Fire Resistance of Timber Panel Structures Under Standard Fire Exposure

Abstract

Timber panel construction using Cross-Laminated Timber (CLT) or Laminated Veneer Lumber (LVL) panels have been developed for cost and construction efficiencies in the building industry. The increased use of timber as a sustainable construction material in buildings is expected to expand the forest industry and increase carbon stock. Heavy timber structural elements with sufficient load bearing capacity could be used in tall buildings. However, sufficient data are not yet available to understand the structural and thermal behaviors of domestic timber panel elements with cross laminations/layers when they are exposed to fire. In this study, fire testing data for timber panels are obtained and the charring characteristics and failure modes of structural elements under standard fire exposure are investigated to develop a simple method for estimating the fire resistance of timber panels. Toward this end, a series of experiments consisting of heating tests and load bearing tests for walls in furnaces with various experimental parameters was conducted. The experimental parameters considered include the adhesive type, thicknesses of laminations and panels, wood species, fire protection, and applied loads of the panels. Experiments without loading showed that CLT and LVL panels and joints of panels with 135 mm thickness showed sufficient thermal insulation and integrity over 90 min in standard fire tests. Smoke leakage from the joints of the timber panels was observed in the early stage of the fire tests because of a lack of air-tightness. Delamination of almost all charred layers glued with an API adhesive was observed in fire tests of CLT panels; however, delamination of LVL and CLT panels with a RPF adhesive was limited. The estimated charring rates of a Japanese cedar CLT panel with API and RPF adhesives were 0.78 mm/min and 0.66 mm/min at 260°C, respectively. The charring rate of LVL panels was ∼0.6 mm/min at 260°C, less than that of CLT panels. The load bearing capacity of timber walls subjected to one-sided fire exposure depended on the buckling strength under the eccentric load caused by asymmetric charring. A prediction method based on the Secant formula was presented to estimate the buckling strength in fire tests. An equation that considered the effect of the degradation of elasticity at high temperatures and eccentricity of loading provided the approximate buckling strength of the timber panel specimens in the fire tests.