LIGHTING/City tests stability of light poles
Last fall, Alexandria, Va., engineers were shocked when one of the city’s traffic signal poles toppled over during routine maintenance. No one was hurt, but David Jones, traffic signal engineer for Alexandria, decided to start testing the city’s remaining light poles to assess their stability.
Most of the poles in the city are more than 20 years old, making them likely hosts for corrosion. “The corrosion on the pole that fell was very alarming,” Jones says. “But we couldn’t just arbitrarily replace poles – the worst one could be way down the line.” Replacing all the poles at once would cause financial strain on the city, he adds.
Damage to the light poles and base units was caused by road salt, high winds, ground vibrations and other natural forces. However, corrosion or damage was not easily detectable because, for aesthetic reasons, the base units for the poles were buried underground when they were installed, Jones explains.
To test its light poles for damage, Alexandria enlisted Roch Services, Cincinnati. Engineers used a vehicle to apply a slowly increasing force to each of the poles. (The applied force can exceed the force of a 100 mph wind.) The applied force and the pole’s movement were measured and recorded electronically.
In two 10-hour periods, spanning two days, the company tested 70 light poles and discovered that two needed immediate replacement. Test results for the remaining poles were used to establish preventive maintenance and replacement schedules. The city plans to replace those poles over the next few years, in order of necessity. The new poles will have above-ground bases so that damage to the bolts and base plates will be visible, Jones says. They will not need to be tested for several years unless corrosion appears.