Japan: Nail laminated timber tested

Wednesday 14 Feb 2018

NLT Char Margin Test Successful - Increased attention is being paid to Nail Laminated Timber (NLT) in wooden building industry in Japan. As opposed to fire resistive PFC buildings, where wooden structures are cladded with gypsum boards, NLT presents an opportunity to visually expose wood. In particular, designers prefer NLT in floor applications because the occupant downstairs can appreciate the wooden ceiling surface above. Those applications are usually in large-scale buildings where fire resistive or quasi-fire resistive performance is required. NLT can be used in quasi-fire resistive structures if a fire test shows that the remaining cross section can be structurally safe after burning. This approach is defined as the “char margin” or “sacrificial layer” design method.

In December 2017, COFI and the Japan 2×4 Home Builders Association collaboratively conducted the fire test to the NLT with Canadian SPF 2x10s nail laminated edgewise. The specimen was burnt in the horizontal furnace at the Tsukuba laboratory of Center for Better Living, one of the MLIT-designated performance evaluation bodies.

After one-hour burning, the surviving cross section of the NLT showed sufficient load bearing capacity against the dead loads applied vertically to the specimen.

This was the preliminary test for the Canada Wood next fiscal year project, seeking the quasi fire resistive ministerial approval jointly with Japan 2×4 Home Builders Association.


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