Headed Stud Shear Research Articles

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

Strengthening of two-way slabs with fiber-reinforced polymer composites: A new system using grooving technique and fans

The flexural capacity of a reinforced concrete (RC) two-way slab can be efficiently enhanced using fiber-reinforced polymer (FRP) composites if FRP debonding is postponed. On the other hand, with the increase in flexural capacity, the vulnerability of the slab to punching shear failure increases. In this context, the current study examines FRP strengthening of lightly reinforced slabs using the externally bonded reinforcement on grooves (EBROG) technique, which has already been proven successful in postponing FRP debonding. Four slab specimens are tested in two groups under concentric loading. The first group consists of two specimens reinforced with headed shear studs: one reference specimen and one specimen strengthened in flexure with FRP. The second group includes two specimens without internal punching shear reinforcement: one reference specimen and one specimen strengthened with a new simultaneous flexural and punching shear strengthening system, taking advantage of FRP fans. According to the results, flexural strengthening of the slab in Group 1 increased its ultimate load capacity by 77%, and the proposed strengthening system in Group 2 led to a 94% enhancement of the ultimate load capacity. A calculation method based on the yield-line theory is presented to predict the load capacity of the test specimens. According to this method, graphs simplifying the estimation of the flexural capacity of FRP-strengthened slabs are proposed.

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 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.

Experimental study of innovative bolted shear connectors in demountable cold-formed steel–concrete composite beams

Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.In this paper, we propose a novel demountable composite connection specifically designed for prefabricated CFS structures. The behavior of this connection was evaluated through fifteen push-out test specimens, with key variables including CFS section thickness and bolt diameter/strength. The ultimate load, stiffness, ductility, and failure modes of all specimens were determined. The results revealed that specimens with a higher thickness of CFS members experienced bolt fracture, exhibiting superior effective stiffness, strength, and ductility. Conversely, specimens with a lower thickness of CFS members failed due to distortional buckling of the CFS members. The test results underscore the importance of carefully designing and providing a proportionate CFS section thickness to ensure shear connectors fracture before the CFS members. This significantly improves the shear strength capacity of the composite connection with CFS sections and precast concrete slabs. Furthermore, the deconstructability of the connection at the end of its service life was investigated. The steel–concrete composite connection with precast concrete slabs and demountable bolted shear connections was also modeled using a 3D finite element method. The numerical model’s accuracy in simulating the observed structural behavior was confirmed against experimental data. Finally, appropriate and straightforward formulations for predicting the ultimate load of the CFS-concrete composite connection were proposed. It was concluded that the predictions of ultimate shear load capacity values by EC4, AISC, and AISI provisions for this composite connection are significantly less accurate.

Study on headed shear studs influencing the interfacial bond behaviour in CFST columns

AbstractThe performance of concrete‐filled steel tubular (CFST) columns with headed shear studs under push‐out loading has been investigated. The primary objective of the research programme was to investigate the bond behaviour between the steel tube and the infill concrete core of the square CFST column. A numerical investigation has been carried out using the commercially available finite element software. For the simulated numerical models, they have been initially validated with existing experimental results. The validations were made in terms of failure modes, bond strength‐slip curves and the initial stiffness. The validated models were further used to carryout parametric studies. The parameters studied include, vertical spacing of shear studs, horizontal spacing of shear studs, and CFST cross‐section slenderness. From the investigation, it is observed that with reduced vertical spacing of studs, the bond strength increases significantly. Specimens having horizontal spacing of studs as width/4 has more bond strength than specimen with horizontal spacing of width/2 and 0. For specimens with reduced vertical and horizontal spacing of studs though leads to higher bond stress, but also drops suddenly due to loss of contact between the stud and concrete. Therefore, 70% of the peak stress value may be considered as the achieved bond stress, as this stress value sustains for higher slip values. Lastly, as the column cross‐section slenderness reduces, there is a trend in increase in interfacial bond strength.

Load introduction for concrete‐encased steel composite columns using high‐performance materials

AbstractDue to the increasing demand for high‐rise buildings and resource‐efficient construction, the demand for innovative construction technologies and materials is growing. High‐performance materials provide resource‐optimized structural solutions providing an important load‐bearing resistance.However, questions arise about the ductility of structural members using e.g., high‐strength concrete that is particularly important for the shear connectors of composite structures. This paper evaluates the load‐bearing capacity of the headed stud shear connectors arranged in the load introduction zone of encased composite columns using concrete compression strength classes C50/60, C80/95, and C100/115. An experimental study consisting of 32 specific push‐tests for circular and square cross‐sections with an embedded structural steel profile HE 160 B has been investigated. The loading procedure defined in EN1994‐1‐1:2004 Annex B was applied. Eight specimens were initially preloaded for six to twelve months to investigate the impact of the long‐term behavior of the concrete.Numerical simulations performed in FE code Abaqus® supported the investigation, using a simplified definition of the bond. The results correlated well with the outcomes of the extremital campaign.The research project thus provides the first approaches to be able to include high‐strength materials in the composite construction regulations for columns in the future.

