Integrated Reliability-Based Seismic Drift Design Optimization of Base-Isolated Concrete Buildings

This paper presents an effective numerical reliability-based optimization technique for the design of base-isolated concrete building structures under spectrum loading. Attempts have been made to automate the integrated spectrum analysis, reliability analysis, and design optimization procedure and to minimize the total cost of the base-isolated building subjected to multiple design performance criteria in terms of the story drift of the superstructure and lateral displacement of the isolation system or corresponding reliability constraints. In the optimal design formulation, the cost of the superstructure can be expressed in terms of concrete member sizes while assuming all these members to be linear elastic under a specified design earthquake. However, the base isolation is assumed to behave nonlinearly and its cost can be related to the effective horizontal stiffness of each isolator. Based on the principle of virtual work, the drift responses and corresponding reliability indexes can be explicitly formulated and the integrated optimization problem can be solved by an optimality criteria method. The technique is capable of achieving the optimal balance between the costs of the superstructure and isolation systems while the seismic drift performance or corresponding reliability of a building can be simultaneously considered. An illustrative example shows that conventional deterministic design optimization cannot ensure designs with satisfactory reliability levels, whereas the reliability-based design optimization can achieve the objective when uncertainties are considered. It is believed that such an optimization technique provides an effective tool for seismic design of building structures.