- Panzeh
- Nov 27, 2006
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"..The high ground"
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pre-stressed and/or post-tensioned concrete
pre-stressed concrete:
essentially you take a piece (or several pieces) of rebar, stretch it out 2-3 inches, then cast concrete around it, and when the concrete cures, you let go of the ends. now the concrete is in compression from the rebar trying to snap back into place, allowing it to span much longer distances since the tension forces acting along its lower surface are much lower (concrete is very strong in compression but fails almost immediately in tension)
post-tensioned concrete:
you get a cable with a big washer at each end, hold it taut, and cast concrete around it (or, sometimes, the concrete is pre-cast and you thread the cable through a hole.) then, once the concrete has hardened, you stretch out the cable and clip it so that the tension presses the washers against the concrete, holding it in compression and allowing it to span longer distances.
both of these have the issue that if the rebar or cable fails, the entire concrete plank or whatever structural member fails. post-tensioning is more common today since you can go back and re-tighten the cables occasionally (up to a point - eventually they snap), as opposed to pre-stressing where you basically have to jackhammer out the whole thing to replace the rebar
(now ask me about engineered lumber and oriented strand board)
also i am an expert on post-tensioning systems and managed a lot of PT projects as well as drafting a lot more PT stuff including the FIU bridge that went down in Florida
let me know if you have any questions about it
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Aug 15, 2018 02:37
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May 12, 2024 12:01
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Aug 15, 2018 02:37
You...drafted...that....bridge?