PSI - Issue 28

Haya H. Mhanna et al. / Procedia Structural Integrity 28 (2020) 811–819 Mhanna et al./ Structural Integrity Procedia 00 (2020) 000–000

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4. Results and discussion 4.1. Failure modes

Figure 6 shows photos of the failed specimens. It is can be seen from Fig. 6 that the unstrengthened specimen (C) failed in a brittle manner by diagonal shear crack that extended from the support up until the loading point in the flange. On the other hand, all strengthened specimens failed by debonding of the CFRP laminates from the concrete substrate with a thin layer of concrete adhered to the surface of the laminates. It can be also observed that debonding occurred in the middle laminates that intersected the shear crack. Specimen BSD12 also failed by fan-to-sheet debonding in the laminate next to the support as shown in Fig. 6. Compared to the unanchored specimens, specimen BSU failed by brittle debonding of CFRP laminates at significantly lower displacement, indicating the advantage of CFRP splay anchors in delaying the debonding failure and enhancing the ductility of the strengthened specimens. 4.2. Load-Deflection curves Figure 7 depicts the load versus mid-span deflection curves of the tested specimens. In addition, Table 1 summarizes the experimental results in terms of the attained yielding load ( P y ), corresponding mid-span deflection at yielding ( δ y ), ultimate load ( P u ), mid-span deflection at ultimate load ( δ u ), load at failure ( P f ), mid-span deflection at failure load ( δ f ), ratio of the ultimate load of strengthened to control specimens C and BSU, ( P u /P u(C) and P u /P u(BSU) , respectively), ultimate strain in the CFRP U-wraps ( ε frp ), and failure modes of the tested specimens. The results shown in Table 1 and Fig 7 indicate that U-wrapping without anchorage enhances the load-carrying capacity of the control specimen (C) by 116%. Anchoring the U-wraps with CFRP splay anchors further improved the capacity of the U- wrapped specimen by 4.5 – 15.3%. On the other hand, the mid-span deflection at failure load ( δ f ) improved substantially in the anchored specimens in the range of 101 – 218% compared to the unanchored specimen BSU. It can be also observed from Fig. 7 and Table 1 that there is no clear trend between the load-carrying capacity of the anchored specimens and the dowel diameter. The lowest enhancement was noted in specimen BSD12 with anchor diameter 12 followed by BSD16 then specimen BSD14. The slight reduction (~6%) in the capacity of specimen BSD16 compared to BSD14 could be due to limitations in the choice of embedment depth or hole diameter (4 mm more than dowel diameter). According to Kim and Smith (2009), the pullout capacity of FRP anchors decreases when the ratio of hole diameter to embedment depth increases. Consequently, for the same embedment depth (85 mm) when the hole diameter

Fig. 6. Failure modes of tested specimens.