Light poles can be found just about everywhere. They line our streetways, sidewalks, parking lots, athletic fields, and more. While the luminaires that provide light for pathways for pedestrians or cars are the usual aim of maintenance efforts, maintenance of the poles and anchoring systems that support them is often overlooked.
It’s important to understand the condition of your light pole inventory. You must become familiar with their basic components and look for conditions that might warn you of conditions that can become hazardous.
It’s important to perform regular light pole maintenance and inspection. It should be performed two to four times a year. This is suggested for the luminaire and light pole to maintain their appearance, long life, and safety.
Light pole components: Here are some tips for their inspection and maintenance.
Light pole foundations are normally made of reinforced concrete piers with jutting steel anchor bolts. Anchor bolts and washers are used to secure the pole to its foundation. Typical problems with concrete foundations include spalls (fragmenting), cracks, and leaning foundations.
When cracks line up with an embedded anchor bolt, the structural capacity of the assembly could be compromised. For example, the ability to resist wind loads could be reduced which could result in the pole collapsing.
Water and debris can accumulate inside a pole at its base, often entering through open spaces. This can occur below the base plate, through the hand hole in the pole, or through other openings. It can cause (or increase) corrosion on the interior surface of the pole. Even when severe, interior corrosion may be visually undetectable from the exterior.
You should visually inspect the exterior pole shaft for areas of corrosion, rust, and any dents or signs that the structural integrity has been compromised. To help determine if there has been any corrosion in the interior of the pole, ultrasonic thickness gauges can be used from the exterior to measure the remaining pole wall thickness.
The easiest way to reduce interior corrosion is to keep the pole interior clean and promote ventilation/drying. This will extend the service life of the pole. You should also regularly apply corrosion-inhibiting coatings on the exterior surfaces of steel poles and base plates.
If you’re purchasing new light poles for a project, galvanized steel poles are recommended. They typically resist corrosion much better than painted steel poles. Galvanized poles also provide better protection for the interior surface of the pole.
Brackets and Arms
Check for metal fatigue in brackets, arms, and luminaires through visual inspection. Metal fatigue can be caused by such things as corrosion, vibration, constant stress, or temperature changes. Signs of metal fatigue include cracks or ruptures.
Covers for handholes, bases, pole caps, and nuts
Make sure that all covers are firmly attached. Loose or partially opened covers allow dust and moisture to get inside the pole and accelerate corrosion.
Visually assess the base plate for nut tightness, appropriate hole size, and bearing. A base plate acts as the main contact point between the light pole and the foundation. It’s designed to transfer forces into the anchor bolts and foundation. Base plates help to prevent wind from tipping over the pole assembly. They do this by pulling up on one or more of the nutted anchor bolts.
If holes in the base plate are oversized compared to the diameter of the anchor bolt and nut, a pull-through failure might happen which would destabilize the whole structure. Washers might be used as part of the design or to accommodate oversized holes. However, the washers require the proper design to effectively transfer loads without becoming deformed.
The connection of the pole to the base plate typically has a socket-type connection. This occurs where the pole is nested within a hole in the base plate, and the welds around the pole edge at both the top and bottom of the base plate transfer loads from the pole and luminaire to the base plate. Weld cracks are usually the result of cyclical wind loading of light poles. Periodic inspections of welds should be performed by qualified personnel.
When possible, avoid using square poles, especially those greater than 30 feet in height. Square profile poles with fillet welds made using a manual process are most susceptible to weld cracking. This is especially true for taller poles. Square poles experience stress concentrations at the corners. By contrast, round poles allow for a more even distribution of stress. It’s recommended that you use round, tapered poles with pole-to-base plate welds performed by an automated process.
Make sure that each anchor bolt nut is in place and firmly tightened. Tight installation of the upper nuts is critical for long-term performance. If nuts are not properly tightened initially, or if they loosen over time, the subsequent gap will permit the pole to rock on its foundation under wind loading. This type of repetitive rocking can cause impact loads on all components. This rocking can increase the risk of developing cracks.
Pole structures are usually anchored to their concrete foundation with anchor bolts which are threaded steel rods. They are embedded during foundation concrete placement. The anchor bolts extend above the foundation surface and are aligned with holes in the pole base plate, and they are secured with nuts.
Accumulating moisture can speed up corrosion of the base plate, pole, and anchoring components. This ultimately leads to early failure. Base plate and anchor bolt covers can hold moisture and debris which can cause corrosion of the base plate, the anchor bolts, and the pole itself. It is recommended that these covers are not used.
Appendages can unintentionally increase the wind loads on the pole. These include banners, signs, and security cameras. They should not be added to a pole unless the pole was designed to handle the additional wind load.
Look for signs of vibration. This includes:
Humming or noise in the pole
Visible movement of the pole and/or the luminaire
Rust just above the weld at the base of the pole
If you are considering replacing the luminaire mounted on the pole, it is important to understand that each luminaire type can have an increased effect on the contribution of wind load. When it’s time to replace a luminaire, an increase in wind load may require a structural analysis and field assessment to make sure that the original design and current condition of the pole can effectively resist the increased wind load.
While normally not a major focus of maintenance personnel or property managers, light poles are among the most common structural systems in the world. Understanding basic principles of light pole construction and implementing routine inspections by qualified personnel will aid in the early identification of defects. When addressed properly, this can prolong service life and prevent failures.
Please see our other blog articles about light pole components, light pole purchasing, and light pole installation.
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About the Author
Neil Peterson is Chief Operating Officer at LED Lighting Supply. He has been active in the LED industry for over 10 years and is responsible for product planning and management as well as revenue and operations at LED Lighting Supply. Much of Neil’s time is focused on customer engagement for large commercial and industrial lighting requirements. When not working, he enjoys family time, camping, fishing, and sports..