Strengthening of Timber Beams using FRP, with Emphasis on Compression Strength: A State of the Art Review

Paper in proceeding, 2009

There is today a necessity to strengthen or repair old timber structures, or to improve the mechanical properties of new timber structures. Research projects dealing with reinforced timber beams to provide enhanced mechanical properties have been conducted for more than 40 years (Wandgaard, 1964). The most recent research projects have been focusing on reinforcement devices such as Fibre Reinforced Polymers (FRP). In addition, the used of Engineered Wood Products (EWP) like glulaminated timber (glulam) have been increasing over the last decades. While solid timber mechanical properties are limited by natural defects, the use of FRP reinforcement on glulam increases the strength both locally and globally, decreases the variation in mechanical properties, introduces the use of lower wood grades and gives the material a more ductile behaviour. Glulam beams tested in bending usually fail at on the tension side due to defects, such as grain deviation around knots or finger joint positions. Therefore, glulam beams are mostly reinforced on the tension side to enhance the tensile properties. This study provides a state of the art review of strengthening devices developed to reinforced straight glulam beams under flexural loads: FRP plate bonded on the tension side, Near Surface Mounted Reinforcement (NSMR) inserted in the tension side lamina, wrapping etc. are some of the techniques used today. The purpose is mostly to make the glulam fail in compression mode, which is more ductile. Compression failure models for FRP reinforced timber are not available, but several studies have been investigating this failure process in FRP and timber separately, and analytical models were presented. A review of these studies is also presented in the present paper.