Stud Connectors Research Articles

Experimental study on non-load bearing multi-span sandwich wall panels for blast mitigation

Sandwich wall panels are known for their ability to provide resistance over a wide deformation range, rendering them suitable for blast resistance applications. These panels consist of layers of concrete with an insulating core, offering a structural solution with enhanced performance. Quasi-static testing was conducted on multi-span sandwich wall panels with intermediate connections to evaluate their behavior under controlled loading conditions. A total of twelve two-span details were examined and selected to match the standard designs employed in the Tilt-Up Construction (TCA) and Prestressed/Precast Concrete Industry (PCI). Among these details, three belonged to the TCA type with two duplicates, while the remaining two were representative of PCI designs with three duplicates. The results obtained from the quasi-static testing indicate that insulated sandwich wall panels possess sufficient deformation capability to meet the current blast response criteria. To assess the findings of the static experiments to the prevailing response limits, the outcomes were distilled into a multi-linear static resistance analysis. The findings support the use of insulated precast concrete (PC) sandwich wall panels, highlighting their suitability for blast-resistant designs within the constraints of current blast design limitations. Specimens with Halfen connectors showed 32 % higher energy absorption and a 58 % advantage over Stud connectors, making them superior for robust blast resistance applications.

Investigation of the electrical quality and long-term stability of aluminum ground stud connections in automotive applications

The rapid advancement in the electrification of modern vehicles has led to a continuous increase in electrical consumers for various comfort and safety functions. Ground studs serve as the electrical interface between the conductive vehicle body and the onboard network. Drawn arc stud welding is an economical and established joining process for producing ground stud joints. The circuits in the onboard network are increasingly subject to greater demands regarding current-carrying capacity and long-term stability. Reliable signal and power transmission require minimal contact resistance at the electrical connection points of the ground stud system and must withstand various operating and environmental conditions over the entire service life. In this study, a ground stud made of AlMg5, with a ZnNi-coated steel cap nut was used on a 2.0 mm thick sheet of AlMg3. The electrical connection of the ground studs was made using tinned copper cable lugs and 35 mm² cables. To analyze the electrical resistance behavior in an accelerated test, the ground studs were subjected to a superimposed load with a cyclic current profile for 1008 hours under changing climatic conditions. The results show that under the chosen operational and environmental conditions, accelerated aging and intermittent resistance behavior occur. A characteristic drop in resistance during the test indicates the failure point of the electrical connection. The cause of failure can be attributed to media penetration into the electrical contact zone. A failure of the electrical connection was observed after 512 hours.

Shear Connectors Behavior Under Elevated Temperature: A review

A composite member is described as a structural steel shape that has been built up or rolled and filled with concrete, covered in reinforced concrete, or structurally attached to a slab of reinforced concrete. The shear connection between the steel beam and the concrete slab is the primary component of the composite beam. In risky situations, like building fires, the performance of a composite structures and steel structures are heavily dependent on the execution of connection. Numerous kinds of shear connectors exist and being utilized in the construction engineering rendering to their use. This paper reviews research conducted in the past years on the performance of shear connectors such as (ASTM A325 bolts, channel shear connector, T, T-mass and T-Proband shear connectors) exposed to raise heat degree. This research covers the experimental testing of push-out specimens, behavior of connectors in steel structures, various shapes of shear connectors under elevated temperatures, main failure modes, finite element modeling of shear connectors, design approaches offered by investigators, and various codes. Compared to the size of work available on shear connectors at room temperature, relatively slight research has been done on the conduct of shear connectors (studs) under high temperature. In addition, this report indicates several topics that need further investigations. Through this article, it was concluded that when temperatures raise, the strength of all shear connectors decreases proportionally regardless of its shape and type. A comparative study showed that the channel connectors are an economic and reliable option to standard shear connectors. Among the findings of some studies is that the effect of temperature on the shear resistance of head stud connector is significantly above 400℃, whether the test is done at temperature or post temperature conditions. Also, adding some materials to the concrete mix such as carbon nanotubes will be not effective on the ultimate shear at temperatures less than 400 ℃, but it reduces the spalling and cracking of the concrete. In general, the influence of elevated temperatures on the ultimate shear capacity of the headed stud connector is noticeably clearer when the test was conducted at exposed to certain temperature compared to post temperature conditions (the test is conducted after exposure the specimen to heat and cooling).

