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Re: Pushover Analysis Techniques

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Bill:
A few comments:

> Remember, Push over analysis is a 1960's era estimated hand analysis
> technique with a stated list of limitations and simplifing assumptions. 
> Similar to the approximate methods of the portal and cantilever methods for
> frame analysis, push over requires the structures to be of shear response
> modes or greatest participation from the first mode and not a flexural
> response.

I don't believe that computational push over analysis is quite as
approximate as the (useful) portal and cantilever methods.  These
truly approximate methods replace compatibility and constitutive
relationships with approximations.  The computational push over
analysis methods approximates the dynamic loading effects by means of
a pattern of monotonically increasing static lateral loads, but the
resulting system is solved exactly (by the FEM).  As you note, this 
method still has limitations and simplifying assumptions, but it is a 
useful tool to investigate likely post-elastic behavior.

> Computational push over analysis has been proposed for non-linear material
> analysis of first mode, shear mode, dynamic response analysis.  This
> disregards any higher modes and any interstory movement differences and
> contributions.

It is possible to reflect some of the higher mode response and 
"interstory movement differences" in a push over analysis by changing 
the pattern of applied loads as the analysis progresses.  One useful 
methods bases the pattern of loads on the modal content at different 
yield states.  The goal here is to monotonically increase the total 
shear applied but to capture incremental changes in the possible 
dynamic response.

-Mike Valley

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201