PSI - Issue 42

Haya H. Mhanna et al. / Procedia Structural Integrity 42 (2022) 1190–1197 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1194

5

2.3. Test setup All beams were tested under four-point bending tests in a universal testing machine (UTM) at a displacement controlled rate of 2 mm/min. The effective and shear spans were 1740 mm and 600 mm, respectively, and the overhang length was 50 mm, as shown in Fig. 3. A linear differential variable transducer (LVDT) that was placed at midspan underneath the beam was used to measure the deflection. In addition, strain gauges (SG) were mounted onto the beams ’ midspan section to monitor the strains at the concrete surface, in the bottom flexural steel reinforcement, and at the center of the FRP laminates, as shown in Fig. 3.

Fig. 3. Test setup

3. Experimental Results and Discussion The experimental results in terms of yield load ( P y ), mid-span deflection at yielding load ( 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 ), maximum strain in the FRP ( ε f ), ductility at ultimate ( μ u ), ductility at failure load ( μ u ), ratio of μ Δ u to μ Δ u(CB) , ratio of μ Δ f to μ Δ f(CB) , and failure modes are summarized in Table 2. It should be noted that all tests were terminated when the load decreased by 20% from the ultimate load. 3.1. Failure modes Figure 4 shows the failure modes of the tested specimens. It can be indicated from Fig. 4 that the control beam failed in a typical manner of an under-reinforced RC beam, i.e., steel yielding followed by concrete crushing in the compression zone. Failure the strengthened beams (C, CP, and PC) was initiated by the formation of the flexure- shear cracks at the tip of the FRP sheets. The cracks propagated parallel to the tension steel reinforcement and caused debonding of the concrete cover (concrete cover separation). It was observed that a thick layer of concrete cover debonded with the FRP sheets, as shown in Fig. 4. On the other hand, the failure mode of the P specimen was initiated by the formation of flexural cracks which resulted in local debonding of the PET-FRP laminate midspan of the beam specimen. The debonding propagated from midspan to the end of the PET-FRP laminate causing FRP debonding andfailure of the specimen. In addition, concrete crushing was visible in the compression zone.

Table 2. Summary of test results

μ Δ u / μ Δ u(CB) μ Δ f / μ Δ f(CB)

Failure mode c

P y (kN) 56.2 72.4 65.1 82.9 65.3

δ y (mm)

P u (kN) 65.9 97.0 81.6 97.8 96.0

δ u (mm)

P f (kN) 52.7 77.6 65.3 78.2 76.8

δ f (mm)

ε f (mm/mm)

μ Δ u

μ

a

b

Δ f

Specimen

CB

8.2 8.4 8.4 9.4 7.0

23.0 18.2 24.5 13.7 13.4

36.0 18.3 40.4 13.8 13.5

-

2.8 2.2 2.9 1.5 1.9

4.4 2.2 4.8 1.5 1.9

-

-

SY, CC

C

0.0085 0.0353 0.0086 0.0065

0.77 1.03 0.52 0.68

0.50 1.09 0.34 0.44

DCC

P

DF, CC

CP PC

DCC DCC

a ∆ = / b ∆ = / c SY: steel yielding; CC: concrete crushing; DCC: debonding of the concrete cover; DF: debonding of the FRP