In order to improve the bending strength performance of three-ply laminated wood panels and use them as construction-grade panel materials, twelve types of three-ply cross-laminated wood panels whose percentages of core lamina thickness versus total lamina thickness were 33%, 50%, and 80% were made with sugi (Japanese cedar), and the effect of component ratio of the face and core laminae on their static bending strength performance was investigated.
The moduli of elasticity (MOE), proportional limit stresses and moduli of rupture (MOR), perpendicular (C type) and parallel (C type) to the grain of face laminae markedly increased or decreased with increasing percentage of core lamina thickness. The percentages of core lamina thickness at which each strength property value of C type became equal to that of C type ranged from 65% to 80%. At each percentage of core lamina thickness, the MOE and proportional limit stress of C type were higher in C (45) specimens having perpendicular-direction lamina of 45° annual ring angle in the core than in C (90) specimens having perpendicular-direction lamina of 90° in the core, whereas there was little difference in MOR between C (45) specimens and C (90) specimens. For 45° specimens having the core lamina thickness from 60% to 70%, MOE as well as MOR parallel and perpendicular to the grain of face laminae exceeded the corresponding requirement values of structural plywood with 21.0-mm thickness specified in Japanese Agricultural Standards.
Sugi (Japanese cedar: Cryptomeria japonica) is the most important afforestation species in Japan. Its growing stock has been increasing year by year. Thus, development of new wood products made of sugi has been a national priority for more than two decades. Development of sugi structural glued laminated timber (glulam) was one of the responses to this push. However, in the 1990s, the Japanese glued laminated timber (GLT) industry did not accept sugi as a raw material for glulam, because several problems existed in the wood quality of sugi such as lower strength properties than those of the major imported species. This drawback spurred intensive research on sugi glulam in Japan. The results contributed to the significant revision of the Japanese Agricultural Standard (JAS) for GLT in 2008. The standard permitted the use of various new laminae and products such as a sugi composite GLT beams using different species of laminae with high modulus of elasticity. Although fireproof GLT is not part of the existing JAS for GLT, several fireproof laminated products with 1-h fireproofing performance have been developed since the Japanese Building Standards Law was revised in 2000.
In this paper, the general process and results of the seismic design on a 3-story building with Japanese Sugi CLT construction based on the time history response analysis as the only legal structural design method in Japan at the present moment, are shown. As a result, it is recognized that the building has enough seismic performance for the regulation of seismic design in Japan.
Cross-laminated timber (CLT) has recently emerged as a new wood product that utilizes a large quantity of domestic lumber. This study aims to analyze the effects of width and lay-ups on the tensile strength of CLT. To this end, the elastic modulus of sugi CLT with different lay-ups was measured by dynamic and static methods. Moreover, tensile tests were conducted for different widths and lay-ups of CLT. Results indicate that the apparent bending Young’s modulus, as calculated using the dynamic method, is directly proportional to the measured Young’s modulus in static method for each lay-up. Furthermore, there was no significant effect of width on the tensile strength in the range of 150, 300, and 600 mm. However, the variations in lay-ups affected the tensile strength as follows: CLT with larger ratio of the major strength direction lamina along the cross-section and with higher grade of lamina in the major strength direction showed higher tensile strength. The estimated tensile strength of CLT, as calculated using the Young’s modulus of the lamina of each layer, and the tensile strength of lamina as simple substance was found to be in good agreement with the measured tensile strength of CLT.
As timber tends to be weak against the load perpendicular to grains, it can be important to study the consequences of applying loads perpendicular to larch cross-laminated (CLT) composed of multiple larch laminae. Compressions tests were conducted perpendicular to the in-plane and out-of-plane grains of Japanese larch CLT. Out-of-pane average compressive strenth, average yield strength, and average compressive stiffness perpendicular to the grain of the larch CLT were 11.94 N.mm2, 7.30 N/mm2, and 7.30 N/mm2, respectively, whereas the in-plane average compressive strength, average yield strength, and average compressive stiffness perpendicular to the grain of the CLT larch were 21.48 N/mm2, 21.18 N/mm2, and 18.72 N/mm2, respectively. The in-plane compressive strength and yield strength showed a statistically significant relationship with the density fo the CLT, the modulus of elasticity measured by longitudinal vibration (MOElv), and the average MOElv of the laminae constructing the cross-laminated timber. The in-plane yield strength was affected by the MOWlv of the outer laminae and the average MOElv of the larch cross-laminated timber. The compressive strength properties were most affected by the loading surface of the CLT. The variation between the moisture content and compressive strength properties of the CLT, however, was not statistically significant.
An investigation was carried out on CLT panels made from Sitka spruce in order to establish the effect of the thickness of CLT panels on the bending stiffness and strength and the rolling shear. Bending and shear tests on 3-layer and 5-layer panels were performed with loading in the out-of-plane and in-plane directions. ‘Global’ stiffness measurements were found to correlate well with theoretical values. Based on the results, there was a general tendency that both the bending strength and rolling shear decreased with panel thickness. Mean values for rolling shear ranged from 1.0 N/mm2 to 2.0 N/mm2.