Abstract: This paper describes a study of four-point bending with shear of full-size KG and KS grade glulam beams using glued-in pre-stressed basalt BFRP, glass GFRP and steel rods. From the tests, it was found that the composite bars as well as the glass bars perfectly compensated for the heterogeneous structure of the timber, showing significant ductility in contrast to the brittle fracture of unreinforced beams, the same applies to the shear area in the support zones and on the supports. Using pre-stressed composite bars and pre-stressed steel bars in tension and compression, the following results were obtained: an increase in load capacity and stiffness, respectively steel bars - 39.2%, 20.2%; basalt bars - 35.4%, 19.4%; glass bars - 32.7%, 17.2% compared to unreinforced beams, also influenced by the distance from the neutral axis. The use of composite and steel bars is an effective, economical, environmentally friendly, ecological and natural technology for the repair of elements, as well as the possibility of increasing the span of the girders and reducing their cross-sections, which gives an increase in the possibility of using wood-based products with other materials, including natural materials - fibre-reinforced polymers - for structural elements.
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