Basis for Cost-Effective Decisions on Upgrading Existing Structures for Earthquake Protection

Abstract

This chapter proposes a systematic approach for formulating cost-effective decisions on the specification of appropriate levels of upgrading existing structures for earthquake protection. This involves the determination of the acceptable risks (or target reliabilities) for damage control and life safety. The approach is illustrated for rehabilitating/strengthening a specific reinforced concrete building in Mexico City that was damaged during the 1985 earthquake. A key decision in the upgrading of existing structures or rehabilitating damaged structures through strengthening or retrofitting for protection against future earthquakes is the specification of an appropriate level of upgrading, which may require a tradeoff between the cost of upgrading and the desired level of protection against potential future losses caused by earthquakes. This approach is based on the minimization of the life-cycle cost as a function of structural reliability against earthquake damage. The economics of upgrading existing structures for earthquake protection is of fundamental concern, which has not been integrated properly or explicitly with the technical issues in the development of criteria for upgrading of structures. This chapter examines such issues and suggests specific models. The purpose of upgrading criteria is to insure adequate level of safety or performance of a structure. During unavoidable uncertainties in the prediction of loadings and in the estimation of structural capacities, structural safety or performance may be measured in terms of probability or risk. Decisions for upgrading existing structures for earthquake protection can be developed systematically by integrating all the important technical factors with the economics of earthquake hazard mitigation.