Stud Shear Connectors Research Articles

Experimental study on mechanical behavior and bearing capacity calculation of steel shotcrete composite structure in the primary support of tunnel

To enhance the synergistic load-bearing capacity between tunnel support steel arches and shotcrete, it is proposed that a composite structure support be formed by arranging stud shear connectors on their contact interface. In response to the loading characteristics of tunnel supports, significant eccentric compression member tests were carried out to analyze the failure modes and load-bearing characteristics of the composite structure support, and a theoretical calculation expression for the ultimate load-bearing capacity of the tunnel steel-shotcrete composite structure was established. The research results show that when the steel and concrete contact interface is naturally bonded, the failure mode is characterized by separation and spalling, consistent with actual tunnel supports’ large deformation failure mode. When stud shear connectors are arranged on the steel web, the failure mode only cracks and crushes, significantly enhancing its anti-slip and synergistic load-bearing capacity. The steel-concrete composite structure with stud shear connectors exhibits good ductility, load-bearing performance, and bending stiffness. Compared to the naturally bonded condition, the ultimate load-bearing capacity is increased by 14.83 %, and the lateral deflection is reduced by 24.27 %. Under natural bonding conditions, extensive eccentric loading greater than 0.4 times the ultimate load cannot satisfy the plane section assumption for the steel-concrete structure section. However, with stud shear connectors arranged on the web and loaded to 0.8 times the ultimate load, the plane section assumption is still well satisfied. At the same time, a theoretical calculation formula for the ultimate load-bearing capacity of the stud-reinforced steel-concrete support structure under significant eccentric compression was established and verified. The research results can provide theoretical support for the design of tunnel initial support.

Stud-concrete interactional model of shear connectors in steel-concrete composite structures

A theoretical calculation method, named stud-concrete interactional model, of load-slip relationship of stud shear connectors in composite structures is presented. This model has been developed based on the elastic foundation beam theory and considers the different stress states of the concrete around studs during the damage process. Two important stud-concrete interaction parameters, called equivalent spring stiffness and yielding slip, are introduced for the first time to quantify the shear contribution of concrete and the relative slip between stud and concrete, respectively. The range of yielding slip has been determined based on a force-flow model and a finite element model. The proposed stud-concrete interactional model has been utilized to derive the load-slip formula considering the elastic, elastoplastic, and plastic stages of stud shear connectors. Experimental results show that the proposed formula are valid and outperform existing formulas. This paper offers new insight into the shear behavior of stud shear connectors.

Experimental study of static and fatigue push-out test on headed stud shear connectors in UHPC composite steel beams

Steel-concrete composite girder bridges utilize shear connectors to connect concrete deck slabs and steel girders. In current practice, the headed shear stud connector is the most used due to its reliability and ease of installation. Several studies are available on the static and fatigue behavior of welded-headed shear studs embedded in normal-strength concrete. However, relatively little is known about the static and fatigue behavior of headed shear connectors in composite beams when shear studs are embedded in ultra-high-performance concrete (UHPC). This study reports a series of pushout results carried out on headed shear connectors embedded in UHPC at pre-fatigue and post-fatigue stages. Six pushout specimens were first tested under static load to collapse. The precast normal-strength concrete slabs in the pushout specimens were reinforced with glass fiber-reinforced polymer (GFRP) bars to promote sustainable construction. This practice, commonly used in Canada, aims to eliminate the corrosion of steel bars caused by de-icing salts used during winter. The results from these tests were used to determine the applied fatigue stress range of another six identical pushout specimens, which were subjected to constant amplitude fatigue loading over 2 million cycles. Results show that the fatigue cycles applied to the specimens prior to testing them to collapse did not alter the failure mode or the crack pattern of the tested specimens. Furthermore, the studied pushout specimens considered 6 different shapes of shear pockets in which the arrangement and spacing of studs were varied. It was found that the studs in a square pocket form yielded a shear capacity of 13.9 % and 16.7 % greater than those for similar studs arranged in a single row-oriented longitudinally and transversally, respectively. The accuracy of the various design formulas specified in design codes in estimating the shear resistance of the tested specimens, as well as empirical formulas proposed to develop load-slip curves of tested specimens, is studied. It was found that the European and Japanese codes significantly underestimated the stud shear capacity, whereas the Canadian code provides a more accurate estimation.

