Fracture kinematics of reinforced concrete slabs failing in punching

Abstract

Over the past decades, a large number of punching shear resistance models with different backgrounds have been developed. Among them, punching shear resistance models based on kinematic failure mechanisms have been found to be in good agreement with punching tests on slender slabs. The existing kinematic models generally determine the punching strength based on suitable failure criteria relating punching failure to a certain slab rotation. Hence, slab deformations are assumed to occur as a result of flexural deformations only. Yet, measurements taken from recent punching tests with varying slenderness reveal differences between fracture kinematics of slender slabs (e.g. flat slabs) and compact slabs (e.g. column bases). In this context, the deformation behavior of compact slabs is rather governed by translational deformations. Consequently, a general application of the existing models to both slender and compact slabs might yield inconsistent results.In this paper, the punching shear behavior of reinforced concrete flat slabs and column bases is investigated in detail. Based on measurements from tests and theoretical investigations, the fracture kinematics of slabs failing in punching are analyzed. The investigations verify that the total deformation of compact slabs at punching failure is significantly underestimated by considering the slab rotation as single degree of freedom (DOF). A more general description of the deformation behavior of both slender and compact slabs is possible by introducing a second DOF considering translational deformations. Based on the aforementioned observations, a general kinematic model is introduced to describe the fracture kinematics of reinforced concrete slabs by means of two DOFs. The proposed model is verified by means of measurements taken from punching tests.