Running Load Combo's and Cases

[Stazz]

Why does Risa run each load combination rather than running the load cases and then superimposing them. I know that you need to run each load combination for a P-Delta analysis, but if you're not using P-Delta then why can't you superimpose the load cases? Is there a reason for this because its much quicker and RAM does is.

 

[JoshPlumSE]

RISA used load combinations because that is more accurate.

That's because of various non-linear effects (P-Delta, Tension only members, compression only springs, Direct Analysis Method's stiffness adjustmenst...et cetera,).

Technically, it would be possible for us to use one solution strategy (Load Cases) whenever non-linear effects should not be present and a seperate solution method when those effects are present. However, we have not chosen to do this at this time.

By the way, when are you allowed to solve without P-Delta these days? Wood design? It seems to me that all the new codes are really emphasizing these types of second order analysis requirements in their analysis requirements.

Josh