No abstract

No abstract

Previous earthquakes have highlighted the seismic vulnerability of bridges due to excessive movements at expansion joints. This movement could lead to the catastrophic unseating failure if the provided seat width is inadequate. Moreover, seismic pounding is inevitable during a strong earthquake due to the limited gap size normally provided at the expansion joints. Various types of restrainers, dampers and other devices have been proposed to limit the joint movement or to accommodate the joint movement so that the damages caused by the excessive relative displacements could be mitigated. To select and design appropriate devices to mitigate the relative displacement induced damages on bridge structures during earthquake shaking, it is important that results from the previous studies are well understood. This paper presents an overview on the various pounding and unseating mitigation devices that have been proposed by various researchers. Based on an extensive review of up-to-date literatures, the merits and limitations of these devices are discussed.

No abstract

No abstract

No abstract

Unseating damages of bridge decks have been observed in many previous major earthquakes due to large relative displacement exceeding the available seat length. Steel cable restrainers are often used to limit such relative displacements. Present restrainer design methods are based on the relative displacements caused by the different dynamic characteristics of adjacent bridge structures. However, the relative displacements in bridge structures are not only caused by different dynamic characteristics of adjacent bridge segments. Recent studies indicated that differential ground motions at supports of bridge piers and Soil Structure Interaction (SSI) could have a significant influence on the relative displacement of adjacent bridge components. Thus the present design methods could significantly underestimate the relative displacement responses of the adjacent bridge components and the stiffness of the restrainers required to limit these displacements. None of the previous investigations considered the effects of spatially varying ground motions in evaluating the adequacy of the restrainers design methods. Moreover, the code recommendation of adjusting the fundamental frequencies of adjacent bridge structures close to each other to mitigate relative displacement induced damages is developed based on the uniform ground motion assumption. Investigations on its effectiveness to mitigate the relative displacement induced damages on the bridge structures subjected to spatially varying ground motion and SSI are made. This paper discusses the effects of spatially varying ground motions and SSI on the responses of the multiple-frame bridges with unseating restrainers through inelastic bridge response analysis.

Pounding and unseating damages to bridge superstructures have been commonly observed in many previous major earthquakes. These damages can essentially attribute to the large closing or opening relative displacement between adjacent structures. This paper carries out an experimental study on the pounding responses of adjacent bridge structures considering spatially varying ground motions by using a shaking table array system. Two sets of large scale (1:6) bridge models involving two bridge frames were constructed. The bridge models were subjected to the stochastically simulated ground motions in bi-direction based on the response spectra of Chinese Guideline for Seismic Design of Highway Bridge for three different site conditions, considering three coherency levels. Two types of boundary conditions, i.e., the fixed foundation and rocking foundation, were applied to investigate the influence of the foundation type. In addition, a detailed 3D finite element model was constructed to simulate an experimental case. The non-linear material behavior including strain rate effects of concrete and steel reinforcement is included. The applicability and accuracy of the finite element model in simulating bridge pounding responses subjected to spatially varying ground motions are discussed. Experimental and numerical results demonstrate that non-uniform excitations and foundation rocking can affect the relative displacements and pounding responses significantly.