Torsional Earthquake Response of Suspension Bridges

The earthquake‐induced torsional response of suspension bridges when subjected to multiple support excitations is analyzed in the frequency domain by means of random vibration theory. Appropriate rocking and torsional ground motion inputs are defined from finite Fourier transforms of recorded translational motions by using a simplified approach based upon wave propagation theory. An example is presented in which the torsional response of the Golden Gate Bridge to earthquake ground motions (the 1979 Imperial Valley earthquake) with characteristics significantly different at each support point is investigated. It is observed that the participation of higher modes in the total response is essential to assess the torsional seismic behavior of such structures. It is also observed that both the vibrational displacement and vibrational cable tension induced by torsional vibration are very small but the flexural stresses induced by the torsional vibration are relatively large as live loads.