Telecom Wind Design section 1609.1.1

[Antnyt23]

I just wanted to confirm that I am correctly interpreting the code for the wind design of antenna supporting structures.

Nearly all building codes call out section 1609.1.1 determination of wind loads where they state that it is calculated in accordance with ASCE 7. It is then followed by exceptions which state 5. Design using TIA/EIA-222 for antenna supporting structures and antennas.

My interpretation is that any antenna supporting structure is to be designed in accordance with the methods and wind speeds outlined in TIA-222 and wind speeds as described within there.

This is how I have always went about design/analysis in telecom. However, I have had someone come back to me in a case in NY where they are saying that the NYC building code (Section 1609.3) states The basic wind speed for NYC 3-second gust speed is 98mph. The NYC building code additionally has the similar building code section 1609.1 as stated above. Several counties under the NYC code have wind speeds at 105, 110, ect. in accordance with the TIA 222 county look up.

My interpretation remains that due to the statements and exceptions in section 1609.1.1 you would immediately go to TIA-222 and use the wind speeds and calculations as stated in it.

I just wanted to see if others agreed with my interpretation or disagreed with it.

I have also contacted the jurisdiction and am waiting for them to return my call but wanted to get other engineers input on this subject matter.

 

[msquared48]

I ran into a similar case where a short 40 foot tall antenna was mounted on top of an old two story wood warehouse in Tacoma, WA. The tower was analyzed using the wind loads of TIA-222G-05, but the building framing analysis used the tower reactions and was analyzed according to the IBC and ASCE7. I factored the wind pressures applied to the tower, and the associated reactions from the tower, to bring them in line with those of ASCE7 for the building framing check.


Got it to pass... But not before I factored the loads.

Mike McCann
MMC Engineering

 

[Antnyt23]

Seems to be some "grey area" to what defines the antenna supporting structure. In your case it sounds like the antenna tower was defined as the antenna supporting structure which were analyzed in accordance with TIA 222. Even though it seems the building is a antenna supporting structure you had to analyze it in accordance with IBC/ASCE 7 and only the antennas and antenna tower were analyzed in accordance with TIA 222. This makes some sense that at least the tower, mounts, and antennas were analyzed in accordance with TIA 222.

In my case they are trying to tell me that the antenna frame and antennas that are connected to the building should be analyzed in accordance with the 98mph wind speeds and not in accordance with TIA 222. I still believe the antennas and antenna frames should be analyzed in accordance with TIA-222 in my case but I could be wrong. Additionally, I think this is a good example where section 102.1 governs that the most restrictive of the two should govern (in this case TIA-222).

I guess in the end the governing AHJ's opinion is all that really matters.

Appreciate you sharing your experience Mike! Would love to hear more examples, experiences, feelings, or interpretations on this issue.