The size effect of adhesively bonded GFRP stirups on the torsional behavior of spandrel beams

The durability of concrete elements reinforced with conventional steel has been questionable. Steel bars will eventually deteriorate due to corrosion especially in harsh environments and water structures. FRP reinforcement bars manufactured made of resin impregnated FRP. FRP bars are non-corrosive with high strength to weight ratio which makes it an ideal substitute for conventional steel bars. However, previous studies showed that the bent of the FRP stirrups could cause reduction in the strength and might lead to inadequate performance. This paper introduces a new technique for forming the stirrup and experimentally investigating the torsional behavior of FRP-reinforced concrete beams. Three spandrel beams were tested under pure torsion while reinforced with FRP bars in both the transversal and longitudinal direction of the tested beam. The three beams had the same cross section dimensions, reinforcement detailing, and stirrup spacing. The main parameter investigated was the stirrup bar size which was taken 6, 8, and 10 mm. The stirrup size affected the stirrup strain, strength, ductility, and toughness. The comparison between the ultimate strength measured while testing the beams and the one predicted by the available conventional design codes showed they are overly conservative for all sizes.