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

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)

Evaluation of bridge damage data from the 1994 Northridge, CA

Data on bridge damage from earthquake is becoming incresingly more available. Such data however, have not been systematically studies with the objective to evaluate damage charactistics and to correlate these to observed or estimated local ground motion. This paper presents the results from a project in which bridge damage data from the 1994 Northridge earthquake are studiesd. Structural characteristics that are highly correlated with the observed damage are identified. Bridge are grouped by these structural characteristics and empirical fragility curves are developed for these groups. Only about two percent of the bridges that were exposed to ground shaking experienced damage and only 6 of these bridges collapsed. The analyses od data on bridge damage showed that concrete structures designed/built with older design standards were more prone to damage under seismic loading. (AU)

Prioritization of bridges for seismic retrofitting

This report presents a prioritization method developed for seismic retrofitting of bridges. The method is used to identify bridges that are in most need of retrofitting and to rank order these bridges based on vulnerability and importance criteria. A detailed review and critique of the existing prioritization methodologies is included. The developed methodology is illustrated by an example application conducted for the Palo Alto, California area.(AU)