DTIC ADA078788: Bending Strength of Large Alaskan pdf

DTIC ADA078788: Bending Strength of Large Alaskan

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Native log stringer bridges are important economical and practical structures for logging roads in remote areas of Alaska. Unfortunately, the current knowledge of the strength of large logs is extremely limited. In the absence of actual test data, design stressess have been estimated by procedures developed for poles and piles. To obtain actual data on the strength of large logs, a field test facility was designed and 40 large logs were tested to destruction. These were probably the largest logs ever tested, with butt diameters up to 4 feet, 10 inches and ultimate bending loads in excess of 120,000 pounds. This study was limited to two species, Sitka spruce and western hemlock. The average breaking strengths were 4,530 pounds per square inch (lb sq in) for Sitka spruce and 4,680 lb /sq in for western hemlock. Both values are reasonably close to those obtained by the current design procedure.

Statistical curves for estimating near-minimum strengths at various confidence levels were developed. It is normal practice in the design of wood structures to reduce the allowable stresses to a 10-year duration of maximum load. This is unrealistic for bridges where the maximum design load is present for only a short period. A cumulative load duration of 2 months is more realistic. A simple curve for stress adjustments at different load periods is presented. (Author

• Creator/s: Defense Technical Information Center
• Date: 1/1/1979
• Year: 1979
• Book Topics/Themes: DTIC Archive, Tuomi, R L, FOREST PRODUCTS LAB MADISON WIS, *LUMBER, *WOOD, PHYSICAL PROPERTIES, STIFFNESS, ALASKA, RUPTURE, STRENGTH(MECHANICS), TABLES(DATA), BENDING STRESS

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