Keywords: progressive collapse, outrigger-belt system, second order effects, bracing, steel structures, direct analysis.

In the past decade research into progressive collapse research has focused on understanding the nonlinear and dynamics behaviour of the structural system after a primary structural member has been damaged. The improved understanding of the post-event performance brought the recognition that structural design that can inhibit progressive collapse is not practical for most building structures. Therefore, emphasis should be on design practices and native systems to mitigate progressive collapse. The outrigger-belt system is typically designed to resist lateral forces and may contribute to mitigation of progressive collapse by transferring load from damaged/removed members to other parts of the structure through an alternate load path.

This paper examines the effectiveness of the outrigger-belt system in mitigating progressive collapse. A case study building is designed according to IBC 2006 and AISC [1] with outrigger-belt system to resist wind forces. One and two outriggers were examined separately in terms of their effectiveness is reducing overall lateral drift. The designed structure with two outrigger-belt systems is then investigated for progressive collapse resistance. Progressive collapse is largely driven by gravity as recognized by building codes and design guides. Therefore, the case study structure is loaded according to UFC [2] gravity load combinations for progressive collapse. Two critical columns at the ground floor level were removed during independent alternate path analyses; a corner column, and an external column. Internal columns were not included as they generally benefit from the possibility of overarching beams over a removed internal column [3,4]. Analysis under gravity load combinations with removed columns was performed using nonlinear static analysis.

It is shown in the paper that the outrigger-belt system was effective in reducing vertical deflection and redistribution of axial forces after the removal of corner columns as well as external columns. This arises from the availability of alternate load paths provided by horizontal stiff outriggers that helped in the transfer of loads from the damaged part of the structure to the other side of the structure.

1

"Steel Construction Manual", 13th Edition, American Concrete Institute, Chicago, IL 60601, USA.

2

Unified Facilities Criteria, "Design of Buildings to Resist Progressive Collapse", UFC 4-023-03, United States Department of Defense, 2010.

3

O.A. Mohamed, "Assessment of Progressive Collapse Potential in Corner Panels of Reinforced Concrete Buildings", Engineering Structures J., 31(3), 749-757, 2009. doi:10.1016/j.engstruct.2008.11.020

4

O.A. Mohamed, "Strategies for Mitigation of Progressive of Collapse of Corner Panels in Reinforced Concrete Buildings", 2nd International Conference on Safety and Security Engineering - SAFE 2007, 2007. doi:10.2495/SAFE070161

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £130 +P&P)