THE APPLICATION OF SPECIAL REINFORCEMENT TO IMPROVE POST-PUNCHING FAILURE

Punching shear failure is usually the critical failure mechanism for flat slab reinforced concrete structures. The special brittleness of slab-column connections is due to the relative ease with which the flexural reinforcement in the top of the slab can be torn out of the concrete once an inclined failure surface has formed. If unpredictable loads are applied to the flat slab-column connections, punching shear failure occurs with almost no warning signs. According to the brittle manner of this failure, the load carried by the slab-column connection redistributes to adjacent supports and can cause overloading to these supports. It is necessary to provide a secondary load carrying mechanism after punching shear failure. In this Paper, Suggestions for establishing a supporting mechanism in the flat slab connections after punching shear failure are proposed. For this purpose, an experimental study was performed to investigate the post-punching behavior of 11 slab specimens with various reinforcement layouts. The effects of integrity, compressive, shear and bent-up reinforcements on the post-punching behavior of slab-column connections were studied. The results of the experiments show that Integrity reinforcements significantly increased the post-punching shear strength. These reinforcements can develop tensile membrane action and through alternative load paths to transfer the load. These reinforcements did not have much influence on the punching shear strength. In the column strip, compressive bars (except integrity reinforcements) did not have much influence on the punching and post-punching shear strength. The bent-up integrity reinforcements significantly increase punching and post-punching shear strength. The additional bent-up reinforcements increase punching shear strength but these reinforcements are not effective to the post punching phase and cannot increase the post punching shear strength. The shear reinforcements increase punching shear strength, but these reinforcements cannot increase post-punching shear strength. Furthermore, if the shear reinforcements are effectively extended, the behavior flat slabs will be more ductile.