The Japanese Building Code provides formulas to calculate the buckling strength for structural lumber and structural wooden engineered products such as glulam and LVL. The adaptability of these formulas against cross laminated timbers is discuss in this paper. To determining the buckling strength properties for cross laminated timbers a series of buckling test were operated for full-size cross laminated timber of certain structural grades. The buckling loads obtained though these tests were compared to those derived from the formulas given in the Japanese Building Code. The measured buckling loads and the calculated buckling loads were almost equivalent. The result indicated that in general the formulas given in the Japanese Building Code can well evaluate the buckling strength of cross laminated timbers.
The national research project to investigate proper structural design method for CLT (Cross Laminated Timber) buildings has been advanced by the subsidy of the Ministry of Land, Infrastructure, Transport and Tourism of Japan since 2011. This paper provides the outline of shake table tests executed as a part of the project in February 2015. Two specimens, one (Specimen A) is five story and another (Specimen B) is three story, were tested. As the result, for both specimens damage was rather slight by the strong input wave according to the Building Standard Law of Japan. Finally, Specimen A survived three dimensional input wave of 100% of JMA Kobe (strong ground motion recorded during Kobe Earthquake in 1995), and Specimen B survived 140% of JMA Kobe.
Rocking of narrow wall panels/columns causes embedding forces on the floor panels during earthquakes. In plain/out of plain compression tests and out of plain embedding tests of CLT panels were conducted. Compression and embedding strengths of in plain/out of plain strengths of Sugi CLT panels were obtained. These strengths of CLT panels with /without edge-glues were compared. Out of plain embedding strength loaded at the corner of CLT panels was fairly less than the normal embedding strength, and it was around the middle of the normal embedding and compression strengths.
Seismic design is required to CLT buildings in Japan. Embedding performance of joints is significant to maintain ductility of timber structures during earthquakes. CLT wall panels are installed on the CLT floor panels, and narrow wall panels and columns make rocking on the floor panels during earthquakes. Both edges of the wall panels apply embedding forces on the floor panels. Tension behaviour of the joints between wall and floor panels is dominated by those of connecters, etc. Compression behaviour of the joints depends on the embedding behaviour of in plain/out of plain CLT panels of walls and floors. In plain/out of plain compressions, out of plain embedding and rotational embedding performance of CLT panes are required to be clarified. In plain/out of plain compression tests and out of plain embedding tests of CLT panels are conducted. Effects of edge-glue of CLT panels are also analysed.
The in-plane shear specimens of full scale CLT panels are tested. From the test results, about the failure behaviour, if there is finger joint near the shear plane, cracks are tended to progress along the joint was confirmed. About the maximum shear unit stress was about 3N/mm2 , and shear stiffness was about 600GPa calculated as the total cross section effective.
CLT is composed of longitudinal layers and cross layers. When the CLT is used as shear wall, it is important to understand the in-plane shear performance in order to control the structural performance of wall and joints and the collapse mechanism. Therefore, the in-plane shear specimens of full scale CLT panels are tested.
Creep and duration of load characteristics of cross laminated timber (CLT) were evaluated from the test results of creep and duration of tests. Japanese Ceder (Cryptomeria japonica) was chosen for the specie for the laminations of the test specimens and API was chosen for the adhesive. The results are summarized as follows: (1) The creep factor [i.e. (Initial deflection + Creep deflection) / Initial deflection] for CLT was evaluated to be 2.0 and was almost equivalent to the creep factor commonly known for solid lumber. (2) The duration of load factor [i.e. Strength for 50 years duration of load / Strength for 10 minutes duration of load] of CLT was evaluated to be 0.66 and was almost equivalent to the duration of load factor measured for solid lumbers.
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.