A new protocol for testing RC beams in combined shear and tension loading conditions

The problem of the shear strength of reinforced concrete members which are simultaneously subjected to an axial tension occurs in a number of practical cases such as continuous beams rigidly connected to columns (where tension results from the restraint of the axial variation of length due to concrete shrinkage and temperature variation), columns or shear walls and foundation piles in beam-column or shear wall-slab frames subjected to high horizontal forces. An original protocol is proposed for testing in these loading conditions, where reaching shear failure represents the main difficulty for designing specimens. This protocol makes use of an original and reliable test setup, in which two horizontal forces are symmetrically applied apart the beam axis, making it possible to generate a constant axial force and a constant negative bending moment along span. The loading protocol is oriented towards a defined value of axial force, while shear at failure may be combined with a negative or positive moment. The loading path for bending moment and axial force is chosen as to remain inside the normal force-bending moment failure curve. The failure in shear occurs at constant axial force and increasing bending moment. The whole procedure was first implemented to perform three rather simple preliminary tests. Their results show the technical feasibility of this protocol. Some limitation of initial parameters was evidenced. So better parameters were chosen for carrying out the main experimental program (presented in another paper).