Flexural Behavior of Full-Scale Damaged Hollow RC Beams Strengthened with Prestressed SCFRP Plate under Four-Point Bending

Abstract

The advantages of using prestressed carbon fiber reinforced polymer (CFRP) for strengthening and retrofitting structures have been reported in recent years. In this regard, most of the studies on prestressed CFRP technique have been carried out in the laboratory test with small-scale and no damage (reinforced concrete) RC beam. However, the real structures that need to be retrofitted in service are often degraded or damaged due to early cracking. This paper aims at studying the effect of prestressed CFRP method on full-scale and damaged RC beams. The damaged levels of four full-scale damaged hollow RC beams taken from an old bridge were evaluated. One damaged beam was tested to check the residual capacity, and the other three were strengthened with prestressed composite strengthened CFRP and steel-carbon fiber reinforced polymer (SCFRP). The flexural behavior of non-strengthened and prestressed strengthened beams was investigated. During the experiments, the failure modes, deflection, yield and ultimate load, strains of concrete, steel reinforcements, and SCFRP were measured and analyzed. The results showed that the stiffness at the elastic stage was increased by 64.9%, 66.9%, and 67.1% after strengthened by SCFRP with 30%, 40%, and 60% prestressing level. Moreover, the ultimate load of damaged hollow RC beams were improved by 19.53%, 21.82%, and 31.9%, respectively. The flexural behavior of the severely damaged RC beam with strength reduction coefficient of 0.65 can be recovered after being strengthened by SCFRP with 40% prestressing levels. Meanwhile, SCFRP-concrete interface debonding failure occurred when the prestressing level exceed 60%, and the characteristics of brittle failure became more evident with increased prestressing level of the SCFRP.

Flexural Behavior of Damaged Hollow RC Box Girders Repaired with Prestressed CFRP

“…The bending capacity of the four girders is listed in Table 1. In previous studies [27], relevant parameters of the damaged hollow box girders were measured, and the degree of damage to the girders were calculated. Fourteen displacement gauges were symmetrically placed at seven control points to measure the deflections of the specimens, including two supports, two quarter-spans, two loading points, and the mid-span.…”

“…The bending capacity of the four girders is listed in Table 1. In previous studies [27], relevant parameters of the damaged hollow box girders were measured, and the degree of damage to the girders were calculated.…”

“…For RC girders strengthened with prestressed CFRP, the main failure modes include CFRP fracture at the bottom of the midspan, concrete crushing at the top of the RC girders, yielding of the main reinforcement steel bars, and CFRP-concrete interfacial debonding failure [7]. Many studies [7,27,35] have shown that CFRP-concrete interfacial debonding failure and CFRP fracture frequently occur with increasing prestress levels. So far, most concrete specimens used for prestressed CFRP strengthening experiments have had rectangular or T-shaped cross-sections, and there have been few studies describing the failure modes of hollow box girders strengthened with prestressed CFRP.…”

“…Defining the extent of damage to the decommissioned bridges studied is crucial for finite element simulation. Based on previous research [27], the damage coefficients for girders G1-G4 were calculated and are shown in Table 1. To simplify calculations and analysis, the cross-sectional area of the steel bars was reduced in the finite element model to simulate the girder's damage.…”

Case Study on Prestressed CFRP Plates Applied for Strengthening Hollow-Section Beam Removed from an Old Bridge

“…Results showed that the post-cracking stiffness, the cracking and the yielding loads increased by increasing the prestressing level and the strengthening amount of the prestressed CFRP plate, and a high prestressing level of 50% could lead to a premature intermediate debonding of the CFRP plate before the yielding of the steel rebars, while the prestressed CFRP plate bonded on the two sides provided a lower flexural strengthening efficacy than that bonded on the bottom of the beam, owing to the shorter force arm and the nonuniform stress of the side-bonded CFRP plate. Li et al [ 36 ] studied the flexural behavior of full-scale and damaged reinforced concrete beams strengthened with prestressed steel-carbon fiber reinforced polymer (SCFRP). Results showed that the stiffness at the elastic stage was increased by 64.9–67.1% after being strengthened by SCFRP with a 30–60% prestressing level, and the ultimate load were improved by 19.53–31.9%.…”