Allowable pole tip deflection for single Pole Wood Structures

[Sen00]

Hi All,

Just wondering what your experience is with wood pole tip deflection limits.
Do you use a limiting value on your tangent structures for a new design ?

 

[transmissiontowers]

We replace single wood poles when rebuilding a line and do not use them on new line designs. For transmission voltages, the big wood poles are hard to get and expensive so we use spun concrete in place of wood. As far as deflection limits, we don't have a limit for wood or concrete or steel poles. 10% of the height has been used but mainly for aesthetics. As long as the conductor does not swing out of the right of way for a 6 PSF wind, we are fine with almost any deflection.

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

 

[leo5cn]

Wood pole would rupture at 10% deflection, so it's a stress limit.

 

[Sen00]

"Wood pole would rupture at 10% deflection, so it's a stress limit."

I have never heard this before, Do you have any studies or documentation you could point me to where this is proven ?

 

[leo5cn]

wood pole is not a manufactured product, the COV is about 20% for MOR under bending.this 10% is a very rough estimate and rather deterministic, it really depends on the pole species and the MOR you use.

 

[transmissiontowers]

If you have PLS-POLE, you can run a few poles and see what the deflection is vs. the stress. When I get a chance I will run a few poles and post the results. It may be a day or 2. I'm in the middle of modeling up a 300' plus lattice tower.

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

 

[leo5cn]

@Transmissiontowers, say a standard pair of tension compression diagnals,in plane effective length factor 0.5, rz also 0.5, what is the factor you use for out of plane buckling unbraced length ? 0.7 ?

 

[transmissiontowers]

I was assuming the OP was talking about a single wood pole. I ran the example single wood pole WPOEX01.POL with the example load file and the deflection was 39 inches for a pole that is 65.5 feet above ground (75' Douglas Fir Class 1 pole buried 10%+2') so that is about 5% deflection. The pole stress was at 91%. The example used a Strength Factor of 0.25 so the pole was only using 2000 psi out of the 8000 psi allowable stress. I don't deal with wood much and if I upped the strength factor to 0.5 and applied more load to the tip, I can get closer to the 10% of pole height deflection.

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

 

[leo5cn]

Here we use 0.5 for western red cedar, 2800psi