Annular Baseplate analysis
Annular Baseplate analysis
(OP)
I was looking at an example of a monopole tower analysis that is openly available on google at:
http://www.usedtowers.com/MONOPOLES/117%20IDAHO/99...
I am trying to better understand where all values come from however am having some trouble understanding how the one item is calculated.
on page 9 the plate moment is calculated as 273.6 in-kip....
I thought I had read somewhere that the actual plate moment of an annular plate could be calculated as the plate being a cantilever beam. So I thought it would be the (Bolt circle-OD of the pole/2)*tension in the bolt
the tension force in the bolt is 184k((30.6875in-25.5in)/2)=477.25kip-in
I have a feeling i'm completely misunderstanding something and was hoping for some clarification on the correct way to calculate this
http://www.usedtowers.com/MONOPOLES/117%20IDAHO/99...
I am trying to better understand where all values come from however am having some trouble understanding how the one item is calculated.
on page 9 the plate moment is calculated as 273.6 in-kip....
I thought I had read somewhere that the actual plate moment of an annular plate could be calculated as the plate being a cantilever beam. So I thought it would be the (Bolt circle-OD of the pole/2)*tension in the bolt
the tension force in the bolt is 184k((30.6875in-25.5in)/2)=477.25kip-in
I have a feeling i'm completely misunderstanding something and was hoping for some clarification on the correct way to calculate this






RE: Annular Baseplate analysis
I can think of several different ways to approach this, and as it appears the design method is somewhat codified, the only way to duplicate somebody else's answer would be to find exactly what that codified method is.
The moment you're calculating would be the moment about a line of bending tangent to the pole, and implies a corresponding width at the bend line. Perhaps the method in question is calculating the moment about a point nearer or at the center, or the moment about a radial line.
Note that the plastic section modulus would be 1"xWx0.5"x2 = W, which implies a 13.35" wide section, and it is not immediately obvious where the width is 13.35" given those numbers.
RE: Annular Baseplate analysis
RE: Annular Baseplate analysis
Design of Monopole Bases, by Dan Horn
It's the most complete treatment of this subject that I have seen. And, I'm not just saying that because I'm with RISA. If it doesn't have the information you want, then the references section will probably show you what articles you want to obtain.
RE: Annular Baseplate analysis
As far as the moment, it looks like it's calculated from the inside face of the hole. So (30.6875-2.25-25.5)/2=1.47 inches. 184 kips times 1.47 inches equals 270.5 in kips.
RE: Annular Baseplate analysis
Jed,
I follow you so the 13.35 is similarly known as the beff calculation correct? My mistake I was thinking beff=(base plate diameter)*pi/(# of bolts) but it looks like it is pole diameter in lieu of the base plate diameter.
Similarly the equation I'm familiar with to calculate Mmax = Pten*((Bolt Circle Diameter - Pole Diameter)/2), where they used the Mmax = Pten*((bolt circle - bolt diameter - pole diameter)/2).
My understanding would be that after they had calculated their Mpl of 273.6in-kip = Mmax they would us it in the equation fact = 6Mmax/(beff*((plate thick)^2)) which would yield = 30.374ksi then fallow = fy*0.75 = 37.5ksi.
But this is just for the tension side correct it is also supposed to be calculated for the compression side.