A multi-parameter method for static behaviour of headed stud with ductile fracture in push-off tests

PurposeThe purpose of this study is to investigate the effects of stud height, stud diameter, ultimate stress of stud and concrete strength on the static behaviour of studs in push-off tests based on the ductile fracture theory.Design/methodology/approachPush-off tests of headed stud shear connectors with different heights and diameters used in concrete of various strengths were designed and implemented. A finite element model was established based on a ductile fracture criterion of ML15 cold-heading steel with stress triaxiality and Lode angle parameter. Based on the results of the parametric study of the numerical model, equations were proposed to evaluate the effect of stud height hs, stud area As, concrete strength fc and stud ultimate strength fsu used in concrete of various strengths on the static behaviour of studs.FindingsThe typical failure phenomenon observed among the test specimens was the fracture of the shank of studs. The microscopic images of the stud fracture surfaces and the verified finite element model indicate that the studs were fractured as a result of the combined action of tension and shear.Originality/valueA new method for calculating ultimate load Pu and ultimate slip Su is proposed in this paper. In the method, Pu is linearly related to fsu0.2143, As0.7790, hs0.0974, fc0.2065. Su is linearly related to fsu1.078, As0.4681, hs(−0.3135), fc(−0.3480).

Three-Dimensional Numerical Simulation for Lateral Distortional Buckling Behaviour of Steel-Concrete Composite Beams

Lateral Distortional Buckling (LDB) is a mode of instability in Steel-Concrete Composite (SCC) beams that is yet to be fully understood by the structural engineering research and design community. This work investigated numerical methods to understand the LDB behavior of SCC beams under negative moments that exhibit nonlinear behavior. Focus of the study was to develop and validate 3-Dimensional finite element (FE) models which capture the LDB behavior of SCC beams precisely. Detailed 3-Dimensional FE models of the SCC beams were developed using ABAQUS. For modeling concrete, a nonlinear damage plasticity model was considered. A quad-linear curve was used to describe the stress-stain relationship for the steel beam. The stress-stain relationship for the rebar was described using a bi-linear curve while an elastic perfectly plastic model was assigned to the headed stud shear connectors. Steel hardening behavior was simulated using an isotropic hardening model. The interaction between the concrete slab, steel beam, and studs was described using appropriate interface elements combined under suitable constraints. The FE model’s accuracy was validated by results obtained from previous experiments found in literature together with a brief description of the experiments done by previous researchers to ensure completeness. Validation of the model was done by comparing Moment-Rotation curves obtained from the experimental tests, lateral displacements of the bottom flange along the axial direction and comparison of the failure modes between the numerical model and experimental test specimens. It was observed that the maximum relative error for the ultimate moment capacity of the composite beams from FE analysis and the experimental tests was less than 2% which shows that the FE model was in strong agreement with the experimental results. Accordingly, the numerical model developed herein proves to be capable of accurately representing the LDB phenomenon.

Development of novel concave shear connector to enhance the composite behavior

In recent decades, the use of composite structures has increased in favor of their quick, simple, and cost-effective construction and shear connectors are the key to attaining this composite behavior by transferring horizontal shear from concrete to steel girder and avoiding vertical separation. The efficiency of the composite connection depends on the stiffness and strength of the shear connector. The current study proposes an innovative concave type shear connector for the composite steel beams-RCC slab structure in buildings and bridges, which is economical and easier to install compared to conventional headed studs. The push-out tests were simulated in ABAQUS software using finite element analysis to assess the connection's ductility, stiffness, and shear strength as well as the connection's ultimate slip. The numerical analysis observed an enhanced strength and stiffness of the concave shear connectors compared to conventional headed shear studs, achieving a material saving of 20% and satisfying the Eurocode ductility criteria.

