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Re: Pushover

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>> The end reactions of a 'failed piece' remain 'locked' at the value at
>> which the piece failed.

>Sounds like the ANSYS EKILL feature. That's one way of doing it there
>are several others.

It will be good know other ways.

>You can get reasonable results using bilinear materials. Done properly it's
>probably a better simulation of reality, since members don't suddenly pop free
>diring a collapse until the deformations become enomous.

In fact, bi-linear model will pop members free suddenly when tangent modulus
changes at the kink from a finite value to zero.

>>Continue increasing the load and altering the model until you get a
>>progressive collapse.

>This takes a very comprehensive FEA capability involving multiple
>restarts. ANSYS can do this, but trying to figure our where to stop or
>set up APDL logic to stop the analysis isn't really a practical way to do
>analysis. It's doable, but not the sort of thing you'd do routinely, in
>any event.

>> I don't think a 'single nonlinear model of everything' is possible because
>> non-linearity implies iteration.

>It's done with ANSYS, LS-DYNA and ABAQUS (to name only 3) every day.
>It's not for the newbie and requires a solid understanding of the physics
>involved, but that's the way non-linearities are done these days.

'Continue increasing the load' and 'single nolinear model of every thing'
refers to algorithm of pushover analysis and not what a user does. Software
takes care of 'increasing the load' and making 'multiple non-linear models'.

>>'Locked' end reactions take care of cumulative effects.
>It does for the elastic/perfectly plastic assumption, but it's a lot more
>straight-forward with bi-linear material assumptions.


>> Moreover, in pushover analysis terms, a 'failed piece'
>> isn't a disintegrated piece but one with zero or nearly zero value of
>> tangent modulus.

>Hence the utility of a bilinear material assumption.

Isn't it a shortcoming of bilinear material assumption? Tangent modulus
has just two values unlike real world situation.

>>Unlike steel, assumption of bi-linear stress-strain curve for concrete is
>>not valid so you can't get away with 'appropriately buggered stress levels'.

>That's how it seems to be done, though.

Those doing it, please be careful!

Rudra Nevatia
Structural Engineers' eBook

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