Structural failures in recent earthquakes and hurricanes have exposed the weakness of current design procedures and shown the need for new concepts and methodologies for building performance evaluation and design. A central issue is proper consideration and treatment of the large uncertainty in the loadings and the complex building behavior in the nonlinear range in the evaluation and design process. A reliability-based framework for design is proposed for this purpose. Performance check of the structures is emphasized at two levels corresponding to incipient damage and incipient collapse. Minimum lifecycle cost criteria are proposed to arrive at optimal target reliability for performance-based design under multiple natural hazards. The issue of the structural redundancy under stochastic loads is also addressed. Effects of structural configuration, ductility capacity, 3-D motions, and uncertainty in demand versus capacity are investigated. A uniform-risk redundancy factor is proposed to ensure uniform reliability for structural systems of different degree of redundancy. The inconsistency of the reliability/redundancy factor in current codes is pointed out.
