An experimental investigation and cost analysis of flexural or shear strengthening pre-damaged RC beams

Abstract

This study conducted a series of experimental works to repair and strengthen beams with different flexural and shear damage levels using various repair/strengthening techniques such as carbon fiber-reinforced polymer (CFRP), steel plate (SP), and mechanical steel stitches (MSS). Within the scope of the study, post-strengthening performances of pre-damaged shear beams and flexural beams were investigated. For this, 1/2 geometrical scaled 20 reinforced concrete rectangular cross-section beams, with dimensions of 125/250 mm and a span of 2500 mm, were produced. Half of these beams (type-SB) were designed to meet shear damage due to insufficient shear reinforcement, while the other half (type-BB) was designed to undergo flexural damage (sufficient shear reinforcement). Subsequently, a reference beam was produced in both shear and bending test groups, the other beams were strengthened with different techniques, and four-point bending tests were performed. Reference (non-damaged) bending and shear beams were vertically loaded and comprehensive data for these specimens were obtained. Later, the flexural beams (type-BB) were vertically loaded until reaching mid-displacement/span length (δu/L) ratios of 1%, 2%, and 3% of the flexural reference beam, while the shear beams (type-SB) were loaded up to 50%, 65%, and 85% of the maximum load-carrying capacity (Pmax) of the shear reference beam to induce different damage levels. Then the specimens were strengthened with three strengthening methods (CFRP, SP, and MSS). The data obtained from the experiments were compared, considering each group specimen's strength, displacement ductility, stiffness, and energy dissipation capacity. In addition, the cost of each strengthening type was calculated, and the ratio of the strengthening costs / the production cost of the element itself was determined. According to load carrying capacity and ductility behavior, experimental studies have shown that CFRP has proven to be more effective for type-BB beams (3% pre-damaged level), whereas MSS has proven to be more effective for type-SB beams (85% pre-damaged level) than other methods. While both MSS and SP have been effective for all damage levels in BB beams, CFRP has only shown effectiveness for a damage level of 3%. In the case of shear beams, the load-carrying capacity has increased for various damage levels with CFRP, SP, and MSS. However, typical bending beam behavior was exhibited for CFRP 85%, SP 65%, and MSS 85% load levels. It was also determined that SP and MSS contributed to the ductility orientation for the 65% damage level. However, in terms of cost, CFRP was the most expensive, whereas MSS was the least expensive strengthening method. CFRP was approximately twice as costly as SP and three times more costly than MSS. Finally, due to its ease of application and low cost, MSS, which is a relatively new strengthening technique, has been found that the MSS method is a better alternative than other methods, especially for the strengthening of beams that have received shear damage. © 2024 Institution of Structural Engineers