Issue 30

W. Changfeng et alii, Frattura ed Integrità Strutturale, 30 (2014) 486-494; DOI: 10.3221/IGF-ESIS.30.59 487 In bridge engineering, restraining blocks are often used to prevent the falling of the girder and increase the safety of the supports during earthquake. For large-span long continuous bridge structures, the self-load of the integrated girder body is high, resulting in a substantial horizontal seismic force mainly concentrated on the fixed supports. To optimise the distribution of seismic force for each pier, anti-seismic pins or restraining blocks can be installed. At the same time, a certain gaps between the blocks (pins) and the girder should be preserved, so that the movable pier is able to carry a part of the horizontal seismic force without affecting the normal stretching of the girder, as shown in Fig. 1. It is pointed out by [3] that if the expected plastic hinge is located in the pier, more piers should be arranged to carry the horizontal seismic force. An ideal way is to install laminated rubber supports on all piers but the number of horizontal force bearing piers may be limited by other design factors which should be taken into consideration during design. Xie xu [4] stated that horizontal seismic force produced by the superstructure of the continuous bridge is good to be carried by all piers and abutments to prevent overbearing of the fixed piers. Relevant engineering procedures such as restraining devices were proposed. (a) (b) (c) Figure 1 : Seismic tectonic measure at movable piers. (a) Longitudinal seismic pin; (b) Lateral seismic pin; (c) Restrainer. At present, few studies are carried out to evaluate the effect of restraining devices and supports on the nonlinear seismic response of the bridge structure. Restraining blocks are only considered as structural component without analysing the effect of them during seismic resisting process according to the seismic resistant standard of bridge engineering in China. Studies focusing separately on the nonlinearity of supports, seismic mitigation and isolation, restraining devices or elasto- plasticity of bridge piers are common [5,6] but studies considering simultaneously the nonlinearity of supports, contact of restraining devices and material nonlinearity are rare. Studies concerning the interaction of the nonlinearity of supports, restraining devices and the elasto-plastic analysis of bridge piers are also rare. At present, the effect of friction at supports and the nonlinearity of restraining devices on the elasto-plastic seismic response of the bridge are rarely considered during the elasto-plastic seismic response of continuous bridge. In this study, on the basis of considering the nonlinearity of supports, piers and restraining devices, the effect of restraining devices and nonlinearity of supports on the elasto-plastic seismic response of continuous girder bridge is evaluated and structural procedures to reduce the seismic response of the fixed piers of continuous girder bridge are proposed. A NALYTICAL MODELS OF EACH ELEMENT Support elements onlinear supports can be simulated by springs with bilinear hysteretic relationship. To simulate the sliding kinetic performance of the support in earthquake, bilinear hysteretic sliding support element [7] is used and the hysteretic model of the element is shown in Fig. 2. Laminated rubber supports which are normally positioned at the top of the piers are not bolted with the top of the pier or the bottom of the girder. If the seismic force exceeds the critical sliding force between the supports and the surfaces of the pier or the beam bottom, sliding will occur. The laminated rubber supports in this case can be simulated by bilinear model; for tetrafluoroethylene movable supports, the support element is also simulated by bilinear model. The stiffness of movable support after sliding is taken as 0, which is the Coulomb friction model. N