Strategies for mitigation of progressive collapse of corner panels in reinforced concrete buildings

Studies have shown that loss of exterior columns at any floor level of a framed structure building results in higher stresses and larger deformations at the elements of a panel located at the corner of the building and supported by exterior columns compared to panels supported by interior columns. Beams supporting interior or exterior panels can be designed to bridge over a failed column, which may not possible for beams supporting corner panels. As a result, corner panels of framed reinforced concrete buildings are particularly susceptible to progressive collapse. Since design of structures to prevent progressive collapse entirely may not be realistic for most buildings, it is desirable to adopt selected measures to achieve a desired level of protection. Most building codes and design guides permit certain damage levels for interior and exterior panels. For corner panels, permissible damage limits can be met by adjusting the spans from the corner column to the first exterior columns. When adjusting spans of beams is not architecturally desirable, a strategy to protect the exterior column must be adopted. Possible options include 1) designing steel bracing to support the additional load from a failed column, 2) designing edge panels and supported beams to cantilever the full length after the loss of column, and 3) stiffening the columns for code specified pressure levels. The first two options are discussed in this paper. A case study is presented in this paper to demonstrate these two options.