Development of Fragility Curves and Assessment of Mass Irregular Structures with Fixed Base and Base Isolated Under Multiple Earthquakes

Structures are usually built to withstand the mainshock, aftershocks offer extra difficulties. Aftershocks frequently occur following an earthquake result in multiple earthquakes, therefore they are not isolated events. Due to damage advancement, and stiffness and strength deterioration, a damaged structure might collapse under a multiple earthquakes. Based to a probabilistic perspective, the current study investigates the effect of multiple earthquakes on the likelihood of buildings to collapse. This study’s primary objective is to determine how multiple earthquakes affect fixed- and base-isolated structures. In this context, recorded 14 single and 7 multiple earthquakes with various properties were used to examine and assess three-dimensional reinforced concreteframes with four-storey, having fixed base and isolated base. Dynamic analysis, of the three-dimensional structures are carried out in SAP2000. Fragility curves for fixed base and base isolated structures were produced using the incremental dynamic analysis approach. To find the effect of mass irregularity due to single and multiple earthquakes, mass irregularity is placed at every floor level in each structure. The results are compared in terms of floor displacements, floor accelerations, storey drift, base shear, residual displacement, and probability of collapse for fixed base and base isolated structures. The findings highlight the importance of analyzing the structures subjected to multiple earthquakes. The probability of collapse is reduced for mass irregular structures with base isolation in comparison with fixed base structures, when subjected to multiple earthquakes. The designer’s should select base isolation over the fixed base system when the building’s location may suffer multiple earthquakes more frequently.

建筑结构通常设计用以抵御主震，而余震则会带来额外的工程挑战。余震常伴随主震发生，形成多震序列，因此并非孤立的地震事件。由于损伤累积以及刚度与强度劣化，受损结构在多震序列作用下可能发生倒塌。本研究从概率视角出发，探究多震序列对建筑倒塌概率的影响。本研究的核心目标是明确多震序列对固定基底（fixed base）与基底隔震（base-isolated）结构的作用效应。在此研究背景下，本研究选取14条单条地震动记录与7条多震序列记录（涵盖多种地震动特性），对分别采用固定基底与基底隔震的四层三维钢筋混凝土框架进行分析与评估。采用SAP2000软件对上述三维结构开展动力时程分析。通过增量动力分析（Incremental Dynamic Analysis, IDA）方法，生成固定基底与基底隔震结构的易损性曲线。为探究单条地震动与多震序列作用下的质量不规则性影响，本研究在各结构的每层均设置了质量不规则工况。研究从楼层位移、楼层加速度、层间位移角、基底剪力、残余位移以及倒塌概率等维度，对固定基底与基底隔震结构的分析结果进行对比。研究结果凸显了对多震序列作用下结构进行分析的重要性。在多震序列作用下，带有质量不规则性的基底隔震结构的倒塌概率相较于固定基底结构有所降低。若建筑所在区域更频繁地遭遇多震序列，设计者应优先选用基底隔震系统而非固定基底系统。