Target reliability, a general framework for code making for new and existing structures
R.D.J.M. Steenbergen1, 2, Á. Rózsás1, A.C.W.M. Vrouwenvelder1
1 TNO, Structural Reliability, Delft, the Netherlands
2 Ghent University, Faculty of Engineering and Architecture, Department of Structural Engineering, Belgium
Target reliability levels, design and remaining working lives and reference periods recommended in various national and international codes and guidelines are sometimes inconsistent. Design working lives for new structures are typically 50 to 100 years for different types of structures. For existing structures the remaining working life is often smaller than 50 years. Recommended target reliability indexes are usually given for one or two reference periods (one year and 50 years), without an explicit link to the design working life. In this paper a general framework is given in order to make the reliability index independent of the design working life and to provide guidance for specification of the target reliability level for different situations. The study is based on probabilistic economic optimization. Using this methodology, annual targets – in terms of failure rates – can be set for new structures, and (deteriorating) existing structures, given the marginal cost for reliability, failure consequences and the uncertainty in loading and resistance.
Key words: Target reliability, optimization, standardization, safety format, structural reliability, codes