Concrete Shear Keys Research Articles

The mechanical performance of concrete shear key for prefabricated structures

The mechanical performance of concrete connection plays an important role in the response of precast concrete structures. Unlike conventional small concrete shear key which is mainly to help with alignment at installation, large concrete shear keys have been often designed in recent engineering practice to improve joint shear resistance. However, the mechanical properties of large concrete shear keys have not been properly studied. This paper utilizes experimental and numerical methods to investigate both direct shear and flexural bending properties of shear keys. Four types of shear keys comprised of trapezoidal shape, semi-spherical shape, dome shape and wave shape are investigated, which are found to strongly influence the mechanical properties of the keyed joint. Laboratory shear test found unlike conventional shear key, with increased tenon size failure moves to concrete mortise. A detailed numerical model is built to help understand stress developed at the key joint. Flexural bending tests are carried out to evaluate the flexural bending properties of these key joints. Through comparing with theoretical derivation for plain flat joint, similar bending moment resistances from the keyed joints are measured with that of plain flat joint, but larger rotation angles are recorded probably because more damages at the key joint. Among the four different joint patterns, shear key with smoothed pattern could effectively relief concrete damages.

Utilizing yielding steel dampers to mitigate transverse seismic irregularity of a multispan continuous bridge with unequal height piers

Multispan continuous bridges built in mountainous areas are typically characteristic of having equal height piers since it is a commonly-adopted solution when crossing steep-sided valleys. To prevent bridge unseating during strong earthquakes, exterior concrete shear keys are usually implemented in the transverse direction as displacement restraining devices. Due to the restraining effect of shear keys, unequal height bridges are very likely to display irregular seismic responses mainly by inducing significant in-plane superstructure rotations. A large superstructure rotation may impose unbalanced seismic demands at different substructures. In this study, yielding steel dampers were proposed to replace exterior shear keys to mitigate the irregular seismic responses of unequal height bridges. A practical design method was developed for the steel dampers to maintain a uniform superstructure movement and balance the seismic demands on different substructures. Deterministic (nonlinear time-history) and probabilistic (seismic fragility) dynamic analyses were conducted, which successfully verified the effectiveness of the proposed design method in achieving a regular and balanced seismic performance for the unequal height bridge.

Seismic behaviour of hybrid-fibre reinforced concrete shear keys in immersed tunnels

This study aims to develop hybrid fibre reinforced concrete (HFRC) for shear keys used in conjunction with immersed tunnels in the Hong Kong–Zhuhai–Macau megaproject. First, HFRC was developed for shear keys, and its mixture proportions were optimised. Second, a testing programme was carried out with 15 specimens, to investigate the seismic behaviours of shear keys with the developed HFRC. The test results reported the failure mode, displacement with respect to the load, energy dissipation capacity, and the ductility of the shear keys with HFRC in the presence of horizontal hysteretic loads. The influences of different material parameters on the seismic behaviours of shear keys were analysed and discussed. Analytical models were also developed to predict the ultimate load-carrying capacity of the shear keys by regression based on the test results. Validations of the predictions from the developed analytical models confirmed their accuracy when compared with test results.

Shake table studies of a highway bridge model by allowing the sliding of laminated-rubber bearings with and without restraining devices

One of the most significant damages for highway bridges during the 2008 Wenchuan earthquake was the sliding of laminated-rubber bearings. The bearing sliding during the earthquake caused excessive superstructure displacement, which subsequently led to the failure of concrete shear keys, damages of abutments and expansion joints, and even span collapse. The main objective of this study is to experimentally investigate the seismic performance of highway bridges considering the sliding of laminated-rubber bearings. Three transverse restraining systems, namely without restraining devices, with concrete shear keys and with yielding steel dampers were tested on the shake table. Test results validate that seismic forces transmitted from superstructure to substructure can be substantially reduced by allowing the bearing sliding. However, if no restraining devices are implemented, the maximum, as well as residual bearing displacements, will be excessively large, making the superstructure-to-substructure connections the most vulnerable components. As restraining devices, yielding steel dampers are more effective than concrete shear keys by withstanding larger earthquakes and dissipating more energy. The tested model equipped with steel dampers can achieve a reasonable balance between bearing displacements and substructure seismic demands. Further, the experimental results are captured and justified by the supplemental numerical simulations.

