The investigation of the DOL (Duration of Load) effect to the timber structure in consideration of the influence of environmental conditions

本研究的目的是建立长期保证可靠性的木结构设计方法。在木结构构件中，当木材的物理局部损伤随着加载时间的增加而累积时，在相对温和的大气条件下，强度性能逐渐下降。DOL(持续期载荷)系数是这种影响的允许应力调整方法，但在日本，温度、湿度等环境因素的年变化随地区变化很大。因此，引入这种仅以物理外力为指标的结构抗力或变形指标可能会因区域环境的不同而产生差异，而成为未来木结构设计方法主流的极限状态设计法，将结构的荷载和抗力都按结构的预计使用年限作为随机变量来处理。为此，本研究从以下三个方面进行了研究：1.考虑环境条件的影响下木材结构的DOL效应的试验研究2.生物攻击对强度退化的影响预测3.建立极限状态设计方法所需的强度退化模拟模型。因此，提出了考虑概率的函数模型，可以较好地表达DOL和生物攻击对构件强度退化的趋势。虽然从收集到的数据判断环境因素的影响是不能忽视的，但认为需要进一步分析。

The purpose of this research is to establish the method of designing the timber structure where reliability is guaranteed over a long period of time. In the member of a timber structure, when physical partial damage of wood accumulates with the increase in load time also under comparatively mild atmosphere conditions, an on-the-strength performance falls gradually. DOL (Duration of Load) factor is the allowable stress adjusting method for such influence.However, in Japan, annual change of environmental factors, such as temperature and humidity, changes greatly with areas. Therefore, introduction of this system which made only physical external force the index may produce the difference by the environment of an area in the resistance or deformation of structure.Moreover, by the Limit State Designing method which becomes the mainstream of the future timber structure designing method, both load and resistance of structure are dealt with as a random variable according to the estimated usable period of a structure. However, the relation between time progress and on-the-strength reduction is not clear.Therefore, research on the following three items was done in this research.1.Experimental investigation of DOL effect to timber structure in consideration of influence of environmental conditions2.The influence prediction to strength degradation by biological attack3.Creation of simulation model of degradation of strength required for establishment of Limit State Designing Method Consequently, it was suggested that the function model in consideration of probability could express the tendency of the strength degradation of members by DOL and biological attack. The effect by the environmental factor is considered that the further analysis is required although judged as what the influence cannot disregard from the collected data.