PSI - Issue 28

Kais Douier et al. / Procedia Structural Integrity 28 (2020) 986–993 Douier et al./ Structural Integrity Procedia 00 (2020) 000–000

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4. Results and discussion 4.1. Failure modes

Figure 5 shows the failure mode of selected specimens. The failure mode for the control unstrengthened beam was the conventional flexural failure of steel yielding followed by concrete crushing, while the failure mode of SMM beam was a full adhesive debonding which caused the beam to have a brittle failure. However, the SMM-EA and SMM-IA had a similar failure mode consisting of flexure failure and local debonding between the anchors, as shown in Fig. 5. Such anchorage systems enhanced the specimen’s ductility and avoided the brittle failure encountered by the SMM beam.

Fig. 5. (a) SMM-IA before testing (b) failed SMM-IA (c) SMM-EA before testing (d) failed SMM-EA

4.2. Load-Deflection curves The load-deflection response relationship for all specimens is shown in Fig. 6. The specimens’ ultimate load capacity ( P u ), mid-span deflation at failure ( δ f ), ultimate load ratio over control unstrengthened beam ( P u /P uC ) and over SMM beam ( P u /P u SMM ), mid-span deflection ratio over control unstrengthen beam ( δ f / δ f CB ) and over SMM beam ( δ f / δ f SMM ), and failure modes are summarized in Table 1. The ultimate load-carrying capacities for CB, SMM, SMM-EA, SMM-IA specimens were 87.1, 132.4, 128.7, and 124.1 kN, respectively. The mid-span deflections at failure for CB, SMM, SMM-EA, SMM-IA were 18.96, 12.42, 45.90, and 44.38 mm, respectively. Moreover, the ratio of ultimate load capacity over CB and SMM for SMM-EA and SMM-IA were 1.48, 0.97, and 1.42, 0.94 respectively. This shows that the external GSM reinforcement increased the beams flexural capacity. However, both intermediate and end anchorage systems did not increase the flexural capacity, as indicated by the ( P u /P u SMM ) shown in Table 1. The ratio of mid-span deflection over CB and SMM for SMM-EA and SMM-IA were 2.42, 3.70, and 2.34, 3.57 respectively. This indicates that both anchorage systems delayed the failure of the strengthened RC beams and significantly increased the ductility of the control and non-anchored strengthened specimens. It also shows that both anchorage systems changed the failure mode of strengthened specimens from brittle adhesive debonding failure to a more desirable ductile localized debonding failure.

Table 1. Summary of test results. Specimen P u (kN) δ f (mm)

( δ f / δ f CB )

( δ f / δ f SMM )

Failure Mode

P u /P u CB

P u /P u SMM

CB

87.14

18.96 12.42

-

- -

-

- -

Conventional flexural failure

SMM

132.35

1.52

0.66

Adhesive debonding Flexural failure + Local debonding Flexural failure + Local debonding

SMM-EA

128.69

45.90

1.48

0.97

2.42

3.70

SMM-IA

124.10

44.38

1.42

0.94

2.34

3.57