Bill wrote: >For a particular material, if you stress it to 100% of its strength, it >will fail immediately. If you load it to 95% of its strength, it will fail >in 3 months. If you load it to 80% of its strength, it will fail in one >year. 60%, 5 years. 50%, never. In wood construction, there is a table for load duration factors, Cd, which shows that wood can take up to 2x it's design strength for impact loading. Load Duration Cd Design Load permanent 0.9 Dead Load ten years 1.0 Occupancy Live Load two months 1.15 Snow Load seven days 1.25 Construction Load ten minutes 1.6 Wind/Earthquake Load impact 2.0 Impact Load >The bottom line here is that some materials (mostly organic, I think) will >fail at some stress level over time that is less than their rated strength. And some organic materials will withstand a much greater stress level for short durations. Of course, this has absolutely no bearing on why I love wooden boats. ;) It is still important to design with a safety factor (read: fudge factor to non-engineering sorts) in mind to prevent failure from ever occurring. Shawn W. Baker 0 46°53'N © 2000 ____©/______ 114°06'W ~^~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ baker_at_montana.com 0 http://www.geocities.com/shawnkayak/ *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced/forwarded outside PaddleWise without author's permission Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Tue Aug 01 2000 - 07:47:06 PDT
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