P-Delta Effect in computer programs.

[JoeyRachel]

I am reading a book which said that by using commercial programs it is easy to include P-Delta effects in a single solution without haveing to use iteration technique. I am just curious how can they do that and what is the theoretical bases.

Happy New Year.

 

[ash060]

It is possible to do it without iteration, I don't remember it much becuase it has been a while since I read about, but CSI as a little black Hardcover book you can buy that has the theory in it.

I am sorry but I don't remember the name of the book, but if you went to their website I am sure you could find it

 

[asixth]

JoeyRachel,

Which book are you referring to. I don't know of any software based on beam element programming that can include P-delta effects in a single analysis. I would always think a iterative solution like Newton-Raphson's would be necessary.

 

[frv]

Unless you are solving the governing differential equation directly (and computers usually cannot), you almost certainly need to apply iterative processes.

On another note, there are very few real world problems that can even be set up to solve directly with a differential equation. Anything statically indeterminate CANNOT be solved directly. Think about it; the simple fact that you MUST select a trial size to solve it means that it is an iterative process. With very few exceptions (certain geometric and loading setups) your loads will depend on the geometric properties of the members so you cannot know the result before you select a trial section and you cannot finalize your section without knowing the results.

 

[MiketheEngineer]

Actaully computers are very good at iterating - that is something they do best.

I have written a number of algorithims that iterate to a solution - you just have to know when to stop....

 

[ash060]

Static and Dynamic Analysis of Structures by Ed Wilson, If I remember ETABS does have an option to do a non iterative solution.

 

[WillisV]

A non-iterative P-delta analysis is certainly possible by using the reduced geometric stiffness technique. Such an analysis is used by RAM as well as one of the options in ETABS. It is fairly accurate for general building structures but it is not exact (as an iterative process is) and can result in errors in buildings with very short stories or cut up-diaphragms, etc.