Evaluation of stress-strain state of FRP strengthened RC elements in bending. Fracture mechanics approach

Abstract

The evaluation of stress state of tensile reinforcements is highly important while examining the technical state of concrete structures. Normal cracks in flexural RC elements are the consequence of stress-strain state, on the other hand, the stress-strain state of fexural reinforced concrete structures, strengthened with various types of FRP reinforcements, could be analysed by observing the parameters of normal cracks. Therefore, here proposed method for analysis of such structures relating normal crack parameters to stress-strain state in the element. Another analysed problem is sudden and brittle FRP debonding like failure modes. In this case failure of the element can occur at load lower than 60 % of calculated load carrying capacity. Such a loose of composite action is taken into account by reducing FRP strain through reduction factor based on built-up bars theory. Afterwards, moment curvature (or moment-deflection) relationship is retrieved using methods of classical mechanics of solids and then numerical results can be reliably compared to experimental ones from the tests of RC beams, strengthened with FRP reinforcements. The experimental results are collected from diferent scientifc publications. A focus is made on a relation of critical parameters of normal section cracks to FRP strains.