Experimental Investigation of Reinforced Concrete Exterior Beam-Column Subassemblages for Progressive Collapse

ACI Structural Journal, V. 108, No. 5, September-October 2011. MS No. S-2009-120.R6 received February 28, 2010, and reviewed under Institute publication policies. Copyright © 2011, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the July-August 2012 ACI Structural Journal if the discussion is received by March 1, 2012. similar to that of GSA5 by designing the building based on redistributed load after the removal of vertical load-bearing elements. Despite the long history of studies conducted on progressive collapse, the majority of the studies were based on case studies of actual collapses and numerical and finite element analyses. There are many drawbacks in the aforementioned methods, however. For instance, the influence of variables cannot be controlled and determined through case studies, whereas numerical and finite element analyses often require calibration and validation. Only recently have researchers begun to investigate progressive collapse through controlled experiments, offering to fill the missing gap in research. Furthermore, with prior knowledge available from numerical and finite element analyses, experimental investigation on specific critical variables that influence the structure’s performance can be performed economically. One such controlled experiment was conducted by Yi et al.,7 where the progressive collapse resistant behavior of reinforced concrete (RC) frame structures was investigated. In the study of progressive collapse, although numerous damage scenarios can be assumed, one of the most probable scenarios is the loss of exterior ground column. The loss of the supporting column changes the boundary conditions of the structure, causing it to seek alternate load paths to redistribute loads, thus maintaining equilibrium. The important question now is whether the structural elements have the capacity for load redistribution and the ability to withstand the increase in load. Otherwise, they will fail due to overloading, resulting in progressive collapse. The beam-column joint is one of the critical elements responsible for resisting and distributing load. Extensive controlled experimental investigations have been carried out, especially in the area of seismic performance. However, there is no known literature on controlled experiments relating to the performance of beam-column joints in a postblast scenario under progressive collapse. It is important to understand that failure in joints will greatly affect the ability of the structure to redistribute loads. Of the different type of joints, the exterior beam-column joint is especially critical due to the following reasons: 1. The loss of an exterior ground column directly affects the vertical load transfer path of the above column. 2. The exterior beam-column subassemblages are subjected to a complete change in the direction and distribution of the bending moment, which the elements were not designed for. Experimental Investigation of Reinforced Concrete Exterior Beam-Column Subassemblages for Progressive Collapse