Codified robust optimal design base shear of structures: Methodology and application to reinforced concrete buildings

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This paper proposes a methodology for codifying the robust optimal design base shear of buildings that minimizes the lifecycle cost (LCC) and its uncertainty. This methodology, while preserving the current format of the base shear equation in seismic codes, calibrates its factors, i.e., the response modification factor, the site class factor, and the importance factor, by minimizing the expected LCC and its variance through a bilevel optimization. Hence, it results in a design that not only is optimal based on the expected cost theory, but also is robust, making large realizations of seismic losses significantly less likely. To showcase the application of the methodology, the optimal design base shear coefficient, optimal response modification factor, optimal site class factor, and optimal importance factor are determined for four- and eight-story buildings of different importance levels on various site classes at 5706 sites across 14 countries in Western Asia. The resulting design base shears are then compared to those obtained from ASCE 7–16 provisions, which are widely adopted by the codes of the considered region. The design base shears resulting from the proposed approach for ordinary buildings are on average twice those obtained through ASCE 7–16 provisions across various combinations of building heights and site classes for the considered region. As such, the proposed approach yields an average reduction of 18% and up to 56% in expected seismic losses while also reducing the expected LCC by 1.9% and 11.6% and its variance by 38% and 55% for different importance levels. The substantial reductions achieved by the proposed approach suggest that the likelihood of incurring high lifecycle costs and catastrophic losses is significantly reduced.