Bolted Shear Connectors Research Articles

Experimental study of deconstructable embedded bolted shear connectors in composite beam subjected to cyclic loading

Bolted shear connectors have recently been introduced and studied as a convenient and demountable alternative for shear studs in steel-concrete composite beams. The major problem of welded studs is their undeconstructability. Bolted shear connectors make it possible to deconstruct and reuse the connection after its service life. In this study, the cyclic behavior of embedded bolted shear connectors in steel-concrete composite beams was investigated. The specimens included prefabricated concrete slabs with a square hole, which was filled with grout after assembling the concrete slab and steel section. Eight specimens were fabricated and tested to examine the effect of the bolt's diameter and strength on the cyclic behavior. To determine its behavior characteristics force-slip curves were applied. Ductility, strength degradation, and energy dissipation were the primary parameters investigated in this study. The results showed that the bolt’s diameter and strength significantly influenced the cyclic behavior of composite beams. Increasing the bolt's diameter and strength improved the connection's ductility and energy dissipation. Furthermore, doubling the bolt's cross-section increased the connection's ultimate strength by more than twice.

Experimental and numerical study on behavior of demountable T-shaped bolt shear connectors in sustainable composite beams

This paper proposed a new type of demountable T-bolt shear connector to improve the disassembly efficiency of composite beams and realize the sustainable of the structure components. The shear behavior of nine groups of push-out specimens was experimentally investigated through monotonic loading push-out tests. The finite element analysis (FEA) models were validated against the test results, specifically in terms of the load-slip responses and failure modes of the T-bolt shear connectors in these push-out specimens. The obtained results show that all the specimens have no obvious deformation and cracks in the steel beam and RC slab. The separation between the slab and the steel beam is no more than 1 mm, indicating that the anti-lifting ability is excellent. Moreover, parametric analysis demonstrates that increasing the bolt pretension of the T-shaped shear connector and the friction coefficient between the bridge gasket and the steel beam significantly enhances the initial stiffness and ultimate strength of the shear connectors. However, the shear behavior is relatively insensitive to variations in the channel thickness and bolt grade. Based on regression analysis, a load-slip mechanical model has been proposed. This model accurately describes the mechanical properties of this type of shear connector, providing a theoretical foundation for the application of demountable composite beams.

Experimental studies on fully demountable P-DBSCs shear connectors in sustainable reinforced concrete beam-slab

To improve the increasingly serious environmental pollution and waste of resources in the construction of traditional buildings, a novel type of shear connector P-DBSCs (Demountable Bolted Shear Connectors with connection Plate) was designed. The shear performance of P-DBSCs in RC beam and slabs were comprehensively evaluated by seven push-out tests and secondary loading. The failure mode, load-slip curve, ultimate shear capacity and ductility of the specimens were carefully discussed. As illustrated by the experimental results, the failure mode of the 7 push-out specimens is bolt fracture with no obvious crack in the beam and slabs, and the demount-ability is excellent after failure. The ultimate slip of all specimens is greater than 6 mm, which meets the requirements of Eurocode 4. The ultimate strength of P-DBSCs shear connectors increased with the increase of steel box thickness and bolt diameter, it decreased with the increase of channel spacing. The ductility of P-DBSCs shear connectors increased with the reducing of channel spacing and bolt diameter. Additionally, the shear performance of P-DBSCs is insensitive to the strength of concrete of slabs. After the first loading, the ultimate shear resistance; ultimate displacement and initial stiffness of the push-out specimen decrease slightly in secondary loading, but the influence code of each parameter remain constant. Finally, a comparison of ultimate strength between the calculated value and the experimental results showed that the theoretical values given by the Eurocode 3, Eurocode 4 and code AISC360–16 were higher than the experimental values, which indicated that the calculations overestimated the shear capacity of connection. Based on this, two formulae were proposed to predict the friction-type shear capacity and pressure-type shear capacity of P-DBSCs and the efficacy of the proposed design formula was proved by the comparison with the test results, which provides a research basis for such shear connectors.

