In a situation where the development of various novel wooden structural materials continues, it becomes necessary to understand the creep properties of wooden screw joints under shear loading. Therefore, shear creep tests for joint specimens were conducted. Screw joint specimens consisting of solid wood (Japanese cypress) and structural plywood made of softwood were used for the tests. The tests were conducted in a testing room controlled at 20°C temperature and 65% relative humidity. The shear load was applied for over 40000 hours. The stress levels were determined as 39.0-70.2% of the standard yield load obtained by monotonic-loading tests. The slip-time relationships were obtained by the tests. This study proposed a method for estimating the creep limit by analyzing the slip-time relationships. By applying the proposed method, the creep limit of the screw joint specimens was estimated as 27.6% of the yield load.
Since the national government doesn't provide preferential treatment to domestic timber due to agreement with the World Trade Organization, the prefectural governments take up the role by prefectural policies. The government of each prefecture implemented the subsidy programs for residential construction which is a major demand for timber; while Akita, Gifu, and Nara prefectures implemented these subsidy programs not only for their citizens but also for house owners outside the prefecture. It is important to promote local timber usage outside the prefecture from the viewpoint of expanding sales channels. On the other hand, it is necessary to gain an understanding by the local citizens and their council because this subsidy program causes an outflow of budgets. For this purpose, it is necessary to evaluate the benefits of these systems for the prefectures. This study evaluated the economic impacts of the subsidy programs on the citizens outside the prefectures and investigated their attitude toward the program. It was found that the rate of induced production-values per payment for timber products of Akita, Gifu, and Nara prefectures was 1.44, 1.47, and 1.37, respectively. The rate of induced gross-value-added per budget of each prefecture was 4.88, 8.85, and 6.70, respectively. Induced tax-effect per budget of each prefecture was 0.129, 0.345, and 0.255, respectively. According to the results of the questionnaire survey conducted for house owners, it is evident that the subsidy program of Nara increased the demand for local timber. Hence, it can be concluded that the subsidy for residential construction outside the prefecture is valid.
In order to clarify the mechanism of change in reflectance of visible light due to painting treatment, X-ray CT observations of the internal structure of the material and measurements of the optical properties of visible light with a spectrophotometer were performed for two types of grain of hinoki cypress (Chamaecyparis obtusa) with various amounts of paint. In the observation of CT images, penetration of the paint into the material was not confirmed in the edge-grain samples, whereas that was confirmed in the end-grain samples. In addition, the permeability of the paint of the end-grain samples was quantified, and that was in a positive relationship with the paint amount. In the optical characteristics measurements, in the medium to long wavelength range, there was no increase in absorption but a decrease in reflectance due to an increase of transmittance. There was also a decrease in reflectance due to an increase in the amount of penetration. From the above results, it was shown that the mechanism of lightness reduction by the clear painting treatment is affected by an increase in the value of the transmittance in the medium to long wavelength regions due to differences in the amount of paint penetration.
In this research, asymmetric four-point bending (AFPB) tests were conducted to obtain the shear strength of Japanese cedar using straight specimens. During the AFPB tests, the locations of the supporting and loading points were varied along the length direction of the specimen at fixed configurations. In contrast, the AFPB test was also conducted using notched specimens, and the obtained shear strengths were compared with those obtained using straight specimens. The shear strength values obtained from straight specimen were similar to those using notched specimens when the supporting and loading points were in a certain range.
The primary object of this study is to investigate the out-of-plane shear strength property of 5-layer 5-ply CLT (Cross-laminated timber) with Japanese larch (Larix kaempferi) or Sakharin fir (Abies sachalinensis). The secondary object is to determine how the shear strength changes as the shear span increases under different loading conditions. We carried out shear strength tests by two loading methods: a three-point bending test and an asymmetric four-point bending test. We prepared several shear span conditions for each method. Results from these tests are as follows: (1) for both test methods, the shear strength of CLT with Sakharin fir was approximately 30% lower than that of CLT with Japanese larch, (2) for the asymmetric four-point bending test, specimens showed shear fracture at all span conditions, but in the three-point bending test, several specimens of CLT with Japanese larch showed bending fracture at the maximum load, and (3) for both test methods, the shear strength decreased as shear span increased according to a power curve regression. In addition, the converged values are approximately equivalent to the rolling shear strength obtained by the compression method.
In order to document the outdoor exposure performance of glued laminated timber, decay and shear strength of structural curved glued laminated timber used for 30 years as the elements of a symbol tower were determined. Decay was observed at the bottom parts of the glued laminated timber, but not at the top and middle parts. Solid wood and adhesively bonded block-shear specimens were obtained from all parts except the decayed area. The shear strength of the adhesive layer and wood were lower at the bottom than the top and middle parts. There was a positive correlation between shear strength of the wood and the density, but no correlation was found between that of the adhesive layer and the density. Also, the shear strength of the adhesive layer was lower than that of the wood. The shear strength of the wood did not differ between the side and center parts in the width direction near the central layer, while the adhesive shear strength at the side part was lower than that of the center part. At the side part of the glued laminated timber, the adhesive shear strength decreased because stresses developed near the adhesive layer when the wood swelled and shrunk due to wetting and drying.