Bolted Shear Connectors Research Articles

Behavior of high-strength demountable bolted shear connectors in steel-concrete girders with prefabricated slabs

Composite structures with prefabricated concrete slabs and bolted shear studs can enhance the effectiveness and sustainability of construction. In this research, non-shrinkage cement grout is proposed to be filled between high-strength fully threaded bolt shear connectors and a prefabricated slab. Six static push-out tests are performed with different bolt dimensions and different pretension forces on the bolts to study the behavior of bolted shear studs. Finite element models for bolted shear connectors using ABAQUS/Explicit solver are developed, and they matched well with experimental results. Moreover, a Parametric study is conducted to investigate the effects of grout strength, bolt diameter, length-to-diameter ratio, bolt preloading, and bolt material type on the performance of shear connectors. Finally, the results of the parametric analysis are compared to the current design codes and previous researches and more precise equations for predicting the capacity and stiffness of bolted shear studs are proposed.

FATIGUE ANALYSIS OF COMPOSITE BEAM WITH BOLTED SHEAR CONNECTORS

AbstractThis paper describes the simulation technique developed to predict the fatigue life of bolted shear connector. As existing composite structures experience complex loading conditions over the entire life of the structure, therefore, the fatigue behaviour of the shear connectors is always critical. Among different types of bolted shear connectors, the installation procedure of the blind bolts is less complex and more rapid than that of conventional systems. Therefore, the concept of fatigue analysis of the blind bolt shear connector has been presented, in this paper here in, under constant amplitudes cyclic loading, using ABAQUS/explicit and FE‐SAFE programs. All fatigue simulations were conducted under load‐control mode based on constant amplitude conditions and a constant mean force. The results showed that the number of cycles to failure decreases with the increasing stress level while every stress amplitude has a certain number of cycles until failure.

Analysis of Shear Performance of Multi-Bolt Shear Connectors.

Bolt shear connectors used in prefabricated steel-concrete composite beams can be arranged into a group to enhance the construction efficiency, which will cause the multi-bolt effect and further affect the shear performance of bolt connectors. This paper developed three-dimensional finite element models of push-out specimens to investigate the shear performance of multi-bolt connectors. Numerical results showed that the friction coefficient at the interfaces between the steel girders and precast concrete (PC) slabs and bolt preload dramatically improved the initial stiffness of bolts; when the longitudinal spacing of bolts was reduced from 100 mm to 60 mm, the decrease in the average peak load per bolt was 3.5%, 9.2%, and 11.4% for bolts of 16 mm, 20 mm, and 24 mm diameters. A modified calculation method for the shear resistance of multi-bolt shear connectors was proposed based on the numerical analysis, and a simplified model of shear load versus relative slip was further developed.

Shear performance of high-strength friction-grip bolted shear connector in prefabricated steel–UHPC composite beams: Finite element modelling and parametric study

As a competitive alternative for accelerated bridge construction (ABC), prefabricated steel–ultra-high-performance concrete (UHPC) composite beams containing high-strength friction-grip bolt (HSFGB) shear connectors offer numerous advantages, including reduced on-site construction time and ease of replacing/removing deteriorated components. However, the failure mechanism of HSFGBs in UHPC remains unclear due to the lack of internal stress analysis, which hinders the design of these innovative composite beams. To clarify the shear performance of HSFGBs in prefabricated steel–UHPC composite beams, an effective finite element model (FEM) considering the non-linearities of materials and geometry was developed through ABAQUS. Based on the experimentally verified model, the internal stress transfer mechanisms of HSFGBs and the failure mechanism of precast UHPC were revealed. According to the extension parametric analysis results, a stronger HSFGB presented better shear performances in terms of ultimate shear strength, initial shear stiffness and slip capacity. Adopting oversized holes with appropriate bolt-to-hole clearance can improve the constructional efficiency without considerable strength and stiffness reduction. HSFGBs with low bolt pretension exhibited unfavorable initial shear stiffness, while smaller slip capacity in high bolt pretension conditions. A smaller ductility was observed as the steel beam tensile strength and slab concrete strength increased. Additionally, the ACI 318–19, Eurocode 3, and AASHTO LRFD specifications underestimated the shear strength of HSFGBs, whereas the Eurocode 4 presented acceptable predictions in determining the ultimate shear capacity of HSFGBs in prefabricated steel–UHPC composite beams.

