Punching shear behavior of eccentrically loaded footings

• Applicant: Professor Dr.-Ing. Josef Hegger
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396630727

The punching shear behavior of centrically loaded footings has been investigated by various researchers in the past. The results of the tests served as the basis for current punching shear design provisions for reinforced concrete footings, which generally assume a symmetrical distribution of shear stresses in the control perimeter. In practice however, centrically loaded footings represent an exception, since unintended (e.g. imperfections) and intended (e.g. crane tracks) load eccentricities apply to the structure. To consider the effects of load eccentricities on the punching shear capacity, the various punching shear design provisions define factors to increase the applied load. A final statement on the level of safety of the different provisions is not possible, since only few punching tests on eccentrically loaded footings have been conducted so far.For point-supported slabs, the superposition of shear and bending stresses results in a multi-axial stress state along the column face. Centrically loaded slabs form a compression ring along the column face, which increases the shear resistance compared to one-way slabs. With increasing load eccentricity however, the formation of this rotationally symmetric, multi-axial stress state is no longer entirely possible on the non-loaded sides of the column resulting in decreased punching shear capacities. Also, the formation of inner shear cracks is strongly influenced by the load eccentricity.The main goal of the requested research project is the fundamental investigation of the punching shear behavior of eccentrically loaded footings. By means of experimental and numerical investigations of the behavior of reinforced concrete footings with uniaxial and biaxial load eccentricities, the multi-axial stress state along the column face (length of compression ring) as well as the formation of inner shear cracks is investigated for different load eccentricities and footing geometries. The main findings are used to derive a consistent model, which allows for the fundamental description of the relation between load eccentricity and length of the compression ring or inner shear crack formation, respectively. Based on the model, existing punching shear design provisions for centrically loaded footings are extended for eccentric loading situations.

• DFG Programme: Research Grants