Reliability Analysis of Fan Type Cable Stayed Bridges Against First Passage Failure under Earthquake Forces
R.A. Khan, T.K. Datta, and S. Ahmad
A reliability analysis of fan type cable stayed bridges against first passage failure under earthquake orces is performed using the method of crossing analysis and the basic theory of reliability. Failure of the bridge deck being the point of interest, the bridge is modeled as a beam supported on springs at different points. The stiffnesses of the springs are determined by a separate 2D static analysis of cable-tower-deck system. The analysis provides a coupled stiffness matrix for the spring system. Using a frequency domain spectral analysis, the power spectral density functions of bending moments at different points of the deck are obtained. Using the first few moments of the power spectral density function, the crossing analysis is carried out to obtain the conditional probability of first passage failure of the bridge deck for a given earthquake ground motion intensity (expressed as r.m.s. ground motion and related to the magnitude of earthquake by an empirical relationship). Probability of occurrence of different magnitudes of earthquake is then combined with the conditional probability of failure to obtain the reliability of the bridge deck against first passage failure. A three span double plane symmetrical fan type cable stayed bridge of total span 689.0 m, is used as an illustrative example. The reliability against first passage failure of the bridge deck is obtained under a number of parametric variations.