Method for the investigation of the punching shear behavior of continuous flat slabs under consideration of moment redistributions and membrane actions

• Applicant: Professor Dr.-Ing. Josef Hegger
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428862959

The punching shear behavior of reinforced concrete slabs has been in the focus of research for more than 100 years. To investigate the complex interaction between bending moments and shear forces in the punching region, a large number of punching tests has been conducted, which served as the basis for various punching shear resistance models. Since experiments on actual reinforced concrete slabs are very complex, almost all punching tests have been performed on isolated specimens modeling only the hogging moment region around the considered slab-column connection. Although isolated punching tests are very useful to investigate the main parameters influencing the punching strength in a systematic manner, the tests are not suitable to describe the behavior of actual slabs since distributions between hogging and sagging moments or compressive membrane action may not occur.The existing punching tests on actual reinforced concrete slabs prove that both the punching strength and the slab deformations are significantly influenced by the effects of slab continuity. Nevertheless, due to the lack of experimental data, the extension of the existing punching shear resistance models for a consistent consideration of the effects of moment redistribution and compressive membrane action is still not possible. A further disadvantage of the existing experiments is the fact that the tests have been performed on scaled specimens due to technical reasons. Hence, the punching shear behavior of the investigated slabs is only marginally influenced by size effects. As a consequence, further punching tests with realistic edge conditions will become necessary in the future to consistently extent the existing punching models for the influences of moment redistribution and membrane action. The main goal of the research project is the fundamental investigation of the punching shear behavior of flat slabs under consideration of the beneficial effects of slab continuity. In a first step, an adaptive punching test setup will be developed, which allows for an experimental investigation of the punching behavior of flat slab systems by means of isolated specimens with varying, load-dependent edge conditions. The control of these decisive load-dependent edge conditions such as compressive membrane action and moment redistribution, which occur in the corresponding flat slab system, shall be performed by simultaneous calculations on the basis of an analytical model. The experimental investigations will be supported by additional numerical simulations to investigate and evaluate the differences between flat slabs systems and isolated specimens in more detail. Subsequently, a physically based punching shear resistance model will be developed, which allows for a realistic prediction of the punching strength of reinforced concrete flat slabs at interior columns under consideration of moment redistribution and compressive membrane action.

• DFG Programme: Research Grants