Sustainable Approach to Strengthening Timber Structures: Performance Evaluation of Basalt Fibre Reinforced Polymer (BFRP) Reinforcement Under Flexure

Timber plays a significant role in sustainable construction, and the growing demands placed on it concern not only the use of renewable materials but also the improvement of the properties of structural members made from them. This paper presents an experimental study on strengthening timber beams with basalt fibre reinforced polymer (BFRP) bars. Twenty full-scale beams of Scandinavian spruce (Picea abies), measuring 70 × 170 × 3300 mm, were tested in four-point bending in accordance with PN-EN 408. Bars of 12 mm diameter were bonded with an epoxy adhesive into near-surface mounted grooves in three configurations: two bars in the tension zone; two bars in the tension zone and one in the compression zone; and two bars in each zone. The fourth series comprised unstrengthened reference beams. The mean load-bearing capacity increased by 35.4%, 75.1% and 112.3%, respectively, and the deflection at the maximum load by 42.4% to 96.5%. The energy-based ductility index rose by up to 199.8%, the highest value being obtained for the beams reinforced in the tension zone only. The increase in bending stiffness, of up to 19.5%, was not confirmed statistically. Failure changed from brittle cracking of the tension zone in the reference beams to a progressive failure in which tension cracking is followed by crushing of the compression zone.