Size Effect of RC T-Beams Strengthened in Shear with Externally Bonded CFRP L-Shaped Laminates

Abstract

For conventional reinforced concrete (RC) beams, it is well established that the so-called size effect tends to decrease the shear strength attributed to concrete at failure when the size is increased. This contrasts with strengthened RC beams using externally bonded (EB) fiber-reinforced polymer (FRP) sheets or laminates, where very few studies have been devoted to the size effect. The main objective of this study is to examine the size effect of RC T-beams strengthened in shear with EB carbon FRP (CFRP) L-shaped laminates. The experimental investigation involved six RC T-beam laboratory tests performed on geometrically similar beams of two different sizes. Three series of beams were considered, each consisting of medium- and large-sized beams with a total depth of 406 and 605 mm, respectively, as follows: one series of control (unstrengthened) beams with transverse steel stirrups, and two series strengthened in shear using EB-CFEP L-shaped laminates in U-wrap schemes, with and without an anchorage system. The anchorage system considered in this investigation consists of embedding the laminates into the compression zone (flange). The results clearly revealed the effectiveness of specimens with embedded laminates, which achieved a substantially greater shear resistance gain compared to those with no anchorage. Results also confirmed the presence of a size effect in all series. In addition, they revealed an additional size effect related to the CFRP strengthening system in both strengthened series, particularly in anchored specimens despite the higher shear resistance gain they achieved. For instance, the losses in shear strength at failure in large specimens with respect to medium ones were 24% and 16% in strengthened specimens with and without an anchorage system, respectively. Therefore, the anchorage system amplified the decrease in shear strength at failure as the effective depth (d) of the beams increased.