Evaluation of the Load-Bearing Mechanisms in Coupling Beams and Shear Walls based on DIC Measurements

Abstract

This work presents two applications of Digital Image Correlation in tests on short coupling beams and shear walls. This type of reinforced concrete members are typically subjected to high shear forces and are susceptible to shear failures along diagonal cracks.

The general principles of DIC and their practical application are studied and described. Based on DIC analysis, the kinematics of the two reinforced concrete members are illustrated and compared to a two-degree-of-freedom kinematic model for short coupling beams and to a three-degree-of-freedom kinematic model for shear-dominated walls in order to assess their performance. It is shown that the kinematic model underestimates the deformations of the beam, while the wall’s deformation patterns are well predicted.

Methods to evaluate the load-bearing mechanisms based on DIC are also presented. For aggregate interlock, three different crack models are used to determine the shear transferred through the critical crack based on crack opening and slip. The shear carried by the critical loading zone is evaluated through constitutive stress-strain relations for the concrete. It is shown that sum of all contributions from shear mechanisms gives a shear force of the same order of magnitude as the measured applied shear force. In the coupling beam, about 45% of the applied shear force is estimated to be resisted by transverse reinforcement, 35% by the critical loading zones, and 20% is transferred through aggregate interlock. The shear wall was only provided with a few stirrups and their contribution was only about 16%, the aggregate interlock contribution was 8%, while the critical loading zone carried about 76% of the applied shear force. These results represent a first valuable insight into how shear is shared among different mechanisms and can be used to inform and improve models for the shear behavior of non-slender reinforced concrete members.