Punching shear at concrete columns is a critical failure mode in a conventionally reinforced or post-tensioned concrete flat plates. Because shear failure is non-ductile, design deficiencies, unanticipated load conditions, and construction defects can result in catastrophic failure with limited warning signs. Therefore, investigation of potential problems in flat plate construction requires an understanding of the structural behavior at failure and the critical components to observe and document during investigation. Modern codes incorporate detailing requirements for continuity in order to reduce the risk of sudden collapse; however, structures constructed prior to these code modifications may represent a risk to occupants and property when the load conditions exceed the nominal capacity. This paper presents expected crack patterns at column to plate connections, relevant code provisions governing the design and detailing of these connections, and what to look for when investigating potential shear problems in these structures. Additionally, efficient methods for repair and retrofit of shear deficiencies in these structures are presented, based upon successfully completed and tested retrofits.
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