Concentric punching shear strength of reinforced concrete flat plates

Flat slabs are very popular and economical floor systems in the construction industry. These floor systems, supported directly on columns, are known to be susceptible to punching shear in the vicinity of the slab-column connection. The punching shear provisions of AS 3600-2009, the current Australian Concrete Structures Standard, for the case of concentric loading are based on empirical formulae developed in the early 1960s and have not improved significantly since then. These provisions do not consider some of the important parameters affecting the capacity of a slab such as flexural reinforcement ratio and slab thickness size effect. AS 3600-2009 only recognises shearheads as an effective shear reinforcement to increase the concentric punching shear strength of slabs, and it does not cover more practical types of reinforcement such as shear studs and stirrups unlike most of European and North American codes of practice. In this thesis, the available methods for calculating concentric punching shear strength of slabs are reviewed. The analytical basis of previous work by other researchers was used to propose a formula to calculate the punching shear strength of flat plates with good accuracy for a wide range of slab thicknesses, tensile reinforcement ratios, and concrete compressive strengths. In this method, it is assumed that punching shear failure occurs due to the crushing of the critical concrete strut adjacent to the column. A large number of experimental results of slab test specimen, reported in the literature were gathered to evaluate the accuracy of the proposed formula, as well as the punching shear formulae in some of the internationally recognised standards such as AS 3600-2009, ACI 318-05, CSA A23.3-04, DIN 1045-1:2001, Eurocode2, and NZS 3101:2006. The proposed formula was also extended to cover the case of prestressed flat plates with the use of the decompression method. Recent experimental results of prestressed slab test specimens, published in journal papers, were collected to assess the accuracy of the proposed formula and provisions of aforementioned standards in the prediction of the ultimate strength of prestressed flat plates. Furthermore, detailing considerations for the design of shear reinforcements such as shear studs and stirrups, which are not recognised by AS 3600-2009, were discussed. Different failure modes of flat plates with shear reinforcement were presented. A method to calculate the strength of the slab assuming a critical crack developing inside the shear reinforced region was proposed. This method considers the contribution of shear reinforcement intersecting with the critical crack and the uncracked concrete zone adjacent to the column. In addition, a control perimeter outside the shear reinforced zone was suggested to be used with the one-way shear formula of AS 3600-2009 to calculate the punching shear strength of flat plates outside their shear reinforced zone. The proposed method and provisions of ACI 318-05, CSA A23.3-04, and Eurocode2 were evaluated against some of the reported experimental results on the flat plates with shear reinforcement.