Seismic performance improvement of elevated highway bridges using high energy dissipation materials

为了提高结构系统的抗震性能，提出了一种结构系统损伤局部化的能量吸收策略：在特殊设计的薄弱结构单元中有意地进行损伤局部化，使其在地震中耗散能量。弱构件的设计使它们先于主体结构屈服，以避免主重力支撑构件的损坏。这种处理方法还将大大减少地震事件后的维修工作量，因为只有增加的不支持重力的弱构件才会屈服。为了实现这种控制损伤的结构设计理念，分三步研究了耗能策略。首先，建立了高架桥耗能装置的优化设计方法，并采用简化的集总质量模型研究了高架桥的损伤分布。第二步，以低屈服点钢（LYPS）为例，建立桥墩损伤控制策略。分析和实验研究表明，LYPS是一种适用于指定弱元素的高吸能延性材料。第三步，以1995年神户大地震时高架桥的地震加速度和损伤记录为研究对象，验证了高架桥损伤控制的可行性。通过对三跨连续桥梁的损伤进行精确评估，可以预测三跨连续桥梁的损伤分布。在基础隔离桥中也观察到响应的局部化。这些证据显示了损害控制的可能应用。对连续跨桥梁进行了三维有限元分析，比较了几种损伤控制设计的性能。尽管在应用之前需要考虑施工细节等实际问题，但本研究工作表明，所提出的设计理念是改善高架公路桥梁抗震性能的有希望的替代方案。

In order to improve the seismic performance, an energy absorption strategy which localizes damage in structural systems is proposed : intentionally localizing damage in specially designed weak structural elements, with which energy is dissipated during earthquake. The weak elements are so designed that they yield prior to the main structure to avoid damage in the main gravity supporting element. This treatment will also reduce the repair works after seismic events considerably, because only the added weak elements which do not support gravity yield. To achieve this structural design concept to control damage, energy dissipation strategy is studied in three steps. At the first step, optimal design method of energy dissipation devices is constructed and distribution of damage is studied using simplified lumped mass model of elevated highway bridges. At the second step, low yield point steel (LYPS) is introduced as an example of the weak element, and damage control strategy is constructed for bridge piers. Analytical, and experimental studies revealed that LYPS is high energy absorbing ductile material suitable for the designated weak element. At the third step, real elevated highway bridges where seismic accelerograms or damage records during 1995 Kobe earthquake are studied to show the feasibility of damage control. The distribution of damage in three span continuous bridges is found to be predicted with precise evaluatoin of damage in bearing. Localization of response is also observed in base-isolated bridges. These evidence show the possible application of damage control. Three dimensional finite element analysis is also conducted for sontinuous span bridges to compare the performance of several damage control design. Although practical aspects, such as construction details needs to be considered before its application, this research work shows that the proposed design concept is promising alternative to improve seismic performance of elevated highway bridges.