Mechanical and Fire Performance of Innovative Hollow Glue-Laminated Timber Beams

Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional β₀ and notional charring rates β_n were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface.