PSI - Issue 64

Muhammad Ishfaq et al. / Procedia Structural Integrity 64 (2024) 1540–1548 Ishfaq et al./ Structural Integrity Procedia 00 (2024) 000 – 000

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Keywords: shear failure; anchorage; experimental study; external CFRP reinforcement.

1. Introduction Externally bonded fiber-reinforced polymer (FRP) composites are widely utilized as a versatile and effective solution to enhancing the structural load-bearing capacity of reinforced concrete (RC) structures in various applications. As a component of many FRP strengthening systems, U-wraps (see Fig. 1) — U-shaped strips made of FRP sheets bonded to the beam soffit and two side faces — are provided either as discrete strips or as a continuous wrap (Tatar et al., 2016). U-wraps may serve as: (i) supplemental shear strengthening (Chajes et al., 1995) or (ii) as anchorage for longitudinal flexural FRP reinforcement (Tatar et al., 2023). While the current ACI PRC 440.2 (ACI, 2023) design guideline recommends U-wraps for shear strengthening and for mitigating end debonding/peeling of flexural FRP sheets, there is a lack of guidance regarding their contribution to mitigating intermediate crack (IC) debonding. Furthermore, instances arise where structural members are deficient in both flexure and shear or become shear deficient following flexural strengthening. These scenarios encourage the concurrent use of U-wraps for anchorage and shear reinforcement.

Longitudinal FRP sheet

Longitudinal FRP sheet

FRP U-wrap

FRP continuous U-wrapping

(a)

(b)

Fig. 1. Typical FRP U-wraps used for strengthening RC beams: (a) discrete U-wraps; (b) continuous U-wrapping.

Existing literature has primarily focused on individual contributions of U-wraps in RC beams, either as shear reinforcement (Alotaibi et al., 2019; Chajes et al., 1995; Chen & Teng, 2003; Khalifa & Nanni, 2000; Kim et al., 2015; Mhanna et al., 2021) or as anchorage of flexural FRP sheets (Fu et al., 2017; Haddad & Marji, 2019; Rasheed et al., 2022; Tatar et al., 2023; Yalim et al., 2008), without considering their complementary effects to both shear and anchorage. This knowledge gap motivates the current experimental study. This experimental study was conducted to quantify the complementary shear and anchorage effects of U-wraps in flexurally-strengthened beams using wet lay-up CFRP composites. The test program consisted of the design and experimental testing of 12 large-scale RC beams under four-point bending. Test variables include the steel shear reinforcement ratio, flexural CFRP reinforcement, and U-wrap cross-sectional area. The effects of these variables were investigated on shear and moment contribution, strain utilization in the longitudinal CFRP, and interaction with internal reinforcement. 2. Experimental Program 2.1. Test Specimens Twelve RC T-beam specimens were designed and constructed using the same cross-section and flexural steel reinforcement (see Fig. 2). The T-section was adopted to reflect the typical condition of a beam with a monolithic slab, which impedes complete wrapping around the section. The 452 mm deep specimens were tested in four-point flexure over a simple span of 4.27 m, with a shear span of 1.52 m resulting in a shear-span-to-depth ratio of 3.89. The beams were constructed using normal-weight concrete having compressive strength of 35 MPa (tested on cylinders of