The present system of posting substandard bridges in Ontario with a single load limit serves only as a vague warning to a driver that the bridge is somewhat deficient. Truck drivers generally disregard the posting sign, because they know they can carry heavier loads across without causing any apparent damage to the bridge. The quantitative definition of the posted value is based upon a design load reflecting vehicles in common use three decades ago, and herein lies the problem. Diverse modern traffic cannot be effectively represented by any single value posting which is generally too restrictive on short span bridges, especially for the long vehicles. Specified loads for the purpose of bridge design can be determined through statistically based load surveys to a significant degree of reliability. The procedure employs the concept of the "Equivalent Base Length" to transform actual vehicles into uniformly distributed loads for mathematic manipulations leading to a single truck model which efficiently represents the wide variation in vehicle types. This report describes the development of live loads and a new triple posting system. Both have been adopted as the basis of capacity rating of existing bridges in the new Ontario Highway Bridge Design Code. The system employs the philosophy of ultimate limit states in evaluation of three levels of posting using an appropriate loading model for each level. Adjustments to the calculated load-carrying capacity are made to account for the operational overloads beyond legal limits, inherent to human nature, and the unusual distribution of loads on various axles in a partially loaded vehicle. /Author/

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 221-229
  • Monograph Title: Bridge Engineering. Volume 1
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00183768
  • Record Type: Publication
  • ISBN: 0309026962
  • Files: TRIS, TRB
  • Created Date: Dec 12 1978 12:00AM