Bridge engineers in many states have been designing bridges using working stress methods and AASHTO HS20 live load vehicles for the past 25 years. Recently, the AASHTO Specifications have permitted the use of load factor design for common structure types. During this same period there has been a significant increase in the number of vehicles that greatly exceed legal loads operating with special permits, as well as a marked increase in the weight of legal vehicles. To accommodate these loads, higher stress levels, defined as "operating stresses " in the AASHTO Manual of Maintenance Inspection of Bridges, are allowed at the discretion of the responsible agency. The practice of designing new structures by one set of rules and comuting overload capacities by another results in a peculiar situation. The overload capacity of new structures varies widely depending upon construction materials and span length. It is inefficient to have the load capacity of a route segment limited by one or two structures while others have far greater capacity than can possibly be utilized. The purpose of this paper is twofold. First, to alert bridge engineers that they will reduce the usability of their highways by adopting load factor design without a corresponding increase in design live loads. Second, to relate how the California Department of Transportation assures uniform overload capacity at "operating stress" levels in new structues by routinely including a family of standard permit vehicles as one of the loading conditions in a load factor design method. /Author/

Media Info

  • Media Type: Print
  • Features: Figures; Photos; Tables;
  • Pagination: pp 230-238
  • Monograph Title: Bridge Engineering. Volume 1
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00183769
  • Record Type: Publication
  • ISBN: 0309026962
  • Files: TRIS, TRB
  • Created Date: Dec 12 1978 12:00AM