This paper focuses on the effects of near-fault motion characteristics on the seismic performance of tall pier bridges. Using the analytical models calibrated by shake table tests, fragility analysis ...was conducted investigating the influence of near-fault motion features (i.e., period (T
v
) and number (N) of velocity pulses). Results show that seismic fragility of the tall pier under near-fault motions is highly correlated to T
v
and the damage states considered, while the influence of N is less significant. Consequently, when considering the seismic behavior of tall piers under near-fault pulse-like motions, choosing records with respect to T
v
may lead to more reliable results.
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.
•Nonlinear models of shear key failure and sliding of laminated-rubber bearings are used in the study.•Conventionally-designed shear keys in China are ineffective in restraining displacements under large earthquakes.•Shear key parameters will produce dynamic coupling influences on bridge performance.•An optimal design is achieved when shear keys and laminated-rubber bearings reach their peak resistance simultaneously.
AbstractSeismic isolation is a commonly adopted approach for designing bridges against earthquakes. However, the period elongation in an isolated bridge will generally lead to a large superstructure ...displacement, which may result in pounding, bearing unseating, or even span collapse. This study focuses on the implementation of energy dissipation devices for retrofitting an existing bridge isolated by lead rubber bearings (LRBs). Four different retrofit measures, namely yielding steel cables (YSCs), viscous dampers (VDs), friction dampers (FDs), and superelastic shape memory alloy cables (SMAs) were considered in this study. Fragility analyses were performed to evaluate the relative effectiveness of these devices in minimizing the seismic vulnerability of the bridge. The results indicate that all the devices show comparable performance in reducing the probability of damage of the isolation bearings without imposing much additional vulnerability on the bridge piers. The SMAs are the most effective in mitigating the seismic vulnerability of the bridge system at all the damage states, followed by FDs, VDs, and YSCs. Due to the superior self-centering capacity, the SMAs retrofitted bridge exhibits better recentering performance with a reduced residual displacement of superstructure compared with the bridges with other retrofit measures.
Abstract
A new lap splice connection by ultra-high performance concrete (UHPC) was proposed to connect precast bridge columns with footings or cap beams. Quasi-static tests were conducted on two ...large-scale precast double-column bent specimens with different aspect ratios to investigate their cyclic behavior. The test results revealed that the specimen with a larger aspect ratio (i.e., slender specimen) failed by core concrete crushing above the lower column–footing connection segments without bond failure. However, the specimen with a smaller aspect ratio (i.e., squat specimen) experienced a shear–flexure failure in the lower column–footing connection segments. In addition, refined finite-element (FE) models that incorporated the effects of bond–slip and shear–flexure interactions were developed to investigate cyclic behavior in the tested specimens further. The numerical results indicated that neglecting the effects of bond–slip and shear–flexure interactions led to overestimating the cumulative dissipated energy of the specimens. The deformation in the slender specimen was dominated by flexure and bond–slip in the UHPC, and the squat specimen was dominated by shear. Finally, the strength and deformation capacities of both specimens were evaluated. The proposed UHPC connection ensured an ultimate drift of >3% for the slender specimen and a shear strength that was comparable to a monolithic cast-in-place (CIP) bent for the squat specimen.
•Typical bridge unseating damages in past earthquakes are introduced.•Specifications on unseating prevention in modern bridge codes are summarized.•Minimum support length and seismic restrainers are ...effective measures to prevent unseating.•The seismic performance of various passive unseating prevention restrainers for highway bridges is reviewed.
Recent major earthquakes worldwide demonstrated extensive bridge collapses caused by span unseating, which highlights the necessity of implementing effective unseating prevention measures in bridges. This state-of-the-art review provides an informative overview of the recent developments of passive unseating prevention measures for highway bridges against earthquakes, which primarily include minimum support length requirements and unseating prevention restrainers. Important aspects of these strategies in terms of their effectiveness, limitations, and future research needs are summarized and discussed. The current study synthesizes the existing information on bridge unseating prevention strategies, presents in a concise manner in the form of useful equations, tables, and figures, and explains the critical aspects for implementing these strategies. The results of this study are expected to motivate researchers and practicing engineers to extend implementation and innovation of bridge unseating prevention strategies.
