Keita Ogawa

Theoretical estimation of the mechanical performance of traditional mortise–tenon joint involving a gap

The mortise–tenon joint, which connects columns and beams of a wooden building, often creates a gap in contact part of members. This gap is considered to affect mechanical performance of the mortise–tenon joint. This study derived a method of theoretical estimation with a gap as parameter for the mechanical performance of mortise–tenon joint. In addition, it experimentally validated the method of estimation and numerically analyzed the influence of a size of such gap on mechanical properties. As a result, the estimated relationship between moment resistance and deformation angle of column shows the agreement with the experimental results, demonstrating validity of the estimation method derived. Results of the numerical analysis quantify the influence of the size of the gap on mechanical properties of the joint. The numerically analysis clarified the large influence of the gap at joints on the mechanical properties.

Theoretical modeling and experimental study of Japanese “Watari-ago” joints

Timber joints used in traditional Japanese constructions have no metal plates or fasteners. Because these joints resist external force by embedment to each member, they show high ductility. The ductile joints get much attention recently. Japanese “Watari-ago” joint used in horizontal structure is one such ductile joint. The joint consists of two beams with interlocking notches, which build resistance against in-plane shear forces. In this paper, the mechanical behavior of “Watari-ago” joints is studied experimentally and theoretically. Experimental results show that “Watari-ago” joints can retain resistance after reaching their yield strength and that mechanical behavior varies depending upon notch shape and size. In theoretical research, a predicting model of mechanical behavior of the joint is developed by applying wooden embedment theory. The model proposed in this study also identifies the size that gives optimal mechanical performance. By numerical calculation on the basis of the model, the authors find it quantitatively that the increase of the sizes of beam width and notch depth has greatly effect on the moment resistance.

Shear properties of metal-free wooden load-bearing walls using plywood jointed with a combination of adhesive tape and wood dowels

In this study, the potential of wood-only (metal-free) load-bearing walls was proposed and tested based on the idea of using the same type of material throughout wherever possible while improving basic properties such as strength, sound insulation, and heat insulation. Specifically, a technique was tested of combining pressure sensitive adhesive tape and wood dowels in place of nails for load-bearing structures with panel reinforcement represented by wood-frame construction. For this paper, its strength was evaluated by conducting in-plane shear tests, which revealed that the initial rigidity and maximum load of the proposed test specimens were greater than that of specimens using nails for jointing. However, the shear load factor, which is calculated based on some strength parameters and which forms the foundation of housing strength design, was slightly lower than that of the nail-jointed specimen. This was because there was a large decline in post-collapse resistance and a lower calculated absorbed energy caused by brittleness. The early detachment of panels was also revealed as a problem in the tests.

Fatigue behavior of Japanese cypress (Chamaecyparis obtusa) under repeated compression loading tests perpendicular to the grain

Abstract The purpose of this study was to gain an in-depth understanding of the fatigue behavior of Japanese cypress as a result of compression. Repeated compression loading tests were conducted on small clear wood specimens in the form of a pulsating triangular wave of frequency 1.0 Hz, and 864000 repeated loading cycles were performed. The change in stiffness and the maximum strain (STRmax) with repeated loadings were investigated, based on the stress-strain relationship obtained from the test. Stiffness hardly changed under conditions of low stress levels (SLs), even under repeated loading. STRmax increased exponentially as the number of loading cycles increased. Furthermore, the fatigue limit was predicted by analyzing the change of STRmax with repeated loading. According to the analysis, the fatigue limit was revealed to be approximately 60% of the SL (standardizing the stress when the strain is 0.05 under static load).

Strength and Rigidity Performance of Laminated Members Using Small Diameter Logs

Abstract Korea and other countries have a high ratio of small-diameter logs in the harvested log volume. Hence, using these small-diameter logs as structural materials is an important issue. The lu...