Effect of exterior concrete shear keys on the seismic performance of laminated rubber bearing-supported highway bridges in China

Typical small to medium-span highway bridges in China are commonly equipped with laminated rubber bearings to accommodate superstructure movements from service-level loadings, and exterior concrete shear keys to restrain earthquake-induced superstructure displacements in the transverse direction. However, the past 2008 Wenchuan earthquake just highlighted the roles of bearings and shear keys in the performance of highway bridges. The bearing sliding as well as shear keys failure were typically observed during the earthquake, which resulted in excessive superstructure displacements and even catastrophic span collapse. The objective of this study is to investigate the effect of shear keys on the performance of laminated rubber bearing-supported bridges in China, with emphasis on the coupling between the shear keys and bearings. Nonlinear numerical models of bearing sliding and shear key failure are utilized and implemented in the finite element model of the global bridge. Incremental dynamic analyses are carried out to evaluate damage and failure process of the prototype bridge, followed by extensive parametric studies on the influences of shear key parameters. Results indicate that the shear keys designed with conventional practices are relatively ineffective in improving the bridge performance under large earthquakes. It is also concluded that the shear key parameters usually have coupling influences, which should be selected as a combination to achieve an optimal performance. Also, the shear key and bearing as a parallel system should be properly designed such that they can reach their peak forces simultaneously, providing an efficient resistance for the bridge superstructure.

Fiber Orientation in Ultra-High-Performance Concrete Shear Keys of Adjacent-Box-Beam Bridges

Fiber Orientation in Ultra-High-Performance Concrete Shear Keys of Adjacent-Box-Beam Bridges

Effect of Thermal Load on the Behavior of an Adjacent Precast, Prestressed Concrete Box-Beam Bridge that Contains Ultra-High-Performance Concrete Shear Keys with Transverse Dowels

Effect of Thermal Load on the Behavior of an Adjacent Precast, Prestressed Concrete Box-Beam Bridge that Contains Ultra-High-Performance Concrete Shear Keys with Transverse Dowels

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations (PGA). The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Seismic behavior of reinforced concrete sacrificial exterior shear keys of highway bridges

Shear keys as sacrificial members are widely used in cap beams and abutments of highway bridges, to limit the transverse displacement of superstructures and control damage to substructures. An experimental program to study the seismic behavior of reinforced concrete (RC) sacrificial exterior shear keys was presented. The influence of reinforcement ratios and construction joint types on the mechanical behavior of the shear keys was investigated, and three failure modes of the exterior shear keys under reversed loads were observed during testing. Two analytical models for predicting the force-displacement backbone curves of the exterior shear keys with sliding shear failure and sliding friction failure were developed, respectively. The analytical models proposed in this paper were in good agreement with the experimental data, indicating that they can be used as a reliable tool for predicting the response of exterior shear keys of highway bridges.

Early-Age Behavior of an Adjacent Prestressed Concrete Box-Beam Bridge Containing UHPC Shear Keys with Transverse Dowels

AbstractAdjacent precast prestressed concrete box-beam bridges have been used in the United States for many years and have performed well. However, the shear keys between adjacent box beams are sus...

Laboratory Evaluation of Ultrahigh-Performance Concrete Shear Key for Prestressed Adjacent Precast Concrete Box Girder Bridges

AbstractPrecast adjacent box girder bridges have become a preferred solution in several states due to their simple structure, economy, and ease of construction. However, longitudinal cracks often appear along the shear keys between adjacent box girders. With its superior strength and durability, ultrahigh-performance concrete (UHPC) has been used as an alternative grout material to reduce shear key cracking and enhance load transfer. The objective of the present research was to evaluate the performance of UHPC in shear keys using direct shear, direct tension, and flexural tests. Also, this study determined the effectiveness and functionality of shear reinforcement bars by applying direct shear load on specimens with shear reinforcement. In the direct shear test, a steel frame was placed around the specimens to allow the shear key to experience pure shear force. The direct shear test established the cracking threshold and ultimate shear strength of each shear key with and without shear reinforcement bars. ...

The effect of concrete shear key on the performance of segmental columns subjected to impact loading

Conventional precast segmental columns with seismic resistance design consist of only flat concrete segments with prestress tendon. This is because friction between adjacent segments is sufficient to resist the lateral forces from earthquake-induced actions. However, the friction between segments is not necessarily sufficient to resist lateral impact loads such as vehicle impact the column might experience during its service life. This article investigates the effectiveness of using concrete shear key in segments of precast segmental column in resisting the lateral impact loading. The precast reinforced concrete segments were designed with concrete shear keys to improve the column shear resistance capacity and minimize the relative displacement between adjacent segments. Two groups of segmental columns with and without shear key were designed and tested using a pendulum impact system. The effectiveness of shear key in resisting lateral impact loads was analysed by comparing the performance of the two groups of segmental columns. The testing results revealed that by introducing concrete shear key to segmental column, the relative displacement between adjacent segments could be effectively reduced. However, the large concrete shear key increased stress concentration in the concrete segments. Relatively, more severe damages to concrete segments were found on the columns with shear key. Further improvements on shear key designs should be made for better performance of segmental columns against impact loading.

