Seismic fragility analysis of a large-scale frame structure with local nonlinearities using an efficient reduced-order Newton-Raphson method

Finite-element dynamic time-history analysis based on stiffness variation is the main approach to analyzing the seismic fragility of a structure, but using it in practical large-scale engineering applications is computationally extensive. This study presents an efficient reduced-order Newton-Raphson method to improve the efficiency. It changes the original nonlinear iterative analysis of the whole system to that of a reduced-order sub-system where only the displacements associated with yielding elements are solved in each nonlinear iteration. A 48-storey frame structure is taken as an example to elaborate the simplified analysis in detail. Subsequently, a multi-stripe fragility analysis is demonstrated. The simulation results show that the reduced-order Newton-Raphson method is reliable, accurate, efficient, and very feasible for assessing the seismic risk associated with large engineered structures, especially those with local nonlinearities.