Experimental behavior of a half-scale steel concrete composite floor system subjected to column removal scenarios

A half-scale three-bay by three-bay steel-concrete composite floor system, which represented gravity framing for a typical commercial building, was studied experimentally to evaluate its structural integrity under four separate column removal scenarios: a corner column, two edge columns, and an interior column. In each test, the load was incrementally applied in the bays that were tributary to the removed column using water in containers that were placed on top of the slab. The tests demonstrated that gravity systems for commercial buildings have a significant level of structural integrity - compared to the load redistribution capability expected for steel framing with simple shear connections - even without specific design against progressive collapse. In the corner and edge column removal scenarios, 2.9 kPa (60 psf) and 4.0 kPa (83 psf) were sustained, respectively, and these loads represent a range of 50-75% of the expected floor load. The interior column removal scenario had an unexpectedly low capacity of 3.2 kPa (67 psf), but the behavior was heavily affected by damage to the test specimen due to the previous edge column removal scenarios. For this interior column removal scenario, the lack of slab continuity at the interior edges of the loaded bays prevented composite action and load redistribution occurred primarily through tension ties. Although tension tie development was observed in this experimental program, composite flexural response also had an important contribution to load redistribution for the corner and edge column removal scenarios. Despite the load redistribution seen in these tests, the observed capacities are below the extreme event load combination that is commonly used when designing to prevent progressive collapse, so the current design practice for steel gravity framing is likely not sufficient to meet this criterion.