On optimal lead rubber base-isolation design for steel moment frames using value-based seismic design approach

This paper employs the framework of value-based seismic design to optimize the geometrical and mechanical properties of lead rubber bearings (LRBs). An optimization problem is proposed within this framework. Con-struction cost and seismic consequences are chosen as the value components. Most failure modes of the LRB, such as strength deterioration, axial buckling, and rubber rupture, have been carefully considered in the seismic response. Besides, a new cost function for LRBs is developed from actual isolated building projects. Moreover, the minimum code requirements for lead rubber isolated buildings are formulated as the design constraints. FEMA P-58 methodology is exploited to predict the seismic consequences, including the repair cost, repair time, injury, and fatality. Endurance time method is used to evaluate the structural seismic responses. A set of three lead rubber isolated buildings are selected for investigation, representing low-to mid-rise moment-resisting frames (MRFs). Each building is optimally designed by two scenarios: the code-based design (CBD) by minimizing the initial construction cost and the value-based design (VBD) by maximizing the total building value. It is observed that the total building values of the isolated MRFs optimized with the CBD approach are somewhat acceptable. However, they can be significantly increased with the VBD approach because it adequately reduces the proba-bility of axial buckling and rupture of LRBs.