Numerical study of the behavior of friction-grip bolted shear connectors in composite beams with cold-formed steel sections

The concurrent use of concrete slab, and cold-formed steel section as a composite beam improves strength and stiffness, thus preventing local and lateral buckling of the beam. The composite action could be fulfilled by suitable shear connectors, though the codes do not prescribe any equation to determine the shear capacity, and design rule of these connectors. The friction-grip bolted shear connectors were introduced and their mechanical performance was studied via the experimental tests and finite element modeling. At first, ANSYS software was used for the 3D finite element modeling of these connections. The obtained results were verified by experimental results. It can be shown that the proposed model can estimate the behavior of friction-grip bolted shear connectors in composite beams with cold-formed steel section. Then, extensive parametric studies with 72 specimens were carried out and the effect of diameter and strength of the bolts, thickness and strength of cold-formed steel sections, clearance between the bolt and concrete hole and pretension force on the behavior of these connectors were evaluated. The effect of each parameter on the shear capacity of the connection was evaluated. Some equations were proposed for figuring out the shear capacity and load–slip curve of these connections based on the experimental and 3D finite element results.

Capacity analysis of advanced bolt shear connectors in composite beams with finite element method using MIDAS FEA software

Prefabricated construction is now familiar and widely used in various parts of the world. The important thing in the composite structure is the shear connection. Advanced bolt shear connectors are one of the innovations for prefabricated construction because their use is more efficient. The shear capacity of the advanced bolt shear connectors was carried out with the nonlinear finite element method using MIDAS FEA software and then compared with the results of laboratory testing and theoretical equations. There were 8 models to be tested with 2 variations of bolt diameters (12 mm and 16 mm) and 3 variations of bolt pretension (without pretension, 0.2Pc pretension, 0.5Pc pretension, and 0.8Pc pretension). The results of the analysis show that the diameter of the bolts has a large effect on the shear capacity of the shear connectors where with the same bolt pretension, the shear capacity increases 71.4286% - 73.0769% on the test models with 16 mm bolts. Bolt pretension also affects the shear capacity of the shear connectors although the impact is small, 1.9231% - 7.6923% (12 mm diameter bolts) and 1.1111% - 6.6667% (16 mm diameter bolts) from the value of the shear capacity of the model without pretension. The most optimal pretension is 0.5Pc for 2 bolt diameter variations. In the results of the analysis of the finite element method and laboratory tests, the deflection is directly proportional to the shear capacity of the models.

Numerical and theoretical research on flexural behaviour of steel-precast UHPC composite beams

In order to promote the utilization of high strength materials and application of prefabricated structures, flexural behaviour of section steel-precast UHPC (Ultra-High performance concrete) slab composite beams prefabricated with bolt shear connectors are numerically simulated by the finite element (FE) software ABAQUS. The model is verified by three prefabricated steel-concrete composite beams tested. Numerical analysis results are in good accordance with experimental results. Furthermore, parametric studies are conducted to investigate the effects of strength of section steel and concrete of precast slab, thickness of section steel, width and height of precast concrete slab, diameters of steel bars and bolt shear connectors. The flexural behaviour of composite beams, in terms of bearing capacity, deflection, ductility and energy dissipation, are compared. The numerical results indicate that the improvement of strength of section steel results in a decrease of ductility, but a significant increase of the ultimate load and energy dissipation. Compared with composite beam made of section steel with thickness of 10 mm, the ultimate load of beams made of section steel with thickness of 14 and 18 mm improve by 29.0% and 58.8%, respectively, the ductility enhance by 2.8% and 8.3%, respectively, and the energy dissipation improve by 8.0% and 12.3%, respectively. With the increase of concrete strength, the ultimate load, deflection and energy dissipation gradually increase. The ductility of steel-UHPC composite beam is the highest, that of steel-HSC composite beam is the lowest. The effect of reinforcement ratio of concrete slab and diameter of shear bolts on the ultimate load of composite beam is limited. Simplified formulae for two different sectional types of proper-reinforced section steel-precast UHPC slab composite beams occurred bending failure are proposed, and the predicted results fit well with the simulated results. The results can be taken as a reference for the design and construction of section steel-precast UHPC slab composite beams.

