The aim of the paper is to investigate the shear failure mechanisms in T-shape, single span and simply supported beams exclusively reinforced with longitudinal glass fiber reinforced polymer (GFRP) bars. Usually the critical shear crack in RC beams without stirrups develops through the theoretical compression strut reducing the shear strength following the shear failure. The main parameter affecting the crack pattern and the shear strength of the beams is the shear slenderness. However, the test results presented in the paper indicated the new arching effect due to the bond losing between the GFRP flexural reinforcement and concrete. This failure mode revealed unexpected critical crack pattern and failure mode. The research of concrete beams flexurally reinforced with GFRP bars without stirrups indicated two failure modes: typical shear-compression and a new one leading by the bond losing between the ordinary reinforcement and concrete.