TRANSVERSE POST-TENSIONING OF LONGITUDINALLY LAMINATED TIMBER BRIDGE DECKS

Longitudinally, nail-laminated timber bridge decks are used extensively in northern Canada, where the cold and dry climate discourages the activities of fungi and termites. The load-carrying capacity of these structures is dependent upon their ability to effectively distribute wheel loads among the laminates; this being a function of the friction and the holding power of the nails. Due to overloads, volumetric changes and environmental effects, the holding power tends to diminish resulting in a subsequent reduction in the load-carrying capacity of the bridge. Construction of these nail-laminated systems involves extensive labour, since thousands of nails have to be driven into hundreds of laminates. Quality control is quite difficult as it requires continuous supervision to ensure that all the nails are properly placed and driven. This report describes the application of transverse post-tensioning to an existing longitudinally nail-laminated timber deck structure in Ontario. This 3-span continuous bridge portrayed the delaminating problem, and as such, presented an appropriate test site for a post-tensioning system. Load testing was done before and after post-tensioning to determine its effects on the structure's response. An evaluation of the test results indicated that the structure's load-carrying capacity was increased by at least 100%. Transverse post-tensioning, in effect, replaces the need for nailing and hence reduces the labour required for construction. Quality control extends only to ensuring that adequate post-tensioning forces exist to provide the friction necessary for load distribution, allowing for anticipated losses due to creep. This confined deck system exhibits better resistance to the environment, as it eliminates the penetration of foreign materials between the laminations. /Author/

Media Info

  • Media Type: Print
  • Features: Figures; References; Tables;
  • Pagination: pp 236-244
  • Monograph Title: Bridge Engineering. Volume 2
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00183801
  • Record Type: Publication
  • ISBN: 0309026970
  • Files: TRIS, TRB
  • Created Date: Dec 12 1978 12:00AM