Moment and shear transfer between columns and concrete slabs

Gravity and horizontal forces cause the transfer of vertical shear and moments between concrete flat slabs and their supporting columns. These forces can cause punching failure. Design equations for safety against punching given in the Canadian Standards Association and the American Concrete Institute codes are critically reviewed. It is shown that the equations give in some cases incorrect stresses which do not satisfy equilibrium. A modification is suggested which makes the equations applicable to all cases. The paper also discusses the codes' approach of sharing the resistance to transferred moment between resistances by flexure and by eccentricity of shear, using the coefficient γ v . Comparisons are made with the result of finite element analyses. It is concluded that the code equations, with the suggested modification, are adequate, provided that appropriate values are used for the coefficient γ v . Key words: columns, connections, flat concrete plates, moments, punching shear, reinforced concrete, shear strength, slabs, structural design.