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Full Scale Piling Tests
Full Scale Tests on both Southern pine and Douglas fir piles were completed in 2000, the first time full-scale tests were conducted to establish design stresses. The tests were run by EDM International of Ft. Collins, Colorado, an independent laboratory. Both bending and compression tests were run.
Sampling
- Samples for these tests were selected in growing regions where piling is produced in proportion to the amount used for piling.
- Southern pine trees were sampled from sites in Virginia, Georgia and Florida.
- Douglas fir trees were sampled from sites in Oregon, Washington and British Columbia.
- Only second growth timber has been used in the production of timber piles for years.
Bending Tests
- Bending tests were run first by applying tension through a cable attached to the tip of the pile.
- Tests showed bending stresses could be 36% to 53% higher than currently used.
Compression Tests
- Following the bending tests, an approximate 3 ft. specimen was cut from both the butt and tip ends of each pile.
- Tests showed compressive stresses could increase 12% more than currently used for stresses in pile groups.
Summary
- This landmark testing program demonstrated that the allowable stresses currently published in AF&PAÕs widely recognized National Design Specification (NDS) are conservative.
- The tests also demonstrated that todayÕs trees are as strong as ever.
- New ASTM standard D7381 provides the protocol for developing stresses from full scale tests.
Field Load Tests
Extensive field load tests have been performed on pressure treated timber foundation piles. Design loads as high as 70 tons have been specified, and ultimate loads as high as 235 tons have been achieved.
The highest ever recorded design loads for timber piles in U.S. highway construction history is a 1,000-foot long viaduct and freeway interchange near Winnemuca, Nevada, supported by timber foundation piling which had a 70-ton design load.
There are timber piles loaded to 60 tons each under bridges spanning the Thames River in London and to 100 tons in bridges spanning the Seine River in Paris. Pressure treated foundation piles provide an economical solution for many soils with insufficient bearing strength.
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