Flexural performance of prefabricated composite beams with grouped bolt shear connectors under positive bending moments

Four prefabricated steel–concrete composite beams (PSCCBs) with grouped bolt shear connectors were designed and tested to investigate their flexural performance under positive bending moments. The effect of shear connection degrees and segmented precast concrete (PC) slabs on the flexural performance of PSCCBs was investigated. Experimental results show that all the specimens failed due to the yielding of steel girders and concrete crushing in the mid-span regions, presenting typical characteristics of flexural failure. Compared to the PSCCB with a monolithic PC slab, the PSCCBs with segmented PC slabs experienced a short fast increasing stage of mid-span deflection after the steel girders yielded, of which the initial flexural stiffness and ductility coefficient decreased by 47.8% and 44.1% at most, respectively. Then, finite element (FE) models of PSCCBs with different design parameters were developed to assess their flexural behaviors under positive bending moments. Numerical results demonstrate that the initial flexural stiffness was significantly affected by the girder web height and the length of the middle PC slab. Enlarging the gap width, the length of the middle PC slab, and the girder web height are beneficial for the ductility of PSCCBs. The research findings might provide references for the design of PSCCBs with segmented PC slabs and grouped bolt shear connectors.

Neural networks-based formulation for predicting ultimate strength of bolted shear connectors in composite cold-formed steel beams

In recent years, the use of artificial intelligence-based methods in engineering problems has been expanded. In the current study, the method of artificial neural networks (ANN) has been employed to predict the ultimate strength of bolted shear connectors in cold-formed steel (CFS) composite beams. For this purpose, multilayer perceptron (MLP) networks with a hidden layer were used. Three parameters affecting the performance of these networks, including the training algorithm, the activation function in the hidden layer, and the number of neurons in the hidden layer, were examined and the most accurate network was selected. The input and target data for training the network were provided by conducting an extensive numerical study on the behavior of bolted shear connectors in CFS composite beams. Consequently, using ABAQUS software, finite element (FE) models validated with experimental results were first developed. Then, 216 models with different characteristics were analyzed and a reliable database was provided for the development of neural networks. Moreover, in order to prove the high accuracy of the ANN method, the stepwise regression (SR) method was also developed as one of the powerful regression-based methods, and the performances of these two methods were compared. Finally, the most important purpose of this study is to propose an accurate ANN-based formulation in order to predict the ultimate strength of bolted shear connectors in CFS composite beams. Due to the fact that so far no relationship has been proposed to predict the resistance of shear connectors in CFS composite beams, the formula presented in this paper can be helpful in the design process of this type of beams.

Design of Composite Joint with Precast Bolted Shear Connectors for The Fabricated Structure

Because of the serious impact on the seismic performance, the joint connection form becomes a critical problem in the prefabricated building. Built on the dry connection, this paper proposes a detachable and recyclable bolt-steel plate connection design for the fabricated structure. Compared to the cast-in-situ method, the biggest advantage of the proposed design scheme lies in convenient construction. The construction process shows that the joint devices both are detachable and recyclable. Adopting a supported beam, the proposed form is simulated with the finite element method (FEM). The deformation results verify the effectiveness of the proposed connection design. The work provides a novel idea for further test research on the fabricated structure.

Repetitive behavior of an advanced demountable bolted shear connection in push-off tests

Currently, the repetitive behavior of the advanced bolted shear connector embedded in non-shrink self-compacting high strength pouring material (HPG) is unclear, restricting its application in steel–concrete composite beams (SCCBs). This study examined the repetitive performance of 21 push-off test specimens using different bolt diameters, bolt loads, loading paths, and loading programs. The failure models, load-slip response, shear bearing resistance, initial slip load, shear stiffness, peak slip, and ductility of this advanced bolted shear connection were evaluated. Bolt shearing off is the typical failure mode for all specimens, along with some concrete crushing underneath the bolts. Under repetitive loading, bolt shear capacity and load-slip response are similar to those under monotonous loading. Peak slip grows with the increase of bolt diameter under repetitive loading compared to monotonic loading. The shear stiffness under repetitive loading is lower than that under monotonic loading and improves with the bolt diameter and the bolt pretension increase. The ductility ratio under repetitive loading is smaller than that under monotonic loading and enlarges with the increase of the bolt diameter. Some design recommendations are proposed based on the existing formulae for predicting this advanced bolted shear connection.

