Analysis of Research and Design Models for the Punchning Shear of Flat RC Slabs

The paper presents the review and analysis of the existing methods and models for calculating punching shear strength. The analysis of the existing design methods has showed that there is no unified theory about calculating punching shear strength. The models are similar in the way that fictitious shear stresses act in the fictitious shear area and are mainly obtained from the test results that may differ in their values. Therefore, the difference between the results obtained employing various calculation methods can be as high as 1,37 times, whereas the difference between the results of theoretical calculations and test research may vary up to 1,8 times. These facts clearly demonstrate that punching shear phenomena are not completely analyzed and require additional researches. The paper also proposes an in-deep analysis of famous analytical punching shear calculation models suggested within the last 50 years like Kinnunen and Nylander (1960), Moe (1961), Breastrup et al. (1976), Georgopoulos (1989), Broms (1990), Hallgren (1998), Menetrey (2002) and Theodorakopoulos (2002). The development of the above mentioned design models, the main assumptions and an algorithm for calculating punching shear strength are discussed in the article. The review of the existing models for calculating punching shear strength has also revealed that two main model types can be distinguished: type 1 – failure occurs when the compression zone is cut by shear and compression stress; type 2 – failure occurs when tensile stresses in concrete punching cone exceeds its tensile strength. A comparison between theoretical models and test results performed by different authors demonstrate that more accurate results can be obtained by calculating punching shear strength using the first types of models. The analysis has revealed it is purposeful to search for more effective reinforcing methods that can change the character of failure from brittle to plastic. A more effective replacement of reinforcement and the behaviour of concrete taking into account complex stress state in the failure zone should be applied.