Investigating the capacity of reinforced concrete framed structures to sustain loss of primary load-carrying members

Abstract

Significant damage or loss of primary load-carrying members of reinforced concrete framed structures can lead to disproportionate failure of large parts of the structure or even the entire structure. Many building codes and design standards require the investigation of the capacity of structural systems to sustain the loss of critical structural elements without experiencing disproportionate damage. The design guide, UFC 4-023-23, published by the Unites States Department of Defense, provides recommendations on the design of structures more than three stories high to reduce the potential for progressive collapse. The document classifies buildings based on the desired level of protection. Medium and high levels of protection categories require the use of the Alternate Path (AP) method to investigate the capability of the structural system to transfer loads safely from a notionally removed column to the remaining structural elements. Transfer of loads from a notionally removed corner column to adjacent structural elements can impose significant stress/deformation demand on structural elements. For example, large torsion can be induced in beams supporting the adjacent panel when a corner column is removed. However, according to UFC 4-023-23, when the panel area exceeds the prescribed floor damage limits, the panel and its structural elements must be designed to support the additional load or the loads must be transferred to adjacent columns. This paper investigates the implementation of UFC 4-023-23 to protect against progressive collapse of frame structures when their dimensions exceed the damage limits.

Keywords: Collapse, Damage, Deformation, Dynamic, Linear, Protection, Shear, Torsion