SEISMIC RESISTANCE OF NONDUCTILE SLAB-COLUMN CONNECTIONS IN EXISTING FLAT-SLAB BUILDINGS

Seismic resistance of slab-column connections in nonductile reinforced concrete flat-slab buildings was studied by testing two-bay connectio n subassemblies under earthquake-type loading. The test subassemblies were designed and detailed according to the gravity load design proced ure practiced during the 1950s and 1960s. Each rest subassembly consis ted of two exterior connections and one interior connection and was a one-half-scale representation of the prototype building. Rapid stiffne ss degradation, significant reduction in drift capacity under increase d gravity load, and limited moment-transfer capacity were among the ma in response characteristics of the nonductile slab-column connections. Flexural yielding of the slab was observed as the primary mechanism f or resisting lateral loads. However, when heavy gravity load was appli ed to the slab, the interior connections punched before the slab reach ed flexural capacity. The lateral drift capacity of the connections wa s also significantly reduced with increased gravity load. The moment t ransfer at connections occurred primarily through negative bending of the slab. Under positive bending, the moment-transfer capacity was lim ited to flexural cracking strength of the slab. Since the nonductile s lab-column connections did not have slab bottom bars continuous throug h the interior column, collapse of the poor slabs immediately followed the punching failure at interior connections.