Progressive Collapse Design using SAP Staged Construction option 1

[cmrdata]

In UFC 4-023-03 documentation, it cited either SAP or other comparable software as a tool to perform necessary Alternate Path Analysis for progressive collapse design.

Example shown starting on p. 139 used the staged construction option in SAP for illustration purpose.

Even though SAP allows either linear or nonlinear analysis, the example seems to imply that a nonlinear analysis should be used. However, throughout the example, I don’t see the presence of any nonlinearity, such as nonlinear properties of the members.

Is this something performed internally within the software?
What is the goal of using “nonlinear” staged construction operation instead of an linear one?

I’m trying to assess the appropriate software for our use, hence this generic question.

Thanks.

 

[bones206]

Since you are adding or removing members, the analysis must be done in a series of piece-wise linear steps. Calling it non-linear or piece-wise linear is sort of semantics, in my mind. But if you apply non-linear material properties then each piece-wise step becomes a non-linear analysis within itself. Also, if you are changing the loading patterns at each stage and want to capture the cumulative effects, you can't really do that with the a single linear analysis using the principal of superposition.

 

[wannabeSE]

Several years have passed since I looked at the UFC. For the steel non-linear dynamic example, the user needs to define non-linear hinges on the beams to simulate the non-linear beam behavior.

 

[MrHershey]

'Nonlinear' in this case may refer to the ETABS level rather than the analysis type.

ETABS has Plus, Nonlinear, and Ultimate levels. The levels have varying degrees of capabilities (and prices) with Plus being the lowest and Ultimate being the highest. Plus is sufficient for most normal structures, Ultimate would be needed for higher end stuff like PBD or looking at creep/shrinkage on a system-wide level. Nonlinear is somewhere in between.

You need at least the Nonlinear level to do staged construction analysis with multiple stages like the example in UFC for Alternate Path Analysis.

ETABS Levels

 

[cmrdata]

Thank you all for your take on this nonlinear analysis issue.

I agree with bones206’s assessment that calling it non-linear or piece-wise linear is sort of semantics. And it is also in line with MrHershey’s statement that of the software “level”, or “degree of capability”.

FYI: the response I received from CSI is this:
“The staged construction analysis is nonlinear because it allows you to add, remove elements at different stages. Yielding and other nonlinear properties are only captured if you have hinges.”