Ultimate Seismic Behavior of Steel Bridge Pier Base-to-Footing Connections and Their Seismic Design

通过对桥墩基础模型进行循环加载试验，研究了桥墩基础与基础连接的滞回特性。在此基础上，提出了“半经验模型”和“简化复合模型”两种桥墩基础滞回模型。半经验模型由解析得到的骨架曲线和实验确定的滞回线组成。将这些滞回模型应用于钢桥墩的非线性动力分析。利用该模型进行的非线性动力分析能够较好地模拟神户地震中观测到的桥墩和锚杆的实际损伤形态，验证了所建立的滞回墩基础模型的有效性。采用半经验桥墩基础模型，分析研究了桥墩基础约束对强震作用下钢桥墩整体极限性能的影响。结果表明：强墩基约束增加了钢墩的损伤，周约束降低了墩的损伤，但增加了锚栓的损伤。似乎存在使最大响应位移和残余位移最小化的最佳桥墩基础约束大小。从设计目的出发，讨论了桥墩基础的破坏不超过钢墩破坏的必要桥墩基础弯矩承载力。此外，我们还研究了基于纽马克能量守恒原理的静态分析作为非线性动态分析的替代方法的适用性。

The hysteretic behavior of pier base-to-footing connections is examined by carrying out cyclic loading tests on pier base models. Based on this result, hysteretic models for pier base, referred to as "semi-empirical model" and "simplified composite model", are proposed. The semi-empirical model consists of an analytically obtained skeleton curve and experimentally determined hysteresis loops. These hysteretic models are implemented in nonlinear dynamic analysis for steel piers. The validity of the proposed hysteretic pier base models is confirmed by the fact that the nonlinear dynamic analysis with the pier base models can simulate the actual damage patterns of piers and anchor bolts observed in the Kobe earthquake. By using the semi-empirical pier base model, we analytically investigate the effect of pier base restraint on the overall ultimate behavior of steel bridge piers under severe earthquake motions. As a result, it is observed that the strong pier base restraint increases the damage to steel piers, whilst week restraint decreases the damage to piers but increases the damage to anchor bolts. There seems to be an optimum magnitude of pier base restraint that minimizes the maximum response displacements and residual displacements. For the design purpose, we discuss a necessary pier base moment capacity where the damage to pier base will no exceed the damage to steel pier. Furthermore, we examine the applicability of the static analysis based on the Newmark's energy conservation principle as an alternative to the nonlinear dynamic analysis.