performance concrete (UHPC) to create a reliable combination between the concrete slab and the steel girder. To investigate the shear performance of this new type of connection, eight push-out test specimens were designed, and finite-element models were built. This study drew a comparison between the BSS and the ordinary headed stud (OHS). The research findings suggested that the BSS is subjected to less bending–shear coupling and offers a 4.5% increase in shear strength and a 31.9% increase in shear stiffness compared with the OHS. The study also analyzed the structural parameters influencing the shear performance of the BSS. It is found that the steel sleeve of the BSS has a negative effect on shear performance, but this can be mitigated by infusing high-strength material into the sleeve. Furthermore, the study examined the effect of construction quality on shear performance and suggested that sleeve deviation and grout leakage considerably reduced the shear performance of the BSS. Accordingly, strict control over the construction quality of the BSS is necessary. Full article

The embedded shear connector with flanges (ESCF) exhibits excellent shear performance in the steel–concrete composite beam. The ESCF consists of embedded corrugated steel web as the shear connector and shape-matched flanges for construction convenience. However, previous research showed that the steel flange of the ESCF was prone to local buckling when subjected to shear force, resulting in insufficient shear strength of the connector. In this paper, head studs were adopted to reinforce the ESCF at the flange with a large width-to-thickness ratio. Nine stud-reinforced embedded shear connectors with flanges (SR-ESCF) were manufactured to conduct the push-out test to investigate the shear performance of SR-ESCF. The effects of the reinforcing studs, thickness of the web, width-to-thickness ratio of the flange, embedding depth of the web, and diameter of the combined rebar on shear strength of the SR-ESCF were revealed and discussed thoroughly. The push-out test results showed that the head studs significantly improved the initial stiffness and load-bearing capacity of the ESCF, which were increased by 17% and 15%, respectively. Moreover, the head studs prevented local buckling of the steel flange. The shear strength of the specimens was greatly influenced by the embedding depth of the web, the width-to-thickness ratio of the flange as well as the reinforcing studs. However, the diameter of the combined rebar and thickness of the web had negligible effects on the shear capacity of the SR-ESCF. According to the test results, the nonlinear finite element model (FEM) and the shear capacity of SR-ESCF prediction formula were created and verified. Furthermore, the layout of the reinforcing studs welded on the flange of the SR-ESCF was optimized by the validated FEM, which indicated that the shear-bearing capacity of the SR-ESCF could be significantly increased by adding studs on the steel flange near the original studs. This research will be of great significance to the design and implementation of the steel–concrete composite beam bridge with corrugated steel web. Full article

Connection behavior significantly influences the design efficiency of steel–concrete composite bridges. This study investigates the impact of shear connectors, specifically headed stud connectors, on the structural response of symmetric and skewed composite steel–concrete bridges. Utilizing bilinear or trilinear slip–shear strength laws for studs, in line with the existing literature and code provisions, a finite element (FE) model is developed. This FE model is applied to a case study for composite deck analysis, incorporating variations in connection strength and ductility for nonlinear analyses. The study assesses ductility demands in connections for symmetric and skewed bridges of varying lengths and angles, considering both ductile and elastic designs. Results emphasize the importance of stud capacity, ductility, and strength on the overall bridge response, analyzing slip and shear trends at the interface. Skewed bridges, crucial for non-orthogonal crossings of roads, are integral to modern transportation infrastructure. However, skewness angles exceeding 20° can result in undesirable effects on stresses in the deck due to vertical loads. The results indicate that shear distribution in studs changes significantly as the skew angle increases, contributing valuable insights into optimizing bridge design. Thus, this research provides a comprehensive analysis of principles, design methodologies, and practical applications for both symmetric and skewed steel–concrete composite bridges, considering various parameters. Full article

The flexural performance of steel and concrete composite beams can be further enhanced by utilizing advanced construction materials such as ultra-high performance fiber-reinforced concrete (UHPFRC) and high-strength steel. In this paper, the concept of critical elastic moment resistance is proposed and the equation for its estimation is derived. It was found that the high yield strength of steel calls for a narrow UHPFRC top layer to reach the critical state, whereas this ideal condition is not realistic for composite beams with normal-strength steel and UHPFRC. Small-scale composite beams composed of both high-strength and low-strength steel materials were tested under four-point bending to verify the critical state and performance of different types of connectors. The headed studs and plate connectors were first tested through small-scale push-out tests and then implemented in the composite beam with different spacing. The connection utilizing headed studs with 150 mm spacing performed the best among the three tested specimens in helping reach the critical elastic moment resistance. Finite element analyses of the composite beam were performed based on the estimated material properties under axial and biaxial stress conditions and the results align with the experiment results. Full article

