Reliability Based Investigation into the Duration of Load Effect for Timber Structure

Abstract:

The strength of wood will gradually decrease at a long-term sustained load. The obvious duration of load (DOL) effect is one of the characteristics that distinguish wood and wood products from other building materials, and such a DOL effect must be properly considered in the design of timber structures. Based on the limit state design and the probabilistic statistical model of wood structure according to the current Chinese timber design code, an exploratory research was conducted in this paper to determine the DOL effect of timber structures at different load combinations including dead load, floor live load, and snow load in five Chinese cities (i.e., Nanjing, Harbin, Beijing, Shanghai, and Jinhua), using the JC method and the Foschi-Yao damage accumulation model. The different ratios of the nominal live load to the nominal dead load ρ, and the different coefficients of variation of wood strength were also considered in the reliability analysis. The value of the DOL coefficient K_DOL in different load combinations was calibrated. The results show that when the load ratio ρ is small, the DOL coefficient K_DOL increases with the increase in ρ.Besides, when the load ratio is large, K_DOL does not change with the value of ρ. Moreover, the coefficient of variation of wood strength has less influence on the DOL coefficient K_DOLwith the increase in load ratio ρ.