Beam Column with sway analysis

[hardman87]

I'm working on the design of a steel column which is cantilevered vertically so it is in a sway frame. I have 10 different point loads from tension of cables at 3 different heights along this column. These point loads are also in 3 Dimensions. I have done a lot of statics work just to get the moments and axial loads in this column. My question has to do with how to calculate the interaction for this. I'm looking at AISC Manual 13th Edition under Section H1. Any help would be greatly appreciated.

 

[cntw1953]

I don't quite get your question.
You have went throgh the most tedious part of getting axial loads and moments along the column. Then for each location, it has a set of loads/reactions, assume you are using ASD, the interaction for that particular section is simply fx/Fx + fy/Fy + fa/Fa. In which fx, fy = Mx/Sx & My/Sy respectively, fa = P/A, and Fx, Fy & Fa are allowable stresses per code. If the results for all sections are all less than or equal to 1.0, then you are good to go, what is the question?

 

[ishvaaag]

To combine hypotheses, there must be first hypotheses. That is, it is assumed that some set of your forces corresponds to wind x, wind y, wind 45º or wind 135º, and symmetrical it the array of cables is not. Then, since you have enough info respect wind rosette, you may elect to make combinations for wind with only for one (and then every) direction of wind, since wind only will act in one direction, every time. If the cause is not wind, first make independent hypotheses of the independent loadings and the corresponding sets of derived forces.

And in the whole process, do not forget the peculiarities of guyed masts, that affect to the derivation of solicitations for the checks.

 

[Stillerz]

Like cntw said.

I am guessing you have biaxial bending and either compression or tension on the column...probably compression.
Chug through Chapter H...you'll get it!!!!

 

[cntw1953]

I think the determination on "k" would be tricky. You will need to find some literature, and/or examples on design of guyed poles. Someone here might have that experience.

 

[Stillerz]

Well, if it is trully in a sway frame "K" should be pretty straight forward, no?

 

[cntw1953]

Could be.

 

[JoshPlumSE]

If this is the AISC 13th edition, then chances are you would use K = 1.0. Especially if you are doing a 2nd order analysis (meaning P-Delta) with a computer program.

Remember the 13th edition is strongly encouraging the elimination of the K factor in favor of including the stability effects directly in your analysis.

 

[Lion06]

I agree with Josh. Why mess around with k? Apply a notional load at the location of the point loads (if you go through the criteria, this may not even be necessary), and do a second order analysis using k=1.

One thing I would say with this method is if you are using an analysis software such as RAM Elements or RISA, be sure to break the column into multiple elements to capture the small P-Delta effects. The analysis programs typically only perform the large P-Delta analysis, so you have to break the member into multiple members to capture the member second order effects.

If you've already gone through the analysis by hand, I'm sure you didn't do a second order analysis. Consider using K=2 (for a cantilevered column) and call it a day.

Other than that, the interaction is as noted above.

 

[hardman87]

I just wanted to thank everyone who posted with help. I was able to figure it all out.