Unified reliability and design optimization for earthquake engineering

In this paper, a methodology is put forward that builds upon the emerging focus on structural damage in earthquake engineering. A versatile “unified” limit-state formulation is employed to complement the traditional focus on collapse limit-states. The methodology underscores the advantages of formulating explicit probabilistic models for all predictions; including ground motion, structural response, damage, and ensuing losses. Next, by formulating limit-state functions in terms of total cost, including construction and damage costs, a novel reliability-based design optimization procedure is offered. Notably, the design optimization is carried out in the tail of the total cost distribution. Consequently, the unlikely but potentially devastating losses are explicitly addressed. This is significant for many real decision makers. This also addresses the criticism of the traditional design optimization that it focuses solely on expected (mean) cost. The proposed approach is shown to be akin to a risk averse decision strategy. Numerical examples including a six-storey structure with random structural properties and random ground motion are presented to illustrate the methodology.