A literature review was conducted to establish the state- of-the-art in safer luminaire support construction. It was established that, to insure low impact resistance, it is necessary to incorporate a base which will breakaway in a collision but which possesses sufficient strength to resist static and wind-induced loads. The four basic concepts that have been developed and are accepted by at least one state in the U. S. Can be broadly classified as: (1) frangible insert bases, (2) progressive-chair bases, (3) aluminium shoe bases, and (4) slip joints full-scale tests were conducted in such a manner that a comparative evaluation could be made of the four basic concepts. The following variations of the basic concepts were also tested and evaluated: stainless steel progressive-shear base coupled with stainless steel davit and mast arm type supports, and a cast aluminium shoe base with an integral riser. One test was conducted on a pre-stressed concrete support. The collisions were performed with nominal 3,500-lb. Vehicles moving generally at about 40 mph. Severity ratios and a severity index were calculated from test data and were used to rank the four concepts tests from the most severe to the least severe, as follows: (1) aluminium shoe base with aluminium shaft, (2) progressive- shear base, (3) frangible insert (aluminium transformer base), and (4) the triangular slip joint. Based on the response of dummies in the vehicles, all collisions tested were judged to be safe, with only the most severe likely to produce minor occupant injury. A mathematical model was developed that was used to study the variables that influence the collision. Research conclusions are that: (1) existing frangible insert (transformer bases) and progressive-shear bases should be of such height as to allow the vehicle bumper to contact them, rather than the luminaire support shaft, (2) the base fracture energy determined from laboratory impact tests can be used as a measure of energy absorbed by the base in a full-scale collision, (3) where the probability of low-velocity collision is high with luminaire supports, the bases should have the lowest possible fracture energy and the support pole should be constructed of lightweight materials, (4) a collision speed of about 35 mph appears to be the lower limit at which a conventional support can be expected to clear the vehicle or hit behind the passenger compartment, (5) large supports with base fracture energies in excess of 9,000 ft-lb, should be considered with caution because low- velocity collisions may be severe, and (6) breakaway-type bases result in considerably lower average accident costs than do the more rigid-type bases.
Samenvatting