Design of steel pole ASCE/SEI 48/11

[rubenpezu]

I hope you could help me. We are thinking in buy PLS-POLE to redesign our steel transmission (octagonal) poles. They are form 90's. But first I want to learn how calculate manually in order to use correctly PLS-POLE. We have bought ASCE /SEI 48-11. And after read it carefully I have some doubts.

Our poles have a vertical force (V), a transversal force or nominal (F) and some times (only in the biggest) a Torsional force applied at 1,5 meters form axis (T). According this and ASCE/SEI 48-11 I want to calculate manually:

Tension (point 5.2.2) P/Ag < Ft

Compression (point 5.2.3.2.1) P/A + Mc/I < Fa

Shear (5.2.4) VQ/Ib + Tc/J < Fv

Bending (5.2.5) Mc/I < Ft or Fa

Combined Stresses (5.2.6)


I have doubts wiht the forces I have to consider to calculate this stresses. For example:

P should be our vertical force (V)?
M I guess is our transversal force (T) * distance from ground. Am I right?
V, shear force wich one should be?
T Torsional moment is the torsional force * distance from axis of the pole. Am I right?

Thanks.

 

[transmissiontowers]

PLS-POLE is a specialized FE analysis program with a graphic front end made specially for the T-Line steel poles. You would need to buy the steel pole option if you don't need the concrete or wood analysis. It is fully compliant with ASCE 48 and will also check (and design) baseplates on the poles according to the latest ASCE 48 baseplate method (many pole suppliers have their own proprietary baseplate method).

The program will handle almost all types of steel poles. The only exception that I know of are the stretched octagon pole AB Chance produced in the 1970's which have 2 very wide flats that cause w/t problems. If you don't have any of these poles, the program will be fine for you. If you are concerned with load points on brackets off the arm tip and pole connections spaced away from the pole shaft, you can use a Vang Plate which is a load transfer mechanism that puts the load point eccentric to the pole centroid to get the moments correct.

If you want to manually calculate the pole shaft stresses using your loads, you can check the stress at the base or at any point along the shaft. I'm not sure if PLS offers a limited period trial license, but you can call or eMail them to check. Be assured that most of the utilities in the USA and many pole fabricators use PLS-POLE to analyze their poles.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Thank you for your answer transmissiontowers, I know how PLS-POLE works. I have used in my previous work.
What I would like to do is calculate the pole by hand and later compare with PLS-POLE when we buy.

 

[transmissiontowers]

You can get an approximate answer by calculating the stress at a cross section of the pole by summing the moments and shears at the point along with the wind on the tapered pole shaft and conductor. You will miss the P-Delta moment from a non-linear analysis.

About 30 years ago I wrote a Fortran program to analyze pole shafts that took P-Delta into account using a finite difference method. I think I also found a FE Fortran program in a book somewhere that I modified to take a multi-sided pole and calculate the stresses at the points.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

I did an approximate calculation and I have obtained the Compression, bending and combined Stress according ASCE. For compression and bending I have more ore less normal efforts but in the combined stress the value is too high. I attached the spredsheet I have done, is very simple. Maybe I have a mistake but I couldn't find.

 

[transmissiontowers]

I see your problem. In equation 5.2-20 from ASCE 48-2011 for the combined stress you have double the bending stress (your cell B85 is added twice for the formula in cell B93). The equation is for bi-axial bending about the XX and YY axis. You probably just calculated the resultant shear and did one bending stress check. You need to split the XX axis forces and moments from the YY axis forces and moments and calculate them separately. If you only have forces in one axis, then the other axis bending stress is zero.

My other problem is I don't do metric units. I do speak a little Spanish but no Portuguese.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Thanks, I really appreciate your help, I couldn't find what I was doing wrong.