Behavior of reinforced concrete beams strengthened with CFRP under long-term load action

Abstract

This article analyses the behavior of reinforced concrete beams strengthened with carbon fiber reinforced polymer under a long-term load action. Two groups of beams were tested. Different longterm load levels were used. The first group of beams was strengthened under external loading. The other group was strengthened without preloading. The experimental investigation showed that the initial deflection of the beams, which prior to strengthening were externally preloaded, at the beginning of the long-term load action was lower than that of the beams which were strengthened without external preloading, but the deflection increment during the long-term load action was higher. It was also found out that the growth of vertical cracks during a long-term load action in the bending zone decreases and the growth of shear cracks increases. Therefore, shear cracks have a more significant influence on deflection than the vertical ones. Observation of cracks revealed that the growth of cracks mainly occurs in the areas affected by shear force and they negatively affect the beam curvature. The evolution of deformations in the compressed and tensioned layers is more intensive in the beams which were strengthened without a prior external load action. However, the increment of deflections and deformations of the beams which were strengthened without a prior external load action after some time becomes lower than in the beams which prior to strengthening were affected by external load action.