approach for designing unbraced 9steel0 frames
 

approach for designing unbraced (steel) frames.
i have a frame where the method of lateral force resistance consists of (entirely) moment connections. rather than go through and figure all the k-values for the members, i thought that i might just set all the k-values equal to 1 and do a analysis & design considering the p-delta affects. do you consider this feasible? after all, isn’t that what the k-values attempt to compensate for (i.e. increased moments from p-delta)?
(as you’ve probably already guessed: the program i am using for analysis can do a p-delta analysis very easily, but the k-values have to be figured manually.)
check out our whitepaper library.
this is a sway structure, i think the k- values for columns should be more than 1.
yes, if a p-delta analysis was not being performed you would need to use k-values greater than 1. but what i am asking here is: does the p-delta analysis compensate for that.
"but what i am asking here is: does the p-delta analysis compensate for that."
hand calculation using code prescribed formulas (k values, etc)is an approximate solution to p-delta effect.
a computer program capable of doing such should be more refined than hand calculation.
does that mean if you do a p-delta analysis and use k values that you are being overly conservative?
there are 3 sources of buckling for this type of frame:
1. - largep large delta effects - due to translation of ends relative to each other.
2. smallp smalldelta effects - due to deformation of member between ends.
3. buckling due to initial out of straightness of member.
in a second order analysis, 1 and 2 are taken care of in the analysis and 3 is allowed for by designing the
thanks csd, et al.
check out the latest aisc specification - they have three methods to deal with structural stability and i think two of these deal with using pdelta analyses and how to treat the k values.
i agree with the above that a proper pdelta analysis can substitute for k values > 1.
so can someone please confirm my understanding?
if i have a sway structure and i am not performing a p-delta analysis using my analysis/design software, i must use the nomograph of sway frames to find the appropriate k values?
if i have a sway structure and i am performing a p-delta analysis using my analysis/design software, i can use the nomograph for non-sway frames despite having a structure that is sway?
i think that based on what was said here you would still have to use k=1.0. if you use nomograph for non-sway frame you will k<1.0.
that being said, i still have to convince myself that you can get away from k values by doing a p-delta analysis.
i am not convinced yet.
alright, thinking about this a little further. i don't think you can use a k=1.0 for a sway frame just because you do a p-delta analysis. to say that p-delta analysis and k values are accomplishing the same thing is imo not correct. k values have been around for quite a qhile, correct? it is my understanding that second order effects being accounted for in the code is relatively new thing.
also, i believe what csd says about the second order effects taking care of two of the three buckling causes, but in chapter h (pg 16.1-70 of the 13th edition), under design of