Shear Connectors Research Articles

Predicting fatigue life of shear connectors in steel‐concrete composite bridges using artificial intelligence techniques

AbstractFatigue limit states often govern the design of shear connectors in steel‐concrete composite bridges. AASHTO LRFD bridge design specifications provides a linear equation in a semi‐logarithmic S‐N curve for predicting the fatigue life of shear connectors. However, this equation can be too conservative in some cases, as supported by the available experimental data. In this paper, artificial intelligence (AI) was incorporated into the prediction of the fatigue life of shear connectors. Six different machine learning (ML) algorithms were considered for this purpose. The predictions of ML algorithms were compared both with the available experimental data and the equation provided by AASHTO. The results showed that the fatigue life predicted by ML methods is more accurate than that predicted by the current equation of AASHTO. The results of this study showed that AI can be a proper alternative to the existing methods for predicting the fatigue life of shear connectors.

Flexural performance of SCSP-concrete composite structures with equidistant transverse rebar

To improve the flexural performance of corrugated steel plate (CSP)-concrete composite structures, composite shear connectors composed of transverse rebar and longitudinal shear connectors are widely used. This study investigated the effect of equidistant transverse rebar on the flexural performance of sinusoidal corrugated steel plate (SCSP) and its composite structure. For a comparative study, specimens of SCSP-concrete composite structure and SCSP-concrete composite structure with equidistant transverse rebar were fabricated and tested under the same test conditions. The results showed that the ultimate load of the SCSP-concrete composite structure with equidistant transverse rebar increased by 58.71 %, while the deflection decreased by 19.19 %. Based on the energy principles, equivalent properties of SCSP with equidistant transverse rebar have been derived. The finite element (FE) analyses adopted the corrugated and orthotropic plate models to simulate SCSP and SCSP with equidistant transverse rebar. The orthotropic plate models corresponding to the SCSP with equidistant transverse rebar were established by using the proposed equivalent properties. The FE analysis results of the corrugated plate models and the orthotropic plate models are consistent, proving that the use of equidistant transverse rebar improves the flexural performance of the SCSP. The FE analysis results of the composite structure modeled using the corrugated plate models are consistent with the test results. For the SCSP-concrete composite structure with equidistant transverse rebar, the FE analysis results of the orthotropic plate-concrete composite structure are different from those of the composite structure using the corrugated plate model. This is because the stiffness of the orthotropic plate model is the same as that of the corrugated plate model, but the orthotropic plate-concrete composite structure does not have equidistant transverse rebar, resulting in lower longitudinal shear resistance compared to the composite structure using the corrugated plate model. At the initial loading stage, the equidistant transverse rebar increased the stiffness of the SCSP in the composite structure and the longitudinal shear resistance between SCSP and concrete when the load increased. When using transverse rebar with a doubled cross-sectional area and increasing the usage of transverse rebar by two times, the ultimate load of the composite structure increases by 1.77 %, and the deflection decreases by 21.68 %. When the arrangement spacing of rebar is halved and the usage of transverse rebar is doubled, the ultimate load of the composite structure increases by 7.56 %, and the deflection decreases by 23.8 %.

Experimental study on the load-bearing capacity of detachable prefabricated concrete slabs with dislocated cover slab units for steel structures

A detachable prefabricated slab with dislocated cover slab units for steel structures, which consists of lower base slab units, upper cover slab units (dislocated covering the base slab units), and connection systems (including concrete shear keys with pre-buried bolts, steel sleeves, nuts, and washers), was proposed in this paper. The cover slab units, the base slab units, and the connection systems form a whole slab that has good continuity and integrity through a dislocated arrangement method. Meanwhile, the whole slab and steel beams are connected with demountable shear connectors. Therefore, this prefabricated slab can completely avoid onsite casting. In this paper, a comparative flexural test of the detachable prefabricated slab with dislocated cover slab units and a cast-in-place slab with the same overall dimensions was conducted. The load-bearing capacity, damage mechanism, stress distribution, and combined effect of the cover and base slab units of this new slab were revealed. A detailed solid-element model was established to investigate the effect of the loading methods on the load-bearing capacity and the failure mode of the slab. Meanwhile, the calculation method of the ultimate bearing capacity of the slab was proposed. This detachable slab without onsite casting can greatly improve the speed of on-site construction and realize the whole system assembly of steel structures.