Explainable AI based slip prediction of steel-UHPC interface connected by shear studs

Recently, ultrahigh performance concrete (UHPC)-steel composite structures with shear studs have garnered interest for their potential high ductility and resilience in infrastructure. Ensuring their ductility is crucial for failure prediction and resilient infrastructure development. However, pull-out tests show that studs in UHPC often fail to meet a minimum relative slip of 6 mm, with no established direct methods for predicting this slip. This study proposes a novel approach to evaluate the shear slip at the UHPC-steel interface connected by shear studs, utilizing explainable artificial intelligence. We integrate a Light Gradient Boosting Machine (LightGBM) algorithm with SHapley Additive exPlanations (SHAP) to predict and interpret shear slip. The model development utilizes a dataset of 184 instances from UHPC-steel pullout tests, encompassing 16 features related to UHPC slab characteristics, shear pockets, and stud shear connectors. Engineered features and shear strength are strategically incorporated as predictors under four scenarios to achieve the most optimal model. The best performing model achieves an RMSE of 0.814 mm, an MAE of 0.598 mm, and an R2 of 0.838. The model’s superiority is reaffirmed through comparative analysis against five alternative tree-based ensemble models. SHAP analysis demonstrates that features related to the UHPC slab and stud shear connectors contribute 65 % and 35 % respectively to slip prediction. The top influential features are dst, sl and fc from the stud, and fu from the slab. The engineered features and ultimate load per stud indicate limited efficacy in improving model precision. Higher values of dst and fu positively contribute to shear slip prediction, whereas higher values of sl negatively impact shear slip prediction. Based on several SHAP analyses, a set of parameters for the potential ductile design of stud shear connectors in UHPC slabs is proposed. Overall, the integration of LightGBM and SHAP maintains high generalizability and enhances model transparency, instilling confidence for practical deployment and promising tangible advancements in real-world structural applications.

Characterization of different longitudinal shear transfer mechanisms for profiles embedded in concrete walls

Concrete walls or columns reinforced by one or multiple embedded steel profiles have gained popularity due to their improved strength, ductility and energy dissipation capacity. However, certain gaps in information are remaining in the available standards regarding the design of such non-conventional reinforced concrete systems. In particular, a proper characterization of the longitudinal shear transfer properties at the steel-concrete interface is required for a reliable design. Although sufficient information is available regarding mechanical connectors like shear studs, detailed information is required for any other types of mechanical connectors such as welded steel plates or for configuration without mechanical connectors. Moreover, even for cases with mechanical connectors, the orientation of the profile – and hence the distance to the face of the concrete – and the tying system can have a significant influence on the load transfer mechanisms. To this purpose, this article presents the outcomes of a set of push-out tests with the objective of comparing the force transfer mechanisms from the steel profile to the surrounding concrete wall for different types of interfaces. 13 tests specimens are investigated, with flexible (shear studs) and/or rigid (steel plates) shear connectors, considering different orientations of the profile and tying mechanisms, as well as a comparison with profiles without mechanical connectors. Based on the test results and subsequent analytical assessment, relevant conclusions are drawn regarding the longitudinal shear transfer at the steel-concrete interface. If necessary provisions are followed, welded steel plates prove to be an effective alternative to the shear stud connectors in terms of connector strength. The orientation of the embedded steel profile, consequent position of the mechanical connectors and their distance to the concrete face are observed to have a significant influence on the compression strut evolution, which therefore dictates the necessity (or not) of horizontal confinement or ties. Furthermore, combining the shear strength offered by different types of mechanical connectors and the steel-concrete bond offer a precise estimate of the longitudinal shear strength and therefore indicates towards the conservative nature of the design provisions suggested by the available standards.

Effect of Concrete Slab Gradation on the Shear-Carrying Capacity of the Headed Stud Shear Connector

Effect of Concrete Slab Gradation on the Shear-Carrying Capacity of the Headed Stud Shear Connector

Shear Mechanism of a Novel SFCBs-Reinforced Composite Shear Connector: Experimental, Theoretical Investigations and Numerical Model.

