CONCEPTS AND DESIGN RECOMMENDATIONS FOR SAFER LUMINAIRE SUPPORTS

A SURVEY WAS CONDUCTED OF STATE HIGHWAY DEPARTMENTS TO DETERMINE THE BASE CONCEPTS BEING USED FOR BREAKAWAY BASES FOR LUMINAIRE SUPPORTS. THE FOUR BASE CONCEPTS USED ARE: (1) FRANGIBLE ALUMINUM AND PROGRESSIVE SHEAR INSERTS, (2) CONVENTIONAL CAST ALUMINUM SHOE BASES, (3) FLANGED ALUMINUM SHOE WITH INTEGRAL RISER, AND (4) SLIP BASES. FULL SCALE TESTS WERE CONDUCTED AND A MATHEMATICAL MODEL, WHICH WAS VERIFIED BY A FULL-SCALE CRASH TEST, WAS FORMULATED TO SIMULATE THE IMPACT RESPONSE OF THE VEHICLE AND SUPPORT. CURVES WERE DERIVED THAT CAN BE USED TO DETERMINE THE VEHICLE AND SUPPORT RESPONSE DUE TO A COLLISION. RECOMMENDATIONS DERIVED FROM THE STUDY ARE: (1) THE BASE FRACTURE ENERGY SHOULD BE DETERMINED BY RELIABLE MEANS (LABORATORY TEST OR ANALYTICAL MEANS), (2) ALUMINUM INSERT BASES AND OTHER BASES MADE OF FRANGIBLE MATERIAL SHOULD BE CONSTRUCTED SO THAT THE VEHICLE BUMPER CONTACTS THE BASE INSTEAD OF THE SUPPORTED SHAFT, (3) THE LOWEST BASE FRACTURE ENERGY THAT IS CONSISTENT WITH STATIC AND WIND STRENGTH REQUIREMENTS SHOULD BE USED, (4) THE INITIAL TENSION OR PRELOAD AND THE CLAMPING BOLTS OF SLIP-TYPE ATTACHMENTS SHOULD BE HIGH ENOUGH TO BALANCE THE STATIC LOADS AND ALSO HAVE A SUITABLE FACTOR FOR WIND LOADS, (5) CONCRETE FOUNDATIONS SHOULD BE CONSTRUCTED SO AS TO BE LEVEL WITH THE SURROUNDING GROUND SURFACE, (6) THE SUPPORTED SHAFT MUST HAVE SUFFICIENT STRENGTH TO RESIST CRUSHING OR DENTING IN THE VEHICLE CONTACT AREA WHEN IT IS SUPPORTED BY A SLIP-TYPE BASE, (7) BASES HAVING PROPERTIES THAT ARE DEPENDENT ON THEIR ORIENTATION SHOULD BE POSITIONED SO THAT THE DIRECTION OF LEAST RESISTANCE WILL COINCIDE WITH THE MOST PROBABLE VEHICLE APPROACH ANGLES, (8) THE SHAFT SHOULD BE AS LIGHT IN WEIGHT AS POSSIBLE, AND THE BASE FRACTURE ENERGY A MINIMUM FOR ALL CASES WHERE THE PROBABILITY OF LOW-VELOCITY COLLISIONS IS HIGH, AND (9) SUPPORTS THAT HAVE MOUNTING HEIGHTS GREATER THAN 40 FEET AND BASES WITH FRACTURE ENERGIES GREATER THAN 9000 FT-LB SHOULD BE CONSIDERED WITH CAUTION SINCE THEY MAY PRODUCE HAZARDOUS CONDITIONS IN LOW-VELOCITY COLLISIONS.

Media Info

  • Media Type: Print
  • Features: Tables;
  • Pagination: pp 1-2
  • Monograph Title: Development of safer roadside structures and protective systems
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00220473
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Aug 11 1994 12:00AM