For many years, native log stringer bridges have served as the primary bridging system for the Alaska forest transportation network. They are constructed from Sitka spruce or western hemlock logs, placed side by side and decked with blast rock, all locally available materials. These bridges have served for ten years or more, and have been economical as well average cost ($54/sq m, or $5 sq ft). Inspection and load rating as required by the national bridge inspection standards raised questions about wheel-load distribution and physical strength properties of the bridges. The procedures used in their analysis were based on limited information and the evaluations were, at best, approximate. This applied particularly to the load distribution criteria. A research program was undertaken to obtain the information necessary to provide more realistic rating information. This research program included four phases: Strength evaluations of full size logs, load distribution tests of four "in-service" bridges (spans 11.6-28.0 m; 38-92 ft), laboratory tests of models of typical bridges, and analytical evaluation of bridge test data and development of revised load distribution criteria. The field and laboratory test results supported the analytical findings of better distribution than that of current design. The strength tests provided current data on the ultimate bending strength of Sitka spruce and western hemlock logs. The final result of the study is revised design criteria which show that significantly higher loads can be allowed than are permitted under current criteria. /Author/

Media Info

  • Media Type: Print
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 228-235
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00183800
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Dec 12 1978 12:00AM