Traditional stud and perfobond leiste (PBL) shear connectors are commonly used as load-transferring components in steel-concrete composite structures. Composite shear connectors fully utilize the advantages of traditional stud and PBL shear connectors. In order to maximize the advantages of composite shear connectors, a novel shear connector for complex environments was proposed. The steel-FRP composite bars (SFCBs) with excellent fatigue resistance and corrosion resistance were introduced to replace the steel bars. This study discussed the failure modes, load-slip curves, and load-strain curves of the composite shear connector. In addition, a finite element analysis (FEA) model was developed to analyze the influence of various factors on its shear behavior. Results showed that compared with traditional composite shear connectors, the introduction of SFCB resulted in a promotion of 7.85% in shear stiffness, and it also led to a significant increase of 63.61% in ductility, further enhancing the mechanical performance. Meanwhile, FEA models were well fitted to the test results, and parametric analysis showed variate effects on shear bearing capacity. In the end, an equation was established to calculate the shear capacity of composite shear connectors, which could provide a reference for further research and engineering applications.

Long-term behaviour of stud connections in composite structures

Being critical components in composite structures, the short-term structural behaviour of stud shear connectors has been extensively investigated. Despite this, there has been somewhat limited attention devoted to their time-dependent behaviour. In this paper, the results of four long-term push-out tests are reported: the test parameters including the loading age and stud diameter. The test results are shown to be simulated accurately by a finite element model established using ABAQUS, in which the long-term behaviour of the concrete is considered by implementing a stepwise approach. The numerical procedure is applied to conduct a parametric analysis, with the effects of different parameters, viz., the loading age, concrete material, external environment, stud size and reinforcement ratio being considered. Based on the numerical results, an analytical formulation is derived for the creep coefficients of composite members with different loading ages. Comparisons with FE model data shows that the derived equation has sufficient accuracy and can be applied for designing composite structures considering their long-term response.

Experimental and theoretical investigations on the static behavior of low aspect ratio shear stud connectors in ultra high performance concrete

In reinforcement project for early-built orthotropic steel bridge decks (OSDs) using ultra high performance concrete (UHPC), low aspect ratio shear stud connectors in UHPC are required. In present study, push-out tests of six static UHPC specimens with and without reinforcement bars were first conducted. The failure modes, load-slip curves and shear capacity of shear stud connectors embedded in UHPC with an aspect ratio of 1.84 were investigated. Subsequently, the experimental results of shear capacity and load-slip curves were compared with the theoretical calculation results. Finally, a new theoretical model of shear stiffness was proposed for low aspect ratio shear studs based on the energy equivalence theory. The experimental results indicated that the failure mode of all specimens was stud shank failure, while the UHPC slabs without reinforcement bars showed extensive cracks. The effect of reinforcement bars on the behavior of shear studs embedded in UHPC slabs can be negligible. The reinforcement bars mainly affected the internal force flow in the UHPC, thus limiting crack initiation and extension. The compressive strength of the UHPC and the weld collar had significant impact on the shear capacity of short studs in the UHPC. In calculating the load-slip curves of short shear stud connectors in UHPC, the theoretical results calculated using the fractional form equations were in better agreement with the experimental results. The proposed theoretical model neglecting the deformation of shear stud in elastic stage can accurately predict the shear stiffness of low aspect ratio shear stud connectors in UHPC.

Study of Fatigue Performance of Ultra-Short Stud Connectors in Ultra-High Performance Concrete

Steel–UHPC composite bridge decking made of ultra-high performance concrete (UHPC) has been progressively employed to reinforce historic steel bridges. The coordinated force and deformation between the steel deck and UHPC are therefore greatly influenced by the shear stud connectors at the shear interface. Four fatigue push-out specimens of ultra-short studs with an aspect ratio of 1.84 in UHPC were examined to investigate the fatigue properties of ultra-short studs with an aspect ratio below 2.0 utilized in UHPC reinforcing aged steel bridges. The test results indicated that three failure modes—fracture surface at stud shank, fracture surface at steel flange, and fracture surface at stud cap—were noted for ultra-short studs in UHPC under various load ranges. The fatigue life decreased from 1287.3 × 104 to 24.4 × 104 as the shear stress range of the stud increased from 88.2 MPa to 158.8 MPa. The UHPC can ensure that the failure mode of the specimens was stud shank failure. Based on the test and literature results, a fatigue strength design S–N curve for short studs in UHPC was proposed, and calculation models for stiffness degradation and plastic slip accumulation of short studs in UHPC were established. The employment of ultra-short studs in the field of UHPC reinforcing aging steel bridges can be supported by the research findings.

