9This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure 10 of glued laminated timber (glulam) beams using bonded-in carbon fiber reinforced polymer (CFRP) bars. A series of 11 four-point bending tests were conducted till failure on unreinforced, passively reinforced and prestressed Douglas fir 12 glulam beams in a simply-supported scheme. The focus of this research was to evaluate the reinforcing efficiency of 13 both passively reinforced and prestressed beams. Test results showed that the flexural capacity of the reinforced, 14 prestressed, prestressed & reinforced (bottom prestressed and top reinforced) beams greatly increased by 64.8%, 15 93.3% and 131%, respectively. While the maximum improvement of the bending stiffness reached 42.0%. Another 16 important finding was that the extreme fiber tensile strain of timber beams at failure could be remarkably increased 17 due to the presence of the tension reinforcement, which indicated it overcomes the effects of local defects and 18 therefore the failure mode was changed from brittle tension failure to ductile compression failure. Based on the 19 experimental results, a theoretical model was proposed to predict the flexural capacity of unreinforced, reinforced 20 and prestressed timber beams, which was validated by the test data. 21 2 in Europe and is widely used nowadays in buildings and bridges [1]. Glulam has an excellent strength-to-weight ratio, 27shape and size flexibility, as well as high strength and dimensional stability. 28However, despite all of these benefits, glulam beams are usually underused due to the naturally defects such as knots 29 and cross grain [2]. Another problem is the relative low stiffness as a result of which the design of glulam beams is 30 often controlled by deflection limits [3]. For these reasons, many attempts have been made to reinforce or strengthen 31 glulam or solid timber beams by using high tensile strength materials. In the earlier decades, the majority of this 32 work focused on the use of metallic reinforcement [4][5][6][7]. More recently fiber reinforced polymers (FRP) was used as 33 structural reinforcement for timber beams, which in the form of sheets, plates and bars [8][9][10][11][12][13][14][15][16][17][18][19]. It showed from these 34 researches that the reinforcement in the tension zone would improve the strength, stiffness and ductility. Furthermore, 35 both short-term and long-term deflections of the reinforced timber beams were decreased [3,20]. 36But the reinforcing materials usually has a notable higher ultimate tensile strain than that of wood, which means it 37was not effectively used while the failure occurs in this kind of timber members with passive reinforcement. Thus its 38 economic efficiency was argued by some researchers [21,22]. Attempt then was made by introducing prestress in 39 reinforcing materials [2,[23][24][25][26][27]. As a result, the flexural strength is further increased due to the full use of both FRP 40 and wood, while bendi...
