Post Tension Timber Beam - Rod Strength
Post Tension Timber Beam - Rod Strength
(OP)
I came across an existing warehouse (old building maybe 70's) with post tensioned timber girders. The entire structure seems to be designed for some fairly high loads. However, when I check the post-tensioned girders, the rods seem to fail badly. The girder's consist of 6x12 beam (top chord) and a 3/4" diameter steel rod with turn-buckle. Depth from top of beam to centerline of rod is 30". Seems very odd that these would have been under designed given the "beef" of everything else.
A few questions come to mind:
A few questions come to mind:
- What grade steel was used?
- Would they have used ultimate strength or yield strength?
- Were these tensioned or just acting as a bottom chord?
- Any ideas on why these rods would be so far overstressed?
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RE: Post Tension Timber Beam - Rod Strength
RE: Post Tension Timber Beam - Rod Strength
-36 ksi
-Yield
-Just bottom chord save some pre-stressing of the turnbuckles to get things taught. This very much depends on whether or not the rods are original construction vs retrofit.
24" effective depth on a 12" beam seems like a pretty shallow truss for this kind of setup.
Span?
One deviator at the middle or two at the 1/3 points?
phamENG's theory is appealing. Maybe the wood was creeping in a way that was deemed unacceptable.
RE: Post Tension Timber Beam - Rod Strength
25'
I'm doubling checking measurements though, again, just very odd. Your assumptions are what I used in the analysis. I played around with post-tension which helps things overall, but still the rod doesn't seem to work.
1/3 points
Agreed. again, I'm double-checking dimensions.
RE: Post Tension Timber Beam - Rod Strength