Headed Stud Connectors Research Articles

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).

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

Investigation on shear behavior of large diameter short stud connectors in steel- thin UHPC bridge deck

Ultra-high performance concrete (UHPC) is a promising alternative for improving the mechanical performance of the steel and reinforced concrete composite bridge deck. Because of the excellent compression and tensile strength as well as the superior durability, the thickness of the UHPC slab can be effectively reduced. Therefore, large diameter short headed stud connector was proposed in this study to match the thin UHPC slab. To investigate the shear behavior of the large diameter headed studs in steel-thin UHPC composite bridges, 6 groups of 12 push-out specimens were designed and tested under the static loading. During the test, the failure mode, load-slip curves, the ductility, shear stiffness and shear strength of the specimens were emphatically focused. Besides, the influences of the aspect ratio of the stud, the thickness of the UHPC slab and the number of the stud in one position on shear behavior of the specimens were evaluated. Furthermore, the ABAQUS software has been used to analyse the large diameter short stud. A proposed modelling strategy used for further parametric analysis was validated with the test results. For the parametric research, different aspect ratio of stud and ultimate strength of stud were evaluated. Test and FEM results showed that the specimens failed in the failure of the root of the stud and the crushing of the concrete. With the increasing of the diameter of the stud, the thickness of the UHPC slab and the ultimate strength of stud, the shear strength and the shear stiffness of the specimens increased. Under the same cross-sectional area of the stud, the shear behavior of a single large diameter short stud connector could be comparable to that of two conventional stud connectors. Finally, after evaluating the results obtained from existing formulas, a predictive equation for the shear bearing capacity of large diameter short studs was proposed, and the accuracy of the calculated results was verified.

The Effect of Connection Ductility on Composite Steel–Concrete Bridges

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.

Effect of Stud Connector Diameter on the Behavior of Steel–Lightweight Self-Compacting Concrete Composite Beams with Partial shear Connection

This study investigates the efficacy of using lightweight self-compacting concrete (LWSCC) in steel-concrete composite beams, focusing on the role of headed stud connectors in shear connection. The research aimed to evaluate the behavior and shear strength of M16 and M20 headed stud connectors within LWSCC. To this end, six push-out test samples and six simply supported steel-LWSCC composite beams were fabricated and tested, with variables including the degree of shear connection (DSC) and stud diameter. The results demonstrated that an increase in DSC significantly enhanced the ultimate load capacity, service load, and stiffness of the composite beams, with marked improvements observed in the beams with M16 connectors (94%, 95%, and 122%, respectively) and those with M20 connectors (43%, 43%, and 20%, respectively). Furthermore, increasing the stud diameter from 16mm to 20mm resulted in a 38% increase in shear strength of the connectors and notably improved the mechanical characteristics of the beams. The study also found that while an increased DSC reduces deflection at ultimate and service loads due to heightened stiffness, a larger stud diameter has only a marginal effect on deflection. This research highlights the potential of LWSCC in enhancing the structural performance of steel-concrete composite beams, particularly with optimized shear connections, offering valuable insights for advancements in construction materials and methods. Highlights : Enhanced Load Capacity: Increase in the degree of shear connection significantly boosts ultimate load capacity and stiffness in composite beams. Stud Diameter Impact: A 38% rise in shear strength is achieved by increasing stud diameter from 16mm to 20mm. Deflection Reduction: Higher degree of shear connection effectively minimizes deflection, though stud diameter has minimal impact. Keywords : Lightweight Self-Compacting Concrete, Steel-Concrete Composite Beams, Shear Connection, Headed Stud Connectors, Structural Performance.

Push-out tests on steel composite sections with engineered cementitious composite

This paper investigates the shear strength and failure modes of steel-concrete-steel (SCS) sandwich composite member with Engineered Cementitious Concrete (ECC) and explores the influences of various shear connectors such as headed stud and bolt on shear behavior of SCS sandwich composite member by carrying out push-out testing program. Based on the test results in this study, the failure modes and the load-slip behavior of the specimens are investigated. In addition, the experimental results on the shear resistance of the headed stud connector with various connector spacing and numbers of connector is compared and explored.

