Pushover Analysis 2

[teckert]

I have done pushover analysis using software. I am wondering if there is a way to check that Force (Capacity) and Displacements obtained from the Pushover Analysis are reasonable? It may not be exactly but it will get me within the ballpark.

Thanks,
Tim

 

[rowingengineer]

Tim might be worth taking a look at the end of the FAQ there are a lot of questions that can help find errors.
faq507-1570

When in doubt, just take the next small step.

 

[abusementpark]

I'm curious what you are doing that would merit a pushover analysis.

There are methods I know of for steel that allow you perform a pushover analysis using linear elastic software. For a particular load case, it requires making a new model each time a hinge forms, and summing up the results from each stage. There are some approximate corrective measures that need to applied to account for axial load (if it significant in your columns).

You have to assume a yield surface for your steel members (the relationship between bending moment and axial load). You also have to assume that plasticization of cross-sections occurs instantly. Also, you need to have a good idea of which load combination will govern, because you don't want to do this three or four times, IMO.

 

[rowingengineer]

There are a few programs running around that claim to be able to perform this type of analysis as a non-linear fashion. However I am yet to hear of this being used for any new structures only ever hear of it in combination with existing structures. Never had to perform a pushover analysis myself, have a friend that is involved with R&D and all he ever said "you needed to treat it the same as normal design but backwards".

When in doubt, just take the next small step.

 

[JoshPlumSE]

There was a time (before push-over software was available) where if you wanted to do this type of analysis, then you had to use linear software.

There is an appendix to one of the early FEMA documents that has an example where they have done this.... I used to have a copy of this. Haven't looked at it in years. I'll see if I can dig it up and let you know the reference.

 

[InDepth]

Pushover analysis...oudated and inaccurate. If you want the real thing, perform non-linear time history analysis.

 

[JoshPlumSE]

InDepth = not a helpful response

I won't dispute that non-linear time history would be considered more accurate than a push-over. But, isn't the whole point of a push-over analysis that it is simpler and less time consuming to perform?

Also, please elaborate on the "inaccurate" comment. We're engineers.... we only care about accuracy on a practical level. We've not all going to go out there and write a PhD dissertation on every project solely for the sake of increased accuracy. I only need enough accuracy to demonstrate that the design / retrofit concept is sound or un-sound.

 

[abusementpark]

What are you guys considering the difference between pushover analysis and non-linear time-history analysis?