Experimental study and acoustic emission monitoring on damage mechanism of stud shear connectors

Stud shear connectors are popular connectors used in steel-concrete composite structures. Assessing the condition and damage process of studs embedded in concrete is difficult. This paper proposes to assess the condition and damage process of stud shear connectors using an acoustic emission (AE) technique. Nine steel-concrete push-out specimens with stud shear connectors were tested, and AE sensors were used to monitor the damage process and explore the damage mechanism. The test results showed that the specimens failed due to stud fracture, accompanied by concrete cracks. The damage process included three primary stages featuring different characteristics of AE energy. An unsupervised machine learning algorithm called fuzzy C-means clustering was used to analyze the AE signals, and AE events were classified into three clusters, and various damage modes (i.e., concrete cracks and steel-concrete interface debonding, stud fracture, and concrete crushing) were identified based on the parameter characteristics and positions of AE events.

Performance evaluation of innovative triangular and spherical ribbed headed studs in composite steel beam-concrete slab junction

Composite structures have now become a popular practice in the construction of bridges and RCC structures. Various advancement has been taken in several decades to ensure the composite action between the concrete and steel interface. Shear connectors were developed to ensure this composite action in between the steel and concrete interface of the composite junction. The two types of connections that are most frequently used in composite construction are headed stud shear connectors and channel connectors. The maximum stress concentration of the headed stud shear connector occurs on the bottom of the headed stud shear connector. As a result of the higher stresses at the bottom of the headed stud shear connector the bending height of the headed stud shear connector varies in between 18 to 33% depending upon the grade of concrete. The present study intends to study the effect of geometric variation in headed stud shear connectors according to the requirement of the cross-section. The geometric variations were made with reference to bending height throughout the shank of headed studs. Based on the stress variation the headed stud shear connector is divided into three different zones. For making these variations the headed stud was distributed into three zones. Zone 1 is the headed region of the connector. Zone 3 is the bottom region with maximum shear concentration and zone 2 is the part of shank connecting the zone 3 and zone 1 of the headed stud shear connector. In present study volume reduction is done in the zone 2 region of the headed stud shear connector and volumetric addition is done in the zone 3 region of the headed stud shear connector. Based on the proposed ideology for creating geometric variations, two different studs are proposed namely spherical ribbed headed studs (SRHS) and triangular ribbed headed studs (TRHS) studs. Performance of the proposed SRHS and TRHS shear connectors was evaluated using six experimental specimen and Finite element analysis. Results show that SRHS and TRHS studs have higher shear carrying capacity, ductility and stiffness compared to conventional headed stud shear connectors.

Experimental and theoretical investigation on the mechanical properties of corroded stud shear connectors

To accurately assess the durability of steel-concrete composite members, the mechanical properties of corroded stud shear connectors were investigated experimentally and theoretically. First, 48 stud specimens were exposed to artificially accelerated corrosion in two corrosion conditions (artificial climate and constant current conditions) and monotonically tested under tensile loads. Results indicated that stud corrosion significantly reduced its strength, while having a negligible effect on its elastic modulus. For the specimen with a 16.1% corrosion ratio in the artificial climate conditions, the yield strength and tensile strength decreased by 35.9% and 33.4%, respectively. The tensile property degradation models in two accelerated corrosion conditions were established. Afterward, the shear properties of corroded studs were investigated through 7 push-out tests. It was found that corrosion also had a significant effect on the stud shear strength and deformation behavior. When the average corrosion ratio of the studs reached 7.6%, its shear strength decreased by 7.8%. Another novelty of the present work lies in the analytical development of a theoretical load-slip relationship of stud based on the Winkle foundation model and a simplified elastic-plastic constitutive relationship of concrete. Furthermore, a significant contribution of this work is the introduction of a series of degradation factors that enabled the derivation of the formulas featured by shear stiffness, shear strength, and load-slip relationship of corroded studs. All these theoretical formulas were well validated against the experiments regardless of whether the stud was corroded.

