A Fundamental Study about the Design of Impact Fatigue Strength for Metal-fastener Joints of Wood-based Board Construction

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In this research, first, the fundamental response behavior of the acceleration pulse and strain developed by impact loading were investigated, and secondly the transition of the response behavior and the decrease process of joint stiffness with the repetition of impact loading were examined. For the experiment, some simplified models of typical joint (nail and wood screw) between various wood-based boards such as plywood, oriented strand board, particleboard, and medium density fiberboard or between wood-based boards and frame materials (wood) were prepared under various joint conditions.First, static bending test with AE (Acoustic emission) measurement was carried out for H-figured joint specimen of particleboard jointed with wood screw as a simple model of a typical wood-based board construction.As a result, itwas evident that the minute destruction progress in the joint, the decrease of joint stiffness and the distribution of stress in the beam were closely related each other. In im … More pact bending test, both the influences of joint stiffness on strain distribution over the beam and of the impact load level on the joint stiffness were elucidated. It was suggested that the amount of the strain in the joint point and the quarter point of the beam was available for the evaluation of the joint stiffness, as a result of analyzing the strain distribution (moment distribution) in the mechanical model of the beam elastically supported at both ends.Secondarily, the static and repetitive impact tests were carried out for the compression type shearing specimen, in which various wood-based boards were connected with nail to both sides of the main member (frame), as a simple model of nailed joint in shear wall. The following results were obtained ; it was evident that the optimum thickness of side member were existed, when the length of nail was constant as used in this experiment. The rate of increase in amount of slipping displacement tended to decrease largely, depending on the combination of the kind of side member and the magnitude of impact load, because of the densification of wood due to the irreversible compressive deformation of members around shank of nail. It was also confirmed that the fatigue process, such as loosening between both members and decreasing of stiffness of joints subjected to repetitive impact loading, depended to a great extent upon the kind and thickness of side member and the magnitude of impact load. Less