Flexural response of textile-reinforced sandwich slab with modified polymeric core

Concrete sandwich panels are thermally insulative but difficult to erect due to heavy weight and thickness, and also require sufficient clear cover to avoid corrosion. Textile reinforcement is a novel field of research in civil engineering. The size, weight, and cost can be reduced using it as reinforcement in sandwich elements. The past researchers focus on sandwich slabs with polymeric cores which are prompt to delamination. Thus, this study compares the performance of steel mesh, and basalt textile fiber mesh reinforced sandwich slabs with conventional concrete and expanded perlite board as core materials. The sandwich slabs are tested under flexure in four-point bending and validated numerically by considering the non-linear characteristics of the material. The sandwich slabs reinforced with steel and basalt textile fiber mesh have similar load-carrying capacities with higher deflection of basalt textile mesh-reinforced sandwich slabs. The core material plays a major role than the type of reinforcement used. Conventional concrete core sandwich slabs did not show any delamination by enhancing the degree of composite action and mitigated the shear failure without shear connectors than sandwich slabs with expanded perlite cores. However, it affects the major property of the sandwich panel due to its density. Using the cast in-situ method in manufacturing sandwich specimens rather than adopting the slab stock method avoids delamination by proper bonding between the layers. Thus, textile-reinforced sandwich slabs have a similar load-carrying capacity as of concrete sandwich panels with steel mesh. The experimental results are validated well with numerical data.

Fatigue behavior of short-headed studs embedded in Ultra-high Toughness Cementitious Composites (UHTCC)

The multi-cracking and strain-hardening capacities of Ultra-high Toughness Cementitious Composites (UHTCC) make it feasible for orthotropic steel bridge decks (OSBDs) applications to control crack width. In this composite bridge deck, shear connectors play an important role in providing good shear strength and ensuring structural service performance. To evaluate the shear resistance of short-headed studs embedded in ultra-thin UHTCC layer, three series of push-out tests were conducted in this study. The test results including shear strength, fatigue strength, failure modes, dynamic slip, stiffness degradation, plastic slip and residual mechanical properties were all considered and carefully discussed. In this study, the shear force of shear connectors was calculated and compared with current codes. The stress amplitude-fatigue life (S-N) relationship of studs was fitted by different codes. Then the empirical formulation was developed to predict the load-slip behavior and stiffness degradation of studs during fatigue loading. The relationship between plastic slip and fatigue life was established and normalized. Furthermore, based on post-fatigue static test results and test results in previous research, a new machine learning model was proposed to predict the residual shear strength of studs and contrasted with previous model. Then Analysis of Variance (ANOVA) with two parameters (i.e. load amplitude, maximum repeated force) was conducted and revealed that the peak load significantly impacted the residual shear strength of push-out specimens compared with load amplitude. Moreover, a parametric study was conducted to further investigate the degradation of studs under various working conditions. By experimental and theoretical analysis, UHTCC could fully develop the shear strength of studs embedded in ultra-thin cover thickness. And related models were established to predict the static and fatigue behavior of steel-UHTCC push-out specimen.

Fire experiment and fire design method of U-shaped steel-concrete composite beams

