INELASTIC RESPONSE OF THE CYPRESS VIADUCT TO THE LOMA-PRIETA EARTHQUAKE

The inelastic damage evaluation of a typical double-deck bent of the C ypress Viaduct which collapsed during the 1989 Loma Prieta earthquake is presented. A model of the bent consisting of spread plasticity-base d beam-column elements to represent the piers and deck, and shear pane l elements to represent the pedestal region was developed. To accurate ly determine beam and column moment-curvature relationships, separate computer analyses using an element fibre model were conducted. In addi tion, a smeared-crack approach finite element analysis was employed to determine the lateral load-deformation relationship of the pedestal r egions. The model of the Cypress Viaduct was subjected to the Oakland Outer Harbor Wharf ground acceleration record in the plane of the bent . The analytical model was calibrated using static lateral load tests, ambient and forced vibration tests, and observed performance. The res ults of time-history analyses, which include a prediction of member da mage, indicate that collapse was initiated by a shear failure of the p edestal regions.