Reliability analysis of the improved four-level assessment standardization for bearing capacity of timber components

Abstract

In practical timber engineering, various problems widely exist in the current reliability assessment for the bearing capacity of components. Improving the current assessment standards of timber components has important guiding significance for their design and repairing optimization. Considering the long-term load effect and the latest code GB50005-2017 of timber structures with a new resistance coefficient, a superior limit state function (LSF) of timber components with bearing capacity was established. Using this realistic LSF, the reliability index values β were discussed and analyzed by two versions of Chinese codes (GB50068-2001 and GB50068-2018) with different load partial coefficients γL and three design reference periods (DRPs) with different statistical parameters. Furthermore, the four-level reliability assessment standardization with bearing capacity was improved based on superior LSF, different load partial coefficients and three DRPs. The results showed that the load partial coefficients γL and DRPs significantly impact the reliability index values β. By contrast, the impact load partial coefficients and DRPs on the limits of four-level assessment (k) is less significant than that on the reliability index values β. The practical four-level assessment standardization is improved based on the target reliability index [β] and superior level principles. The reasonableness and superiority of the four-level reliability assessment standardization were verified by calculating the 28 different load cases, 3 different DRPs and 26 kinds of ratios k of resistance to load effect. To meet the requirements of the minimum reliability index values β, this study suggests that the bearing capacity design values of R/γ0S are set to 1.0, 0.93, and 0.87 as the limits of au/bu, bu/cu, and cu/du for main timber components, while values of R/γ0S are set to 1.0, 0.87, and 0.82 as the limits for general timber components.