Shear resistance and deflection prediction of steel–concrete–steel sandwich panel with headed stud connectors

Bending tests were conducted on eight specimens to investigate the mechanical behavior of steel–concrete-steel (SCS) sandwich panels with headed studs, taking into account the effects including loading mode, steel plate thickness, concrete core thickness and connectors spacing, and one sandwich panel was used as a control specimen. The failure characteristics and crack patterns of the specimens were recorded and the vertical displacement in the span was measured. The test results were used for the validation of the finite element model (FEM). Further parametric studies of the FEM yielded the effect of steel plates on the load-bearing capacity of the sandwich structure. Analytical models applicable to the initial stiffness and shear resistance of specimens with headed studs were proposed. The shear strength considered the effect of steel plate and pin action. The deflection calculation models of the sandwich panel were obtained based on the energy method and were in good agreement with the load–displacement response curves obtained by FEM results. The research results of this paper will have an impact on the large deformation and ultimate strength prediction of sandwich protective panels.

Structural Performance of Prefabricated Composite Girders for Railway Bridges along with Girder-to-Deck Interface Connections for Mechanical Injection

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.

Finite element analysis on shear behavior of headed studs in steel-UHPC composite slab

Headed stud connectors play a key role in steel- ultra-high performance concrete (UHPC) composite slab, which has many applications in long-span bridges. In this paper, a finite element (FE) model is validated by a series of push-out tests to study the shear behaviors of headed stud in steel-UHPC composite slab. After validation, the interaction between stud and UHPC is explored and parametric analysis is performed. The influence of weld collar, diameter and spacing of stud on the failure mode, shear bearing capacity and load-slip relationship of stud connector are discussed. From FE results, the group stud effect should be considered, as the ratio of stud spacing to diameter is less than 3.5, 5.0 and 6.5 for the diameter of 13 mm, 16 mm and 19 mm respectively. A formula to predict the shear bearing capacity of stud is proposed by considering the influence of weld collar and group stud effect. A shear-slip model of stud is established based on experimental and FE analysis results.

Push-out test of headed stud connectors subjected to freeze-thaw cycles and artificial corrosion

To obtain the shear capacity calculation method and competition failure mechanism of headed stud connectors of steel–concrete composite structures under the influence of freeze–thaw cycles (FTCs) and artificial corrosion (AC), the material performance of concrete specimens after the FTCs and push-out tests of 36 headed stud connectors specimens were tested under the influence of FTCs and AC. The cubic compressive strength, dynamic elastic modulus, and mass loss rate of C50 concrete were obtained under different FTCs. Failure modes, load-slip curve, shear capacity, and shear stiffness of stud connectors were investigated based on push-out tests of miniaturized specimens. Based on the nonlinear fitting of test data, a formula for calculating the shear capacity reduction factor is proposed. Results show that the shear capacity and stiffness of stud connectors will deteriorate due to the deterioration of concrete performance caused by FTCs or the weakening of stud section caused by AC. The two failure modes of stud breakage or concrete cracking will change with the aggravation of FTCs and AC effect.

NEW EUROCODE 4 DESIGN RULES FOR COMPOSITE BEAMS WITH PRECAST CONCRETE SLABS

AbstractAs members of Project Team SC4.T5, the authors of this paper present the main outcomes from the work that is intended for implementation within the second generation of Eurocode 4. General design and application rules for composite design of precast concrete elements will be presented, with a particular focus on: the effective width of flanges using precast concrete elements for shear lag; design resistance to longitudinal shear; and the design resistance of headed stud connectors in the presence of precast hollow core slabs.

A Trilinear Model for the Load-Slip Behavior of Headed Stud Shear Connectors.

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.

Auto-tuning deep forest for shear stiffness prediction of headed stud connectors

The shear stiffness of headed stud connector is a critical parameter for the calculation of deflection and interfacial shear force for steel–concrete composite structure. Thus, this study presented a promising data-driven model auto-tuning Deep Forest (ATDF) to precisely predict the stud shear stiffness, where the novel Deep Forest algorithm is integrated with the Sequential Model-Based Optimization method to achieve automatic hyperparameter optimization. Six variables having causal relationships with shear stiffness were extracted via mechanism and model analysis, including the effect of weld collar that cannot be considered in existing models and subsequently constituting a database of 425 push-out tests. Then the ATDF model was trained by combining the advantages of deep learning, ensemble learning, and auto-tuning techniques. It was approved to significantly outperform representative benchmark models with R values of 0.91 and 0.87 for training and testing sets. The ATDF was subjected to attribute importance analysis, which quantified the stud diameter and concrete elastic modulus as the most significant variables for shear stiffness, with the stud elastic modulus having the minimal effect. The model uncertainty of ATDF was further evaluated, revealing that it had the lowest bias and variability than those in existing empirical or semi-empirical models. Finally, the reliability analysis was conducted and the partial factors of ATDF under specified target reliability were derived.