Four U-shaped steel-concrete composite beams (USCB) were designed and tested under the ISO-834 standard fire curve and distributed vertical load. The research parameters were the load ratio and shear connector form. The temperature distribution, fire resistance, and failure modes of the USCB specimen were investigated. The fire tests showed that the failure mode of the specimen is flexural damage and the connection interface between the flange and web of the composite beam remains intact. The temperature of the fire-resistance reinforcements is below 500°C when the specimens reached the fire resistance, which is in the early stage of material degradation and has high residual strength. The fire resistance increased (improve by 51%) with the decrease of load ratio (0.7 to 0.4) and was not affected by the shear connector form. Then a numerical simulation was applied to establish the temperature field model and fire resistance model of USCB, and the simulation results of the temperature field and fire resistance were in good agreement with the test results. The parameter analysis indicated that the load ratio, the diameter of fire-resistance reinforcement and fire protection layer have an obvious impact on the fire performance. Based on the heat transfer mechanism analysis, the temperature calculation methods for U-shaped steel, fire-resistant reinforcement and concrete were proposed. Moreover, a flexural bearing capacity calculation method for the USCB under the standard temperature rise curve is proposed, which can be applied to calculate fire resistance.

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.

Flexural Behavior of Composite Beams with Angle Shear Connectors

Flexural Behavior of Composite Beams with Angle Shear Connectors

Numerical Study on Mechanical Behaviors of New Type of Steel Shear-Connection Horizontal Joint in Prefabricated Shear Wall Structure

The shear connection joint is an important component of the prefabricated shear wall structure system, which plays a dual role in ensuring reasonable force transmission and structural integrity. A new type of steel shear-connection horizontal joint was proposed in this study. In order to verify the effectiveness of the proposed new joint, the established numerical model and its constitutive relationship were first verified based on the existing experimental results. Then, the influence effect on the mechanical behaviors of this new type of joint was further investigated with 20 computational cases. The corresponding influencing laws were established, and optimal parameter ranges were suggested. Finally, a simplified constitutive model—namely, a bilinear constitutive model based on the M-θ relationship—of the new steel shear-connection joint is further advanced and deduced. The results show that the proposed new joint can provide stable shear capacity and superior energy dissipation capacity. The interlocking slot in the new steel shear-connection joint is suggested to be designed with a slot length of 20~30 mm, a slot number of two or three, and a slot thickness of 20~30 mm so as to guarantee superior mechanical behaviors. The advanced bilinear constitutive model can effectively capture the mechanical characteristics of the new joints, in which the maximum error is only 7.67% between theory and simulation.

Flexural behavior of modular steel channel–concrete composite floor systems with bolted connections

This paper presents an innovative modular steel channel–concrete composite floor system designed for rapid assembly. This system, compared to traditional steel–concrete composite floors, connects adjacent modules solely through the use of high-strength bolts. This design eliminates the need for on-site wet construction, thereby yielding superior economic benefits. To investigate the proposed system’s mechanical behavior, bending tests were conducted on four composite floors with various support conditions, the numbers of bolts, and the degrees of shear connection. The load–displacement responses, torsional behavior of the channel beams, interfacial slip, and strain development of the composite floor systems were analyzed. The test results show that the simply supported composite floor, without bolted connections, undergoes flexural failure. In contrast, the semi-continuous composite floors, with bolted connections, display punching shear-flexural failure. The pre-tension forces applied to the bolts can effectively mitigate the torsional deformation of the channels and module separation, ensuring that the system maintains excellent structural integrity, sufficient load-bearing capacity, and adequate ductility. The semi-continuous composite floors, when fitted with high-strength bolts, demonstrate an increase in ultimate load-bearing capacity by 13–15%. However, there is a corresponding decrease in ductility by 18–23% when compared to the simply supported composite floor without bolts. The use of perforated steel plates as shear connectors offers efficient shear resistance between the steel channels and concrete slabs, facilitating full composite action of the system throughout the loading process. The paper concludes with the development of a model that calculates the flexural strength and punching shear strength of the composite floors based on the yield-line theory.

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.

Study on the Influence of Steel Fiber Distribution on the Mechanical Properties of Perfobond Leiste (PBL) Shear Connectors

In order to study the influence of steel fibers on the mechanical properties of Perfobond Leiste (PBL) shear connectors and improve the utilization of steel fibers in this structure, four push-out test specimens and eight finite element numerical models were produced to study PBL-type shear connector specimens with different steel fiber blending amounts and blending forms. The results show that in this structure, when the blending amount of steel fiber was 0.5% to 1.5%, the ultimate bearing capacity of the specimen improved linearly, and the steel fiber helped to give full play to the performance of the PBL shear connector. The steel fibers distributed in the Z-direction have a significant impact on the mechanical properties of the PBL shear connector, and the steel fibers distributed in this direction have a significant effect on increasing the ultimate bearing capacity of the specimen. Steel fibers distributed in the Y-direction can greatly improve the plasticity of concrete. In addition, the effective action area of steel fibers is the triangular area from the bottom of the PBL shear connector to the two tops of the concrete.

