How does SAP2000 calculates (I/L) in nonprismatic columns

[cprr0107]

How does SAP2000 calculates (I/L) in nonprismatic columns for the calculation of the effective length k factors.

You may see Chap. 2 p.13 design algorithms of SAP2000.

thanks..!!

 

[IJR]

I think it will set K to 1.00 when there is a nonprismatic member framing. And if it does, dont blame it.

What version is that you are using?

I personally quickly calculate K myself and input it into software.

 

[cprr0107]

-IJR

thank you for your reply.

i use v14.

I need to verify how does Sap2000 approach for these value for nonprismatic steel columns. i have modeled a moment frame and my model shows value of k=2.703(major) and k=1.150(minor).

I have already verified the output of sap 2000 for prismatic columns and its correct.

but i cannot verify the output k factor for the nonprismatic steel column output by Sap2000 v.14 (k=2.703&k=1.150 above).

can you please tell how to quick calculate the value of k factor for nonprismatic steel columns?

thank you again!

cprr0107

 

[IDS]

I don't know how SAP does it, but this thread:

http://eng-tips.com/viewthread.cfm?qid=278129&page=1

has details of a hand calculation method and a spreadsheet that will do it.

Or go straight to:

http://newtonexcelbach.wordpress.com/2010/08/09/buckling-of-columns-with-varying-cross-section/

for the spreadsheet.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[IJR]

cprr

Depends on your convenience.

With SAP2000 it is still possible to find K-factor by performing a buckling analysis. You need to master the theory of buckling analyis very well before attempting this. It is easy to make an error especially if the frame does not sway much. It can be very reliable when the frame sways a lot.

My old copy of AISC specification had Appendix D which covered nonprismatic columns

DIN 18800(old German code that still influences European codes) had a special chapter on buckling, and it enabled you to find equivalent prismatic moment of inertia and area for any shape of taper(wide at end, wide at mid etc).

Rule of thumb: For single story buildings use K=2.5 and for multistory use K=1.5. You will rarely be dissapointed unless your structure is too slender.

respects
ijr

 

[cprr0107]

Thanks for all your replies.

I already know what to look at and how does SAP does it(buckling theory).

thanks again..

cprr0107