Shake Table Test and Numerical Analysis of a Bridge Model Supported on Elastomeric Pad Bearings

Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.

Shake-table tests and numerical simulation of an innovative isolation system for highway bridges

Damage investigation of small to medium-span highway bridges in Wenchuan earthquake revealed that typical damage of these bridges included: sliding between laminated-rubber bearings and bridge girders, concrete shear keys failure, excessive girder displacements and even span collapse. However, the bearing sliding could actually act as a seismic isolation for piers, and hence, damage to piers for these bridges was minor during the earthquake. Based on this concept, an innovative solation system for highway bridges with laminated-rubber bearings is developed. The system is comprised of typical laminated-rubber bearings and steel dampers. Bearing sliding is allowed during an earthquake to limit the seismic forces transmitting to piers, and steel dampers are applied to restrict the bearing displacements through hysteretic energy dissipation. As a major part of this research, a quarter-scale, two-span bridge model was constructed and tested on the shake tables to evaluate the performance of this isolation system. The bridge model was subjected to a Northridge and an artificial ground motion in transverse direction. Moreover, numerical analyses were conducted to investigate the seismic performance of the bridge model. Besides the test bridge model, a benchmark model with the superstructure fixed to the substructure in transverse direction was also included in the numerical analyses. Both the experimental and the numerical results showed high effectiveness of this proposed isolation system in the bridge model. The system was found to effectively control the pier-girder relative displacements, and simultaneously, protect the piers from severe damage. Numerical analyses also validated that the existing finite element methods are adequate to estimate the seismic response of bridges with this isolation system.

Seismic Performance of Highway Bridges with Different Transverse Unseating-Prevention Devices

AbstractTypical small-to-medium–span highway bridges in China are often installed with economical laminated-rubber bearings that allow for thermal movement of girders and concrete shear keys that restrain transverse girder displacement. However, the damage investigation after the 2008 Wenchuan earthquake had shown that sliding between the girder and the laminated-rubber bearings was a common phenomenon that caused excessive girder displacement and damage to shear keys, expansion joints, and abutments. The bearing sliding can actually act as isolation for the piers, which suffered from a small amount of damage during the earthquake. Therefore, a new seismic design strategy for typical girder bridges has been proposed in which the bearing sliding acts as a fusing mechanism to mitigate the seismic demands of piers, and unseating-prevention devices are used to control the bearing displacement. This paper investigates the seismic performance of three transverse unseating-prevention devices (concrete shear keys...

격자형 강합성 바닥판의 수정된 이음부에 대한 휨성능 평가

프리캐스트 방식에 의해 제작이 가능한 격자형 강합성 바닥판의 이음부로서 콘크리트 전단키와 고장력볼트 체결로 구성된 조립식 이음부가 제안된 바 있다. 본 연구에서는 콘크리트 전단키와 고장력볼트로 구성된 이음부의 휨강성과 휨강도를 향상시키고자 단면상세를 개선하였고, 구조실험을 통해 얻은 결과를 기존 볼트체결 이음부와 비교 분석하였다. 비교분석 결과에 의하면, 전단스터드와 가외철근에 의한 이음부 콘크리트 보강으로 뚜렷한 전단균열 감소효과가 있었다. 모멘트-곡률 관계로부터 구한 휨강성을 서로 비교해 본 결과, 단면개선 전의 이음부에 비해 약 47% 정도 휨강성이 증가한 것을 알 수 있었다. 또한, 휨강도 비교결과에 의하면 개선된 이음부의 휨강도는 개선 전에 비해 약 32% 증가하였다. 개선된 이음부의 휨성능을 이음부가 없는 단면과 비교하면, 휨강도의 경우 동등 수준 이상이었으나, 휨강성의 경우는 약 37% 정도 더 작은 것으로 분석되었다. For the joint connection of the precast steel grid composite decks, the prefabricated joint which is composed of concrete shear key and high-tension bolts was already proposed. In this study, for the purpose of increasing the bending stiffness and bending strength of the proposed prefabricated joint section details of the proposed joint are modified, and through experimental tests the bending performance, such as stiffness and strength of a modified joint, is compared with those of the proposed joint. Test and analysis results show that the shear cracks in the concrete shear key are clearly reduced by the strengthening of the shear key using shear studs and additional rebars. According to analysis results of the moment-curvature relationship, bending stiffness of the modified joint is about 47% greater than the stiffness of the proposed joint. Furthermore, the modified joint has about 32% greater bending strength than the proposed joint. Compared to specimens without the joint the modified joint has same or slightly higher bending strength, but about 37% lower bending stiffness.

