Keywords: progressive collapse, realistic modelling, alternative path method, sudden column loss, unforeseen events, dynamic displacement, modelling technique.

Current codes [1,2,3,4] from around the world have made different recommendations with respect to progressive collapse assessment methodology. However, none of these codes specifically recommend how sudden removal of column can be modelled to realistically capture the instantaneous loss of critical structural elements. This has resulted in the application of various methods in modelling sudden column loss. Some researchers have proposed, in the existing literature [5], simplified ways in which progressive collapse assessment can be done. The alternative path method has been recommended by common design codes and guidelines for progressive collapse evaluation of unforeseen events.

Kim et al. [6] and Pujol et al. [7] observed that the technique adopted in modelling column loss significantly affects the nature of results obtained. Furthermore, the poor concept could be misleading in making a well informed judgment with respect to the tendency of progressive collapse based on the code acceptance criteria. For instance, there has been a research based controversy with respect to the dynamic amplification factor of 2 in GSA [1]. Some researchers based on their modelling technique, have concluded that it is conservative while others argue that it is a good approximation.

This research work addresses this fundamental issue in progressive collapse assessment using one of the leading commercial finite element programs, SAP 2000 [8]. A five storey moment resisting steel frame building was used for this assessment. Four possible ways in which sudden column loss can be modelled was considered to account for techniques adopted in the literature and a proposed approach to realistically model sudden column loss was recommended. Significant variation in joint rotation and dynamic displacement was recorded.

1

General Service Administration (GSA), "Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects", 2003.

2

Department of Defence (DOD), "Unified Facilities Criteria (UFC), Design of Buildings to Resist Progressive Collapse", UFC 4-023-03, 2005.

3

Eurocode 1, "Actions on structures. Part.1.7: General Actions - Accidental actions. BS EN 1991 -1 -7", European Committee for Standardization, 2006.

4

Japanese society of steel construction council on tall building and urban habitat, "Guidelines for Progressive Collapse Control Design", 2005.

5

B.A. Izzudin, A.G. Vlassis, A.Y. Elghazouli, D.A. Nethercot, "Progressive collapse of multi-storey buildings due to sudden column loss- Part I: Simplified assessment framework", Engineering structures, 1308-1318, 2008. doi:10.1016/j.engstruct.2007.07.011

6

H. Kim, J. Kim, D. An, "Development of Integrated System for Progressive Collapse Analysis of Building Structures Considering Dynamic Effects", Advances in Engineering Software, 40, 1-8, 2009. doi:10.1016/j.advengsoft.2008.03.011

7

S. Pujol, J.P. Smith-Pardo, "A new perspective on the effects of abrupt column removal", Engineering Structures, 31, 869-874, 2009. doi:10.1016/j.engstruct.2008.11.022

8

SAP 2000, "Version 14, Analysis reference manual", Computers and Structures, Inc.,Barkeley, California.

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