PSI - Issue 54

Rami A. Hawileh et al. / Procedia Structural Integrity 54 (2024) 287–293 Hawileh et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Material properties Compressive strength tests were performed in accordance with ASTM C109/C109M-16a standards [54] for three cube samples and three cylinder samples at stress control rate of 0.25 MPa/sec. The average compressive strength of concrete was 45 MPa. Tensile strength tests on coupon specimens were conducted to find the mechanical properties of steel reinforcement according to ASTM A370-18 standards (2018). Three coupon tests were conducted on steel bars with a diameter of 12 mm. The average yield strength was 568 MPa. The CFRP sheets consisted of high strength unidirectional CFRP material. The dry and laminate (fiber + epoxy) properties of CFRP sheets as provided by the manufacturer are presented in Table 1.

Table 1: Mechanical properties of CFRP sheets and laminates

Elastic Modulus (GPa)

Tensile strength (MPa)

Elongation at failure (%)

Material

Thickness (mm)

CFRP sheets and anchors

V-Wrap ™ C200HM-N V-Wrap ™ C200HM-N

-

289.550

5440

1.90

CFRP laminates

1.02

73.770

1240

1.1

Epoxy Adhesive

V-Wrap ™ 770

-

2.760

60.7

4.4

2.3. Test setup Beams were tested under four-point bending tests in a Universal Testing Machine (UTM) under a displacement controlled rate of 2 mm/min. To measure the deflection of the specimens, one linear variable differential transformer (LVDT) was placed under the beam’s soffit. One strain gauge was mounted onto the concrete near the top mid -span of the beams to monitor the strain in the concrete. In addition, two strain gauges were fixed on the bottom steel bars to measure the strain in the flexural steel reinforcement. Furthermore, a strain gauge was placed on the CFRP laminates at midspan to measure and study the CFRP strain distribution in the unanchored and anchored laminates. 3. Results and Discussion 3.1. Failure modes The failure modes of the tested specimens are illustrated in Fig. 2. The unanchored beam (BU) experienced failure initiated by the development of flexure shear cracks at the tip of the FRP sheets. These cracks propagated parallel to the tension steel reinforcement and resulted in debonding of the concrete cover, also known as concrete cover separation. Fig. 2-b shows the failure of the beam specimens anchored with one anchor of diameter 14 mm on each side (A2). The specimen failed by delamination on one side. However, the failure is quite different than the BU beam. It can be seen that the concrete cover layer was not totally separated from the rest of the beam. This indicates that the anchor has held the concrete cover with the upper part of the beam and prevented it from total separation. Specimen A4 demonstrated excellent behavior in terms of the failure patterns as shown in Fig. 2-c. Although debonding occurred in this specimen, the difference between this debonding failure and the debonding that occurred in specimen A2 is that the FRP sheet remained connected to the concrete with the help of the FRP anchors. Thus, the existence of two FRP anchors on each side improved the failure behavior of strengthened beams.

(a)