ROOF TOP POLE DESIGN

[Ayando]

Any Idea on how to design rooftop poles for Telecommunication Equipment

 

[DamsInc]

You're going to have to be more specific.

Usually, the mast is connected to a ballast mount to avoid penetrating the roof. The antennas which are attached to the mast often have criteria limiting the amount of rotation of the antenna under specified wind speeds.

 

[Ayando]

Thanks for the response. I agree, basically for a MW, we would like to ensure a deflection check that will not throw the MW out of the line of sight. I am looking for solutions-like excel based work sheets that will be able to provide member sizes based on specified design code for rooftop pole mounts. The Software I am currently using-SAP2000 is not able to analyze these structures based on the TIA-EIA-222-G Code. Any help?

 

[DamsInc]

To be honest, we did very little calculations for the mounts. The ballast mounts we used were a standard design and very robust which would work for all wind load cases. The only real calculations for the mounts which had to be done were to resize the HSS mast based on the required height for the antenna. If the mast got too long then you might need to modify the bracing, but again this depends entirely on your design. You should be able to create a spreadsheet very easily for your standard design.

I only did this for a few months and was very junior at the time so I don't really have a lot of advice to offer.

 

[graybeach]

I do a lot of these and the most difficult part is to establish a moment connection at the base of the pole. Usually it is necessary to penetrate the roof and attach the pole to both a rafter and a joist. Sometimes it is necessary to install additional members to connect adjacent joists and rafters so the loads can be shared among multiple bents. Make sure you model the connection properly in your deflection analysis. If you just assume fixity at the top of the roof, you may underestimate deflections. I am sure you know this, but keep in mind that wide flange sections have virtually zero torsional stiffness. Just attaching the pole baseplate to the one flange of a wide flange section does not provide fixity in the transverse direction.

 

[Ayando]

Thank you both for the information. Very helpful. The pole is expected to be mounted on a concrete rooftop. My major concern has to do with sizing up the members based on 1 -3 load combinations-taking into consideration dead load and wind load. See attached Photo of what is proposed.

 

[dhengr]

Ayando:
If you can’t do this problem without a bunch of help, you probably shouldn’t be doing this problem for the sake of public safety. And, a spreadsheet isn’t going to turn you into an instant engineer, either. You should be getting your mentoring from your boss, right in the office, where someone can guide you step by step until they know you understand what you are doing. This helps keep you and the company out of trouble. If the boss doesn’t know how to do this, or help you, then the company probably shouldn’t be doing this work either. There may be a few bldg. code issues which need to be considered in the placement of these poles on a bldg. roof, but otherwise sizing your pole members, base plates, stiffeners, welds, etc. should not be that difficult an engineering problem, if you are an engineer and have a little experience. What is your engineering education and background? You’ve actually got some pretty good drawings as a starting point, but some of the details may also be dictated by the bldg. structure which is involved, and you have to verify that the existing structure can take the added loads.

 

[Ayando]

Thanks for your comments. I thought this forum was for learning. Not every engineer is well versed in all areas of engineering. It depends really on what you have been exposed to in your career from the beginning and you have to take all the time to learn new things. My research in this area of work is not limited to this forum.

 

[DamsInc]

This forum is definitely for learning. However the question you have posed to the forum is essentially "how do I design steel members". The answer to this question begins with basic steel design courses in university and can't be answered in a forum post. If you haven't been exposed to steel design in your career, then you need to be working under somebody who has.

 

[Ayando]

My question was not " How do I design steel members?". Please refer to my first post...Question: Any Idea on how to design rooftop poles for Telecommunication Equipment? Now if you have the information and you are not willing to share that's fine. Your comments as far as I am concerned are not useful.

 

[NOLAENG]

Design poles to withstand applicable loads. Simple enough.

 

[Ayando]

Thanks

 

[djrexy]

Ayando,

Structural calculations for telecom equipment are a particular engineering field. Also there's different levels of equipment positioning: Ground, telecom structures (towers) and building structures.

IF project is located in US, use ASCE-7 to determine your WIND, ICE, SEISMIC (OPTIONAL) AND LIVE LOADS.
Use TIA-222-G (table) to accurately determine the wind, seismic and ice thickness on the structural / equipment (based on state / county).

For wind you need to consider the roof height, and as a safe practice NEGLECT any covers. Use Exposure C (default) or D if near shore on ANY COAST (CA, OR, WA (West), TX, MO, LA, AL, FL (Gulf), and up the East Coast) This usually translates into higher wind loads and reactions. Usually wind governs but don't take that for granted.

For Seismic use non-building structure design with corresponding values for seismic coef. (CH 13) If one prevails over the other just perform a single lateral design load (wind OR seismic) and just do a check for the other.

Live loads: consider 300 lb concentrated moving load ( at least) in addition to all new and existing equipment. Consider all work stages (before, during and after construction) with all load combos (especially check Dead Ice + Wind Ice). Use common sense and think of any possible scenarios.

On roof tops you need to consider the minimum 20 psf live load ( with some reduction factors if applicable) in addition to your platform and equipment dead load for roof structural elements.

Dead loads: Consider everything and try to approximate if unknown. Count all cables, antennas, dishes, RRU, RRHS, panels, batteries, etc. both existing and proposed. Mix the ingredients based on the loading scenario.

Antenna Mounts: just check the pipe and the bolts for vertical and lateral worst combo. Don't worry about the antenna itself or attachments since it's the manufacturer's responsibility.

Always request a MOST RECENT site inspection and don't just go with Google / Bing maps or any inspection older than 6 months. Things can changed quickly especially in the telecom field, as far as new carriers or new equipment.

If unsure, use your peers to double check your assumptions / design. Ask colleagues or your superior for information and feed-back.

Hopefully this will give you a good head start for your design.



DJ,
5+ruc+r@1 3ngin3(ER)

 

[hokie66]

Depending on the height of your building, there may also be dynamic issues involved. On very tall buildings with masts, it is often necessary to employ damping devices.

 

[Ayando]

Thank you both so much for this vital information. We are designing for a client who prefers the EIA-TIA-222-G

 

[BUGGAR]

The pole is expected to be mounted on a concrete rooftop.

You will want to use ACI Appendix D to design the concrete anchors at the base. Let us know if you have any questions on this aspect of the design. What type of anchors are you thinking of? Do you have any input on concrete rooftop slab reinforcing design?