考虑墩-梁碰撞效应的大跨高墩连续刚构桥近断层地震损伤分析

Seismic Damage Analysis of Long-Span Continuous Rigid-Frame Bridge with High-Rise Pier Considering Pier-beam Pounding Effect Under Near-Fault Ground Motions

为研究连续刚构桥的主梁与过渡墩(墩-梁)地震碰撞效应对其地震反应和损伤的影响,以一座跨径为(120+220+120)m的连续刚构桥为例,基于MIDAS/Civil软件模拟实际施工过程并获得成桥内力状态,而后在OpenSees平台建立考虑该内力状态的动力弹塑性分析模型,同时采用Hertz-damp模型,着重考虑包括墩-梁碰撞在内的伸缩缝处的碰撞效应.选取具有向前方向性效应、滑冲效应和无速度脉冲效应的30条近断层地震动沿纵桥向输入,探讨了考虑墩-梁碰撞效应对桥墩峰值位移、残余位移、碰撞力及地震损伤的影响,以及不同类型近断层地震动作用下的差异性.结果表明:由于过渡墩处主桥与引桥梁体底面不在同一高程,强震下主桥梁体不仅与引桥梁体发生碰撞,还会与过渡墩发生碰撞;若忽略过渡墩与主桥梁体的碰撞效应会严重低估过渡墩的位移反应,尤其在向前方向性、滑冲效应地震动下过渡墩的位移反应分别被低估近3倍和5倍;其中滑冲效应作用下的影响最为显著,主桥和引桥墩均为中等损伤,过渡墩为严重损伤,不考虑墩-梁碰撞会导致对过渡墩地震损伤程度和震后残余位移的错误判断.

A continuous rigid-frame bridge with a span arrangement of(120+220+120)m was selected to investigate the influence of the pounding effect between main girder ends and transition pier on the seismic response and damage condition of the bridge.This work simulated the actual construction process of the bridge in MIDAS/Civil and extracted the real internal force state at the completion stage of the bridge.Based onOpenSees platform,the study developed a dynamic analysis model considering the internal force state,in which the pounding effects at expansion joints were simulated by the Hertz-Damp model.30 near-fault ground motions with forward directivity effect,fling-step effect and non-pulse were selected and inputted along the longitudinal direction of the bridge.The influence of the pier-girder pounding effect on the peak displacement,residual displacement,pounding force and seismic damage of piers was discussed.The difference of seismic response under three types of near-fault ground motions was analyzed.The results show that the girder end of main bridge not only impacts the girder end of approach bridge but also impacts the transition pier top under strong earthquake excitation because the height of the main girder is not equal to that of the approach girder.When the pounding effect is ignored,the displacement of the transition pier may be largely underestimated,especially under the forward directivity pulse and fling-step pulse the displacements are underestimated by nearly 3 times and 5 times,respectively.The pounding effect is the most significant under the fling-step ground motions with which the transition pier is severely damaged and the other piers are moderately damaged.Ignoring the pier-girder pounding effect may has a significant underestimation on the seismic damage condition and post-earthquake residual displacement of the transition pier.