Fatigue strength of repair‐welded headed studs

AbstractWelded connections of headed studs are highly stressed details in bridge structures in steel‐concrete composite construction and are largely responsible for the functionality of the supporting structures. At the same time, this detail requires a lot of resources due to the high welding effort and therefore has a major influence on the economic success. An important criterion for the economic and ecological balance of the structure is the durability of the welded joint, which is quantified by the fatigue strength. The welding of headed studs for composite bridges is usually carried out using fully mechanised drawn arc stud welding in accordance with EN ISO 14555. Due to the process, stud welds that do not fulfil the standard requirements for flawless condition may occur in individual cases. The design rules for stud load‐bearing capacity in accordance with EN 1994‐2 are based on tests and only apply to connections produced using drawn arc stud welding. In the past, there were practicable and tacitly accepted solutions for repairing such sporadically occurring faulty welds, but these were never systematically investigated. Particularly against the background of fatigue loading, repair‐welded stud connections are now to be systematically investigated in a project funded by the AIF. The article provides an overview of the execution of stud welded joints and presents the tests planned in the project in order to achieve a practicable recommendation for the repair welding of headed studs.

Experimental Study on the Competitive Failure of Headed Stud Connectors under Freeze–Thaw Cycles

Experimental Study on the Competitive Failure of Headed Stud Connectors under Freeze–Thaw Cycles

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.

Shear behavior of stud and SFCBs‐reinforced PBL composite connectors in steel‐concrete structures

AbstractIn order to fully utilize the advantages of stud and perfobond leiste (PBL) connectors, a new composite shear connector was proposed in which the studs were welded to the H‐beam of the PBL shear connectors. In addition, to further improve the durability performance of the structure, steel‐fiber‐reinforced polymer composite bars (SFCBs) were used to replace steel rebars as penetrating rebars. In this study, the shear behaviors of SFCBs‐reinforced composite shear connectors were investigated by push‐out tests. The effects of the number of studs, the number of holes, and the type of penetrating rebars on the failure mode, load–slip curve, and shear behavior of the composite shear connectors were analyzed. The specimens' failure modes were mainly shearing the studs and crushing the concrete. Increasing the number of studs and holes has resulted in an increase of at least 7.47% in the shear resistance and 12.36% in the stiffness. SFCB had little effect on the shear resistance and reduced the stiffness but could improve ductility, with a maximum improvement of 11.49%. Additionally, a finite element model was established for parametric analysis. The results showed that the diameter of the SFCB and hole had a significant impact on the shear resistance. An equation for calculating the shear resistance based on the contributions of various components has been established that was applicable to composite shear connectors and has good accuracy and applicability.

Shear Performance Study of Sleeved Stud Connectors in Continuous Composite Girder.

In order to reveal the mechanism of sleeved stud connectors, 15 push-out specimens were designed, and static loading tests were conducted to evaluate the mechanical performance. The shear performance differences between the novel sleeved studs and conventional welded studs were compared. Referring to the experimental results, an Abaqus nonlinear finite element model was established to study the shear mechanism of sleeved stud connectors. Parametric analysis was conducted to investigate the effects of stud height, sleeve filling material, and sleeve diameter on the mechanical performance of the connectors. The experimental and finite element analysis results indicated that the ultimate shear bearing capacity and shear stiffness of the sleeved stud connectors were higher than those of ordinary welded studs, and the maximum slip was relatively small. Compared to conventional welded studs, the ultimate bearing capacity of sleeved studs increased by 4% to 8%, and the shear stiffness increased by 25% to 35%. Since the shear behavior of sleeved studs mainly occurred at the base of the studs, the influence of stud height on shear performance was relatively small. However, sleeve and stud diameter have a great influence on bearing capacity and stiffness. As the Ultra-High Performance Concrete (UHPC) near the base of the stud effectively enhanced the shear carrying capacity of the sleeved stud connectors, the shear carrying capacity and shear stiffness increased with the increase in the sleeve diameter.

