基于可靠度的木结构荷载持续作用效应

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

摘要:

木材在长期荷载作用下强度会逐渐降低，在工程设计中需考虑该效应的影响来确定木材强度设计值。为探究荷载持续作用对木材强度的影响，基于现行木结构设计标准规定的木结构极限状态设计及荷载的概率统计模型，采用JC法和Foschi-Yao累积损伤模型，针对我国恒荷载、楼面活荷载以及南京、哈尔滨、北京、上海和金华的雪荷载条件，对不同荷载工况、活荷载与恒荷载比率ρ及木材强度变异系数等对木结构荷载持续作用效应的影响进行研究，给出了不同工况下的荷载持续时间影响系数。结果显示，当荷载比率较小时，荷载持续时间影响系数K_DOL随ρ的增大而增大；荷载比率较大时，K_DOL不随ρ值变化；且材料强度变异系数对K_DOL的影响随着荷载比率的增大而减小。

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.