Abstract: Bio-based insulation boards, with excellent thermal insulation and environmental benefits, could be utilized as protective layers for cross-laminated timber (CLT) load-bearing elements. However, current research on the fire performance of CLT elements is insufficient, especially regarding the protection mechanisms and effectiveness of bio-based materials for CLT walls. This study has developed a sequential thermo-mechanical finite element model for CLT walls with bio-based protection. Based on the model, systematic investigations were carried out to evaluate the effects of fire protection thickness, thermal conductivity, peeling behavior, peeling time, number of CLT laminae, wall dimensions, load ratio, etc., on the temperature, deformation, charring rate, and fire resistance rating of CLT walls. Results show a linear relationship between CLT wall fire resistance rating and protection thickness (positive), protection thermal conductivity and load ratio (negative). A 150-min fire resistance target is achievable only when the thermal conductivity of the bio-based material remains constant. The charring rate of walls with bio-based protection differs from that of gypsum-board and cannot be assessed using the EC5 model. This research provides a foundation for optimizing bio-based fire-CLT composite structures and developing relevant standards.

Key words: cross-laminated timber, load-bearing wall, bio-based material board, fire resistance, charring rate