混凝土斜拉桥桥塔有限延性设计理论与方法研究

The lack of fundamental research of damge behavior and the damage process of cable stayed bridges under earthquake excitation,the bridge tower,as the major load-carrying capacity component of the bridge，is explicitly required to remain almost elastic even under the excitation of occasionally happened earthquake according to our current bridge seismic design codes. To achieve this seismic performance objective, usually the steel ratios of tower base and strut are required to be increased by a large margin in addition to its static loading demand, causing engineering inefficiency as well as a rising seismic demand for the substructure. Therefore, using limited ductility design for the concrete bridge tower is proposed in this project as a new seismic strategy for this circumstance. Considering the structural features of cable stayed bridges,three key issues including the nolinear seismic analysis and the ductlie demand with taking into account the hysteretic energy dissipation mechanism of tower and its ductile demand,the performance objective and ductility index and seismic efficency are going to be mainly investigated. Combined with the numerical analysis,the single tower model quasi-static test and full bridge model shake table test are going to be carried out to study the nonlinear damage behavior so as to establish the appropriate performance objectives and the ductile indexes of components with different ductile levels.The limited ductility design theory and its corresponding design method will then be developed and proposed to study the limited ductility capacity and its contributory factors.On the basis of the above research progresses, the overall seismic performance and efficiency of the cable stayed bridge by adopting the limited ductility design of tower will be investigated through a real typical mid-span concrete cable stayed bridge.

由于缺乏对斜拉桥在地震作用下的损伤和破坏过程的基础研究，我国目前的桥梁抗震设计规范要求在偶遇地震作用下，斜拉桥的桥塔也需基本保持弹性。为达到此性能目标，在工程实践中往往需要在满足静力需求的基础上大幅度提高塔底和横梁的配筋率，造成经济上的不合理，同时也增加了下部基础的抗震需求。因此，本项目提出了桥塔采用有限延性设计的抗震新策略。针对结构受力特点，重点围绕考虑斜拉桥桥塔滞回耗能的非线性地震反应与延性需求、性能目标与延性指标以及抗震效能三个主题开展研究。结合数值理论分析，进行中等跨度斜拉桥桥塔模型拟静力试验和全桥模型振动台试验，研究桥塔的非线性损伤过程，确立各构件合理的性能目标及其与各层次构件之间的损伤量化关系，进而建立混凝土桥塔有限延性抗震设计理论并提出相应的设计方法，研究其有限延性能力及其影响因素。在此基础上，结合典型中等跨度混凝土斜拉桥，评估桥塔经有限延性设计后混凝土斜拉桥的整体抗震效能。

由于缺乏对斜拉桥在地震作用下的损伤和破坏过程的基础研究，我国目前的桥梁抗震设计规范要求在偶遇地震作用下，斜拉桥的桥塔也需基本保持弹性。为达到此性能目标，在工程实践中往往需要在满足静力需求的基础上大幅度提高塔底和横梁的配筋率，造成经济上的不合理，同时也增加了下部基础的抗震需求。因此，本项目针对斜拉桥的结构受力特点，重点围绕考虑斜拉桥桥塔滞回耗能的非线性地震反应与延性需求、性能目标与延性指标以及抗震性能三个主题进行了研究。结合数值理论分析，进行了中等跨度斜拉桥桥塔模型拟静力试验和全桥模型振动台试验，研究桥塔的非线性损伤过程，确立各构件合理的性能目标及其与各层次构件之间的损伤量化关系，提出了中等跨度斜拉桥有限延性抗震设计的初步延性性能指标：以可修复性损伤状态作为H型混凝土桥塔的性能目标，其对应的材料层面的要求为纵向钢筋应变小于0.55倍极限拉应变，约束混凝土小于0.75倍极限压应变；结构层面的位移角限值为下横梁相对于地面的层间位移角不超过0.0163，上横梁相对于下横梁的层间位移角不超过0.0183。但值得一提的是，该性能指标的量值目前还不能直接应用到除原桥以外的实际工程，但本项目提出的思路和研究方法完全可以针对特定的斜拉桥进行计算分析，得到定量的性能指标。针对H型混凝土桥塔的斜拉桥，本项目结题后的研究工作将提供考虑不同轴压比和上、下横梁与塔柱相对高度位置变化的相对通用性能指标，通过后续的试验和理论研究不断的完善已提出的有限延性性能指标，最终建立的有限延性指标将对斜拉桥的抗震设计提供更为经济的设计方案。