Process to evaluate lattice tower wind rating

[photoengineer]

I am looking at doing engineering calculations on lattice towers. I have read through TIA-222-G and believe I understand what needs to be done in order to verify the tower is safe to a specific wind load. Can someone verify that my process is correct?

1) Determine max wind speeds based on TIA-222-G or local jurisdiction requirements.

2) Calculate wind loads on tower using equations / process defined in TIA-222-G.

3) Create model of tower for FEA analysis.

4) Apply loads calculated in (2) to tower model. (Ensure dead loads are included in model.)

5) Compare maximum stress from FEA to max stress of tower material / guy wires / etc. If max stress is less than tower material rating, we're good to go.

Of course, that assumes I'm not concerned with earthquake loads (I'm not right now). I would have to do the same process with ice loads to compare tower under icing conditions.

Cedar Bluff Engineering

http://cedarbluffengineering.webs.com

 

[JoshPlumSE]

Towers can be trickier than you might think. Some other items that are perhaps just expansions of what you've already said.

2b) Apply appurtenance loads to tower.
2c) Account for shielding effects for tower.
2d) Evaluate icing loads on the tower to see if they have the potential to control the design (with a reduced wind load).

3b) Make sure you account for non-linear geometric effects in analysis i.e. P-Delta effects. These are much more likely to have a significant impact on the design of a communications tower because they are so much more slender than typical building or idustrial structures.

5b) Capacity is not just based on material rating, but on member behavior. Local Buckling of a cross section, member buckling or overall tower buckling.

 

[transmissiontowers]

If you are in the tower analysis business, you will need a program that automates the loads and capacity calculations of the EIA/TIA. We use the suite of programs from PLS-CADD which has a pole program for the monopoles and a Tower program for guyed and free standing lattice towers. Look at their web site

http://www.powline.com

for some info. There are also some others and I think RISA has a tower package along with a few others.

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