Probabilistic Assessment and Cost-Benefit Analysis of Nonductile Reinforced Concrete Buildings Retrofitted with Base Isolation: Considering Mainshock–Aftershock Hazards

Abstract

Nonductile reinforced concrete (RC) frame buildings were found to be vulnerable to earthquakes. Thus retrofitting of these buildings is necessary, as addressed in the recent retrofit program of Los Angeles. A potential retrofit strategy is base isolation, which has many advantages but is not yet routinely used in the United States because of its high cost. To determine whether base isolation is economical when the advantages and costs are compared, seismic performance assessment and cost-benefit analysis are performed on two nonductile RC frame buildings before and after being numerically retrofitted with base isolation, which makes consideration of uncertainties. Location of the buildings is assumed to be Los Angeles, CA. Aftershock ground motions are generated to examine the influence of aftershock hazard. Direct loss, downtime, fatalities, and total loss for each of the buildings are investigated. Results suggest that base isolation can reduce the seismic loss, downtime, and fatalities effectively. Besides, the benefits can outweigh the retrofit costs. The effect on the results caused by indirect losses from downtime and fatalities is quantified and shown to be substantial. Aftershock hazard is also found to be at a relatively significant level.