SEISMIC ANALYSIS OF SKEWED HIGHWAY BRIDGES WITH INTERMEDIATE SUPPORTS.

DUE TO THE DAMAGE SUFFERED BY MANY SKEWED HIGHWAY BRIDGES DURING THE SAN FERNANDO EARTHQUAKE, 1971, A STUDY IS MADE ON THE DYNAMIC RESPONSE OF THIS TYPE OF BRIDGE.USING A BEAM MODEL CAPABLE OF FLEXURAL AND TORSIONAL DEFORMATION, THE MODE SHAPES AND FREQUENCY EQUATIONS ARE PRESENTED.DUE TO THE SKEWNESS OF THE INTERMEDIATE SUPPORTS, COUPLED FLEXURAL AND TORSIONAL VIBRATIONS ARE SHOWN TO BE EXCITED BY THE VERTICAL COMPONENT OF GROUND MOTION.AN ANALYSIS IS CARRIED OUT FOR THE FOOTHILL BOULEVARD UNDERCROSSING, S.E.BRIDGE IN THE SAN FERNANDO VALLEY, CALIFORNIA WHICH SUFFERED DAMAGE TO THE INTERMEDIATE SUPPORTS.THE RESULTS OF THE ANALYSIS CORRELATE WELL WITH THE OBSERVED DAMAGE PATTERN OF THE BRIDGE.(A)