Experimental Fatigue Evaluation of Prestressed Concrete-Filled Steel Tube I-Shaped Bridge Girders

This paper investigates experimentally the fatigue capacity of prestressed concrete-filled steel tube (CFT) I-shaped girders. The girder consists of steel plates, PT tendons, concrete, and steel shear keys. Three 10 m long girder specimens were prepared for different fatigue stress ranges and subjected to a three-point bending test producing a positive moment along the entire girder span. Displacement control was used to prevent sudden failure of the specimens. The test girder specimens exhibited fatigue capacities classified as Category B′ or C′ of the AASHTO criteria for positive and negative moment, respectively. The special testing arrangement used to produce the negative moment is presented, as well as the fatigue testing procedures and results. At the end of the paper, a modified equation for the S–N curve is derived for predicting the remaining life of the girder.

Influence of Test Method on Direct Shear Behavior of Segmental Retaining Wall Units

Abstract This paper reports the results of interface shear testing carried out to investigate the influence of test methodology on shear-displacement behavior of five different segmental (modular) masonry concrete block configurations. The tests were carried out in general conformance with existing ASTM and National Concrete Masonry Association test protocols. Three different normal load arrangements were investigated: (1) flexible airbag, (2) fixed vertical piston, and (3) an adjustable vertical piston. A video-extensometer camera device was used to record block deformations in the vertical plane during testing. The test results showed that the three load arrangements gave similar shear capacity failure envelopes for the frictional block system with flat concrete surfaces. For more typical block systems with concrete shear keys and trailing lips that exhibit dilatant interface shear behavior, or a system with shear pins, the most consistent test results were developed using the flexible airbag arrangement. The results of this paper can be used to guide the selection of the loading arrangement for conventional laboratory modular block shear testing.

Parametric study on performance of bridge retrofitted by unseating prevention devices

Over the past decade, seismically induced damage to bridges has been widely reported following major earthquakes such as the 1994 Northridge, 1995 Kobe and 1999 Chi-Chi events. Since these earthquakes, restrainers and stoppers have been installed on bridges to prevent unseating and excessive displacements, respectively. Alternatively, column jacketing has also been proven to be effective. However, the enhanced shear strength may result in extra retrofitting works on the footing. For bridges damaged in the Chi-Chi earthquake, investigations revealed that most bridge columns experienced none-to-minor damage in the longitudinal direction. The reason for this unexpected performance was the construction practice of using a rubber bearing, which is an unbolted design that may slide under large lateral forces. In this paper, parametric studies on simply-supported bridges retrofitted by a restrainer or concrete shear key along the longitudinal and transverse axes were carried out. The research focuses on finding suitable combinations of the design force and gap spacing so the restrainer and concrete shear key can be used as an unseating prevention device, with respect to the allowable column damage in terms of displacement ductility under near-facult type earthquakes. A two-lane PCI-girder bridge was selected as the benchmark model. In the longitudinal direction, a total of nine combinations considering yielding strength and gap spacing for the restrainer were analyzed; while parameters for the concrete shear key were divided into three shear force levels and three gap spacings. In the transverse direction, a similar approach was adapted, except smaller gap spacing was used. For each of the above mentioned earthquakes, seven input ground motions were selected and their PGAs were adjusted to 0.36g and 0.45g as the Design earthquake and Maximum Considerable Earthquake, respectively. Based on the results of nonlinear time history analyses, proper parameters to design the restrainers and concrete shear keys are obtained. Responses obtained from numerical simulations under the Chi-Chi earthquake leaded to new implications to design those devices. Restrainer should not exceed its breaking strain and sufficient unseating length will be needed always. Concrete Shear key was determined by considering both displacement demand of the superstructure and displacement ductility of the column at the same time. Further study is needed to provide optimal design parameters for use in performance based bridge design.

Girder/Deck Connection for Rapid Removal of Bridge Decks

This paper presents a debonded shear key system for prestressed concrete bridge girders with composite cast-in-place decks. The system utilizes the mechanical anchorage of concrete shear keys created on the top flange of a concrete girder combined with shear reinforcement crossing the interface. The system has the advantage of facilitating future deck removal, while protecting the top flange of the girder from damage, which is particularly significant for bridges in cold climates where deck concrete is subjected to deterioration due to freeze-thaw cycles and deicing chemicals. Theoretical background, experimental results, production issues, design criteria and construction specifications of this system are discussed.