COMPREHENSIVE ASSESSMENT OF THE DEFORMATION PROCESS OF RC BEAMS STRENGTHENED WITH CFRP SHEET

The paper investigates the behavior of reinforced concrete beams reinforced with CFRP sheet under static loading. The experiment involved 22 large-scale samples – reinforced concrete beams with a size of 120х220х1290mm. One part of the specimens was reinforced with CFRP before loading, the other – under load after the appearance of the first cracks in concrete and their injection. The beams were loaded according to the 4-point bending scheme. The deformation state of the beams was assessed using strain gauge and deflection meter. The debonding of the carbon fiber sheet was evaluated by infrared thermography directly in the process of loading.

The effect of CFRP on the bearing capacity and stiffness of beams reinforced before and during loading is evaluated. The ability of CFRP to restrain the opening of a crack was demonstrated.

The effectiveness of the method of reinforcing beams with CFRP in combination with injection of cracks to restore the rigidity of the structure was evaluated. The pattern of crack formation in samples is presented. The influence of the quality of surface preparation on the nature of the debonding of carbon fiber and the features of cracking and destruction is shown. The parameters and features of CFRP debonding were determined for various debonding mechanisms. The parameters and intensity of CFRP debonding for beams reinforced in the unloaded state and under load are compared. The experimental values of debonding strains are compared with theoretical values determined by 8 known methods.

It is shown that the actual deformation of CFRP debonding is 15-75% lower than the values calculated in accordance with Russian Building Codes SP 164.1325800.2014, and the fact of CFRP debonding does not determine the limiting state of the reinforced concrete beam in the presence of reliable anchoring of the longitudinal strip of the composite on supports.

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