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LOAD CONSIDERATIONS IN THE SELECTION OF POLES

The proper selection of a light standard (pole) for a particular application always requires careful consideration to ensure that the pole will not be overstressed from loading forces that are applied to the pole structure potentially creating a safety hazard should the pole ultimately fail. To this end, all luminaire/pole assemblies require a careful evaluation to ensure that the structural integrity of the assembly is not compromised when subjected to various load forces.

The loads that are placed upon a pole are called static (dead weight) loads and dynamic loads. The weight of the luminaire and any other attachments affixed to the pole are considered dead weight loads and generally do not vary (an exception of an intermittent increase would be due to icing in cold climates). Dynamic loads are variable and are created by the pressure of the wind based on its velocity against the surface area of the pole and luminaire assembly. The surface area in square feet of the luminaire and all attachments are expressed as Effective Projected Area (EPA) and are calculated as a product of the actual exposed surface area multiplied by a drag coefficient.

When selecting a pole and luminaire assembly, the stresses put upon the pole from both the dead weight load in pounds and the total EPA in square feet of the luminaire and any additional attachments to the pole must be assessed.

First select the luminaire to be used and decide how many will be mounted to the pole.

     ALX                                    AS1                                         KAD                                    KSE

  

Fixture Drilling Option Drilling Nomenclature Total Fixture EPA Total Fixture Weight
ALX (1) at DM19 DM19AS 0.7 37 lbs
(2) at DM28 DM28AS 1.4 74 lbs
AS1 (1) at DM19 DM19AS 0.7 26 lbs
(3) at DM39 DM39AS 1.6 78 lbs
KAD (1) at DM19 DM19 1.2 36 lbs
(2) at DM28 DM28 2.4 72 lbs
KSE (1) at DM19 DM19 1.3 26.6 lbs
(4) at DM49 DM49 4.5 106.4 lbs

Determine the EPA of the luminaire which is given in the dimensional information table located on the product page or specification sheet for the luminaire product (link to EPA CHART). Next establish the appropriate mounting method of the luminaire; options include mast arms, cross arms, bullhorns or other bracket types.

Additional attachments may include signs, banners, decorations, antennas, solar panels, overhead wiring, et cetera. These additional attachments require special consideration on a case by case basis and you should always consult the pole supplier for assistance prior to final pole selection. Add together the EPAs of the luminaires and brackets (and any additional attachments) that will mount to the pole. Add together the weights of all luminaires and attachments as well.

Next, utilize a mean recurrence isotach 50 year wind map to verify the fastest mile per hour velocity of the wind for the installation site; when in doubt contact your local building department or your pole supplier.

Please note that there are areas of special concern regarding wind velocities. These include areas subject to high wind velocities due to hurricanes or special wind zones such as the Chinook winds of the eastern Colorado Rockies or Santa Ana winds in California to name a few. Additionally, open areas such as airports and the Plains regions of the United States can have low velocity (10 to 25 mph), steady wind conditions that may cause a pole assembly to vibrate; this is known as induced harmonic vibration or resonance and is a local, site specific condition. This condition is associated with the movement of air currents around the product and is unpredictable. If left unchecked, harmonic vibration can cause severe damage to the pole assembly and its ultimate failure. This type of vibration is not an indication of substandard material, workmanship, or pole design. Heavier poles and/or the addition of special devices called vibration dampers installed at the factory during the pole manufacturing process, or field installed at a later date, can help reduce or eliminate harmonic vibration in many instances.

Once you have determined the total EPA and weight of all attachments to the pole and verified the fastest wind velocity for the location of the pole installation, you can then establish which pole type may be suitable for the application. Select the material (steel, aluminum, concrete, fiberglass or wood) and shape (square or round, straight or tapered) of the pole. Refer to the “Technical Information” chart on the appropriate pole page. Find the desired nominal mounting height for the selected pole and verify that the total EPA and weight do not exceed the maximum values listed for the wind speed in your area. If both the EPA and weight are less than the maximum values for which the pole is rated, you have selected an appropriate pole. If any value is exceeded, compare the values to the next larger pole of the same mounting height or consider a pole of a different material and/or shape.

