Time variant component and system reliability analysis of bridges

Ghasemnejad Berenji, Vahid
This study aims to develop a time variant reliability algorithm for a bridge component or system capable of incorporating multiple deterioration and live load models to be selected by the user. The algorithm is developed as a shell program built over a previously developed core program (RELSYS) which is based on the First Order Reliability Method (FORM). After reviewing previous research performed on both time invariant and time variant bridge reliability, the fundamental concepts of time variant reliability such as time to failure and failure rate are discussed and formulated. Furthermore, Load and capacity formulations start with the most simple deterministic load and deterministic capacity cases. As a first step toward time variant reliability study, load and capacity reliability problems are solved using the computer program RELSYS. Reliability problems including limit state functions containing normal and non-normal random variables as well as correlation cases are studied for both component and system analyses. Within this context, parallel, series and series-parallel systems are evaluated. Prior to developing a time-variant reliability algorithm, different time variant reliability approaches are reviewed and separately formulated. These formulations included: repetitive loading and three periods of failure, the bathtub curve, stochastic load model containing two independent Poisson processes and random strength degradation function, and the load and capacity formulation. Finally, a computer algorithm in the form of a shell script is developed for time variant reliability analysis, based on five different deterioration models, two separate live load models including Nowak’s and Sivakumar’s models, and the RELSYS as the core program. Deterioration models or resistance degradation functions include corrosion, diffusion control, traffic spray, sulfate attack and load carrying models. Effects of these models on time variant reliability problem are observed. The developed computer program has the capability to read input data for both time variant or time invariant problems. Moreover, it provides the user with different options of defining deterioration and live load models for the problem at hand for a given time horizon along with the option of defining specific input data. This study showed that, because of highly uncertain nature of time-variant reliability, the selection of a degradation model and a live load model to be used for a given analysis may have an important effect on time variant reliability computation. Furthermore, implementation and testing of available or newly developed deterioration and load models into time-variant bridge reliability programs is an area that requires further study.
Citation Formats
V. Ghasemnejad Berenji, “Time variant component and system reliability analysis of bridges,” M.S. - Master of Science, Middle East Technical University, 2015.