Fire resistance of protected glued laminated timber columns: Geometry, load and cladding effect

Timber, as a sustainable and renewable building material, is becoming increasingly popular in modern architecture due to its aesthetic appeal, low environmental footprint, and structural ability. Glued-laminated timber (GLT) is commonly used for columns and beams in mid to high-rise buildings due to its strength and spanning ability. However, concerns about timber's combustibility raise safety concerns that demand the use of effective fire protection materials. One such method is the application of gypsum cladding, which provides thermal insulation and delays heat transfer to the timber, thus enhancing fire resistance. This study investigates the fire resistance of gypsum-protected GLT columns, focusing on the effects of geometry, load level, and cladding configuration. The European Charring Model (ECM) and the effective cross-section design method are used alongside with three experimental tests, full three-dimensional computational model and a parametric study. The results provide valuable insights into the thermal insulation performance of gypsum cladding, the charring behaviour of timber under fire, and the influence of different protection layers and load levels on overall fire performance. Under 36 % load level, doubling the protection layer, increases the fire resistance up to 95 %. Changing the material grade from GL24h to GL28h, increases the fire resistance, from 2 % to 12 %, depending on the slenderness of the column, while increasing the load level from 6 % to 36 % reduces the fire resistance up to 47 %. This research contributes to fire safety and supports the expanded use of engineered timber in sustainable building designs by improving knowledge of its fire performance characteristics.