PSI - Issue 64

Mehdi Aghabagloo et al. / Procedia Structural Integrity 64 (2024) 1516–1523 Mehdi Aghabagloo/ Structural Integrity Procedia 00 (2019) 000 – 000

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2.1.1. Material properties For the experimental program, ready-mix concrete sourced from a local plant was utilized. Its mechanical properties, determined in accordance with UNE 12390-3 (2011) and ASTM C469/C469M-10 standards (2010), revealed a compressive strength ( f c ) of 41.6 MPa and an elastic modulus ( E c ) of 33.9 GPa based on tests conducted on 150 × 300 mm cylindrical specimens. The precured CFRP laminates used in the experiments exhibit an elastic modulus ( E f ) of 170 GPa, an ultimate tensile strength ( f u,f ) of 2800 MPa, and an ultimate tensile strain (  u,f ) of 0.0164, according to the manufacturer datasheet (S&P Cfrp laminate., 2017). To bond CFRP to concrete, a high-performance, solvent-free, thixotropic, two-component epoxy adhesive was used. Per the manufacturer ’ s guidelines, components A (resin) and B (hardener) should be mixed at a 2:1 weight ratio, with a recommended curing time of 7 days. The epoxy adhesive has an elastic modulus ( E e ) of 7.1 GPa and a tensile strength ( f u,e ) of 15 MPa as per manufacturer specifications (S&P Resin 220HP., 2019). Finally, the steel capping plate and bolts, used for the HB-CFRP, are respectively made of steel S235 and high tensile steel alloy with a grade of 12.9. 2.1.2. Test setup and instrumentation Tests were conducted in a single shear configuration (Fig. 1) using 200 × 200 × 400 mm concrete blocks, and load was applied under displacement control at a rate of 0.2 mm/min. Full-field displacements were measured with a 3D-DIC system, consisting of two Stingray F-504 digital cameras (SONY IT CCD ICX655, 2452 × 2056 pixels) positioned 1160 mm apart and at a 22º angle perpendicular to the specimen's surface. The cameras captured a 300 × 300 mm area of interest with f/2.5 aperture, 500µs diaphragm closing, and 1.4 f-number lenses. To create contrast, the specimen surface was uniformly painted white, with black speckles (mean diameter: 4 pixels) sprayed randomly. VIC-3D software (Correlated Solutions., 2012) processed the images using 29 × 29 pixel subsets and a 7 pixel step size, employing the zero-normalized sum of square differences correlation method. For the EBR specimen, DIC measured full-field displacements to record strains to later compute slips and shear stresses at four positions along the bonded length: specifically, at distances of 35 mm, 75 mm, 100mm and 130 mm from the border of the bonded region at the load-end (Fig. 1c). For the HB specimen, slips at the loaded end of the CFRP laminate were computed from DIC measurements, and five strain gauges were positioned on the CFRP laminate at distances of 40 mm, 65 mm, 110 mm, 135 mm, and 205 mm from the border of the bonded region at the load-end to compute shear stresses and slips at these locations (Fig. 1b). Holes were cut on the steel anchor plate at these specific positions to allow the strain gauges to be attached on to the CFRP surface and the wires to come out. For the EBR and HB specimens, slip was measured on the border of the bonded region, 70 mm from the top of the concrete block. The cameras and strain gauges were sampled at 1 Hz.

Fig.1 (a) Picture of the single shear test on HB specimen with DIC system and sketch of single shear test setup for (b) HB specimen and (c) EBR specimen