A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1988

The stochastic response and reliability of the cable system of a cable-stayed bridge under earthquake loading is studied. A linear-elastic dynamic analysis has been carried out by modelling the bridge as a two-dimensional frame system. As a case study, the Karnali cable-stayed bridge in western Nepal is investigated. From the historical earthquake data of Nepal, the statistics of earthquake magnitude and epicentral distance are estimated for the region of the bridge site. The power spectra of stress in the stay cables are computed using the Kanai-Tajimi model for the earthquake process. The standard deviation and the relevant moments of the response power spectrum are calculated numerically and the probability of first-passage of stress across a specified barrier is computed. Based on the conditional probability of barrier crossing for given values of magnitude and epicentral distance and the corresponding probability distributions, the probability of exceeding a barrier during one event is found. Assuming that the average number of earthquakes per year in the magnitude range of interest in the source zone is constant, the first-passage probability for any desired period of earthquake exposure can be determined. Finally, the probability of failure of one cable or a group of cables simultaneously is computed from the probabilities of first-passage failure of individual cables. The fatigue damage to the cables due to seismic action has also been investigated. In addition, the problem of cable vibrations is studied.