A shear model for FRP reinforced concrete elements based on refined Critical Shear Crack Theory parameters

Making physical sense of the shear behavior of reinforced concrete (RC) elements remains an open challenge and an ongoing investigation that often leads to upgrades of design codes/provisions. The physically sound Critical Shear Crack Theory (CSCT) which forms the basis for shear design in some popular design codes has been mainly successful in steel-RC members, but not adapted to concrete members reinforced with fiber reinforced polymer (FRP) bars, given that the shear behavior of the latter is significantly less comprehended compared to that of the former. The present study, therefore, aims to develop a model for the shear strength of FRP-RC elements by refining the CSCT parameters. An extensive experimental database is compiled with a total of 420 shear-controlled slender FRP-RC beams without stirrups from 56 investigations – the largest database of this structural material type ever compiled. In addition to being physically sound, the strength predictions by the developed model are found to be accurate, compared to existing design methods. It is adaptable for predicting the shear strength of slender FRP-RC as well as being valid for steel-RC elements. The new model's size effect consistency is verified, and it proves to be more robust than that of the traditional CSCT. In the case of FRP-RC members, the latter wrongly signifies size effect behavior that mostly obeys the linear elastic fracture mechanics (which is believed to be too strong for concrete) while the former predicts a more physically logical behavior similar to that of the nonlinear fracture mechanics.