Augmented Data-Driven Machine Learning for Digital Twin of Stud Shear Connections

Existing design codes for predicting the strength of stud shear connections in composite structures are limited when adapting to constant changes in materials and configurations. Machine learning (ML) models for predicting shear connection are often constrained by the number of input variables, resembling conventional design equations. Moreover, these models tend to overlook considerations beyond those directly comprising the connection. In addition, the data used in ML are often biased and limited in quantity. This study proposes a model using AutoML to automate and optimize the process for predicting the ultimate strength and deformation capacity of shear connections. The proposed model leverages a comprehensive dataset derived from experimental studies and finite element analyses, offering an advanced data-driven solution to overcome the limitations of traditional empirical equations. A digital twin model for the static design of pushout specimens was defined to replace existing empirical design codes. The digital twin model incorporates predictions of the geometry model, ultimate strength, and slip as input parameters and provides criteria for evaluating the limit state through a bilinear load–slip curve. This study advances predictive methodologies in structural engineering by emphasizing the importance of ML in addressing the dynamic and multifaceted nature of shear connection behaviors.

Shear strength damage model and damage removal FE modeling of stud shear connectors embedded in UHPC

The study conducted a series of push-out tests to study the shear strength of studs as shear connectors in steel-UHPC (ultra high-performance concrete) composite structures. The damage removal modeling was developed and utilized to simulate stud damage caused by welding defects, concrete cracking, and lifting effects. The study investigated the impact of stud damage on the static performance and shear strength of studs. Results indicated that when the root area of the stud was damaged, the shear strength and stiffness of the stud decreased with the damage degree. When the stud root was damaged within 5%h (h is the height of stud shank), it had a significant effect on the shear strength of the stud. Damage outside the 5%h range of the stud root had no significant effect on the shear strength of the stud. And a shear strength damage model was firstly proposed to reveal the damage mechanism of studs. A reduction factor K was proposed to account for the loss in shear strength caused by stud damage. Two methods for calculating K, namely the area reduction method and the equivalent area method, were developed. The calculated values of shear strength considering stud damage were obtained and verified by comparing the calculated values with the test results. The proposed method offers a better prediction of shear strength for damaged studs in UHPC.

The behavior of Shear Connectors in Steel-Normal Concrete Composite Structure under Repeated Loads

In today's construction industry, the use of composite beams is becoming more and more important, particularly for long-span bridges that must withstand repeated loads from moving automobiles. This work investigates the behavior of composite beams through experimentation. Six push-out steel-concrete specimens are made and tested with various levels of static and repetitive loading applied. The specimens are made of rolled steel sections that are joined to concrete decks on both sides by stud shear connectors. Two approaches—one static and the other repeating—applied a push-out load to two sets of samples. One has a stud shear connector measuring 16 mm, and the other measures 25 mm. Three specimens were made for each group. To determine the final load, one specimen from each group underwent a static push-out test in the first stage. In the subsequent phase, repeated loads of 0-80% and 25-80% of the maximum static load were applied to the remaining ones. The analysis process measured the variation in slip between the concrete decks and the steel section over several load cycles. It was found that the recorded slip values at the ultimate load increased about four times just before the failure. The recorded values of the residual slip at the end of each load cycle decreased with the increase in load cycle numbers. Also, it was found that the values of the residual slip depend on the values of the lower and upper limits of the load level. Doi: 10.28991/CEJ-2024-010-01-013 Full Text: PDF

Experimental Response of Headed Stud Shear Connectors in Steel-UHP-FRC Composite Slabs

Ultra High-Performance Fiber Reinforced Concrete (UHP-FRC) is widely used nowadays with the aim to obtain more resilient and sustainable structures. Specifically, interest is rising on the use of UHP-FRC for replacing existing slabs in steel-concrete bridge decks, which generally leads to a possible reduction in thickness and, consequently, results in a lower material demand.In this context, as the possibility of replacing existing slabs with UHP-FRC ones is strictly related to the effectiveness of beam-to-slab connection, the present paper presents the results of an experimental campaign aimed at investigating the mechanical behavior of the shear connection between concrete slab and steel joist by performing nine push-out tests by considering the possible variation of the concrete strength class (C25/30 – C60/75 and UHP-FRC), the slab thickness (150 mm, 120 mm and 75 mm) as well as the slab steel reinforcement (unreinforced in the case of UHP-FRC). All the experimental tests were performed at the Structural Engineering Testing Hall (Str.Eng.T.H.) of the University of Salerno. Moreover, Nelson-type headed stud shear connectors (16 mm in diameter and 64 mm in height) were also considered for all the produced samples. The present contribution summarizes the results of the push-out tests and compares the different force-slip curves obtained for the three groups of tested steel-concrete stubs, in view of future developments intended at understanding their influence of global behavior of steel-concrete composite bridge decks.

