Study on the Influence of Column Size and Slab Slenderness on Punching Strength
Reinforced concrete slabs with uniform thickness, supported on columns without capitals, are common in residential and commercial buildings in many parts of the world. In engineering practice, these elements are typically only reinforced with flexural reinforcement and no transverse reinforcement is provided.
Such slabs are susceptible to punching shear failures, where a supporting column penetrates through the slab and leads to an immediate local collapse that can propagate throughout the building. Such failures are usually associated with barely noticeable deformations and cracks prior to failure and, as a consequence, can occur without visible warning signs.
To this day, the failure mechanism of punching shear is not completely understood. Unsurprisingly, the punching provisions in various codes of practice can lead to quite different strength predictions and, in some cases, may result in conservative and costly solutions.
This paper presents the results of a punching test campaign on 13 full-scale slabs representing symmetric interior slab-column connections. The study focuses on the influence of varying the size of the columns and the span-to-depth ratios of the slabs.
Other investigated parameters are the amount of flexural reinforcement and the presence of transverse reinforcement in the slab. The results of the present campaign and of previous tests are compared to the predictions of several codes of practice and to the critical shear crack theory (CSCT), a mechanical punching model developed by the authors.
The predictions of ACI 318 are overall conservative in the investigated range, especially in the case of small column sizes, whereas the results of Eurocode 2 for small columns have a large scatter. The CSCT gives the most consistent predictions, whereas fib Model Code 2010 is conservative for larger column sizes.
This study demonstrates that the span-to-depth ratio has a strong influence on the punching strength of slabs with shear reinforcement, although it is often neglected in codes of practice.
The research can be found in a paper titled “Study on the Influence of Column Size and Slab Slenderness on Punching Strength”, published by ACI Structural Journal.