Reliability of redundant ductile structures with uncertain system failure criteria |
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Authors: | Baidurya Bhattacharya Qiang Lu Jinquan Zhong |
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Affiliation: | (1) Fraunhofer IZM, Volmerstrasse 9 B, 12489 Berlin, Germany |
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Abstract: | Current reliability based approaches to structural design are typically element based: they commonly include uncertainties
in the structural resistance, applied loads and geometric parameters, and in some cases in the idealized structural model.
Nevertheless, the true measure of safety is the structural systems reliability which must consider multiple failure paths,
load sharing and load redistribution after member failures, and is beyond the domain of element reliability analysis. Identification
of system failure is often subjective, and a crisp definition of system failure arises naturally only in a few idealized instances
equally important. We analyse the multi-girder steel highway bridge as a k out of n active parallel system. System failure is defined as gross inelastic deformation of the bridge deck; the subjectivity in
the failure criterion is accounted for by generalizing k as a random variable. Randomness in k arises from a non-unique relation between number of failed girders and maximum deflection and from randomness in the definition
of the failure deflection. We show how uncertain failure criteria and structural systems analyses can be decoupled. Randomness
in the transverse location of trucks is considered and elastic perfectly plastic material response is assumed. The role of
the system factor modifying the element-reliability based design equation to achieve a target system reliability is also demonstrated. |
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