Antenna Mount Tieback Connection

[ENGINEER92]

I have posted a document showing my calculations for checking a tieback connection for an antenna mount. The equations I used to check this connection were pulled from TIA-222-REV H, Section 4.9.11.3. Section 4.9.11.3 is for determining the a U-bolt capacity against sliding and torsional forces. The tieback connecion I am checking is V-notch with a saddle bracket. I used section 4.9.11.3 since this connection is all about the pretension and friction coefficient.

I have never seen anyone fail a mount for the tieback connection before. So I am a little hesitant to do it. I would appreciate a second opinion on this connection and how to check it.

 

[ENGINEER92]

I apologize I forgot to attach my calculations.

 

[spieng89]

Are you confident in the reaction you calculated? From the picture, the antenna that appears to be on the mount doesn't have a solid surface area which would reduce wind pressure loading. Have you taken into account any possible shielding of the mount surface area from the antennas?

From your calc you are only considering one threaded rod resisting torsion. Would both not contribute resistance?

Also I am having a hard time seeing how the torsion comes into play with the bolts. Seems as if slippage caused by torsion of clamp around pipe would be the check

 

[ENGINEER92]

Thank you spieng89 for responding.

I am confident in my loads. The existing antennas in the picture are being replaced with new antennas and we are checking the mount for new proposed equipment loading. As for shielding, our office references two documents when we run mount analysis. The first being the TIA-222 tower code and the second being the mount analysis standard, that the telecommunication carrier we are working for has created. In this standard it states "No shielding of mount members shall be considered due to a supporting structure or from antennas, mounting pipes or mounted appurtenances."

The Tp in my calculation is the installed pretension in each bolt. That is correct, but when I calculate the nominal sliding strength (Rns) I take into account the both bolts pretension. Rns=0.3(2Tp-Tut) the 2 in the equation is used to take into account both bolts.

The torsion comes into play due to the 5.5" eccentricity of the connection to the tower leg. The eccentricity of the connection causes a moment around the tower leg and I am checking the clamping forces of the 5/8" rods to resist this moment. I attached a file showing a simplified free body diagram of the mount. Let me know if this is still unclear.