RELIABILITY-ANALYSIS OF OPEN DRAINAGE CHANNELS UNDER MULTIPLE FAILUREMODES

Open drainage channel design involves variables that are uncertain. Be cause the performance of the channel system is also uncertain, reliabi lity analysis is used to measure the reliability of the system perform ance. In this paper, the reliability of open drainage channels under t hree possible failure modes is examined. The first failure mode occurs when the runoff exceeds channel capacity. The runoff and channel capa city are random variables that are estimated using the rational method and the Manning equation, respectively. The second failure mode occur s when the actual now velocity exceeds the maximum allowable velocity for erosion control. The third failure mode occurs when the actual flo w velocity is less than the minimum allowable velocity for deposition control. The minimum and maximum allowable velocities are considered r andom variables. The failure probability of each mode is estimated usi ng the advanced first-order second-moment (AFOSM) method. The overall failure probability of the system that accounts for the correlations b etween the failure modes is presented. The method was applied to an ex ample and was verified using Monte Carlo simulation. In practice, the method can be used to find the reliability of an existing channel unde r multiple failures, to evaluate the effects of alternative improvemen ts, and to design a new channel for a specified reliability level.