STUDY ON SURVIVAL STRENGTH OF WOOD SCREWED JOINT AFTER TERMITE ATTACK

 It is important to evaluate that the existing strength of wooden construction has maintained enough strength performance experiencing a long time for using long term safely. Therefore, it is necessary to understand the survival strength of structural members and joints damaged by biodeterioration in the wooden houses and building. But there is very limited database covering the survival strength of damaged materials in relation to the measurements from diagnostic tools. Many wooden constructions have been damaged by subterranean termites. The aim of this study was to investigate the relationship between the survival strength of single shear of a wood screwed joint damaged by termites and biodeterioration measurements made from the diagnostic tools. In addition, it was proposed the estimating method of a survival strength of wood screwed joint using the penetration depth that is a biodeterioration measurement value.<br> In this study, a test specimen made of Todomatsu (Abies Sachalinensis) and Norway spruce (Picea abies). The wood screw is 45 mm in total length, 40 mm in screw length, and 5.4 mm in outside diameter. The steel plate is 3.2 mm in thickness and has a hole of 6.0 mm in diameter. The damaged specimens were carried out in pine forest close to the sea in Kagoshima and Wakayama. The diagnostic tools were used from measuring the penetration depth is called Pilodyn® and the ultrasonic propagation velocity is called Dr.Wood. The both of measurement positions are closed to the joint part.<br> As a result, the specimens shows the four failure modes, which included the fracture of wood screw head, embedded failure of wood, splitting failure of wood, and shear failure of wood. The yield strength was decreasing accordance with the increase in the penetration depth or decrease in the ultrasonic propagation velocity. It was found that there was a good correlation between the survival strength and the penetration depth.<br> The survival strength was estimated by a small damaged part and a damaged part using the penetration depth. The estimated strength was calculated by the EYT and the improved EYT for CLT by Uible. The damaged part was separated by subtracting the penetration depth measured from the sound penetration. The damaged part was assumed to be the strength was lose, and the small damaged part was assumed to have the same strength as the sound part. As a result of estimating, the estimated values indicate the good correlation with the experimental values. In addition, it was estimated by the material strength exchanged to AIJ standard from the experimental value in the same way for using generally. As a result, it was shown the good correlation between the experimental strength and the estimated value by using the boundary value obtained in the experimental values.