Spaulding Lighting Lighting Poles and Vibration Read before installation - Manual

Lighting Poles and Vibration
Read before installation
Wind is usually an unseen, but always potentially very powerful natural force. All lighting poles, regardless of
design and choice of material are vulnerable to these wind forces. Destructive pole vibration is not a common
phenomenon, but when it occurs, the results may be devastating.
Lighting poles are generally affected by winds in two ways. The most common type is called “sway”
or first mode vibration. When this happens, the maximum movement occurs at the pole top and is
perpendicular to the wind direction. The movement is low frequency and usually not harmful to the
pole. Small movement at the top of the pole is normal. Excessive movement is a reason for
concern and requires close inspection for cracks.
The second, and less frequent vibration type, called second mode vibration, can be destructive to
both the lighting pole and the luminaire. This vibration movement is higher in frequency and the
point of maximum movement is located half to two thirds up the pole. The pole movement
is again perpendicular to the direction of the wind. Under very rare circumstances, the wind
induced vibration exaggerates the pole movement as it synchronizes with the
pole/luminaire system natural frequency. Excessive pole movement and even pole failure
can result.
There are signs to look for when checking for the effects of second mode vibration.
Premature lamp failure, loosening of screws or accessory components and a rapid,
unfamiliar “ticking” sound as the pole vibrates are all typical conditions indicating possible
second mode vibration. Hairline cracks just above the pole base weld are further indicators
of vibration induced metal fatigue and of a need to repair or replace materials. You should consult a licensed
structural engineer to confirm your concerns.
Predicting which location and which luminaire/pole assembly will be susceptible to destructive vibration is not
easy, if even possible. Typically the most vulnerable lighting poles are located in wide open areas with no
buildings or structural features to break up the constant wind patterns. Wide open parking areas, bridges, airport
structures and mountain passes are examples of prime concern areas. It takes a low steady wind, usually
5 – 20 mph to set up conditions for damaging vibration.
Your Hubbell Lighting agent can supply lighting poles with vibration dampeners to minimize the destructive
effects of wind induced vibration. Some Hubbell dampers are impact type, consisting of a solid mass supported
loosely inside a hollow tube, that when forced to vibrate, collides with the tube sides and prevents harmonic
vibration build-up quickly. Factory installed, internally mounted dampers can be supplied in most poles. Other
Hubbell dampeners are friction type that can be installed in the field.
If your lighting application calls for luminaire and pole assemblies located in a wide open windy area, we
strongly recommend the use of vibration dampeners. Consult local authorities to determine if such conditions
are common in your area. If you note any of the above listed signs of destructive vibration in your newly
installed lighting equipment, a dampener may be an answer to minimize your vibration problems. Contact your
Hubbell Lighting Inc. agent for availability.
Lighting Poles and Vibration
The Hubbell Warranty for poles specifically excludes fatigue failure or similar phenomena associated with wind and /or
structural induced vibration. See Hubbell Lighting’s Limited Warranty and Limitations of Liability for details.
Follow the installation and maintenance guidelines
on these pages