ON THE EXISTENCE OF THE CENTER OF ROTATION AROUND A SHEAR CRACK; NUMERICAL INSPECTION OF DIGITAL IMAGE CORRELATION MEASUREMENTS

Despite extensive research in the past few decades, design of beams without shear reinforcement is still considered to be a challenging task. With the goal to provide realistic and simple engineering models many researchers have contributed to the development of analytical and numerical approaches that improved our understanding of the mechanical background of shear failure. Still, some assumptions in these approaches have raised critical questions in the scientific community that are open for further discussion. Several semi-analytical models existing in the literature, based on rigid body kinematics are based on the assumption of a uniquely identifiable center of rotation. This assumption has led to a discussion calling for an experimental evidence and explanation of the shear crack kinematics in a coherent way. A systematic experimental program on RC beams under shear loading using 3D Digital image correlation (DIC) has been conducted to record the displacement and strain fields. These DIC images are processed to deliver a history the displacements on a grid of points covering the observed zone. To include a large range of design configurations, an automatic crack detection algorithm based on DIC controlled finite-element simulation has been developed. With the history of cracking and state fields at hand, further valuable data can be automatically derived, including the history of opening and sliding displacements along the cracks, detection of the relative center of rotation between two neighboring concrete teeth solved as an optimization problem, and moment-rotation curve. These studies provide a steppingstone for the quantification of the stress transfer mechanisms across the shear crack ligament that can support further refinements of the shear zone models.