Finite Element Modelling of Bolted Shear Connectors

Finite Element Modelling of Bolted Shear Connectors

The effect of cross section type on the performance of different sized bolted shear connectors for composite cold-formed steel beams

The effect of cross section type on the performance of different sized bolted shear connectors for composite cold-formed steel beams

Experiments on flexural behavior of the prefabricated RAC and NWC composite slab

The development of prefabricated buildings is a long-term industrial policy in China. In the prefabricated frame structure, the slab is one of the critical components. However, two kinds of famous prefabricated slabs in China need the template system and sometimes need a particular fabrication site. The paper proposed a novel prefabricated concrete composite slab, which adopts the high-strength bolt as the shear connector. Compared with the traditional precast concrete composite slab, the novel prefabricated concrete composite slab does not need a template and temporary support. Compared with the conventional composite slab, it has analogous rigidity. Still, it does not require a fireproof coating. It has fast construction speed and a low comprehensive cost. The paper conducted 13 slab specimen bending tests on the novel composite used recycled aggregate concrete (RAC) and normal weight concrete (NWC) to reveal the slab's flexural behavior. The test data and analysis show that the three-inch-high profiled steel sheeting as a shear connection can have an excellent composite effect. The neutral axis of the whole section always locates within profiled steel sheeting. And the profiled steel sheeting has been participating in the load-bearing work of the composite slab. The composite slabs showed good bending bearing capacity and ductility. The RAC with a replacement ratio of 50% recycled aggregate has the same material performance and member performance. The composite slab proposed can meet most civil buildings' design requirements. The standard push test revealed that the bolt shear connectors' ultimate bearing capacity meets the Chinese design code with the floor's considerable slippage.

Behavior of T-shaped embedded-nut bolted shear connectors in prefabricated steel-concrete composite beams

Steel–concrete composite beams joined by shear connectors are extensively used in building and bridge engineering owing to their favourable structural performance, ease of construction, and low cost. Recently, owing to the demand for prefabricated structures, research on demountable shear connectors for prefabricated steel–concrete composite beams has become widespread. In this study, innovative T-shaped embedded nut bolted shear connectors (T-ENBCs) with superior mechanical performance and demountability are proposed and investigated. Push-out tests were conducted to evaluate the shear behavior of T-ENBCs in a steel–concrete composite beam, including twenty-one T-ENBC steel–concrete (EN) specimens and three high-strength friction-grip bolt connector (HF) specimens. For the EN specimens, various types of T-ENBCs were examined to ascertain the effect of variables, such as the diameter of the bolt, length of the embedded nut, and embedded nut type. Accordingly, the failure modes, load–slip curves, ultimate shear resistance, and shear stiffness of the specimens were obtained. Finite element (FE) models for T-ENBCs, validated with test data, were employed to analyse the influence of a number of parameters. Using the experimental and FE results, the properties of the connector, such as its shear resistance, stiffness, ductility, and failure modes, are discussed. The study shows that T-ENBCs have larger shear resistance and higher shear stiffness than high-strength friction-grip bolt connectors. Finally, specific design formulae are proposed for predicting the ultimate shear resistance and load–slip relationship for members with T-ENBCs.

Interlayer behavior investigation of box profile shear connectors in steel-concrete-steel sandwich structures

The present study introduces box profile (BP) shear connectors for steel-concrete-steel sandwich composite structures. The shear connectors were joined to steel faceplates using slot and fillet welding. The advantages of this shear connector include unlimited thickness, easy application, high strength, and low cost compared to other available shear connectors. A total of eight experimental specimens were fabricated to evaluate the interlayer shear behavior of BP shear connectors. The effects of geometric parameters, including the BP thickness, BP width, concrete thickness, and BP configuration, on the shear behavior of the BP shear connectors were studied. The results of experiments and comparison with other shear connectors show that BP shear connectors have improved the composite behavior and interlayer shear strength. Also, the effect of geometrical parameters was analyzed on the shear strength. The BP shear connector is dependent on its width. A 20-mm rise in the width of the BP connector increased the ultimate strength and energy absorption by 76% and 41%, respectively. The use of BP shear connectors in a V-WEB configuration reduced ductility by 52% (from 501.4 to 239 kN.mm) and initial strength by 43% (from 192 to 109 kN). Therefore, V-WEB BP shear connectors are not recommended. Then, a model was offered to predict the load-slip behavior of BP shear connectors and was compared with the relations of previous researchers. Finally, the proposed shear connector was compared with different available shear connectors in terms of strength and load-slip behavior. It can be concluded that the BP shear connector had higher stiffness and ultimate strength than other shear connectors, e.g., stud bolt, bi-steel, J-hook, CSC, and headed stud shear connectors.