Performance evaluation of triangular and circular bulged perforated headed stud shear connector in composite junction

Composite construction is widely increasing in today’s construction practice. Shear connections are essential components for ensuring the composite action in composite structures made of steel and concrete elements. Headed studs and channel shear connectors have been widely used in recent composite construction. In the present study, two new variations of headed stud shear connectors are developed using volumetric alterations: circular and triangular bulged perforated head stud shear connectors (CBPHS & TBPHS). For making these alterations, the headed stud shear connector is divided into three zones with reference to bending height. The bulge in the shank of the headed studs has a perforation to allow the reinforcement to pass through it. The performance of the proposed CBPHS and TBPHS studs was evaluated experimentally. The performance of CBPHS and TBPHS shear connectors was evaluated using six experimental and ten numerical specimens. Results show that CBPHS and TBPHS shear connectors have 29–33 % more ultimate shear carrying capacity with more ductility and stiffness than conventional headed stud shear connectors with almost the same material volumetric consumption. The reinforcement passing through the perforation helped CBPHS and TBPHS connectors attain higher ultimate strength, ductility, and stiffness than specimens without reinforcement passing through perforations. Based on results and comparisons made with other codal provisions, two new equations were developed to evaluate the strength of CBPHS and TBPHS shear connectors with and without reinforcement passing through the perforation.

3D finite-element analysis of innovative coconut palm stem shaped headed shear connectors

Headed studs are shear connectors in composite structures used at the adjoining face of a steel beam and a concrete slab. In this research, the conventional shape of a headed stud was restructured to resemble the shape of a coconut palm stem (royal palm) without a change in the overall material volume, with the aim of improving the shear strength of the composite connection. Six innovative shear connectors for composite structures, named coconut palm stem royal shaped headed stud shear connectors (CPSR studs), were examined. Abaqus/Explicit was used to model a push-out specimen and the finite-element model was successfully validated using published experimental results. The six different CPSR studs encased in three grades of concrete (C40, C50 and C60) were tested for shear strength, stiffness and load–slip performance. The results for the innovative CPSR studs were compared with those for uniform cross-section headed studs; when embedded in C40, C50 and C60 grade concrete, the results showed, respectively, 35–41%, 37–44% and 41–52% improvements in the ultimate strength of the shear connection. The improved shear strength capacity of the CPSR studs without a change in the overall volume of stud material means that fewer studs are required, leading to economic benefits.

Prediction of the Shear Resistance of Headed Studs Embedded in Precast Steel–Concrete Structures Based on an Interpretable Machine Learning Method

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

CHARACTERIZATION OF THE LOAD‐SLIP BEHAVIOUR OF HEADED STUD SHEAR CONNECTIONS IN NARROW PROFILED SHEETING

AbstractAlthough headed stud shear connections in profiled sheeting represent an efficient solution to transfer the longitudinal shear along composite beams, current EN 1994‐1‐1 may overestimate their design resistance in case of open trough profile steel sheeting with narrow ribs. Project team CEN/TC250/SC4.T3 proposed new equations based on a “cantilever” model which depends on the concrete tensile strength and the bending resistance of the connector. However, by increasing the slips, the internal forces redistribute, and the system can be represented by a “modified strut and tie” model. At large displacements, a “strut and tie” model was also developed accounting for the influence of the tensile forces in the connector. The respective analytical equations for predicting the load per stud were finally derived and compared with experimental load‐slip curves. It was found that the analytical models proposed lead to satisfactory predictions of the load‐slip behaviour of the shear connection.

DEFORMATION CAPACITY AND DUCTILITY OF SHEAR CONNECTORS

AbstractDeformation capacity and slip range (eventually called “ductility”) of shear connectors are key parameters for the design of shear connectors in composite beams, especially in partial shear connection. Existing design rules require a deformation capacity of at least 6 mm for the use of shear connectors with plastic design methods. This rule is combined with the assumption of rigid‐ideal plastic behaviour of the shear connectors. Still, the real characteristics of most of today's usual shear connectors differ considerably from these assumptions, even more for shear connectors used in combination with metal decking. The paper describes the results of a literature research conducted in order to obtain reliable values for the deformation capacity and the slip range of headed stud shear connectors. Based on these results, advanced design methods can be used to realise composite beams with more realistic lower limits for the degree of partial shear connection and thus better economic performance.

