Structural performance of RC flat slabs connected to steel columns with shear heads

This paper investigates the structural performance of hybrid members consisting of reinforced concrete flat slabs, with and without shear reinforcement, connected to steel columns by means of fully integrated shear-heads. A detailed account of the results from a series of six large scale tests on this form of hybrid structural system is provided. The test results offer a direct evaluation of the full load-deformation behaviour of the specimens as well as the ultimate punching shear strength attained prior to failure at the critical slab perimeter outside the shear-head region. The experimental findings enable the development of analytical models that depict the rotational response and flexural strength as a function of the shear-head embedment length, layout and section size. Additionally, the test results support the definition of a shear-head dependent control perimeter which is used in conjunction with the analytical slab models for full assessment of punching shear strength. The adequacy of strength predictions incorporated in current design methods for conventional reinforced concrete members are also examined in the paper. It is shown that existing design procedures either lack direct guidance for members provided with shear-heads, or lead to overly conservative strength predictions. Finally, in order to provide a reliable evaluation of the ultimate punching shear strength of hybrid elements, analytical design expressions which account for the characteristics of the shear-head system, are proposed. In comparison with conventional reinforced concrete design provisions, the suggested approach captures in a more realistic manner the influence of the embedded length of the shear-heads for such hybrid members with or without shear reinforcement.