Benefit–Cost Evaluation of Seismic Risk Mitigation in Existing Non-ductile Concrete Buildings

Abstract

The risks of damage and collapse to older (non-ductile) reinforced concrete buildings and the cost-effectiveness of seismic retrofit are investigated through analyses of archetypical designs representative of construction in California prior to the introduction of more rigorous seismic design requirements in the mid-1970s. These risks for older buildings are compared to those in buildings that are designed to modern building code provisions that employ capacity design and ductile detailing requirements. The comparisons indicate that older non-ductile buildings have expected annual economic losses that are about twice those of the ductile buildings and risks of collapse and fatalities that are about 35 times higher. The cost effectiveness of seismic retrofit is examined to reduce damage and life safety risks. Considering the monetary benefits of both reduced damage and lives saved, these cost–benefit comparisons justify retrofit costs of up to about 20–40% of the building replacement value, implying that in most cases the retrofit of non-ductile concrete buildings would be cost-effective.