Improving strength and reliability assessment methods considering a specified service life

In the current Russian framework for limit state design, partial safety factors are commonly calibrated for a reference service life (typically 50 years) and a conventional set of uncertainties. Modern practice increasingly involves temporary, modular and transformable facilities, as well as service-life extension of existing structures, where a consistent adjustment of target reliability and local safety factors to a specified service life is required. This paper reviews contemporary probabilistic concepts used in structural reliability and code calibration (Eurocodes, JCSS, ISO 2394 and service-life design). Based on R&D results obtained at NRU MGSU, an engineering procedure is proposed to map a reference reliability level to a target service life T by (i) converting the accepted total failure risk over the reference period into an equivalent annual target reliability index and (ii) adjusting local partial factors for actions and resistances using sensitivity factors from FORM under a lognormal representation of basic variables. The approach indicates that for variable climatic actions (snow, wind) the design partial factor γf may be reduced by approximately 10–20% for T≈10–15 years while keeping the accepted total risk over the service life constant; for permanent actions and resistance factors γm, the correction is usually minor. A step-by-step algorithm and an illustrative calculation example are provided.

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