U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design

Abstract

The application of externally bonded fiber-reinforced polymer (EB-FRP) as shear transverse reinforcement applied in vulnerable reinforced concrete (RC) beams has been proved to be a promising strengthening technique. However, past studies revealed that the effectiveness of this method depends on how well the reinforcement is bonded to the concrete surface. Thus, although the application of EB-FRP wrapping around the perimeter of rectangular cross-sections leads to outstanding results, U-jacketing in shear-critical T-beams seems to undergo premature debonding failures resulting in significant reductions of the predictable strength. In this work, five shear-critical RC beams with T-shaped cross-section were constructed, strengthened and tested in four-point bending. Epoxy bonded carbon FRP (C-FRP) sheets were applied on the three sides and along the entire length of the shear-strengthened T-beams as external transverse reinforcement. Furthermore, the potential enhancement of the C-FRP sheets anchorage using bolted steel laminates has been examined. Test results indicated that although the C-FRP strengthened beams exhibited increased shear capacity, the brittle failure mode was not prevented due to the debonding of the FRP from the concrete surface. Nevertheless, the applied mechanical anchor of the C-FRP sheets delayed the debonding. Moreover, the design provisions of three different code standards (Greek Code of Interventions, Eurocode 8 and ACI Committee 440) concerning the shear capacity of T-shaped RC beams retrofitted with EB-FRP jackets or strips in U-jacketing configuration are investigated. The ability of these code standards to predict safe design estimations is checked against 165 test data from the current experimental project and data available in the literature.Strengthening of existing low-capacity RC structures using externally bonded fiber-reinforced polymers (EB-FRP) has become very popular because of the advantages of these materials such as their superior strength-to-weight ratio, their easy-to-apply character, their durability and their chemical and corrosion resistance [6][7][8]. For shear-critical RC elements with rectangular cross-sections in particular, full jacketing application of EB-FRP sheets wrapping around the cross-section and along their entire length provides increased strength and enhanced structural performance since it alters the shear brittle response to a ductile one [9][10][11][12]. However, common constructional limitations, such as the existence of a slab, usually prevent the wrapping of EB-FRP sheets around the cross-section. Thus, most RC beams with a T-shaped cross-section are shear strengthened using EB-FRP sheets (jackets or strips) on the three sides of the web of the beam (U-shaped retrofitting). A significant deficiency of this technique is the premature failure of the strengthened member due to the debonding of the EB-FRP at the adhesive composite and concrete interface [13][14][15][16][17][18][19][20].Several experimental studies have demonstrated the effectiveness...

Experimental Study on the Effectiveness of Inorganic Bonding Materials for Near-Surface Mounting Shear Strengthening of Prestressed Concrete Beams

“…The review of past studies shows that the NSM shear strengthening of prestressed concrete beams with different bonding materials has not been explored in detail [26][27][28][29][30][31]. However, the effectiveness of organic resins such as epoxy and vinyl ester are compromised when exposed to elevated temperature and extreme weather conditions.…”

Effectiveness of the Novel Rehabilitation Method of Seismically Damaged RC Joints Using C-FRP Ropes and Comparison with Widely Applied Method Using C-FRP Sheets—Experimental Investigation

“…To achieve shear strengthening, various types of FRP exterior application shapes have been investigated, such as U-shaped [48][49][50][51][52][53], X-shaped [54][55][56] and T-shaped [57]. In addition to local strengthening of the joint area, others have attempted to improve the performance of the surrounding components, such as bond enhancement of the beam's bottom reinforcement bars [58][59][60], improvement of the columns' flexural performance and column confinement [16,[60][61][62][63][64]. The most common mode of failure in FRP-strengthened specimens that were tested was the debonding of FRP composites from the concrete surface.…”

Punching Shear Strength of Reinforced Concrete Flat Plates with GFRP Vertical Grids

“…As one of the effective shear reinforcements, the method employing a fiber reinforced polymer (FRP) has received the most attention due to the benefits of FRP such as it being lightweight with a high tensile strength and its ability to be manufactured in various shapes. FRP sheets, strips, laminates and rods have been extensively applied for the reinforcing and strengthening of reinforced concrete structures [1][2][3][4]. Bouguerra et al [5] evaluated the punching shear performance of a flat plate by manufacturing a glass fiber reinforced polymer (GFRP) bar and used the manufactured GFRP bar instead of a steel tension reinforcement for the flat plate.…”