Temperature Dependence of Adhesive Strength and Fire Resistance of Structural Glued Laminated Timber Beams

In order to discuss how adhesive strength at elevated temperature affects the fire resistance of glued laminated timber (GLT), structural GLT beams using adhesives of phenol-resorcinol-formaldehyde (PRF) resin, aqueous polymer isocyanate (water based polymer-isocyanate, API) resin or polyvinyl acetate (PVAc) resin were made and their fire performances were evaluated. The PRF-GLT beams and API-GLT beams exhibited the fire performance required for the 45-minute fire test. However, the PVAc-GLT beams failed to withstand the fire test because the laminae separated earlier than PRF-GLT and API-GLT. The adhesive shear strengths in laminated wood at elevated temperature were evaluated. They decreased with rising temperature, and were found to be RF>API>PVAc at 100°C, 150°C and 200°C. In particular, PVAc decreased drastically, where the adhesive strength at 150 °C was almost null. The fire resistance degradation of GLT beams is dominated by the loss of laminae, and depends on the adhesive shear strength in laminated wood. If the adhesive shear strength at 200 °C is enough to keep laminae from separating, the GLT beam specimens are expected to exhibit 45minute quasi-fireproof performance.