Time-dependent response of continuous steel-concrete composite beams under sustained loading

Although the long-term behavior of composite beams raises critical concerns in their application, only a few investigations have been conducted on the time-dependent response of continuous composite beams (CCBs). Herein, long-term tests were conducted on four two-span CCBs with different loading ages. The shear stiffness and time-slip relationship of flexible shear connectors were evaluated by carrying out short-term and long-term push-out tests. The experimental results revealed that loading age substantially affected the development of deflection, interface slip, crack, and internal force redistribution of CCBs under sustained loads. A finite element model (FEM-2) of test specimens was developed, considering the damage evolution, creep and shrinkage of concrete slab, and stiffness degradation of connectors. After the FEM results were verified against the experimental data, the developed FEM-2 model was implemented to further investigate the influences of loading age and loading level on the long-term performance of CCBs.

Experimental study on longitudinal shear behavior of prefabricated steel-concrete composite beams with notched connections

To address the fit-up issues caused by the interference between shear connectors and extended transverse bars, a novel deck-to-girder connection detail, notched connection, is applied to steel-concrete composite bridges with partial-depth deck panel (PDDP) systems. In the novel joint detail, protruding transverse reinforcement is replaced by evenly distributed notches at the ends of precast panels, and tie bars inserted in the notches are anticipated to resist longitudinal shear stress, achieving shear connection between steel girders and precast deck slabs. Considering the discontinuity of bottom transverse reinforcement, a four-point bending test was performed to investigate the longitudinal shear behavior of composite beams incorporating notched connections. Experimental findings indicate that the configuration of transverse reinforcement critically influences the failure modes of composite specimens, which involve crushing of concrete slabs, longitudinal shear cracking and splitting. Notably, tie bars sufficiently anchored in notches function equivalently to extended bars spliced by welding, and the specifically designed U-shaped notches enhance the anchorage performance of tie bars. Transverse reinforcing bars placed in the concrete topping prove more effective in resisting longitudinal shear than those in the bottom layer, and therefore asymmetrically reinforced concrete slabs experience reduced longitudinal shear cracking and splitting. Moreover, interface shear reinforcement effectively ensures the full composite action, while concentrated point loads can induce excessive local longitudinal shear stress. The study also provides design recommendations for notched connections.

Structural behavior of steel-concrete-steel sandwich slender and deep beams considering different connectors

Steel-concrete-steel (SCS) sandwich deep beams, with a shear span ratio of less than 2.0, are commonly employed in high-rise buildings and bridges. However, their failure mechanism differs from that of SCS sandwich slender beams, which have a shear span ratio greater than 2.0. This study systematically investigates the failure mechanisms of SCS sandwich deep beams and compares them with those of SCS sandwich slender beams. To improve their structural performance, ultra-high performance concrete (UHPC) was utilized as the core material to form S-UHPC-S sandwich deep beams, with shear studs serving as the sole shear connectors. The influence of these shear connectors was explored in comparison to cross ties. Three S-UHPC-S sandwich deep beams were subjected to static loading, and their performance was compared with ten existing SCS sandwich deep and slender beams. The analysis focused on failure modes, mechanical behaviors, and contributions of each component, including the steel plate (SP), core concrete (CC), and shear connectors. The results revealed distinctions in force transferring models, load-displacement curves, and the contributions of cross ties in deep beams compared to slender beams. Additionally, finite element (FE) analyses were employed to examine the force transferring mechanism of shear connectors. Based on both experimental and FE simulation analyses, theoretical models for predicting the ultimate capacity of S-UHPC-S sandwich deep beams and slender beams were proposed, accounting for different shear connectors. These models offer valuable insights for practical structural design and application.

