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

Abstract

This paper describes how 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 that is located at the corner of the building and supported by exterior columns compared to panels supported by interior columns. Beams that can support interior or exterior panels should be designed to bridge over a failed column, which may not be possible for beams that support 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 and 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 and a case study is presented to demonstrate these two options.