Seismic design of bridges in some respects is more complex than other structures especially due to, in some cases, the a priori unknown shape of the displacement profile of the structure. Bridges of irregular nature and of a certain length can have transversal horizontal displacement profiles (THDP) of the deck that are very dependent on higher frequency modes. Furthermore, the THDP might change significantly during the earthquake action, due to loss of stiffness of some elements rather than others. This makes most nonlinear static pushover methods inaccurate and introduces difficulties in the seismic design of these structures. In this study, several RC bridges which vary in length and irregularity, are analysed with nonlinear dynamic analysis and optimized via genetic algorithms with performance and cost as objectives in the longitudinal and transversal directions separately. The optimized solutions are analysed in terms of their effective stiffness and compared with each other. The results show correlation between the displacement of the stiffer piers and the overall effective stiffness of the structure. This correlation is closely linked to other parameters such as the relative stiffness index. The results and the parameters allow to identify cases in which the bridges develop “long bridge behaviour” in the THDP of the bridge, and also in which situations the longitudinal and transversal peak displacement of critical piers are similar, which is useful knowledge to optimize seismic design in terms of cost and performance. Practical recommendations for the optimization of the seismic design of irregular bridges are offered.

桥梁的抗震设计在某些方面比其他结构更复杂，尤其是在某些情况下，由于结构位移剖面的先验未知形状。不规则性质和一定长度的桥梁可能具有非常依赖于较高频率模式的桥面板的横向水平位移剖面 (THDP)。此外，由于某些单元的刚度损失而不是其他单元的刚度损失，THDP 在地震作用期间可能会发生显着变化。这使得大多数非线性静力推覆方法不准确，并给这些结构的抗震设计带来困难。在这项研究中，几个长度和不规则性不同的钢筋混凝土桥梁，在纵向和横向分别以性能和成本为目标，通过非线性动力学分析和遗传算法进行优化。优化的解决方案根据其有效刚度进行分析并相互比较。结果表明，较硬的桥墩的位移与结构的整体有效刚度之间存在相关性。这种相关性与其他参数（例如相对刚度指数）密切相关。结果和参数允许识别桥梁在桥梁的 THDP 中发展“长桥行为”的情况，以及在关键墩的纵向和横向峰值位移相似的情况下，这是优化地震的有用知识成本和性能方面的设计。