Experimental studying bending behavior of cold-formed steel-concrete composite beam using perfobond shear connection

An experimental program was carried out on two large-scale steel-concrete composite beams to investigate the effect of the concrete slab dimension on the bending behavior of these beams. The steel-concrete composite beams used cold-formed steel and perfobond shear connectors. The webs of two cold-formed steel and perfobond shear connectors were attached by screws. The parameters evaluated in this program were load capacity, vertical deflection, and the relative slip between the steel beam and the concrete slab. The results showed that the thickness of the concrete slab and the shear connector width enhanced the load capacity and reduced the vertical deflection of steel-concrete composite beams.

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.

Cyclic shear test and stiffness study of a cross-section-type shear connector connection

In a prefabricated concrete frame-eccentrically steel brace structure, a solid connection is needed between the shear link damper and the concrete member to ensure successful plasticity developments in the damper. A new cross-section-type (CST) shear connector connection has been proposed as the critical component of the assembly connection to improve shear resistance. Four cyclic shear tests were performed to investigate cyclic shearing performance and failure modes with different connector configurations. Failure modes, hysteretic shear strength developments, skeleton curves, and strain distributions at the CST shear connectors were analyzed. Parametric numerical simulations were conducted to investigate the extended influences of various design parameters on shear bearing performance. Nonlinear behaviors primarily begin with concrete cracking, and the failure of CST shear connectors mainly occurs due to concrete damage around CST shear connectors. Increasing concrete strength, connector number, and connector section dimensions can enhance shear stiffness and strength. However, the thickness of the connector endplate and the length of the connector have limited influence. A theoretical calculation method with clear physical meanings and comprehensive considerations for influencing factors was proposed for calculating the initial shear stiffness. The theoretical equation demonstrates high efficiency, with a maximum error of 7.69%. Finally, the design method of the proposed CST shear connector connection was proposed.

Flexural vibration of elastic composite beams using a third-order deformation kinematics

The present study introduces a one-dimensional finite element (FE) model that utilizes third-order deformation kinematics to analyze the flexural vibration of two-layered composite beams with partial shear slip. The proposed model incorporates a three-node straight beam element, utilizing the field-consistent approach and full numerical integration of the stiffness matrix. This approach is adopted to effectively address stress oscillation and shear locking issues, ensuring accurate and reliable results. The analysis focuses on the third-order deformation kinematics of longitudinal displacement within the beam depth, examining each of the two layers individually. The interface between the two material layers is joined using deformable shear connectors, which are represented as dispersed shear springs over the length of the beam. This study focuses on conducting a flexural vibration analysis of two-layered composite beams. The analysis includes the examination of both free vibration and forced vibration responses while considering or omitting the influence of damping under various loading conditions. The validity of the proposed FE model is assessed by the utilization of a two-dimensional model developed within the ABAQUS software. Additionally, the suggested model is evaluated through the process of verification by comparing it with previously published results.

Shear stress at joint of prefabricated-composite box girders with corrugated steel webs

This paper studies the shear stress at the connection joints of a segmental prefabricated-composite box girder with corrugated steel webs. As the shear bearing capacity of the top and bottom concrete flanges of the segmental girder is weaker than that of an integral girder, this study focuses on the shear behavior at the combined joints of bridge segments under vehicle loads. The effects of concrete shear connector, concrete friction, the adhesive layer and steel web on the shear bearing capacity are considered. Laboratory tests were carried out for the segmental girder and an integral box girder as a reference. The structural behavior of the test girders' joint surfaces was also simulated through finite element analysis. Results show the shear bearing capacity formula for concrete box girders from the AASHTO Standard can be factored by a reduction coefficient of 0.9 to achieve a more accurate calculation. It shows that the modified formula can accurately reflect the shear stress variation trend of composite joints, and the percentage differences between the calculated values using the modified formula and those from experimental tests and simulations are both within 5%.