Experimental and numerical investigations on RC beams with stirrups scaled along height or length

Abstract

Reinforced concrete (RC) beams with transverse reinforcement (stirrups) subjected to four-point bending were experimentally and numerically investigated. Beams were scaled along the height or length. They were over-reinforced to avoid longitudinal bars’ yielding. First, laboratory tests on RC beams with stirrups were conducted. Due to the lack of a geometrical similarity, two separate failure modes were observed depending upon the ratio of the shear span to the beam depth ηa = a/D. In experiments, a shear-compression failure mode dominated for small values of ηa, and concrete crushing in a beam compression zone prevailed for high values of ηa. Next, the finite element method (FEM) was used in calculations to directly simulate the experiments. A coupled isotropic elasto-plastic-damage constitutive model for concrete under plane stress conditions was adopted. The constitutive model was enhanced by integral-type non-locality in the softening regime to provide mesh-objective results. A bond-slip law was assumed between concrete and longitudinal bars. Numerical simulations under plane stress conditions satisfactorily reproduced the experimental shear strengths and failure modes for all beams with the same set of input parameters. A wide parametric study regarding the numerical influence of the longitudinal and transverse reinforcement ratio and shear span parameter on beam strength and failure mode was performed. In addition, one full three-dimensional (3D) calculation was also carried out for comparative purposes.