Study on the Flexural Behavior of Steel-Concrete Composite Beams Based on the Shear Performance of Headed Stud Connectors

Headed studs have been widely used as shear connectors in steel-concrete composite beams for a long time. Studies on the influence of the different shear properties of headed studs on the flexural behavior of the composite beams have been inconclusive. In this research, we studied the shear performance influence of headed studs by conducting static push-out tests on seven designed push-out specimens. The flexural behavior of a steel-concrete composite beam connected by studs was discussed in detail by conducting a two-point symmetric monotonic static loading test. Based on the actual situation of the composite beam test, a finite element numerical model was established and validated, in which the elastic connections units were used to simulate the studs, and the force–slip data obtained from the push-out tests were used as the constitutive model of the studs. The effects of the stud diameter, stud height, the number of studs arranged, and concrete strength on the flexural behavior of the composite beams were analyzed and compared. The results showed that the number of studs arranged had a significant influence on the flexural behavior of the composite beams, followed by the strength of the concrete. The specifications of the studs had little effect on the flexural behavior of the composite beams within the study scope using the modeling method in this paper.

Shear Strength of Headed Stud Connectors in Self-Compacting Concrete with Recycled Coarse Aggregate

This study investigated the use of self-compacting concrete (SCC) made with recycled coarse aggregates (RCAs), which represents a trend of producing environment-friendly concrete, integrated with hot-rolled steel sections by means of headed stud shear connectors in composite structures. Therefore, thirty-six push-out test specimens were examined to assess the shear strength and behavior of the headed stud connectors embedded in RCA-SCC, with the concrete compressive strength, stud diameter, and RCA ratio as the main variables. Four ratios of RCAs ranging from 0 to 60% were used to produce concrete with three different compressive strengths (25, 33, and 40 MPa) for each one. It was found that the use of SCC with RCAs had a negative effect on the shear strength of headed stud connectors. This negative effect could be reduced by increasing the concrete compressive strength and/or the stud diameter. Similarly, a reduction in the shear stiffness of the tested specimens was inversely proportional to the RCA ratio, while the ultimate slip was directly proportional to the RCA ratio. An evaluation of the test results was made by comparing them with those determined by Eurocode 4 and AASHTO LRFD.

Numerical Study on the Tensile Performance of Headed Stud Shear Connectors with Head-Sectional Damage.

An extensive numerical study was carried out due to the concern that head-sectional damage caused by corrosion poses a threat to the tensile performance of headed stud connectors. Three-dimensional finite element models of pull-out tests were established, with both material and geometric nonlinearities being considered. In particular, the concrete weak region due to bleeding was simulated. The simulation method was verified by the results of pull-out tests on two connectors with different damage degrees. Tensile performance of headed stud shear connectors of various shaft diameters (ds = 10 to 25 mm) with various damage degrees (up to 50%) was simulated. It was observed that the connector with a high damage degree exhibited low capacity and a failure closer to pull-out failure than concrete cone breakout failure. Based on the numerical results, reduction factors for quantitatively assessing the influence of head-sectional damage degree on the loading capacity and stiffness of connectors were proposed. With reference to the Concrete Capacity method, the reduction in tensile capacity of connectors with head-sectional damage was found to be caused by the decrease in the projected area of the concrete cone due to the reduction in head diameter, concrete cone angle, and embedment depth. Meanwhile, numerical results showed that the stiffness of a connector at a high embedment depth or in high strength concrete was more sensitive to head-sectional damage. It was also found that the elastic modulus of the weak region significantly affected the stiffness of connectors, while the influence of its thickness on the capacity and stiffness was insignificant.

Machine learning models for predicting resistance of headed studs embedded in concrete

The design model for the resistance of headed stud connectors was originally developed from push test investigations conducted in the 1970′s and 1980′s. As more push test data has become available, the earlier design model has been updated from results of reliability analyses, or completely new models have been developed from experimental observations. In this paper six machine learning (ML) models are trained to predict the stud resistance based on a comprehensive database containing 242 push test results. To investigate the performance of the ML models, comparisons are made with five existing design models (or ‘physics-based’, Pb models). It was found that the super vector machine (SVM) model, which is an advanced and powerful ML model, outperformed other ML and Pb models. The SVM model with an R2 value of 0.95 can readily predict the stud resistance with an accuracy of ± 8.70kN, which is less than 5% of the mean measured resistance. PDP plots and ICE plots also are presented to visualize relationships between seven predictors (or ‘basic variables’ according to EN 1990), including geometry and material variables, and response (i.e. stud resistance) to show interactions among two features in the SVM model. A decision tree model, which is an interpretable ML model, is used to analyse the importance of the input variables within the predicted resistance. Results of importance analysis reveal that the diameter of stud shank and the compressive strength of the concrete are the most significant influencing features in the predicted stud resistance. From this same analysis, it was also shown that the short-term secant modulus of elasticity of concrete is relatively insignificant for studs embedded in normal weight concrete.

