Wood Scienceand Technology 30 (1996)323-337 (~ Springer-Verlag 1996 Glass fibre reinforced holes in laminated timber beams S. Hallstriim Summary An experimental investigation of glass fibre reinforcement of glued laminated timber beams is presented. A polyester resin is used both as matrix and adhesive between the reinforcement and the wood. The main part of the work considers beams with large holes tested in three point bending. Circular and rectangular holes, centred at quarter length of the beams make the strength of wood perpendicular to the grain become critical. Great improvements of strength are obtained with the glass fibres. A comparison between various kinds and combinations of glass fibre reinforcement is made. Further, the reinforcement applied as repair of earlier cracked beams is invest- igated with positive results. One series of beams without holes is reinforced and tested in four-point bending. Introduction Wood is a material very well suited for building applications. It has a high strength to weight ratio, a good resistance to corrosive environment and is easily crafted. One major disadvantage, however, is its poor strength perpendicular to the grain. No matter how skilled a wood constructor is, it is sometimes impossible to avoid situations were this weakness becomes critical in dimensioning. Curved beams, holes and cut-outs are often causing trouble. The rectangular cross section of glued laminated timber (glulam) contributes with yet another drawback when compared to I- and H-beams of other materials. When large holes are made the cross section area is strongly reduced. Unfortunately large holes in beams are often required, for instance to let ventilation ducts through, and holes could enlarge the dimensions of a glulam construction to a state where it's competitiveness to alternative construction materials. At present, two methods of reinforcing glulam beams with holes are described in the Swedish glulam code ( Carling and ]ohannesson 1988). The first method is to glue steel bolts through the stack of lamellae, near the hole, and the second method is to glue and nail plywood around the hole. A problem with the steel bolt method is that high stresses in the wood could be caused by the high differences to steel in temperature and 323 Received 18 September 1995 S. HallstriSm Department of Aeronautics, Division of Lightweight Structures, Kungliga Tekniska HGgskolan (Royal Institute of Technology), S-100 44, Stockholm, Sweden This reseach project was initiated to improve the ability of glued laminated timber to compete with steel and concrete, in large free span constructions. The project was funded by the Nordic Industrial Fund (NI), Svenskt Limtr~i AB and the Swedish National Board for Industrial and Technical Development (NUTEK)