Experimental and numerical study on behavior of demountable shear connectors in sustainable reinforced concrete beam-slab

Developed herein is a novel fully demountable shear connector, P-DBSCs (Demountable Bolted Shear Connectors with End Plate), aimed at enhancing the economic and environmental advantages of traditional buildings undergoing disassembly and reconstruction. This work numerically and experimentally assessed the shear performance of P-DBSCs via seven push-out tests and finite element simulations. Results revealed a uniform failure mode across seven specimens characterized by bolt fractures, absent of significant beam or slab cracking, evidencing remarkable post-failure demountability. According to the assessments of the specimens' force state, encompassing Digital Image Correlation (DIC) and anti-lifting capacity analyses, established that specimens fitted with larger bolts maintained better integrity and the concrete beam is under compression state, with lifting displacements remaining below 1.2 mm. Further, a verified finite element model's parameter study explored the influences of factors such as slab concrete strength, channel spacing, steel box thickness, channel thickness, steel box strength, and the diameter and strength of bolts on the shear performance of these connectors, finding these attributes to significantly affect shear performance within specific ranges, except for the slab concrete strength, to which shear performance displayed lesser sensitivity. Regression analysis facilitated the proposition of a mechanical constitutive model and stiffness degradation model for this connector type, validated through correlation with experimental results. These models provide a solid theoretical foundation for implementing demountable reinforced concrete (RC) beam-slab systems.

Push‐out tests of demountable shear connectors for sustainable composite structures

AbstractThe demountable shear connector is the most important component of sustainable composite structures, as it allows the elements to be reused. The ongoing research and development project – in the cooperation of the Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd., Hungary – aims to design a new demountable steel‐concrete composite structural system. In the current research, bolted shear connectors with embedded bolts and threaded rods, which can fit the applied technology of the industrial partner, are being developed and studied. One of the main aspects of this connection is to consider the bolt hole clearance – to decrease initial slip and stiffness reduction – and also to provide the proper strength and ductility features. A push‐out experimental programme was designed and completed to study the behaviour of the developed shear connections. It is observed that the examined shear connectors have proper structural behaviour with adequate resistance and ductility, which is applicable according to the Eurocode 4 standard and fits the objectives of the current research project. This paper presents the developed structural details, the observations and the evaluation of the push‐out experimental results with the conclusions and statements.

Modeling of innovative bolted shear connectors in demountable cold-formed steel-concrete composite beams: Validation of finite element model and parametric study

Composite cold-formed steel (CFS)-concrete structures have been widely used due to their benefits such as more ultimate strength, stiffness, and postponement of lateral buckling compared to bare CFS steel. Appropriate shear connectors should be used in order to establish composite performance between the CFS section and the concrete component. Traditional welded-stud connectors cannot be used due to the low thickness of the CFS members. Therefore, in this paper, a novel composite connection consisting of bolted-shear connectors embedded in grout is proposed and its performance is investigated by numerical models of push-out tests. A three-dimensional finite element model of the composite connection considering the non-linearities of the material and geometry, interfaces, and interactions between the components and materials are developed and verified against the results of the experimental study. After that, an extensive parametric study is carried out and the effects of different parameters, such as bolt strength and diameter, CFS section thickness, concrete compressive strength, and pretension load on the structural behavior of this type of composite connection are investigated and discussed in detail. It is concluded that the behaviour of the composite connection is significantly influenced by bolt strength and diameter, CFS section thickness and strength. The available design models provided in different provisions, including AISI, EC4 and AISC that predict the shear load capacity of connections with preload bolted shear connectors are reviewed and assessed. The results show that the ultimate shear load capacity values predicted by these provisions were found to be relatively less accurate. Finally, a new and more accurate design equation based on the results of this study is then proposed.

