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

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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.