Cyclic performance of prefabricated composite shear stud connectors for accelerated bridge construction

This study examines the cyclic shear-slip performance of a novel prefabricated composite shear stud (PCSS) connector designed for accelerated bridge construction (ABC) of composite structures. An in-depth experimental procedure is employed involving the design and fabrication of four push-out specimens with two different stud configurations. The specimens are then tested under both monotonic and cyclic-to-monotonic loading protocols. Upon completion of the testing phase, a meticulous inspection of the fractography is conducted to delineate and qualify the failure mode of the PCSS connectors. Simultaneously, a comprehensive shear-slip curve is derived from the measured data, enabling a detailed analysis over the mechanical performance. Furthermore, the study calculates a series of deformation-associated indicators from the shear-slip curve, effectively quantifying the ductility, recoverability, and capacity of the PCSS. The test results accentuate a well-deformed and ductile failure mode of the tested PCSS specimens, marked by the stud fracture and crushing of surrounding concrete. This could be attributed to the constraint of vertical plates of the PCSS on the concrete, which improves the capacity and recoverability of the PCSS. Whereas, the performance of the PCSS is also notably influenced by the group nail effect, for which the ductility and per-stud capacity degrade with the increase in the number of studs. Especially, the PCSS specimen exhibits full elastic-to-plastic hysteresis loops under cyclic loads, together with the satisfied ductility, implying an excellent potential of the PCSS to dissipate energy under impact loads. In addition, the PCSS displays a robust stiffness across different cyclic loading blocks. Hence, satisfactory post-damage ductility has still been observed in the PCSS under the monotonic loading after the cyclic loading. In conclusion, this work elucidates the superiority of the PCSS in terms of capacity, ductility, and recoverability, providing a promising basis for their application in the accelerated construction of composite bridges.

Effects of Recycled Concrete on Structural Behavior of Composite Beams with Y-Rib Shear Connectors

This study inspects the structural behavior of composite steel concrete beams connected together by Y-Rib shear connectors using recycled concrete. The main method involves using stud shear connectors with normal concrete. By comparing the structural performance of Y-Rib shear connectors with conventional stud shear connectors, the study aims to determine the benefit of using this type of connector with recycled concrete. Improved results in terms of maximum load-bearing capacity before failure and maintaining structural integrity until failure would indicate a viable solution to the sliding issue seen in traditional composite beams. Regardless of challenges in acquiring traditional shear connectors, the study also explores an alternative: 20mm diameter reinforcing bars. Although this falls outside the primary research scope, the main focus remains on the behavior of composite beams connected by Y-shaped shear connectors with recycled concrete. The investigation encompasses 18 shear connector types, divided into two groups: 9 models with normal coarse aggregate concrete (35.17 MPa) and 9 models with recycled coarse aggregate concrete (33.48 MPa) to determine the benefit of recycled aggregate concrete usage.

Shear capacity evaluation of studs in steel-high strength concrete composite structures

The shear capacity of stud shear connectors was the main parameter affecting the mechanical performance of steel-concrete composite structures. In this paper, three artificial neural networks (ANN) were developed to evaluate the shear capacity of stud shear connectors in steel-high strength concrete composite structures. The models was applied to high strength concrete, covering the compressive strength of concrete in 61.19 MPa∼200 MPa. Based on the correlation analysis, the main influential parameters, including the compressive strength of concrete, the diameter, height, yield strength, number, and pretension force of stud shear connectors, were selected as input variables to the models. The proposed models were trained and tested with 100-group test data gathered from previous studies. By comparing with existing empirical models, it was proved that the proposed Elman network and RBF network had high applicability and reliability for predicting the shear capacity of stud shear connectors in steel-high strength concrete composite structures. Subsequently the parametric sensitive analysis was carried out based on the BP network.