Experimental and numerical study on the mechanical properties of embedded double-row-pins connectors

In the structure of prestressed concrete box-girder bridge with corrugated steel web, the shear connectors are arranged to ensure the concrete slab and corrugated steel web work together. For the headed stud connector and PBL connector, the flange plates are arranged on the upper or lower edges of the steel webs, so the concrete slab is not easy to be vibrated during the bridge construction, resulting in insufficient compaction of concrete. For the embedded connector, to solve this problem, no flange plates are installed on the edges of corrugated steel webs. However, the embedded connector’s ultimate shear load is smaller than that of headed stud connector and PBL connector. The connector’s essence is the reinforced concrete pin. Therefore, compared with other structural measures, increasing the reinforced concrete’s number is more effective to improve the ultimate shear load of connectors. The ultimate shear load of embedded double-row-pins connector is improved due to arranging two rows of reinforced concrete pins. In this paper, 45 push-out specimens of embedded connector were designed and loaded to failure. The failure mode, shear capacity and shear stiffness of the embedded double-row-pins connector were studied. Furthermore, 44 nonlinear finite element models were performed to study the effects of structural geometric parameters and concrete strength. The parametric results were generated to evaluate these parameters’s influence on the ultimate shear load of embedded double-row-pins connector. At last, a equation was genrated to predict the ultimate shear load of the embedded double-row-pins connector.

Experimental investigation on fatigue behavior of composite beams with different studs arrangements

Connections between steel beams and concrete slabs that reduce the number of shear connectors by using studs with a larger size or partial shear connections could be advantageous by reducing installation time and provide additional working space for construction workers to move on the top steel flange. In this paper, steel and concrete composite beams with different headed stud shear connector arrangements were tested under fatigue loading to evaluate the crack patterns in concrete slabs, deformations, and strains in the composite sections and shear connectors. These arrangements included full shear connections achieved by 22.2 mm and 15.9 mm diameters headed stud connectors arranged in one and two rows, respectively, and a partial shear connection with two rows of 15.9 mm diameter shear connectors. Distributing the required resistance of shear to a larger population of smaller studs produced more beneficial behavior over that of a smaller population of larger diameter studs. The concrete slab fully shear connected by the one-row arrangement experienced longitudinal cracks during fatigue loading, which led to more stiffness degradation and strength deterioration, while such cracks were eliminated in the two-row arrangement. Therefore, 77.1%, 177.7%, and 152.5% increase in the incremental deflection, slippage, and studs’ strains, respectively, were obtained for this specimen. Moreover, reductions of 83.0% and 66.7% were obtained in the composite action in terms of the cyclic slippage for the specimens with the one- and two-row arrangements, respectively. Final residual static tests up to failure were conducted to explore the residual behavior of the fatigued specimens. Degradations in the residual stiffness and strength of the fatigued specimens occurred and more partially composite effects were obtained, which led to higher residual strains in the headed stud connectors and extreme fibers of the composite sections of 12.6% and 16.6%, respectively.

Shear behavior of short headed studs in Steel-ECC composite structure

Engineering cementitious composite (ECC) is a promising candidate as the overlay material of orthotropic steel bridge deck (OSBD), to improve the durability and extend the service life. The mechanical performance of short headed stud connectors in steel-ECC composite structure has been limited studied. This study investigated the shear behavior of short headed studs embedded in ECC through experimental push-out tests and validated finite element (FE) analysis. The experimental and analytical results were analyzed accordingly in terms of shear strength, shear stiffness and failure mode. The push-out testing results showed that the existence of natural interfacial bond was beneficial for improving the initial stiffness of the specimen. The FE simulation results agreed well with the experimental ones. Base on the validated FE model, a parametric analysis was then conducted to investigate the influence of the stud diameter, stud height, stud strength, corrosion of stud, and compressive strength of ECC on the shear capacity of short headed studs. The analysis indicated that the diameter and tensile strength of headed stud had a significant improvement on the shear strength of headed studs, while the stud height and compressive strength of ECC exhibited the opposite trend. The corrosion of stud drastically reduced the shear performance of headed studs in terms of shear strength and ductility. It was also observed that AASHTO LRFD specification overestimated the shear strength of short headed studs embedded in ECC, while the Eurocode 4 and Chinese code were relatively conservative.