Evaluation of Missing Member Analyses for Progressive Collapse Design of Steel Buildings and Girder Bridges
Date
2010
Authors
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Publisher
University of Delaware
Abstract
The most common analysis method prescribed in progressive collapse
specifications is the alternate load path analysis, which is a means for ensuring
adequate structural integrity and load redistribution capability in a building. This
approach is generally viewed as “threat-independent” in that it assumes the removal of
individual columns (and is therefore termed a “missing column analysis” in this work),
but does not consider the initiating event leading to the failure of these members.
However, for reasons described herein, it is of interest to determine the blast loading
that corresponds to column failure, which is an underlying threat implicitly assumed
by these provisions. This is carried out through dynamic finite element modeling
using the commercial software LS-Dyna. The modeling methods are validated using
experimental results available in archival literature and sensitivity studies are
performed to assess meshing requirements. As a result, the charge size and stand-off
distance producing failure of an individual member is determined.
The alternate load path analysis has been shown to be a relatively simple, yet
effective method for progressive collapse mitigation in buildings, as they are made up
of many members in a three-dimensional frame, resulting in redundant structures with
high capacities for load redistribution. To investigate if a similar analysis method may
be used for girder bridges, which are also susceptible to progressive collapse, theirload redistribution capabilities are of interest. This is explored by removing the load
carrying capacity of a single girder, redistributing this load, and evaluating whether
adjacent girders have enough strength to withstand the new service loading. By
analyzing the results of these analyses, insight into the potential use of this method as
a means of evaluating girder bridge redundancy and collapse resistance can be
obtained.