Influence of stirrup detailing on punching shear strength of flat slabs

Most concrete design codes agree that it is important for punching shear reinforcement stirrups in slabs to engage the tensile longitudinal reinforcement bars. However, due to the practical difficulties that this anchorage detail entails, it has been common construction practice in some countries (including Spain) to place closed stirrups without encircling the main tensile reinforcement. The Structural Concrete Research Group at the Polytechnic University of Madrid tested eight slabs with four different shear reinforcement dispositions and the results show that slabs with the shear reinforcement disposition that matches Spanish practice show punching shear strength that is quite similar to the one shown by slabs with the transverse reinforcement disposition specified in the codes. The results also show a significant reduction in punching shear strength when longitudinal reinforcement does not pass through the slab–column connection.

► Experimental testing of RC slabs with different punching shear rebar dispositions.
► Stirrups that do not meet codes’ specifications show good punching shear strength.
► Punching shear strength decreases in slabs with interrupted longitudinal rebars.
► Comparison of experimental results with code-type theoretical models.