Role of cable dynamics in transverse seismic response of sea-crossing cable-stayed bridges

Stay cables in cable-stayed bridges are sensitive to vibrations caused by earthquake excitations. The present study investigates the cable nonlinear vibration under transverse near-fault ground motions, focusing on the resonant response and its effect on the main structure. Two sea-crossing cable-stayed bridges, one with an inverted-Y-shaped tower and the other with an H-shaped tower, are employed for comparison. Analytical results show that both 1:1 and, occasionally, 2:1 resonant forced vibration might be induced in stay cables, which significantly amplified the cable force variation. The cable performs as a "tuned mass damper" that in most cases reduces the seismic response of the tower while increases the vertical displacement of the deck. The reduction effect would be more significant for the H-shaped tower than the inverted-Y-shaped tower. Vertical ground motion input would amply the cable force variation significantly compared to the transverse earthquake input only, but the forced resonant vibration of the cables would not be significantly affected. Cautions should be taken in designing the anchor zone of the towers as its seismic response might be increased greatly with the participation of cable dynamics and vertical ground motions.