RC beams retrofitted by FRP oriented in any direction: Influence of the effectiveness factors

Abstract

Shear strength of FRP-retrofitted RC beams is usually influenced by different brittle failure modes characterizing the collapse of the FRP reinforcement. The most significant analytical models for assessing the shear strength of FRP-retrofitted RC beams reflect the effect of brittle failure through an effectiveness factor “R”, which reduces the ultimate tensile strength of FRP. The brittle collapse of FRP reinforcement often leads to a lower shear contribution by steel stirrups due to hindering of the yielding of all stirrups involved by critical cracking. Some analytical models consider this phenomenon introducing a further effectiveness factor “r”, which reduces the yielding strength of stirrups. The key differences characterizing many of the shear models are represented by the expressions used for assessment of the effectiveness factors. This paper focuses on the influence of effectiveness factor models in analytical predictions provided by different shear models. The reduction of the shear contribution of steel stirrups due to FRP brittle failure is modeled as dependent on the FRP wrapping scheme, through the ratio between FRP effective strain and steel yielding strain. To highlight the influence of the effectiveness factor for steel stirrups, two analyses are performed through different shear models, considering the effectiveness factor for FRP only, and considering the effectiveness factor for both FRP reinforcement and steel stirrups. The results are discussed considering two databases, one constituted by beams whose FRP reinforcement and steel stirrups are arranged at right angles to the beam axis, and one in which the FRP is arranged at angles different from 90◦.