Behavior of Partially Composite Beams with Demountable Bolted Shear Connectors

Behavior of Partially Composite Beams with Demountable Bolted Shear Connectors

A numerical study on a novel demountable cold-formed steel composite beam with profiled steel sheeting

Cold-formed steel composite beams are known for their unique advantages, like being lightweight and ease of installation. The use of profiled steel sheeting in cold-formed composite beams reduces construction time and costs by acting as a permanent formwork in the composite beams. The current study presents a 3D finite element model of cold-formed steel composite beam specimens comprising a cold-formed double-lipped channel section, profiled steel sheeting, concrete slab, and bolted shear connector. Employing bolted shear connectors, structural components can be deconstructed and replaced after their service life expires or if they are damaged. The characteristics of the materials obtained from an experimental program were assigned to the finite element model. Geometric characteristics, material nonlinearities, and loading procedures were attentively simulated, and a dynamic explicit procedure was employed for the numerical analyses. A comparison of the results obtained from the finite element models and the available experimental results validated the precision of the models. Then, numerical studies were conducted to investigate the effects of various parameters, including compressive strength of concrete, thickness of concrete slab, height and grade of cold-formed steel section, thickness of profiled steel sheeting, number and diameter of shear connectors, on the behavior of the composite beam. The results showed that the height and grade of the cold-formed steel section and compressive strength and thickness of the concrete slab have a significant effect on increasing the capacity of the composite beam.

Experimental Study of Novel Demountable Shear Connectors for Steel-concrete Composite Buildings

Sustainable composite structures in building construction are assembled using demountable structural elements that can be reused in the circular economy. The current research and development project, in cooperation with Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd., Hungary, aims to design a novel demountable steel-concrete composite slab and frame system for buildings. The key component of this construction is the demountable shear connector. In the current research, novel bolted shear connectors with embedded bolts and threaded rods are developed and studied that can fit the applied technology of the industrial partner. One of the leading aspects of this connection is the consideration of bolt hole clearance, since it occurs initial slip and stiffness reduction of the composite beam. In the first phase of the research program, demountable and economical structural details were developed, which can reduce the stiffness reduction with the proper resistance and ductility features. To study the behavior of these shear connections, a push-out experimental program was designed and completed in March and April 2023. It is observed that novel shear connectors have a proper behavior with sufficient resistance and ductility, which is applicable according to the Eurocode 4 standard and fits the objectives of the research and development project. In the paper, the developed structural details and the push-out experimental program are presented with general results and statements besides a detailed evaluation of a specified specimen type.

Study on Fire Resistance of Prefabricated Demountable Composite Beams Using Bolted Shear Connectors

Study on Fire Resistance of Prefabricated Demountable Composite Beams Using Bolted Shear Connectors

Structural Behavior of Steel-Concrete Composite Girders Composed of Demountable Shear Connectors

In recent years, many studies on demountable shear connectors have been conducted to facilitate the dismantlement and replacement of precast slabs for steel–concrete composite bridges. Welded headed studs are still mainly used for the horizontal shear synthesis of steel girders and precast concrete slabs, and are adopted in Korean design standards. Because the service life of concrete slabs is much shorter than that of steel girders, however, easy replacement of damaged or old slabs will improve the economic feasibility of the entire bridge during its service life. Therefore, in this study, a new concept of bolted shear connectors is proposed for easy deconstruction and reconstruction of precast concrete slabs. The structural behavior of the proposed connector was verified through horizontal shear and bending tests on composite girder specimens. The connector demonstrated sufficient synthesis performance to replace the conventional welding stud. It also satisfies the current ductility design criterion and flexural performance for slip displacement; hence, we conclude that the novel connector can be used under the existing design standards.

Investigation of cyclic behavior of partially concrete-filled steel tubular columns

A partially concrete-filled steel tubular (CFST) member is formed by partially filling concrete into a steel hollow section (SHS). Partially CFST members are mainly used as bridge piers and frame columns due to the improved structural performance, since the potential plastic hinge is expected to occur at the composite section when subjected to an earthquake. In practice, the shear transfer between the upper SHS and the lower CFST part of a partially CFST column needs careful consideration, sometimes leading to complex details. In this study, two types of shear connectors, namely bolted shear connectors and diagonal-rib shear connectors were proposed and arranged below the concrete-filling interface. Five square partially CFST specimens and a reference steel tubular column were designed and tested under combined constant axial compression and cyclic lateral loading. The test variables included the concrete-filling ratio, types of shear connectors, and strength of shear connectors. The results demonstrated the effectiveness of the two types of shear connectors, and the specimens with diagonal-rib shear connectors showed excellent performance. The method and corresponding formulas about the full shear connection were proposed to calculate the resistance of square partially CFST columns under combined compression and flexure.

