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低周反复荷载试验，研究了桥墩基础-基础连接的滞回性能。在此基础上，提出了桥墩基础的滞回模型，即“半经验模型”和“简化组合模型”。半经验模型由一个分析得到的骨架曲线和实验确定的磁滞回线。将这些滞回模型应用于钢桥墩的非线性动力分析。采用该模型进行的非线性动力分析能够模拟科比地震中观测到的桥墩和锚栓的实际破坏形态，验证了所提出的滞回模型的有效性。采用半经验墩底模型，分析研究了强震作用下墩底约束对钢桥墩整体极限性能的影响。结果表明，墩底约束强时，钢桥墩的损伤增大;墩底约束弱时，钢桥墩的损伤减小，但锚栓的损伤增大。墩底约束似乎存在一个最佳值，使最大响应位移和残余位移最小。为了设计的目的，我们讨论了一个必要的桥墩基础的弯矩能力，桥墩基础的损坏不会超过钢桥墩的损坏。此外，我们检查的适用性的静态分析的基础上的Newmark的能量守恒原理作为替代的非线性动力分析。

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.