Monopole Retrofit (RisaTower) 1

[crawdaddy1983]

I've got a new one on my plate. I'm trying to work out the best way to design a monopole with channels attached to the outside edge. I have RisaTower but can't seem to find any function for this design. I'm thinking of splitting the tower/channels into 5 ft sections. Using the bending moment and shear diagrams from RisaTower and then creating a builtup section in Enercalc that will handle the shear and moment.

The only problem is i'm not sure how to finish out this calculation. Right now the Enercalc only gives Section modulus and moment of intertia. Does anyone know a calc that can tie this together?

 

[ishvaaag]

I assume you are not talking about the sectional properties, that you can deal with with Steiner's theorem. You can also use generic sections in RISA, only that the completitude of the results can't make for a complete design. As long you have for your built-up sections a proper value of the solicitations, taking intou account material and geometrical (mainly P-Delta) nonlinearities, and your monopole divided by segments, you can use checks by section H in AISC with K=1 for each segment. The P-delta procedure will have sorted out all effective length issues by the time you have the proper solicitation values, and so you only need to care about strength-like checks (sinc K=1 known). Normally, practical channels won't make you to think much about local slendernesses, yet give a look.

 

[JoshPlumSE]

Seperating the pole into 5 ft sections and then using an "arbitrary" shape in RISATower is probably the best way to go.

RISATower will give you the ability to do generic code checks (F standard mainly) based on the properties (Ix, Iy, A, QaQs, Sx, Sy, et cetera) that you enter for the shape. You would have to use another program (or hand calcs) to come up with those values. Enercalc could work, RISASection would work, but there are a number of others as well.

Let me know if you're using the TIA G standard. If so, then I'd have to check to see exactly how the code checks on an arbitrary sections are done.



Josh

 

[crawdaddy1983]

I am designing to the G-standard.

Do you know of a hand calc for QaQs?

 

[ishvaaag]

I don't know in TIA G, in AISC 360-05 would be section E7. MEMBERS WITH SLENDER ELEMENTS, you find the worst case and applies, so better not to add something that, out of being as slender, undermines the strength that you can exact of what existing.

 

[JoshPlumSE]

For QaQs, you should look up the AISC or TIA equations. For the most part, they should be the same. Though, for now the G standard ignores this for arbitrary shapes.

I looked up what we do for the design of arbitrary sections to LRFD based design (Rev G):

phi*Mn = 0.9 * 1.5 * fy * S

Where S is the smaller of S_top and S_bot, for each bending axis.

The next release will revise this slightly to be:
phi*Mn = 0.9 * 1.5 * fy * S * QaQs