Allowable EPAs for aluminum poles

[greencircle]

I have a chart of allowable EPAs that can be mounted on a street light pole.

The charts goes something like this.

Pole material being Aluminum, the epas listed in the table are good when the light fixture is mounted directly on top of the pole. But when the light fixture is installed on a long arm ( say 8ft long) then we cant use the same values.

ex : 10' tall pole @ 100mph is a max of 8.3sft on the table. But, when installed on an extended arm, then we cant say the max allowable epa is 8.3 will need to much lesser. May be we will have to consider only 60% of the EPA. Is there a way to calculate this?

I am looking to develop a chart of percentage that can be used for various length of arm / wind speed.

Can any of you guys share your thoughts on this?

 

[jayrod12]

I see it as you are changing it from a bending stress situation, essentially a sign on the top of a pole, to a torsional stress situation when mounted on an arm. If wind is the only load at play (not including self weight of the fixture and arm) I see it trying to twist the column.

I think in order to determine a useful chart that isn't 80 pages long you'd need a standard (or a couple standard) arm length(s).

Then you need to figure out the pole's capacity due to both the bending induced by the self weight of the fixture and arm, and the torsional stresses induced by wind on the fixture.

 

[greencircle]

I agree with you Jay. There will be torsional force due to the offset. I wish there was a way to convert the bending stress to torsional stress. I can use a 3 fixed lengths 3ft, 6ft & 8ft of arm.

Trying to help our sales group to be able to determine if they are selling safer assemblies by considering reduced values when on arm.

 

[jayrod12]

They're completely different stresses. You may (key word may) be able to determine the allowable stress from the capacities in that table and then calculate the torsional stress from that.

Although I would bet you'd have more luck using the sizes and grade of aluminum they show in the table and calculate it the long way.

I'm not well versed in aluminum design so I unfortunately can't direct you to any specific resources regarding that.

 

[BUGGAR]

The Aluminum Association is the governing code body for aluminum. If the wind is perpendicular to the arm, you could have torsion combined with biaxial bending. How about wind induced vibration now that you are introducing more degrees of freedom in the whole system. The Aluminum A$$ociation has design rules for this. Open that wallet.

 

[bridgebuster]

You can design the pole in accordance with the AASHTO Luminaire Manual or find a different pole supplier, one that can give you EPAs for poles with mast arms. Also, check various DOT sites, many have standard designs and drawings for luminaries.

 

[chicopee]

Here is a guide: Volume 3 - Florida Department of Transportation

http://www.dot.state.fl.us/.../StructuresMa..

Note the comment about aluminum on page 10 paragraph C6.1

 

[bridgebuster]

Here's the link to the FDoT Manual; the one above seems to have been cut off.

http://www.dot.state.fl.us/structures/StructuresManual/CurrentRelease/Vol3LTS6.pdf

Aluminum is still acceptable for luminaires. The problems with aluminum sign structures is a different issue.