Mohammadkhani-Shali, Soheil (2007) Study of systeme redundancy in bridges : failure machanism analysis using response surface methods. PhD thesis, ENPC p.197.

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Abstract

In this thesis, a system redundancy analysis for reinforced concrete bridges has been presented. This analysis is performed in order to appraise the load redistribution effects based on a serviceability requirement of excessive deformation. In order to specify the effects of damage in both the bridge serviceability and the individual components serviceability, several damage scenarios have been considered. In order to consider uncertainties related to the various parameters, calculations are carried out through a probabilistic approach. Traditional techniques of the theory of reliability allow today to calculate in various manners, the failure probability of the specific failure modes associated to the individual components, subject to have a probabilistic characterization of the variables and an explicit limit state. Reality is however different. For complex structural systems, it is almost impossible to get explicit limit states. Limit state function can be evaluated only by calculations, in particular with finite element analysis are often called “finite element reliability methods (FERM)”. If traditional techniques of reliability remain costs of reasonable calculation for the study of a failure mode, they quickly become prohibitive in a complex structural systems analysis. So to reduce the number of evaluations of the limit state function to a reasonable level, an approach consists in constructing “artificially” the limit state function by using a polynomial adjusted with the results of small number calculations of finite element analysis. This function can then be used to evaluate the failure probability in traditional techniques of reliability. This kind of approach is named “Response Surfaces Method (RSM)”. The response surfaces method was programmed in MATLAB© and implemented in the “Reliabtbx” toolbox developed in LCPC, which combined with the finite element code CESAR-LCPC© or bar element code ST1-SETRA©, according to cases, for the realization of the numerical experiments. An original study on reliability of structural systems has been also realized by the response surfaces method. So, the redundancy analysis in bridges passes by adjusting a polynomial function describing its whole structural behaviour; it is why response surfaces methods have been used. It is also shown that redundancy is a measure of the performance and the system reserve ratio of the bridge between the loss of member serviceability and loss of serviceability of the overall system. That means redundancy can be used as both the bridge safety and the importance of the individual members to the performance of the bridge system in the damaged conditions for the serviceability limit state.

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