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RE: Sanitary Structures[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Sanitary Structures
- From: Harold Sprague <harold.sprague(--nospam--at)neenan.com>
- Date: Wed, 10 Feb 1999 14:57:11 -0700
Chris, You are on the right track. Stay in strength design and make the checks. The load factors for tanks are higher, and it helps to be consistent. You did touch on why working stress stayed around so long with the environmental engineers. Give yourself a break and create a MathCad template. It lets you play around with the steel spacing and sizes to zero in on the optimal design very quickly. And your calculations can be checked by non-computer guys. I designed in working stress and "ultimate strength" design for several years, and I did it with hand calculations & slide rule (in the real old days). I developed a pile of eraser crumbs on my lap as I optimized. MathCad keeps the eraser crumbs in the CRT. Once the loads are identified it only takes about 10 minutes to design and optimize the steel even checking stresses, the Z factor, and deflections using the MathCad (about 4 pages of calculations). If you do a couple of tanks, you have paid for the software. Regards, Harold Sprague The Neenan Company -----Original Message----- From: Chris Towne [mailto:ctowne(--nospam--at)newwave.net] Sent: Wednesday, February 10, 1999 2:28 PM To: SEAINT List Server Subject: Sanitary Structures I do a lot of concrete tank design and I was wondering how other engineers tackle the problem of cracking. The process I go through is vigorous and time consuming, but I feel it is necessary. Step 1: Find Steel that satisfies phiMn >= Mu Step 2: Find the actual steel stress (unfactored) Step 3: Find the maximum spacing for that steel stress and bar size that satisfies Z <= 115 k/in. Step 4: If that spacing is less than I found in Step 1, I shorten my spacing and perhaps change bar size and go to Step 3. I repeat steps 3 and 4 until I have the most economical section that satisfies both strength and cracking. I've found out that most of the time if the steel stress is under about 24 ksi, cracking is ok. I was wondering if others just use working stress design and make the whole process simpler. I was taught using ultimate strength and I feel the need to check it even though it never governs. Chris Towne, E.I.T.
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