Determining EPA Wind Load Specifications for Lights|
Article - March 26, 2018 By LarsonElectronics.com
Determining EPA Wind Load Specifications for Lights
Wind speed and frequency can affect the stable and reliable nature of industrial light towers, antennas and mounted fixtures in outdoor locations. Such conditions place stress on elevated structures.
This article provides information about Effective Projected Areas (EPA), its calculations, as well as the coefficient’s benefits.
EPA and Lighting Systems
Understanding EPA and its benefits for lighting manufacturers and industrial operators is equally as important as the calculation itself. By finding the EPA, individuals can determine the strength of the pole holding up the lighting system, during exposure to strong winds or powerful storms.
Furthermore, lighting manufacturers may use the coefficient to analyze the amount of force a lamp will have on a mast, pole or mounting bracket, when exposed to certain, wind-related conditions.
Calculating for EPA
Generally speaking, it is possible to calculate for the EPA by taking the projected area and relevant drag coefficient variable:
EPA = (Frontal Project Area [FPA]) x (Drag Coefficient[DC])
The FPA is typically expressed in square feet or ft2. It takes the measurement of the front cross sectional area of the fixture (maximum), along with the mount. This is the side or surface that is exposed to wind.
In this equation, the drag coefficient refers to resistance arising from the object or shape of the surface in relation to air movement. Drag coefficient variables can be found in technical specification handbooks, such as the American Association of State Highway and Transportation Officials Handbook (AASHTO Standard).
Examples of existing drag coefficient variables include:
• Round Surface Object: 0.5*
• Rectangular Flat Object: 1.2*
*Source: AASHTO LTS-5 table 3-6
The drag coefficient variable is considered to be a dimensionless constant, which can be calculated using the following formula:
DC = Drag / Air Density x Frontal Area x 0.5 x (Air Velocity)(sq)2
Sample Application: Find the EPA for an LED Floodlight (assuming FPA is given), with a drag coefficient of a flat plate.
• FPA: 2.30 ft(sq)2
• Drag Coefficient: 1.20
Plug in the variables, based on the EPA formula above:
EPA = 2.30 x 1.20
EPA = 2.76 ft(sq)2
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