Crack propagation and fracture of plain concrete beams subjected to shear and compression

This paper describes the crack propagation and fracture behavior of plain concrete beams with Iosipescu-type geometry and loading in four-point bending with and without the presence of axial compression. Both experimental studies and numerical analyses are presented. The analytical studies utilized finite element codes, with linear elastic fracture mechanics and nonlinear fracture mechanics (CRACKER and the fictitious crack model augmented with shearing tractions along the crack faces). The beams without axial compression displayed crack patterns that generally conformed to the maximum tangential stress concept. The patterns were dependent on the presence or absence of starter notches and included a splitting-tension type of failure. The beams with axial compression in addition to transverse loads experienced failure in splitting tension regardless of the magnitude of the axial compression (stress levels up to 0.11 f'c). The associated energy for this mixed-mode loading was much higher than for Mode 1 loading for similar concrete and must be due to the extensive influence of friction and aggregate interlock.