Evaluation of bridge damage data from the Loma Prieta and Northridge, California earthquakes

ABSTRACT

This report presents the significant findings from a study of damage to bridges during the 1989 Loma Prieta and the 1994 Northridge, C A earthquakes. In both earthquakes, less than five percent of the bridges that were exposed to ground shaking were damaged. AS experienced in the past earthquakes, bridges with non-monolithic abutment types, discontinuous spans and single column bents performed poorly. High skew contributed to high damage levels. Data on bridge damage were compiled, reviewed and analyzed to correlate observed bridge damage to structural characteristics of bridge, ground motion levels and estimated repair cost. Damage states reported after the earthquakes were investigated and new damage state definitions for concrete bridges were proposed. bridges were grouped by their structural characteristics and correlation studies were perfomed to obtain ground motion-damage relationships and ground motion-repair cost ratio relationships. Logistic regression analysis was used to obtain empirical fragility curves. Currently available fragility curves and damage probability matrices were compared to observed damage data and the empirical relationships developed in this study (AU)