Life cycle cost‐based optimization framework for seismic design and target safety quantification of dual steel buildings with buckling‐restrained braces

Abstract

AbstractThis study proposes an efficient risk‐targeted framework for integrated optimal seismic design and quantifying target safety of Special Moment‐Resisting Frames (SMRFs) with Buckling‐Restrained Braces (BRBs) in the typical dual steel buildings. This framework provides an automated design procedure formulated as a constrained single‐objective optimization problem to achieve the minimum Life Cycle Cost (LCC) within the Particle Swarm Optimization (PSO) algorithm and can be the basis of current seismic codes for target safety calibration. LCC includes initial construction cost and lifetime seismic losses such as repair cost, repair time, and casualties. FEMA P‐58 methodology is employed for the LCC analysis of the building under possible earthquakes during its lifetime, which is able to take into account potential uncertainties in the hazard‐response‐damage‐loss relationship. An appropriate cost model is developed to estimate the initial and repair cost of the studied BRBs. Minimum requirements of ASCE and AISC codes are considered as design constraints. Nonlinear response history analysis through the Endurance Time (ET) method is utilized to estimate the structural responses versus seismic intensity. Three 4‐, 8‐, and 12‐story steel buildings with dual seismic force‐resisting system consisting of SMRF and BRB (called steel SMRF‐BRB) are selected as the case study. Each building is optimally designed with two approaches: (1) LCC‐based design within the proposed framework and (2) code‐based design to minimize initial construction cost. Comparison of optimized buildings with the two design approaches in terms of structural responses and seismic consequences demonstrates that fulfilling the minimum code requirements at a given seismic hazard level is not sufficient to minimize lifetime seismic losses of steel SMRF‐BRBs. This is because the optimal designs obtained from the code‐based approach are associated with damage concentration, irreparability, and high collapse probability, especially in seismic events more severe than the design level. The proposed LCC‐based approach provides useful information for improving the lifetime seismic performance of steel SMRF‐BRBs.