Ductility and Stiffness of Laminated Veneer Lumber Beams Strengthened with Fibrous Composites

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin adhesive were used as reinforcement. Two reinforcement layouts were used: (1) sheets glued along the bottom surface and (2) sheets glued to the bottom and side surfaces. Based on the test results, the flexural strength, flexural ductility and stiffness were estimated. Compared to the reference beams, the maximum bending moment was higher by 15%, 20%, 30% and by 16%, 22% and 35% for the Aramid Fiber Reinforced Polymers (AFRP), Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP) HS sheets, respectively. There was no significant increase in the flexural bending capacity for beams reinforced with UHM CFRP sheets. Similar values of bending ductility indices based on deflection and energy absorption were obtained. Higher increases in ductility were observed for AFRP, GFRP and CFRP HS sheets in “U” reinforcement layout. The average increase in bending stiffness coefficient ranged from 8% for AFRP sheets to 33% for UHM CFRP sheets compared to the reference beams.