Buckling Analysis in SAP

[naggary]

Dear All,
Kindly, I asked about the Scale factor obtained from SAP buckling analysis for Simple supported Column (attached) , I found it totally different from value determined from Sec. E3 AISC 2010.

Can anyone explain why?

Thanks alot

 

[osquro]

Hi. I can't open the file. Could you please send the s2k?

 

[Jatfuentes]

Naggary,,
Also I can´t open your file. This is because you are using a more recent version of Sap 2000 ( I think V14.02). Better send the text file .$2k or s2k,in order to open the file.

jatfuentes

 

[ishvaaag]

Since it was 2 years I had not touched SAP 2000 I am revamping my moderate knowledge about using it. I have made a doubly hinged column model (the same square tube box 100 mm outside dimensions, 6 mm thickness 6 meters long example I have been using when dealing with axial capacities at the Structural engineering other technical topics forum here) and I have not found any fault in SAP 2000. I have followed more or less the example provided in the Help system of SAP 2000 to generate the buckling case.

The most likely cause of difference with classical formulas (for buckling analysis here is for an elastic critical load value, through a factor on the applied loading) is the inclusion of the self weight of the member, that is not usually accounted in the classical derivations.

I post a pdf explaining what made.

 

[IJR]

When you model for buckling in SAP2000, then even if sway is likely, make sure you have at least one intermediate node in the column.

Just like ishvaag, I have tried many models vs books and I get satisfactory results. But only after good meshing.

respects
ijr

 

[naggary]

Dear all,
I thanks all for your time and efforts.
I found my mistake, i compared with Pcr not with Pey(correct).
Excuse me, there is another example when i tried to compare the SAP out put value to Pey in the moment frame with fixed base(attached-s2k file), i found difference in the results as the following:
for W12x72 cols(L=3m)and beam(L=6m)section
a=136.13 cm2, r3=13.51 cm, r2= 7.72 cm
1-for manual calculation:
GA=1, GB= Lb/Lc = 6/3 = 2 because the E and I are the same
K from alignment chart-sides way uninhibited= 1.45
Fey=?²*E/(KL/r2)²=?²*2038.9/(1.45*300/7.72)²=6.34 t/cm2
choosen r2 because the first mode from sap buckling about axe2-2
2-for SAP file
Pey from the first mode (buckling about axe 2-2) = 308
Fey= 308/136.13=2.26 t/cm2

please,Can anyone explain why and if any one has a source for solved example in the buckling analysis in sap?

your co-operation will be high appreciate
thanks alot