Seismic Resistance of Existing Buildings

A particular opportunity to upgrade the seismic resistance of existing buildings arises when their lifetime is extended by major renovations. There is lacking, however, a set of guidelines that relates the cost of strengthening a structure to the probable reduction in earthquake-induced damage and life loss. This paper offers a recommendation for strengthening buildings undergoing renovations in zones where intensity of expected seismic shaking is low. Two buildings, one a masonry bearing wall and heavy timber floor warehouse and the other a reinforced concrete flat slab factory, are studied to determine the existence of weak links in seismic resistance and the cost of upgrading such resistance during major renovations. The expected damage from three levels of earthquake for the two buildings is summarized in damage probability matrices; these matrices are then used to compute mean damage ratios (MDR). Each MDR is shown as a function of strengthening cost, providing a means for estimating the reduction in seismic risk of these buildings from their present condition when they are either strengthened to a recommended practical level or replaced with new construction.