匝道桥固结墩地震受力状态及抗震加固力学行为研究

The irregularity of the ramp bridges, such as the structural curvature and different pier stiffness, is highly strong, which is obviously different from other types of bridges. In the earthquake the complex loading states of pressure, bending, shear and torsion in the consolidated piers of ramp bridges are induced.It has been found that the consolidated piers severely destroyed in past earthquakes, and there is urgent need for seismic evaluation and strengthening of the consolidated piers in existing ramp bridges. However, at present there are very few studies on this issue. In this project the research approaches of field tests, model tests, nonlinear finite element analysis and theoretical analysis are adopted, and the model updating technology of the response surface method is used to improve the precision of finite element analysis. First, the seismic response characteristics of ramp bridge structures, as well as the earthquake loading states of consolidated piers and the calculation methods, will be studied based on plenty of three-dimensional nonlinear seismic time history analysis. Additionally the seismic strengthening performance of the ramp bridge consolidated piers and the mechanical behaviors of FRP will be analyzed through the hysteretic behaviors of the consolidated piers strengthened with FRP under complex stress states of pressure, bending, shear and torsion. Then the theoretical calculation models of restoring force and FRP force will be established. At last it is expcted to establish the fundamental theory of seismic response and seismic strengthening of the ramp bridge consolidated piers.

匝道桥多为曲线结构，桥墩刚度差别大，为极不规则桥梁结构体系，与其它类型的桥梁有明显不同，地震中匝道桥固结墩受到压、弯、剪、扭荷载的复合作用，容易发生严重的震损破坏，急需对在役匝道桥固结墩进行抗震评价与加固。鉴于相关研究的不足，本项目拟采用实桥现场测试、室内模型试验、非线性有限元分析和理论分析相结合的技术路线展开系统的研究工作，并采用基于响应面的模型修正技术提高有限元计算的精度。首先基于大量的非线性地震响应时程分析研究三维地震作用下匝道桥结构的地震响应特性，分析固结墩的地震受力状态并建立理论计算方法。进而通过压、弯、剪、扭复杂受力状态下FRP加固固结墩的滞回行为，研究匝道桥固结墩的抗震加固性能，建立恢复力理论模型，并分析复杂受力状态下加固桥墩中FRP的力学行为及受力计算模型，最终以期建立匝道桥固结墩地震响应和抗震加固的基础理论。

混凝土固结墩是一种与上部梁体固结在一起的桥墩，在非规则桥梁中有大量的应用，特别是在匝道桥中应用广泛。由于桥梁曲线不规则和桥墩刚度不规则的影响固结墩在地震作用下受力复杂，容易发生严重的震损破坏。本研究分析了地震作用下不规则匝道桥结构的地震响应规律，确定了固结墩压、弯、剪、扭耦合的地震受力状态，研究了复杂受力状态下固结墩的破坏模式、滞回曲线、骨架曲线、刚度退化曲线、延性性能、耗能曲线等，分析了扭弯比、长细比、纵筋配筋率和箍筋配筋率等参量对桥墩弯扭耦合抗震性能的影响，并给出了考虑弯扭耦合的四线式剪力-位移骨架曲线和三线式扭矩-扭转角骨架曲线的理论模型，确定了复杂受力状态下混凝土桥墩的抗震力学行为。.结果表明随着桥梁曲率和桥墩刚度比的增加，固结墩弯扭耦合效应增大，会造成混凝土桥墩的抗震性能发生明显的变化。根据扭弯比的不同桥墩会发生弯曲为主或者扭转为主的破坏模式，较大的扭转效应会使桥墩在达到最大抗弯性能前发生扭转破坏，而弯曲效应会大幅降低桥墩的抗扭承载力。塑性铰长度随着扭转效应的增加而增大，约为0.8d-1.1d。扭弯比增大，最大剪力和最大侧向变形降低，抗弯承载力未充分发挥而抗扭承载力和极限扭转角大幅增大，抗弯刚度和抗弯耗能降低，抗扭刚度和抗扭耗能增加。随着长细比的减小，抗弯承载力、抗弯刚度和抗弯耗能增加，侧向变形和延性性能降低，而对桥墩抗扭能力影响不大。随着纵筋率提高，抗弯承载力、抗弯刚度和抗弯耗能增加，对弯曲极限变形和抗扭能力影响不明显。随着配箍率的增加，桥墩抗扭承载力和抗扭刚度增加，但对桥墩抗弯性能影响较小。理论骨架曲线模型揭示了钢筋混凝土桥墩弯曲和扭转的关键影响因素及耦合效应，其中剪力-位移理论骨架曲线主要取决于混凝土桥墩破坏截面的弯矩-曲率关系，扭转承载力主要来自于混凝土和箍筋两个部分，其中混凝土部分受到弯曲效应的明显影响，墩顶扭转角可以根据桥墩的弹性扭转角和扭转塑性铰的扭转角叠加计算。工程中应采用考虑弯扭耦合的方法进行抗震设计。.本项目的工作具有基础性和原创性，研究成果可指导匝道桥固结墩的抗震设计、评价及加固维修，可为相关设计规范的制定提供理论依据和实验数据，并可推动复杂桥梁结构地震动力学理论的发展，具有重要的科学意义。