Reliability Index for Structural Health Monitoring of Aging Bridges

This paper presents a reliability-based methodology for health monitoring of aging bridges. Initially, critical failure criteria are proposed depending on the type of bridge. Safety margins are then defined based on these criteria. It is assumed that quantities in the failure criteria are random variables that are normally distributed. Based on this assumption, elementary reliability indices and thereby elementary failure probabilities are estimated for each critical failure mode. Having found the elementary failure probability values, system failure probability of the bridge is calculated for the period under consideration. Finally, the system failure probability is used to obtain a system reliability index of the bridge. The system reliability index is a quantative way to express the condition of the bridge for the period under consideration. As a case study to illustrate the proposed reliability procedure, a wrought iron railway bridge was selected from the national railway bridge network of Sri Lanka. For this bridge, fatigue and corrosion were selected as the most critical forms of failure. Application of the proposed methodology showed that the present condition of bridge was satisfactory for current loading conditions. Predicting reliability, as opposed to damage, is a positive outlook approach to health monitoring that is useful for infrastructure management.