Degradation of shear resistance of nailed joints by wood decay was estimated experimentally. We conducted decay treatments of Todomatsu Abies Sachalinensis specimen for compressive and single-shear tests of nailed joints with Todomatsu main members, steel side plates and CN50 nails by brown-rot fungus Fomitopsis palustris , which is commonly observed in Japan. After the decay treatment, we measured the compressive strength parallel to the grain and the single shear resistance of nailed joints, and the depth of steel pin penetration burst into the wood. Test results showed that degradation of the maximum shear resistance of the nailed joints at an early stage of decay was not as rapid as the degradation analogized by compressive strength, which is often fitted with an exponential curve. Tearing of nail heads, which caused brittle joint failures, was typically observed in the tests of sound nailed joints in this study. The nails of decayed joints, however, were pulled from the wood members before being torn off at their heads. This difference in failure mode resulted in a gradual decrease of lateral loads beyond the maximum resistance without sudden drops of loads. The degradation of the maximum shear resistance of decayed nailed joints was compared with the estimated resistance by the European Yield Theory EYT based on the bearing strengths of the wood members derived empirically from the depth of steel pin penetrations, which showed the ultimate shear resistance of decayed nailed joints could be estimated from onsite measurement of the depth of steel pin penetration.

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Cross laminated timber (CLT) are composed of longitudinal layers and cross layers. And as the laminations of the adjoin layers are glued orthogonally deterioration of the laminations such as check and shake and delamination can be rather frequently come out when CLT is exposed to humid and dry cyclic climate. In Japan more than 100 CLT buildings have been constructed and the number of CLT building is increasing. In some buildings the CLT is designed as to be the exterior members and exposed to the outdoor climate. Several CLT buildings that have CLT as exterior members was investigated to make clear what was ongoing on the CLT panels exposed to outdoor climate. Remarkable check and shake, warp and delamination was observed for the CLT in some of the investigated buildings. To bring out the mechanism of the distortion of CLT under humid and dry cyclic climate and to give a solution to prevent deterioration of CLT a series of laboratory tests were conducted. The CLT panels were set in a climate chamber and exposed to a humid and dry cyclic climate. And the moisture content and the movement of the laminations of CLT were measured. The movement was affected by the species of the laminations and also by the direction of the surface, sap-side or heart-side. And the film forming type painting worked well as to prevent the deterioration and the penetrating type painting could slightly reduce the deterioration.