Bolted shear connectors in steel–concrete composite structures: Shear behavior

The use of bolted shear connectors is of great importance to the sustainable development of steel–concrete composite structures. In this paper, an experimental program consisting of four push-out specimens is performed to investigate the effects of bolt length and fabrication method of concrete slabs on the shear behavior of single-nut embedded bolted shear connectors in terms of failure mode and load-slip response. The concrete slabs are fabricated either as cast-in-situ monolithic slabs or precast slabs with reserved pockets which will be filled with grout in the final construction stage. The obtained results demonstrate that the fabrication method based on grouting, which is commonly utilized for strengthening and retrofitting works, does not affect the behavior of the bolted shear connection. Based on the experimental observations, a finite element (FE) model of the bolted shear connection is developed, after the obtained numerical results are verified against the test results obtained in this paper and those presented in other existing literature, a parametric study is carried out to further investigate the effects of the concrete strength, bolt strength, bolt diameter, bolt pretension load, and the length-to-diameter ratio of bolt on the performance of the bolted shear connection. Moreover, based on the obtained results, a design formula is proposed to obtain the ultimate shear resistance of the bolted shear connection, and the efficacy of the proposed design formula is proved through the comparison with the test results shown in the existing literature.

Test and design of built-up cold-formed steel-lightweight concrete (CFS-LWC) composite beams

Cold-formed steel (CFS) products are extremely versatile and can be used in multiple applications. To further extend their applicability, this investigation assesses the structural behaviour of innovative built-up CFS-lightweight concrete (LWC) composite beams through experimental testing and numerical modelling. First, four full-scale CFS-LWC simply supported composite beams were tested. The specimens included two distinct configurations of the innovative CFS built-up composite beams. The tested CFS-LWC composite beams comprised a lightweight concrete slab supported by profiled metal decking, connected to a CFS built-up beam using bolted shear studs. Following EN 1994-1-1, the degree of shear connection attained in the specimens ranged from 21 % to 57 %. The test procedure, setup, and collected results are described in detail, including load-bearing capacity, deformation, flexural stiffness, and failure modes. Numerical simulations and calibration against the experimental data were then performed, and the CFS-LWC composite beams with different degrees of shear connections were investigated using the calibrated finite element model. The validity of the available design code for the innovative CFS-LWC composite beams was assessed by comparing experimental findings and analytical predictions using EN1994-1-1 (equilibrium and simplified methods) and AISC 360 methodologies. The results showed that the maximum bending resistance of the composite beam obtained from the equilibrium method of EN1994-1-1 and AISC 360 was unconservative due to the overprediction of shear resistance for the bolted shear connectors. Consequently, a calibrated finite element modelling technique determined the bolted shear connectors’ shear resistance. Finally, the bending resistance design prediction of CFS-LWC composite beams following EN1994-1-1 and AISC 360 methodologies, incorporating the shear connector resistance obtained from simulations, was compared with experimental and numerical results from the parametric study. An excellent agreement was observed between experimental and numerical results with the design predictions according to EN1994-1-1.