In view of the insufficiency of bidirectional seismic control of long-span cable-stayed bridges as well as the limitations of existing schemes, a multi-direction damping system (MDDS) was proposed ...and investigated in this manuscript, which can provide seismic resistance bidirectionally. The new damping system owned a unique middle connecting structure, which overcomes the disadvantages that axial instability caused of excessive long rod and the demand of large installing space of traditional dampers. Both the performance stability and constitutive relationship of MDDS were verified by engineering tests, and the equivalent design method was then proposed and proved to be applicable. A detailed finite element numerical model of a super-long (main span over 800 m) column-type pylon cable-stayed bridge which equipped with MDDS in practice was established, the fragility curves of critical components were obtained by non-linear time history analysis, which exhibited the high efficiency of MDDS seismic performance in both transversal and longitudinal directions. Through extracting the median fragility value of 35 sections of the pylon under four damping cases, i.e. setting dampers transversely (TDS), longitudinally (LDS), bidirectionally (BDS), and MDDS, it can be concluded that MDDS performed far better on seismic resistance than LDS and TDS, and made the similar contribution with BDS. On account of half number of damper setting and the reduction in installing space demand, MDDS becomes the optimal choice in practical application for its economic efficiency and superiority. Furthermore, the optimal horizontal installing angle of MDDS was derived through six angle cases which was based on the system-level fragility curves comparison.
Assembly of precast elements is a widely adopted technology for achieving accelerated bridge construction (ABC) owing to the increased construction speed and quality. Connection methods between ...precast structural members, if designed properly, can facilitate a convenient postearthquake replacement of damaged members and hence enable rapid function recovery of bridges. This study proposes a new precast bridge pier–footing connection using external sockets. The external sockets are prefabricated on the top of bridge footings and the precast piers can be directly inserted into the sockets with postgrouting. Quasi-static cyclic loading tests were conducted on four 1/4-scale pier–footing specimens, including three external socket pier specimens and a cast-in-place (CIP) specimen for comparison purposes. The experimental results show that the external sockets with normal design sizes are effective precast pier–footing connection methods, ensuring that plastic hinges are formed in the piers without damaging the external sockets and footings. Because of the shortened effective pier height, the socket piers show increased lateral stiffness and strength but decreased displacement capacity compared with the CIP pier. The measured peak horizontal forces for the precast socket pier specimens PCS-1, PCS-2, and PCS-3 are increased by 7.5%, 34.5%, and 51.4%, respectively. However, the ultimate displacements are reduced by 11.1%–22.0% compared with the CIP pier. The hysteretic energy dissipation of the socket piers is compared with that of the CIP pier, with a difference less than 20%. Postexperiment replacement of a tested precast pier was carried out, which demonstrates the feasibility of rapidly replacing damaged bridge piers when using the proposed external socket connections. A subsequent experiment reveals that the newly replaced pier specimen could show an equivalent seismic performance to the previous specimen. The maximum differences of the peak force and initial stiffness between the two piers are within 6.7%, and the difference of the dissipated energy is only 3.8%. The experimental results verified the effectiveness of the rapid replacement.
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.
•A new isolation system for bridges installed with rubber bearings is proposed.•A large-scale, two-span bridge model was designed and tested on three shaking tables.•Seismic forces on substructures and bearing sliding are well controlled.
AbstractThe performance of concrete shear keys as restraining devices for laminated rubber bearing–supported highway bridges was examined in past earthquakes such as the 1999 Chi-Chi and the 2008 ...Wenchuan earthquakes, where the widely observed shear key failure and bearing sliding significantly increased the risk of span unseating. To avoid such scenarios, economical yielding steel dampers are proposed to replace conventional shear keys as restraining devices on bridges. If designed properly, the steel dampers are expected to control bearing displacement within limit without imposing much additional demand on the substructure. The primary objective of this study was to develop a simplified procedure for designing the yielding steel dampers to control sliding displacement of the laminated rubber bearings to a specified value for the considered earthquake hazard. By treating the global bridge system as a serial-parallel combination of different components, the correlations of various parameters were investigated. On that basis, a simple formulation was developed, followed by a series of nonlinear time history analyses and a shake table test as verifications. The outcome of this study highlights the cost-effectiveness of using yielding steel dampers and laminated rubber bearings as an earthquake-resistant system for highway bridges compared with other popular isolation systems. The proposed design procedure was also verified to be quite efficient in properly designing the yielding steel dampers for a satisfactory bridge seismic performance.
This study attempts to investigate the effect of the BRB distribution on the seismic performance of retrofitted multi-story RC tall bridge bents. Different BRB distributions were compared, from which ...the most efficient one was identified. The results showed that uniform distribution was not necessarily an efficient retrofit option. By controlling the same damage, using triangular cumulative distribution to design multi-story BRBs led to the least consumption of brace material. Alternatively speaking, with the same consumption of BRBs, the triangular cumulative distribution of braces was the most effective in controlling the damage of the tall bridge bents.
