Issue34

I. Ivanova et alii, Frattura ed Integrità Strutturale, 34 (2015) 90-98; DOI: 10.3221/IGF-ESIS.34.09 92 Figure 1 : Details of corbel geometry and steel frame. M ATERIALS ormal strength concrete materials are rolled gravel, dried sand and ordinary Portland cement. The cement:sand:gravel proportion in the concrete mix are 1:1.73:2.93 by weight and the water/cement ratio is 0.50. Portland cement type CEM II is used and the maximum size of the aggregate is 12.5 mm. Five concrete cylinders 160 mm x 320 mm are also cast and tested when each short corbel is tested to find the compressive strength of concrete at 28 days of age. The actual mean compressive strength was 33 MPa, Young module of 30 GPa and Poisson's ratio is equal to 0.25. Steel bars, S500 are used for different diameters: 6, 10, 14 mm. The steel specimens were characterized by simple tensile test. The stress f u and the modulus of elasticity E s are obtained to 610 MPa and 210 GPa. The Poisson's ratio is equal to 0.29. The high strain in the user steel at the failure is 11.04%. In fact the experimental results of unidirectional carbon fiber fabrics are given by failure tensile stress of 2000 MPa, elastic modulus of 232 GPa, Poisson ratio of 0.42 and the high strain of 9182.10 -6 . But, the glue used for carbon fiber fabrics and for bonding technics are generally into two parts: a resin and a hardener. Then, they are mixed. The glue had an elastic modulus of 8.7 GPa and yield stress of 19 MPa. In according of experimental results yield strength corresponds to the tensile strength. Finally, the carbon composite sheets have a linear elastic behavior up to failure. P REPARATION OF THE BONDED SURFACE AND TESTING PROCEDURE Surface preparation and bonding of carbon fiber fabrics. he surface preparation was of primary importance and calls for care. However, preparation of the concrete surfaces must be carried out to remove any loose or weak material, oil, grease etc... In this case grit blasting was a good method, Fig. 2a. The four corners of the corbel are rounded to reduce the decrease in strength and to prevent tearing of composite material. Preparation of surface should be carried out just prior to the bonding operation to prevent any contamination. After, the contamination can be avoided by applying glue on concrete and carbon fiber fabrics is applied. The concrete surface already become roughened and then leveled before sticking on the wraps using epoxy adhesive. Pressure must be applied to squeeze out excess glue and held the plate in place until the glue has hardened. The epoxy adhesive used was Sikadure-330 composed of two components laminating compound on epoxy resin. Resin components A and B were thoroughly mixed at a ratio 4:1 proportion. The resin and hardened glue is just mixed before the gluing operation, because, the pot life is not long. The greater the amount of material mixed, the shorter was the pot life. To achieve a longer pot life at high ambient temperatures, the mix may be divided into smaller units or the components cooled before mixing. So, epoxy is applied on concrete with a brush and then, fabric is placed on epoxy. Second coat of epoxy is rolled into the fabric like Fig. 2b. The fabric is wrapped completely around the corbel and the fabric is overlapped on the face of the corbel. Pressure must be applied to squeeze out excess glue. N T