Modelling of demountable steel-concrete composite connections: Validation of finite element model and parametric study

A three-dimensional finite element modelling and parametric analysis of a composite connection having prefabricated concrete slabs and preload bolted shear connectors are presented in this study. The load-slip relationship for this type of shear connection subjected to monotonically loading with the effect of different parameters including bolted shear connector size, bolt grade, hole size in precast concrete slab and steel beam top flange, concrete strength, and bolt preloading force is studied by means of ABAQUS software. A finite element model of the composite connection considering the non-linearities of the geometry, interfaces between the components, and materials is developed and verified against the results of the experimental study. An extensive parametric study is conducted, and the influences of different parameters on the structural behaviour of demountable steel-concrete composite shear connection are discussed in detail. In addition, a comparison of the estimated values obtained from design equations proposed by current standards, including EC4 and AISC for headed stud shear connectors, and the design recommendations provided in other studies for bolted shear connectors are conducted. According to the calculation result, the accuracy of different design methods is evaluated. Finally, a regression analysis of the data produced by the FE analysis has been employed to propose a new design equation to determine the ultimate strengths for the post-installed preload bolt shear connectors. It is concluded that the ultimate shear load capacity values predicted by EC4 and AISC provisions for composite connections having prefabricated concrete slabs and preload bolted shear connectors found to be relatively less accurate but conservative.

Numerical study on behavior of bolted shear connector used in composite cold-formed steel beams

The use of concrete slab in cold-formed steel (CFS) beams can not only increase the ultimate resistance, but also can prevent their lateral buckling. Since the formation of composite action in this type of beams requires the use of appropriate shear connectors, in this paper, an extensive numerical study was conducted to investigate the behavior of 8.8 grade bolted connectors in CFS composite beams. For this purpose, at the first, advanced numerical models of concrete-CFS section connections were developed. Geometric details, material nonlinearities, material damage models and loading protocols were carefully simulated. Next, the results obtained from the numerical models were validated in detail against the experimental results. It was proved that the developed models have the ability to simulate the behavior of the 8.8 grade bolted connectors in these connections. At the end, an extensive parametric numerical study consisting of 216 connections was conducted. The examined parameters included CFS thickness, CFS ultimate strength, concrete compressive strength, embedded bolt’s height and bolt diameter. Consequently, the effect of each of these parameters on the ultimate strength, ductility as well as the failure modes of the bolted shear connectors was carefully investigated.

Behaviour of embedded bolted shear connectors in steel-timber composite beams subjected to cyclic loading

This paper concerns the cyclic behaviour of embedded bolted shear connectors in steel-timber composite joints. The effect of the strength and size of the shear connector and the orientation of the cross-laminated timber panels with respect to the direction of the load on the cyclic behaviour of this type of composite connection were investigated through an extensive experimental study. In total, eleven steel-timber composite connections having a steel section and mechanical shear connectors embedded in grout were tested under a low-cycle, high-amplitude loading regime. The equivalent viscous damping, ductility, strength impairment, energy dissipation and the failure modes of all composite connections were assessed in detail to characterise the behaviour of a mechanical shear connector under cyclic loading conditions. The experimental results show that embedded bolted shear connectors have high energy-dissipating capacity and ductility if adequate edge distances of the bolts and shear pockets are provided. In addition, a finite element model of the composite connection considering the non-linearities of the geometry, and interfaces between the components and materials is developed and verified against the results of the experimental study. Based on the results obtained from the simulation, it can be demonstrated that the developed FE model is able to predict the behaviour of the composite connection at the local and global level.

Feasibility and performance of novel tapered iron bolt shear connectors in demountable composite beams

The performance of tapered iron bolt (TIB) shear connectors and their feasibility to be used in demountable composite beams are investigated in this study. The typical TIB shear connector consists of six components, i.e., a connecting bolt, conical iron plug, top covering plate, top fixing bolt, retaining washer and inner sleeve. The connectors are expected to 1) reduce the initial slip between the concrete slab and steel beam, which generally exists for steel-concrete composite beams using bolted shear connectors, and 2) be capable of being replaced for composite beams in-situ without damaging other components. Two series of pushout tests were conducted on the specimens with TIB shear connectors in accordance with Eurocode 4 (EC4). The demountability of TIB shear connectors after severe corrosion induced by accelerated corrosion, i.e., wet-dry cycles, was examined. All pushout test specimens failed in shear fracture at the bolts while the concrete slabs remained undamaged. The test results demonstrated that the replacement of TIB connectors would not affect the failure mode of TIB connectors but have a moderate influence on the shear capacity. Therefore, a reduction factor was proposed to account for the influence of replacement in design. The design equations of TIB shear connectors under bolt shear and local concrete failure were proposed. The proposed design method is able to provide a reasonably accurate prediction for the failure mode and shear strength of the TIB connectors.