SSS Square Straight Steele Poles

Technical information
          EPA (ft2) with 1.3 gust      
Catalog Number Nominal Shaft Length (feet) Pole Shaft Size
(in x ft)
Wall thickness (inches) Gauge 80 mph Max weight 90 mph Max weight 100 mph Max weight Bolt Circle (inches) Bolt Size (in x in x in) Approximate ship weight (pounds)
SSS 10 4C 10 4.0x10.0 0.125 11 30.6 765 23.8 595 18.9 473 8--9 3/4x18x3 75
SSS 12 4C 12 4.0x12.0 0.125 11 24.4 610 18.8 470 14.8 370 8--9 3/4x18x3 90
SSS 14 4C 14 4.0x14.0 0.125 11 19.9 498 15.1 378 11.7 293 8--9 3/4x18x3 100
SSS 16 4C 16 4.0x16.0 0.125 11 15.9 398 11.8 295 8.9 223 8--9 3/4x18x3 115
SSS 18 4C 18 4.0x18.0 0.125 11 12.6 315 9.2 230 6.7 168 8--9 3/4x18x3 125
SSS 20 4C 20 4.0x20.0 0.125 11 9.6 240 6.7 167 4.5 150 8--9 3/4x18x3 140
SSS 20 4G 20 4.0x20.0 0.188 7 14.0 350 11.0 275 8.0 200 8--9 3/4x18x3 198
SSS 20 5C 20 5.0x20.0 0.125 11 17.7 443 12.7 343 9.4 235 10--12 1x36x4 185
SSS 20 5G 20 5.0x20.0 0.188 7 28.1 703 21.4 535 16.2 405 10--12 1x36x4 265
SSS 25 4C 25 4.0x25.0 0.125 11 4.8 150 2.6 100 1.0 50 8--9 3/4x18x3 170
SSS 25 4G 25 4.0x25.0 0.188 7 10.8 270 7.7 188 5.4 135 8--9 3/4x18x3 245
SSS 25 5C 25 5.0x25.0 0.125 11 9.8 245 6.3 157 3.7 150 10--12 1x36x4 225
SSS 25 5G 25 5.0x25.0 0.188 7 18.5 463 13.3 333 9.5 238 10--12 1x36x4 360
SSS 30 4G 30 4.0x30.0 0.188 7 6.7 168 4.4 110 2.6 65 8--9 3/4x18x3 295
SSS 30 5C 30 5.0x30.0 0.125 11 4.7 150 2.0 50 -- -- 10--12 1x36x4 265
SSS 30 5G 25 5.0x30.0 0.188 7 10.7 267 6.7 167 3.9 100 10--12 1x36x4 380

Let’s walk through an example of how this works. You want a 30 foot tall pole to mount two Lithonia Lighting KAD series luminaires at 180 degrees from each other to illuminate a small parking lot located in a 90 MPH wind region. The total loading for the pole will be 2 times 1.2 EPA for the KADs which will give you a total EPA of 1.4. The weight of each fixture is 36 lbs. or a total of 72 lbs. Using the chart above the SSS 30 4G pole will work as it will handle 4.4 EPA and 110 lbs.. The SSS 30 5C pole will not work as it will only handle 2.0 EPA and 50 lbs. The SSS 30 5G will work as it will handle a 6.7 EPA and 167 lbs. So you would order either the SSS 30 4G DM28 DDB pole or the SSS 30 5G DM28 DDB pole from your local ABL distributor or agent.

Let’s walk through a more complicated example of how this works. You want a 30 foot tall pole to mount two Lithonia Lighting KAD series luminaires at 180 degrees from each other to illuminate a small parking lot.Additionally, you would like to mount a TFA series floodlight with a horizontal arm bracket at 25 feet between the two KAD series luminaires to illuminate the storefront. You’ve determined that the wind zone for your area is 90 mph with 1.3 gusts.

First determine the total EPA and weight that will load the pole. Per the Lithonia Product Selection Guide or the KAD specification sheet, you will find that the KAD has an EPA of 1.2 square feet and weighs 35.9 Lbs. The guide or specification sheet for the TFA flood lists 2.6 EPA and 65 Lbs. Finally, we have to consider the bracket arm that will support the flood. The H1-18S horizontal arm bracket has and EPA of 0.50 EPA and weighs 11 Lbs. The total loading for the pole will be 2 times 1.2 EPA for the KADs plus 2.6 EPA for the single flood plus 0.50 EPA for the bracket arm for a total EPA of 5.5 EPA. By following the same formula for the weight values, we can calculate that the total weight for the luminaires and bracket arm is 147.8 Lbs.

You have decided you would like a square straight steel (SSS) pole for the application and by consulting the Technical Information Table for the SSS pole you will find that the SSS 30 4G is rated for a maximum of 4.0 EPA and 100 Lbs at 90 mph and the SSS 30 5C pole is rated for 2.0 EPA and 50 Lbs at 90 mph. In these cases, the poles will fail in the application as the intended loading for the pole exceeds the pole’s rated maximum load limits. Continuing down the column, however, reveals that the SSS 30 5G pole is rated for 6.7 EPA and 167 Lbs at 90 mph with 1.3 gusts. This pole is suitable for the application and will withstand the dynamic load created by the wind because both the total 5.5 EPA and 147.8 Lbs is less than the maximum load ratings for EPA and weight for this pole. Though this pole will handle the loading at 90 mph, it will fail at 100 mph as its rating drops to 3.9 EPA and 100 Lbs. If you determine you really need the pole to handle the loading at 100 mph then you will need to go to a heavier duty pole such as the next larger size in the table and use the SSS 30 6G pole with a 9.0 EPA and 225 Lbs rating for 100 mph zones.