STRENGTH OF CONCRETE‐FILLED STEEL DECK COMPOSITE DIAPHRAGMS WITH REINFORCING STEEL

AbstractConcrete‐filled steel deck floors are the most commonly used diaphragm system in steel buildings. While a considerable amount of testing has been performed on bare steel deck diaphragms, a limited amount of data exists on concrete‐filled steel deck floor diaphragms subjected to cyclic loads. As part of a testing program at Virginia Tech, a total of eight cantilever diaphragm tests were performed on diaphragm specimens that were 5.2 m by 4.1 m with varied parameters such as deck height, total concrete thickness, concrete type (lightweight and normal weight), layout of headed shear studs, and reinforcement. Three of the specimens included reinforcing steel: two with reinforcing bars and one with welded wire mesh. The goal of this paper is to investigate strength predictions for these concrete‐filled steel deck diaphragms with varying types of steel reinforcement. A prediction model for the shear strength of concrete‐filled steel deck diaphragms was proposed and validated using the results of this experimental program, as well as the results of a testing program performed at Iowa State University.

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.

Experimental and analytical investigation of innovative wing plate headed stud shear connector in composite structures

The most widely employed components in concrete-steel composite constructions to achieve composite action are headed stud shear connectors. Although headed studs are widely employed, their behaviour causes shank failure at the interface, and incomplete composite action is unfair due to unused residual concrete strength. This study intended to enhance the shear capacity of the stud by enlarging its bearing area by introducing triangular-shaped steel wing plates at the base of the stud on either side of it. The effectiveness of integrating wing plates to the headed stud on the shear carrying capacity of composite connection was evaluated using experimental testing on ten pushout specimens. Ultimate shear capacity, ductility, stiffness, and modes of failure were investigated. Furthermore, the ABAQUS dynamic-explicit has been used to analyse the pushout specimens. A proposed modelling strategy used for further parametric analysis was validated with the test results. For the parametric research, two different grades of concrete and wing plate sizes were evaluated. The innovative stud's performance was compared with the traditional stud, demonstrating that the suggested studs give 34–74 per cent greater shear capacity, increased stiffness, and slip with superior ductility. Finally, based on the FE parametric and regression analysis, two equations for predicting the shear strength of the wing plate headed stud shear connector was developed and proposed for composite constructions.

Experimental study on the longitudinal shear transfer mechanisms and resistance in CSTC composite beams

This contribution presents an experimental study on composite steel truss in concrete (CSTC) beams consisting of prefabricated structural steel latticed girders embedded in concrete. Unlike typical composite beams with downstand steel profiles using headed stud shear connectors, CSTC beams are composed of straight and sinusoidally bent bars with a circular cross-section, in which the transfer of the longitudinal force is ensured via a mechanical interlock between the steel diagonals and the surrounding concrete slab. Because of the lack of specific tests, it is necessary to comprehend the local behaviour (stiffness, resistance and slip capacity) through new experimental investigations which support the development of a reliable design model able to predict the respective longitudinal shear resistance.This paper presents and discusses the setup and results of a wide experimental campaign of more than 30 push-out tests on CSTC beams. Different geometrical and mechanical parameters were varied in accordance with their typical range of application. Based on the experimental results, it was found that the shear transfer mechanism and resistance is governed by localized concrete failure combined with plastic bending deformation of the diagonal bars. The load-slip behaviour was found to be qualitatively comparable with headed stud shear connectors and the significant slip capacity, in most cases beyond 20 mm, indicates that the sinusoidal web bars lead to a shear transfer mechanism that may be considered to be ductile according to EN 1994-1-1. In addition, to isolate the local contribution to the resistance provided by the bars near the weld seams, the diagonal bars of some specimens were intentionally sawed off in some of the specimens, resulting in a “steel tooth”. The load carried by this isolated component was found to be about 58 % of the full longitudinal shear resistance. The experimental values of the resistance were finally used to calibrate statistically an analytical equation for predicting the design of longitudinal shear resistance in compliance with the reliability levels given in EN 1990. Additional considerations concerning the potential interaction with the vertical shear load capacity given by the diagonal bars were included in the final design proposal.

Shear resistance determination of concrete dowel in shallow concrete-steel composite floor-beam based on push-out tests

Unlike conventional composite beam which use headed-shear studs, in shallow concrete-steel composite floor beam system, the web opening of steel beam infilled with in-situ concrete is considered as shear connector. In this paper, empirical formula for the shear resistance determination of trapezoid concrete dowel in shallow concrete-steel composite floor-beam is formed. This established process is based on the failure mechanism and the ultimate loading of push-out tests. The push-out test results were retrieved from our previous experimental investigations which showed that the shear resistance of the shear connector is mainly contributed by con-fined compressive strength and splitting tensile strength of concrete. By performing a combined mechanical-analytical analysis, an empirical formulation originating from the shear transferring mechanism of concrete dowel has been proposed. The formula was then verified against existing data and other equations in the pub-lished literature. The comparison demonstrates that the proposed formulation is the most suitable for the trape-zoid concrete shear connector.