Experimental investigation on the cyclic behaviour of full-scale reinforced concrete columns under biaxial shear loading

Although reinforced concrete (RC) elements frequently undergo biaxial shear forces, limited experimental investigations on RC elements subject to biaxial shear have been conducted, and studies about the different types of biaxial shear failure (i.e., flexural-shear and brittle shear) are even scarcer. The focus of this experimental study is on the flexural-shear and the shear failure modes of shear-deficient full-scale RC columns tested under constant compression and subject to an oblique cyclic lateral load with respect to the principal axes of the cross-section. Twelve columns with square and rectangular cross-section have been tested by applying the shear load along different directions. A comprehensive set of experimental data is critically presented to investigate the effect of biaxial loading condition on damage patterns, strain distribution of longitudinal and transverse reinforcement, force-displacement curves of the columns, shear capacity, displacement ductility, stiffness and energy dissipation. It has been found that: i) biaxial loading condition affects the cracking morphology and distribution, as the cracks appear steeper and denser for columns subjected to uniaxial loading, and diffused and more gradually inclined for columns subjected to biaxial loading; ii) stirrups being more parallel to the loading direction are more prone to yield than orthogonal ones, while yielding of longitudinal bars occurs subsequently under biaxial loading; iii) the quadratic interaction domain underestimates the shear capacity of brittle shear columns with low amounts of stirrups by around 10%; iv) the quadratic interaction domain provides reasonable predictions of the displacement capacity under biaxial shear.