Fire Safety Challenges of Tall Wood Buildings – Phase 2: Task 4 – Engineering Methods

Recent architectural trends include the design and construction of tall buildings with visible structural members comprised of mass timber. Cross-laminated timber (CLT) is such a mass timber material and is increasingly used for tall buildings because of a combination of advantages regarding its structural performance, low environmental impact and more. As timber is a combustible material, CLT can become involved in the fire if it is not protected against the fire. Previous tests have shown that the contribution of the timber possibly leads to sustained fires that do not burn out, because of failure of the base layer of gypsum boards, debonding of CLT lamellas (delamination) or due to an excess of unprotected timber. If it cannot be assumed that the fire brigade or sprinkler activation will suppress a fire, it can be needed to design for burn-out without successful fire suppression. Engineering methods to limit the impact of gypsum failure, delamination and an excess of exposed timber are needed. Additionally, a method for structural design for CLT structures considering natural fires is needed. This report proposes and evaluates pragmatic design methods using parametric design fires. The methods using parametric design fires can only be valid if delamination and failure of the base layer of gypsum boards are avoided. Therefore, an additional method to predict gypsum fall-off is presented. A method to avoid delamination is presented in other work. The parametric fire design methods proposed, resulted in conservative predictions of the damage of exposed CLT and conservative predictions of the occurrence of gypsum board fall-off. Parametric design fires can be used for structural predictions of the timber building exposed to fire using recently developed methods