a case in calculation of lateral stiffness !!
a case in calculation of lateral stiffness !!
(OP)
I have posted same problem in Seismology department here , but i think i explained in a not clear way , i got no reply ,,
well , the problem is , i am calculating lateral stiffness for frames , steel frames , and to reach story lateral stiffness and CR point .
problem is , i have an oblique grid line due to architect plan , and i dont know what to do with the oblique frame lateral stiffness ,
if i neglect it , i have to deal with great deal of torsional moment due to eccentricity ,,,
plz guide me !
well , the problem is , i am calculating lateral stiffness for frames , steel frames , and to reach story lateral stiffness and CR point .
problem is , i have an oblique grid line due to architect plan , and i dont know what to do with the oblique frame lateral stiffness ,
if i neglect it , i have to deal with great deal of torsional moment due to eccentricity ,,,
plz guide me !






RE: a case in calculation of lateral stiffness !!
RE: a case in calculation of lateral stiffness !!
here is the pic :
RE: a case in calculation of lateral stiffness !!
Then don't neglect it, however it will cause a different type of torsional moment due to it's orientation.
But it's likely this torsional moment will be easier to deal with then if you neglected it altogether.
RE: a case in calculation of lateral stiffness !!
As for preliminary member sizes for the frames, I usually do this by concentrating on limiting drift and second order amplification effects. It's pretty involved reall, especially by hand.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: a case in calculation of lateral stiffness !!
KootK@ i dont get you , by fictional frames ,, i mean , i only need to calculate in NS direction , and in that direction under E and F we have only one column , do u mean i add imaginary columns under E and F ?
what about calculating the lateral stiffness of D1 TO F4 , and then divide it into horizontal and vertical components of stiffness , does it make sense at all?
Tnx guys
RE: a case in calculation of lateral stiffness !!
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: a case in calculation of lateral stiffness !!
okay , i will attach the actual plan here :
RE: a case in calculation of lateral stiffness !!
Kudos to you. I like to understand things too. Is it correct to assume that you have moment frames around the perimeter of the building and not in the interior?
With hand calcs, we basically convert all of our lateral resisting vertical elements into equivalent lateral springs. What I was proposing was to take the oblique lateral spring, representing your oblique moment frame, and convert it into equivalent N-S/E-W springs using trigonometric projection.
I believe that this is precisely what I have proposed.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: a case in calculation of lateral stiffness !!
umm , as the specifications tell me , in the NS direction my lateral bearing system is moment frame , yeah , but that is not the case for the EW directiom , i assumed that bracing system will act on that direction only , and frame is simple ,,
....
so , i take your advice and will divide the stiffness of the oblique frame into NS EW directions ,
it is simply interesting how trigonometry involves everywhere )) !
RE: a case in calculation of lateral stiffness !!
RE: a case in calculation of lateral stiffness !!
FYI: For Seismic Design Category D and higher, ASCE-7 does not allow equivalent lateral force analysis for buildings with this type of irregularity unless it is risk category I or II and two stories or less. I encourage you to do the hand calcs, but the code may require a different analysis
RE: a case in calculation of lateral stiffness !!
I believe that the non-orthogonal effects can be captured in the hand analysis so long as the frames in all directions are represented in the analysis.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.