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Re: Sanitary Structures[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Sanitary Structures
- From: "Kipp Martin" <KAMartin(--nospam--at)carollo.com>
- Date: Thu, 11 Feb 1999 07:44:27 -0800
My company works almost exclusivly in the field of water and wastewater plant design. I understand your frustration. The approach that I use is to just use working stress design. I go one step farther and adjust my allowable steel stress, fs, based on the reinforcing spacing and max Z factor. For example, if I'm designing a wall for a wastewater basin and I think that #7 @ 12" will work, I use an allowable design stress of 17.88 KSI. On several occassions I've tried to design using the Load Factor provisions of ACI 350 but almost without fail, I need to redesign the steel after checking service load stresses for crack control. I do use the LFD provisions for any load case with seismic loads. Kipp Martin, P. E. Portland, Oregon Chris Towne wrote: >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 >=3D 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 <=3D 115 k/in. > >Step 4: If that spacing is less than I found in Step 1, I shorten my = >spacing and perhaps changr 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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