Pull-out test of hybrid connection in steel-UHPC composite slab

This paper presents an experimental study on tensile behavior of steel and ultra-high performance concrete (UHPC) composite structure connected by different connections including epoxy resin adhesive, headed stud, and hybrid of the former two. Thirty-two pull-out tests are conducted by taking the connection type, specimen size and steel fiber content of UHPC as the main parameters. The influences of these main parameters on the failure mode, load-separation behavior, and ultimate resistance of connection are researched. The failure modes of specimens with hybrid connection are UHPC interface debonding and UHPC cone failure, which is identical with the epoxy resin adhesive connection and headed stud connection, respectively. The tensile resistance ratio of headed stud connection to epoxy resin adhesive connection has a significant influence both on the separation performance and tensile resistance of hybrid connection. An empirical equation for predicting the tensile resistance of hybrid connection was proposed by taking the tensile resistance ratio of headed stud to epoxy resin adhesive. The ratio of predicted to test result was 0.973with standard deviations of 0.070. The pull-out tests and analysis of the hybrid connection in steel-UHPC composite structure were still needed to study to get it improved.

Cyclic behavior of rubber-coated stud-UHPC shear connectors exposed to reversed cyclic loadings

Steel-ultra-high performance concrete (UHPC) composite structures that could maximize the benefits of two materials have gained ground in bridge structures for accelerating construction speed and reducing self-weight. However, the shear stiffness of ordinary stud connectors (OSCs) in UHPC might exceed the actual demand, leading to the insufficient deformation capacity of OSCs. Therefore, the flexible rubber-coated stud connectors (FRSCs) were developed to replace the OSCs for improving the ductility of shear connectors. The shear performance of FRSCs in UHPC subjected to reversed cyclic loadings has been not understood, which limits its application in the practical construction. The cyclic behavior of FRSCs was examined through modified push-pull test specimens, and the static loading tests were carried out to determine the characteristic slip capacity and shear strength. Numerical models were established to reveal the damage process and failure mechanism of FRSCs and employed to conduct detailed parametric studies. The results demonstrated the FRSCs exhibited high ductility and large energy absorption capacity than OSCs and possessed sufficient shear bearing capacity, indicating their potential application in steel-UHPC composite systems. Increasing the height and thickness of rubber sleeve could enhance the slip capacity of FRSCs under monotonic loadings, while having no effect on the cyclic ductility. Finally, an empirical equation was developed to accurately predict the FRSC shear strength.

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.

APPLICATION OF MACHINE LEARNING MODELS AND GSA METHOD FOR DESIGNING STUD CONNECTORS

The design of stud connectors is aided by determining the relationship between shear strength and the input variables (number, diameter, height, tensile strength and elastic modulus of the studs, and compressive strength and elastic modulus of the concrete) that influence strength. Since strength is nonlinearly related to the influencing variables, which makes the predictions of the relevant empirical equations unreliable, the use of machine learning (ML) models is preferred. The prediction results of eight machine learning models were evaluated, including linear regression (LR1), ridge regression (RR), lasso regression (LR2), back-propagation artificial neural network (BP ANN), genetic algorithm optimized BP ANN (GA-BP ANN), extreme learning machines (ELM), random forests (RF), and support vector machines (SVM). The results show that the GA-BP ANN model is the most accurate model for prediction with a mean absolute percentage error (MAPE) of 6.17% and an R2 of 0.9599. Based on the GA-BP ANN model and the global sensitivity analysis (GSA) method, a new parameter importance analysis method was developed to compare the magnitude of the effect of different input variables on strength. It was found that stud diameter had the greatest effect on shear strength.

