SEISMIC BEHAVIOR OF A CABLE-STAYED BRIDGE TO NEAR-FAULT VERTICAL GROUND MOTIONS

Pulse characteristics of near-fault vertical seismic ground motions were introduced, and V/H acceleration spectral ratio at C site in 1999 Chi-Chi earthquake, Taiwan, was statistically analyzed. Vertical acceleration response spectra were produced based on recommended spectra of a guideline and calculated from statistical V/H spectral ratio. Vertical acceleration spectrum analyses were performed on a built large-span cable-stayed bridge. Vertical and three-dimensional time-history analyses were carried out, imposing near-fault pulse-type, non pulse-type and common ground motions, and artificial seismic motions. The analytical results show that remarkable V/H ratio exist in short and medium-to-long period range at least on C site in near-fault regions. Near-fault vertical seismic motions will impose enormous influence on vertical displacement and moment of main beam, tensile stress of long cables for the cable-stayed bridge. It is negligible influence of vertical seismic motions on horizontal seismic responses, but it is important influence of horizontal motions on vertical seismic responses with prominent increase.