汶川地震动特性及临近断层高墩桥梁破坏机理深入研究

Miaoziping Bridge with piers about 100 meters high has been damaged during Wenchuan earthquake because the combined actions of near-fault ground motions and the fault ruptures. The bridge damage mechanism is studied in this project considering the interaction of the fault ruptures, near-fault ground motions and bridge responses. In order to study the characteristics of near-fault ground motions, the elastic and nonlinear response spectrums are calculated using ground motions recorded in Wenchuan earthquake, Chi-Chi earthquake and the other countries. Responses of box girders、bearing and columns of Miaoziping Bridge are presented using both time history analysis by beam-column and spring element model and the equivalent static analysis according to the time series based on the fine finite element model. Unseating damages for simply supported bridges of Miaoziping Bridge due to the fault ruptures are also studied using the analysis procedure for multi-support excitations with the displacements input mode. A new type pier with the prestressed tension steels in the center of the thin-box section under the water is proposed and its seismic performances are verified by the cyclic test and the pseudo-dynamic test. The performance and the method for seismic design of the piers under the water are given, which requires that the piers can sustain a minor earthquake without any cracks, a moderate earthquake with rapidly repairable structural damage, and a strong earthquake with limited damage. The design concept of functional separation of the bearings at the boundary piers and the self-center stoppers which can dissipate energy are introduced to the frame bridges with the new type pier for the seismic damages control.

汶川地震庙子坪大桥为百米高墩桥梁首次遭受检验，调查表明严重震害是强烈近断层地震动及地表破裂联合作用所致。本项目拟从断层-地震动特性-结构反应紧密结合角度，对临近断层高墩桥梁地震破坏机理作系统研究。首先，基于汶川、美国、日本和集集近断层强震记录的弹（塑）性反应谱对比，获得汶川近断层地震动特性深入认识；其次，以庙子坪大桥震害为例，以杆系简化模型动力时程分析结合板壳精细模型依时间序列的静力分析，实现主桥箱梁、支座等的受力及破损模拟；借助地震多点激励位移输入模式，提出断层地表破裂下桥梁倒塌分析方法及实现引桥落梁模拟；最后，提出中心配预应力束的水下薄壁高墩新型构件，以提高抗开裂能力和降低大震残留位移。基于拟静力、拟动力试验等提出"小震不裂，中震简单修复，大震有限损伤"水下高墩性能抗震设计准则和方法；进一步结合过渡墩处"支座功能分离" 设计理念和设置自复位耗能限位装置，综合实现高墩桥梁地震损伤控制。

汶川地震庙子坪大桥为百米高墩桥梁首次遭受检验，调查表明严重震害是强烈近断层地震动及地表破裂联合作用所致。本项目从断层-地震动特性-结构反应紧密结合角度，对临近断层高墩桥梁地震破坏机理作了系统研究。. 首先，基于汶川、美国、日本和集集近断层强震记录的弹（塑）性反应谱对比，获得汶川近断层地震动特性深入认识。提出了汶川近场含速度脉冲地震波在0.2s-0.8s周期内反应偏小，与Kagawa等（2004）提出的大震伴随地表破裂将使周期1s左右地震动成份缺失的地震学研究论断一致。 关于远场（盆地效应）谱的认识合理解释了西安、宝鸡等城市烈度异常现象，提出了远场（盆地效应）与近场地震动的弹性反应比谱和弹塑性位移比谱的概念。项目还发展了近断层地震动脉冲周期识别HHT方法，避免了其它方法中先验函数、物理假设的影响，与目前广泛接受的Baker提出的小波方法相比，还具有严格的能量守恒性。. 其次，基于数值分析对庙子坪大桥主梁开裂机理进行了研究，一方面加深了震害的理解，另一方面对结构震后评价也具有价值，如弄清预应力束在地震时的应力增长。进行了薄壁高墩倒塌破坏的变轴力拟静力试验，认为是混凝土保护层脱落以及箍筋约束不足，纵筋突然屈曲导致；还有可能是薄壁易于发生类似“板”的局部屈曲也会诱发倒塌，这方面工作为薄壁高墩的动力灾变的数值模拟提供了很好的试验基础。. 最后，研究了临近断层刚构桥和减隔震桥梁的地震反应特性和能量反应情况，涉及断层夹角、竖向地震动和纯速度脉冲影响等；提出了设置BRB的多种桥梁减震控制体系，发展了附加BRB双柱墩基于保险丝理念的位移抗震设计方法；提出了临近断层桥梁逐级设防，减隔震设计、延性设计和位移控制统一的概念设计及全套性能化设计方法。特别是提出了主结构系统（SDOF）的弹塑性地震反应谱模型，拓展了地震工程弹塑性反应谱理论上的认知。适用于减震装置仅提供刚度而增加的质量可以忽略，且减震装置与主结构的位移可由约束方程描述（如借助Pushover分析实现）的一类耗能减震结构。