25 January 2005
Connections and Beam-Columns.
Partially restrained connections can be modeled in both linear and nonlinear
analyses in accordance with the provisions of FEMA 356. The methods of FEMA 356
and 350 provide a way to verify the performance of standard shear connections of
secondary structural members that are attached to the primary members associated
with the response in progressive collapse analysis.
The majority of the Deformation Limits given in the UFC were provided by the
Protective Design Center of the Omaha District of the US Army Corps of Engineers.
These values were derived from tests and analysis and their application is
straightforward. The following sections describe those portions of the Deformation
Limits that bear further discussion.
Reinforced Concrete Deformation Limits.
As shown in Table 4-4, the Deformation Limits for slabs and beams depend
upon the tension membrane effect, which is an extension of the yield line theory of
slabs, acting to increase the ultimate resistance. Guidance for calculating the tension
membrane response is provided in Park and Gamble 1999 and UFC 3-340-01.
Also, as noted in the UFC, Table 4-4 does not contain deformation limits for
connections. Per FEMA 356, monolithic joints between beams and columns or walls
are represented as rigid zones. Thus, the deformation limits are applied only to the
Structural Steel Deformation Limits.
With the exception of the connection limits, the structural steel deformation
limits in Table 5-3 were provided by the US Army Corps of Engineers Protective Design
The values for the fully restrained and partially restrained connections for
MLOP and HLOP were taken from GSA 2003. These values were developed by GSA
based on the FEMA series of documents, with modifications to account for: the results
of post-Northridge full-scale cyclic testing; corroborative nonlinear analyses performed
by FEMA and others; and monotonic test results from Georgia Tech on riveted
connections. The magnitudes were also modified to account for the fact that failure of
only one or two connections can trigger a progressive collapse, whereas, in seismic
engineering, the category of Life Safety permits the failure of up to 10-15% of the
connections. The values for connection deformation limits for LLOP were derived from
the MLOP/HLOP values by using the ratio of ductilities for Life Safety and Collapse
Prevention from the FEMA values, i.e., the increase from MLOP/HLOP to LLOP is the
same ratio as FEMA uses to go from Life Safety to Collapse Prevention.