Current formulas to assess the shear capacity of headed steel stud anchors and post-installed (PI) anchors in case of pryout failure (sometimes known as pull-rear failure) have been derived either based on the indirect-tension resistance model or are fully empirical based on push-out test results. In both cases, the predicted pryout capacity is clearly conservative and underestimates the true pryout capacity of anchorages, especially for stiff anchors with low embedment-to-diameter ratios (h_ef/d < 4.5). This paper proposes an empirical and a semi-empirical formula to predict the concrete pryout capacity of headed steel studs and PI anchors. They were derived based on an improved indirect-tension model which accounts for the stud diameter and the stud spacing in a group of anchors. Furthermore, a database of 214 monotonic shear tests from the literature, including own tests (push-off and horizontally shear tests), is reevaluated and compared to the provisions of EN1992-4. The scope of this assessment proposal includes single and group of headed steel studs and PI anchors attached to a stiff steel plate as well as shear connectors in composite structures without metal deck embedded in normal-weight concrete. Full article

Recently, to resolve a growing need for durable and resilient railway bridge construction/reconstruction systems, a great amount of research has been carried out in many countries. As a part of such studies, prefabricated composite girders with an innovative girder-to-deck connection have been proposed that facilitate construction by eliminating interference during on-site processes. In this study, a railway bridge prototype of prefabricated composite girders with girder-to-deck connections was designed to facilitate future application enhancement of off-site construction. Then, prefabricated composite girders were developed by deploying different girder-to-deck connections through geometric detailing of reinforcement, headed stud connectors, and precast decks. Based on the calculation theory of interface shear transfer, the detailed design of different girder-to-deck connections was carried out, in particular the reinforcement spacing. Furthermore, finite element analysis of prefabricated composite girders was conducted to determine the flexural moment strength of prefabricated composite girders. Parametric studies were carried out to consider the factors affecting the detailed design of the connection, ensuring that the connection is correctly designed, thereby ensuring the structural performance of prefabricated composite girders. From the results, conclusions were drawn. The developed cases satisfied the interface shear criteria according to both conventional and plastic approaches. There was no significant difference in flexural moment strength between the developed cases since all cases were designed with the full shear connection. In all cases, the flexural performance was ensured and can be used for railway bridges. The most optimum case of prefabricated composite girders is selected in specific design situations. Full article

Headed shear studs are an essential interfacial connection for precast steel–concrete structures to ensure composite action; hence, the accurate prediction of the shear capacity of headed studs is of pivotal significance. This study first established a worldwide dataset with 428 push-out tests of headed shear studs embedded in concrete with varied strengths from 26 MPa to 200 MPa. Five advanced machine learning (ML) models and three widely used equations from design codes were comparatively employed to predict the shear resistance of the headed studs. Considering the inevitable data variation caused by material properties and load testing, the isolated forest algorithm was first used to detect the anomaly of data in the dataset. Then, the five ML models were established and trained, which exhibited higher prediction accuracy than three existing design codes that were widely used in the world. Compared with the equations from AASHTO (the one that has the best prediction accuracy among design specifications), the gradient boosting decision tree (GBDT) model showed an 80% lower root mean square error, 308% higher coefficient of determination, and 86% lower mean absolute percent error. Lastly, individual conditional expectation plots and partial dependence plots showed the relationship between the individual parameters and the predicted target based on the GBDT model. The results showed that the elastic modulus of concrete, the tensile strength of the studs, and the length–diameter ratio of the studs influenced most of the shear capacity of shear studs. Additionally, the effect of the length–diameter ratio has an upper limit which depends on the strength of the studs and concrete. Full article

Headed stud shear connectors are most broadly applied in various composite structures. There exist plenty of empirical formulae for load–slip curves. However, most of them are fitting formulae in particular forms. Due to the lack of physical model support, fitting empirical formulae apply only to cases with similar parameters to the tests. Therefore, this paper analyzes the load–slip curves of existing headed stud connectors, proposes three stages of slip deformation in the shear connectors and the corresponding trilinear model, and presents the analytical formulae for the stiffness and strength of headed stud shear connectors. Firstly, we model the headed studs and surrounding concrete as beams on the foundation model, derive the equivalent shear stiffness equations for headed studs, and establish the load–slip behaviors for the first two stages. Then, the connectors’ shear stiffness and shear strength in the third stage are derived based on the head stud’s plastic deformation characteristics and failure mode. Finally, the numerical results are presented and verified with the existing test results, showing that the trilinear model is conceptually straightforward, easy to apply, and has sufficient accuracy. Full article