Hi, Calculor;
I have been thought that U2<1.4 can control Cf small enough, it seems wrong.
here is a result using SAP2000 to calculate a cantilever column (it's easy to check ), W14X665.
P=1192kip, Vx=6.5kip, My=-2000kip-in, L=500in
Result: U2=1.1, stress ratio=0.502 for k=1.
According to...
Some engineers told me, when we use U2, we don't need condiser the effect of k > 1.
I used SAP200 to calculate a cantilever column W14X665.
L=500", P=-1191kip, v=5kip, Mz=2000kip-in.
for K=2, Ce=1193kip, Cr=1005kip.
In this case, U2=1.1, if k=1, stress ratio=0.5
k=2, ratio=1.3
P-delta...
Hi, tg;
No all structural engineer paid enough attention to stability because most time they deal with the concrete structure and concrete columns are "short column" in general.
U2 is a simplified method to consider P-delta effect, it is used in both moment-resistant frame and braced...
Even the UBC 1997 are contained the seismic and wind design data of other countries, I don't think you can use it. You see, every country has its design and load code
Hi, trainguy,
k was not deal with moment amplification due to sway in stability analysis. k is a effective length factor for no-simple support member that compare with ideal simple support member with axial compress, it means, in that support condition, member with l length have same stability...
Hi, VOD,
My friend told me they use k=2.0 for sidesway permitted, I thank it will waste material in most situation.
It make me confuse that Appendix B told us k should be greater than 1.0 for sidesway permitted, but did not tell us how to calculate it.
I contacted one member of CISC committee...
Hi, VOD;
In CISC appendix B, k=1, 2, 2 for three special situation of sway permitted column, so I don't thank k=1 is suitable for sway permitted column.
k is a theory value for structure, no matter what kind of method to calculate, it should be almost same, if not completely equal.
CISC...
Thanks, VOD.
I understand your means, but the problem is how to calculate
the effective length factor k. P-delta analysis can't solve the problem.
For example, a column with 1000 kN axis force and 10 kN.m moment. If consisting P-delta effect and M change to 20 kN.m, it did not change a lot...
In CISC handbook, you can't get effective length of columns in a sidesway unprevented frams. It really suprise me. I wonder if I could consult other codes, let say, AISC?
In this case, you must calculate the bend moment cause by self weight. You can calcalate Fb according to AISC F.3. In the other hand, we also control l/r<=200.