Experimental, numerical and analytical investigation of bending performance of bolted demountable composite beams with profiled steel decking

This paper presents the results of a detailed experimental, numerical and analytical study to investigate the flexural bending performance of prefabricated demountable composite beams (PDCBs) with bolted shear connectors. Four full–scale tests were carried out for two profiled steel decking configurations (parallel and perpendicular to the steel section) with two different degrees of shear connection. The experimental results were used to validate a numerical simulation model established by the ABAQUS platform. A detailed parametric study was then performed using the validated numerical model to evaluate the effects of using different numbers of bolted shear connectors. The experimental results show that the final failure modes of the demountable composite beams are the same as conventional composite beams using welded shear studs, and the demountable composite beams behavior is ductile. The results of a comparison of load carrying capacity and elastic stiffness of the demountable beams calculated using the analytical equations for conventional composite beams against the experimental and numerical simulation results for the demountable composite beams confirm that the conventional composite beam theory can be used for the demountable composite beams. However, the experimental results indicate that longitudinal cracking in the grout between concrete slabs along the steel beam can happen, due to unsymmetrical location of the shear studs. Anti-cracking mesh would be necessary in practical applications for crack control.

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.

Flexural resistance of Cold‐formed steel‐lightweight concrete (CFS‐LWC) composite beam

AbstractThis paper discusses the flexural behaviour of innovative built‐up cold‐formed steel lightweight concrete (CFS‐LWC) composite beams through an experimental study. Two full‐scale CFS‐LWC composite beams were tested. The specimens included two distinct configurations of the innovative CFS composite beams. The tested CFS‐LWC composite beams consisted of a lightweight concrete slab supported by profiled metal decking, connected to a CFS built‐up using bolted shear connectors. Two degrees of shear connection were considered. The specimens were uniformly loaded, and the load was increased until failure occurred. The test procedure, setup, and results were recorded in detail, including load‐bearing capacity, deformation, and failure modes. The validity of the design predictions following EN 1994‐1‐1 for the innovative CFS‐LWC composite beams was investigated. Both equilibrium and simplified methods were used to predict the bending resistance of the CFS‐LWC composite beam. The results showed that the design predictions following EN 1994‐1‐1 (equilibrium method) accurately predicted the bending resistance of the CFS‐LWC composite beam, while the simplified method underpredicted the experimental results.

Demountable shear connectors – constructional details and push‐out tests

AbstractThe sustainable composite structures are built by demountable elements in order to reuse them which can fit to the circular economy. The current research and development project – in the cooperation of Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd, Hungary – is aiming to design a new kind of demountable steel‐concrete composite structural system. The key component of this construction is the demountable shear connector. In the current research, bolted shear connectors with embedded bolts and threaded rods are developed and studied which can fit to the applied technology of the industrial partner. One of the main aspects of this connection is to consider the bolt hole clearance since it occurs initial slip and stiffness reduction of the composite beam. In the first phase of the research program, the aim is to develop demountable and economical structural details which can reduce the stiffness reduction with proper strength and ductility features. To study the behaviour of these shear connections, a push‐out experimental program is developed and tested in March 2023. In the paper, the developed structural details and the push‐out experimental program with the first results are presented.

Structural performance of friction-grip bolted shear connectors in cold-formed steel composite beams

Nowadays, composite beams consisting of steel beams and concrete slabs are widely used in the construction industry. In this research, an experimental study was carried out to investigate the performance of friction-grip bolted shear connectors in composite beams with cold-formed steel sections. For this purpose, 17 full-scale push-out tests were examined according to EC4 in order to investigate the performance of this connection. Of particular interests were load-slip curves, the maximum shear capacity, ultimate slip (ductility) and failure modes. Experimental results show that the behavior of this connection is different from that of headed-stud shear connector. The diameter and strength of bolt and thickness of cold-formed steel section have the most critical effects on the shear capacity and ductility of these connections. Furthermore, 3D finite element modeling was performed and validated against experimental results. The results reveals that numerical models can estimate the capacity of friction-grip bolted shear connectors with acceptable accuracy. The results also highlight that the predominant failure mode in all specimens is bearing. Thus, the use of AISI equations to determine the bearing capacity of the screw holes as the shear capacity of friction-grip bolted shear connectors is recommended. It is also concluded that this connection possesses the necessary ductility according to the EC4 (= 6 mm) and is suitable for use in composite beams with cold-formed steel sections.

Behavior and Design of Reinforced CFST Columns with Bolted Shear Connectors Under Eccentric Compression

Behavior and Design of Reinforced CFST Columns with Bolted Shear Connectors Under Eccentric Compression