Japan’s First CLT Building Completed
The first Japanese building constructed with cross laminated timber (CLT) structure was completed in Ootoyo Town in Kochi Prefecture. This dormitory building with a total floor area of 266 m2 was built as a pure CLT structure without beams and columns. Despite the fact that this building is small in size, many challenges had to be overcome. In Japan, the CLT material standard (JAS 3079) has been established, but that alone cannot provide architects with sufficient working environment. They still need CLT structural design criteria (standards) for allowable stress design method. Nihon System Sekkei, a structural design office for this project, adopted a “Time History Analysis”, which is a rather complicated process, but is currently the only way without taking allowable stress design route of the Building Standard Law. The building with 3 storeys has 6 dwelling units, 9.15 m eve height and maximum building height of 9.95 m. Total volume of the CLT used for this building was approximately 120 m3. The thickness of the CLT was 150 mm for the wall panel and 180 mm for the floor and the roof. Number of plank layers was 5 for the wall/header panels and 6 for the floor/roof panels. The CLT manufacturer, Meiken Lamwood Corporation in Okayama Prefecture, used Sugi (Cryptomeria japonica) planks as the raw material. For fabricating the floor diaphragms, plywood splines were used. The CLT manufacturer did not router the window openings in the panel, but used CLT headers connected to the CLT shear wall panels. Therefore, this project has been positioned as a valuable showcase to demonstrate the performance of drop-in-panels with connectors.