Issue 30

W. Changfeng et alii, Frattura ed Integrità Strutturale, 30 (2014) 486-494; DOI: 10.3221/IGF-ESIS.30.59 492 It can be seen from Fig. 7 and 8 that when the effect of the supports and restraining devices is considered: (1) For movable piers, due to the effect of friction at movable supports, the moment and curvature of bottom section of the piers when the effect of friction at movable support is considered (Model 2) are larger than that in the case when the friction at movable supports is not considered (Model 1), and the seismic response increases with the increase of coefficient of friction; For fixed piers, under the action of artificial wave, the moment and curvature of bottom section of the piers when the effect of friction at movable supports is considered are smaller than that in the case when friction at movable supports is not considered, and the response decreases with the increase of coefficient of friction. However, the seismic response of the bottom section of the fixed piers when the friction at movable supports is considered under Tianjin Wave increases, which suggests that the friction at movable supports is not always favorable for the seismic resistance of bridge structure. The effect of friction at movable supports on the seismic resistance performance of bridge structures depends on the spectrum of the seismic wave and the characteristics of the structure. It is recommended that for structures of which the natural vibration period is similar to the period of the surrounding ground when the contribution of stiffness of movable supports is considered, or structures on soft ground foundation, the effect of friction at movable supports should be considered. (2) When the effect of friction at movable supports and the elasticity of restraining devices are considered, the moment and curvature of bottom section of the movable piers increase and the response increases with the increase of the coefficient of friction at movable supports; the seismic response at the bottom section of the fixed piers in the case when restraining devices are considered (Models 3 to 5) is smaller than that in the case when only the friction at movable supports is considered (Model 2). (3) When the nonlinearity of the restraining devices is considered (model 4), the seismic response of the bottom section of the movable piers is smaller or similar with that in the case when the elasticity of restraining devices is considered; the seismic response of the bottom section of the fixed piers is slightly larger than that in the case when the elasticity of restraining devices is considered due to the fact that the restraining devices are in nonlinear stage which limits the bearing of seismic force by movable supports. The restrainers should be designed energy intensive to protect the movable pier from being destroyed by the violet pounding force, so model 4 was suggested in practice [14-16]. The bump rubber can be also used to decrease the pounding force. (4) If only the restraining effect of the middle piers is considered (Model 5), the seismic response of the bottom section of the side movable piers is smaller than that in the case where the nonlinearity of the restraining devices is considered (Model 4) but the seismic response of the middle movable piers and fixed piers increase. (5) For side movable piers, the seismic response in the case when the effect of supports and elasticity of restraining devices is considered (Model 3) is the largest; for middle movable piers, the seismic response in the case when only the restraining effect of the 3# piers is considered (Model 5) is the largest; for fixed piers, the seismic response in the case when the effect of supports and elasticity of restraining devices is considered (Model 3) is the smallest, suggesting that restraining devices effectively reduce the seismic response of the bottom section of the fixed piers and enable the movable piers to bear a part of the seismic input energy to distribute and isolate the seismic effect. Comparison of displacement of the girder and shear displacement of the supports The vertical displacement of the girder and shear displacement of the movable supports in different models are given in Fig. 9 to 10. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0 0.05 0.1 0.15 0.2 Displacement(m) μ Displacement of the girder under the first artificial wave Model 1 Model 2 Model 3 Model 4 Model 5 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0 0.05 0.1 0.15 0.2 Displacement(m) μ Displacement of the girder under Tianjin wave Model 1 Model 2 Model 3 Model 4 Model 5 (a) (b) Figure 9 : Comparison of displacement of girder in each model.