Fatigue performance of stud connectors in joints between top slabs and steel girders with corrugated webs subjected to transverse bending moments

Steel-concrete composite box girders with corrugated steel webs (CSWs) are broadly used in bridge engineering, in which the joints between top RC slabs and steel girders with CSWs are usually subjected to transverse bending moments caused by off-center vehicle loads. Stud connectors arranged in the joints usually bear repeated pull-out forces in this case and are prone to fatigue failure. Therefore, two reduced scale joints between top slabs and weathering steel girders with CSWs were designed and tested, on which variable amplitude fatigue loads were applied to investigate the fatigue performance of studs incorporated in the joints. The two joints presented similar fatigue behavior, i.e., cracks of not more than 0.26 mm in width appeared on the surface of the top slab during the fatigue loading, and the separation of the top RC slabs and the top girder flanges was observed; meanwhile, minute cracks developed along the welds connecting the CSW with the bottom girder flange, and the stiffness of the joints gradually decreased due to the accumulation of fatigue damage. The two joints underwent 2,650,000 and 2,103,600 load cycles respectively before fatigue failure occurred. After partially demolishing the RC slabs, several welded head studs in the joints were observed fractured at the roots and detached from the top girder flange. Whereafter, finite element (FE) models referring to the test joints were developed and analyzed, and the effect of the wave height (WH) of the CSW and the transverse row spacing (TRS) of studs on the distribution of pull-out forces among studs was investigated. It showed that the pull-out force bore by each stud in the joint was distributed unevenly even in the same row. Then, a modification factor α was introduced to revise the pull-out forces of studs calculated in the theoretical method. An equation to determine the factor was fitted, considering the effect of the WH of the CSW and the TRS of studs. Finally, the detail category for studs bearing pull-out forces in the joints was discussed based on the experimental results and the collected test data, and it was preliminarily recommended studs subjected to pull-out forces can be classified into detail category 45 specified by Eurocode 3 in fatigue design.

Flexural Performance of Ultrathin UHPC Slab–Steel Composite Beams with Ultrashort Stud Connections

Flexural Performance of Ultrathin UHPC Slab–Steel Composite Beams with Ultrashort Stud Connections

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.

A Constitutive Model for Stud Connection in Composite Structures

The complexity of finite element analysis for composite structures can be significantly reduced by representing the connector and adjacent concrete as a macroscopic element. Nevertheless, the prevailing macroscopic models for shear connections predominantly employ nonlinear elastic theory. This approach introduces inaccuracies in estimating structural stiffness and load-bearing capabilities, primarily due to its inability to precisely capture the cumulative effects of plastic damage. In response, this study introduces a novel macroscopic elastoplastic model grounded in plasticity theory, aimed at accurately characterizing the nonlinear behavior of stud connections subjected to concurrent shear and tensile forces. This paper meticulously delineates the implementation of the elastoplastic constitutive model using the backward Euler method for numerical integration. It further articulates the derivation of the consistent tangent stiffness, which aligns with the convergence efficiency of the Newton–Raphson iterative approach. The computation of the element stiffness matrix for a two-node element is executed via the governing equation inherent to the finite element method. An exemplar macroelement test conducted in ABAQUS affirms the implicit backward Euler scheme’s stability and consistency across varying tolerances. Validation of the elastoplastic model against empirical test outcomes corroborates its efficacy, demonstrating the model’s precision in predicting the load–displacement behavior of stud connections under the influence of shear and tensile forces.

