Multi-stage and multi-objective design optimization for improving resilience of base-isolated hospital buildings

The hospital is a critical infrastructure for treating the injured after the earthquake. The hospital is a complex system composed of structure, non-structural components, and medical equipment that are located on different floors, have different importance and seismic performance, and need different control objectives, enhancing any component could improve the hospital's functionality. It is imperative to economically and rationally choose enhancement measures to minimize initial functionality losses and improve hospital resilience. This study provides a hospital functional evaluation method that takes into account the physical dimension of the damage to the structure, non-structural components and medical equipment, as well as the organizational dimension of the treatment process of earthquake casualties. Bayesian networks and discrete event simulation methods are used to calculate the availability probability of medical rooms and the functional indicator of the number of earthquake casualties that can be treated. Then, a two-stage and multi-objective functionality improvement method was proposed to improve hospital functionality. The first stage is the design optimization of the isolation system with the objectives of minimizing the functionality loss and displacement of the isolation layer. The second stage optimizing the enhancement strategies for non-structural components and medical equipment aims at minimizing the functionality loss and enhancement budget. The proposed method uses a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) approach to optimize the design of the isolation system and the enhancement of non-structural components and medical equipment. The method is applied to a hypothetical hospital to highlight the proposed method's capability of improving the hospital's functionality.