Response of suspension bridges to travelling earthquake excitations: Part I. Vertical response

The vertical response of suspension bridges to travelling earthquake exciatations is investigated in the time and frequency domains. The ground motion inputs at one support are assumed to propagate, with different speeds, such that they hit the other supporting points of the structure with no change of shape (non-dispersive waves). The response of the Golden Gate Bridge of San Francisco, California, to these ground motion inputs is calculated in the time and frequency domains. Ground motion inputs are taken from the records of the 15 October 1979 Imperial Valley earthquake. Propagation of the earthquake wave train is simulated by taking one array record (array no. 5) as the input at the left anchorage of the bridge, and adding appropriate time delays to the other inputs. Several different cases are studied for various seismic wave speeds, and several reference cases such as uniform ground motion and different simultaneous inputs, etc. are included from comparison. Vibrational displacements, flexural stresses, and shear forces are calculated at critical sections of the bridge in the time domain and compared with the root mean square response values obtained from the frequency domain. Peak factors are calculated and compared with expected values from the random vibration analysis.