Effects of Freeze-Thaw Cycles on Interfacial Shear Transfer Characteristics in Section Steel Reinforced Concrete Composite Structures with Stud Connectors

This study examines how freeze-thaw cycles influence the shear transfer characteristics at the interface of section steel with stud connectors and concrete. Push out tests were performed on fourteen section steel reinforced concrete composite structures with stud connectors (SRCSC) and two without them. The analysis focused on examining the impact of variables such as the number of freeze-thaw cycles, the diameter of studs, and the arrangement of studs on the interfacial shear capacity of the SRCSCs. Experimental results showed that with an increase in the number of freeze-thaw cycles, the damage morphology of the SRCSCs transitions from stud shearing to concrete splitting. Concurrently, the interfacial shear capacity and shear stiffness of SRCSCs diminish. Large-diameter studs could effectively improve the interfacial shear properties of SRCSCs. Additionally, SRCSCs with studs positioned in the web demonstrate enhanced interfacial shear transfer capabilities compared to those with studs located in the flange. The proposed method for the residual interfacial shear capacity of the SRCSCs after freeze-thaw cycles was based on experimental data analysis. Results from this calculation method were consistent with the experimental observations.

Structural Design and Mechanical Behavior Investigation of Steel–Concrete Composite Decks of Narrow-Width Steel Box Composite Bridge

Steel–concrete composite decks are commonly employed in narrow-width steel box composite girder bridges to augment their lateral spanning capabilities, while the concurrent omission of longitudinal stiffeners leads to a substantial reduction in the number of components, thereby yielding a structurally optimized bridge configuration. This paper delineates the structural design parameters of a narrow-profile steel box composite girder bridge and assess the mechanical behavior of its incorporated steel–concrete composite deck under static and fatigue loading conditions. To this end, two full-scale segment specimens from the composite bridge decks were subjected to equal amplitude cyclic fatigue tests. The investigation specifically concentrated on the impacts of two types of shear connectors—namely, perforated steel plates combined with shear studs and perfobond rib shear connectors (PBL connectors)—on the static and fatigue performance, including fatigue stiffness, of the steel–concrete composite bridge decks. The results indicate that, under the static bending condition, the composite deck specimen equipped with stud connectors demonstrates superior overall flexural stiffness in comparison to the specimen featuring PBL connectors. Furthermore, the flexural stiffness of the steel–concrete composite specimens experiences a negligible alteration across two million fatigue loading cycles. Upon the completion of two million fatigue loading cycles, the composite deck specimens incorporating the shear connectors composed of perforated steel plates and shear studs exhibit relatively wider crack widths under the static peak load. Both configurations of the steel–concrete composite bridge deck specimens manifest evident interfacial detachment, signifying insufficient tensile pull-out stiffness of the shear connectors. It is recommended to increase the quantity of the shear connectors or select the pertinent types in order to enhance the interface shear resistance.

Shear performance of headless studs in ultra-high performance concrete bridge deck

Conventional stud connectors were proved to be inconvenient for the later disassembly and replacement in ultra-high performance concrete (UHPC) bridge decks. In this study, the headless studs which is a type of studs with their heads removed were employed as a substitute for conventional stud connectors, aiming to enhance the detachability of the bridge decks on the premise of ensuring the anti-lift bearing capacity of the decks. Three push-out specimens containing the headless studs with a diameter of 13 mm were carried out to study the mechanical properties of headless studs. In addition, the finite element model was developed to reveal the failure mechanism of headless studs in UHPC. Results indicated that the load-slip curve of headless stud connector can be divided into elastic stage, plastic stage and failure stage. The failure mode of headless studs was the shear fracture at the root of stud shank. Headless stud connections under cyclic loading can produce greater plastic deformation. The ultimate shear capacity and shear stiffness of headless studs were lower than those of conventional studs. Additionally, the UHPC slabs configured with headless studs have a small quantity of separation at the steel-UHPC interface, so it is suggested to use headless studs and conventional studs together in UHPC slabs to ensure the necessary anti-lift bearing capacity. Finite element analysis indicated that in the elastic stage, the bearing capacity of the push-specimen was dominated by the material properties of the headless stud. After entering the plastic stage, the bearing capacity of the push-specimen was mainly controlled by the UHPC below the headless stud.