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RE: Steel Fibers Replacing Structural Reinforcing?[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Steel Fibers Replacing Structural Reinforcing?
- From: PeterSHiggins(--nospam--at)cs.com
- Date: Thu, 17 Jun 2004 15:51:48 -0400
Perhaps this is a bit off the topic, but having designed many rack supported buildings (including some very heavily loaded ones over 120' tall), I have to ask: what are they storing which generates a load which would require such a slab? Or is the soil really pathological? For posts on roughly 8' centers both ways, and decent dirt, using even rudimentary slab-plate/soil-halfspace methods, your design would be good for at least 180 kips per post working load or 2,800 psf. Even at 120' high, this is 23 pcf gross volume. I don't know of any rack supported building with that sort of density. The pallet itself is usually this value, and they're typically less than 1/4 of the total building volume (the rest is mainly air). My personal record is less than 35 pcf of reserved pallet volume (the actual pallet was 45-50 pcf including the volume of the skid), and that one was only 85 ft tall for around 10-12 pcf of building volume. Either your're sitting on a world record holder for density (by a very wide margin), or someone's not computing the loads properly. I'd ask them to recompute the design load and see if they forgot to divide by 2 somewhere, before I'd embark on such a monster slab for an ASRS building. Peter S. Higgins, SE "A Miraftab" <seaosd(--nospam--at)hotmail.com> wrote: > > > >Professor Bayasi in San Diego State University has done lots of research >about SFRC (Steel Fiber Reinforced Concrete) and has valuable >publications for that. > >as far as design, it is really simple. (like a rectangular section of >concrete with tensile capacity bellow N.A and compression at top) >tensile strength value you can get is a function of the type of fiber >you use (length and shape of fiber are really important) > >In general: >the common percentage of fiber is btwn .5% to 2% and what they are >providing in your case is about 1.5% (which is in range) >it improves impact ,toughness,tensile strength,cracking behavior and >shear resistance of concrete. (advantages) >needing more cement in mix (more shrinkage), being usually more >expensive (for equivalent design), and its workability are the major >disadvantages of that. >my main concern in your case is adequacy of using only fiber instead of >#7 @12. based on my rough calc I get half of moment strength. so I think >their design should be something like 1.5% fiber in addition to #7 >@24"o/c (or equivalent) > >other concern would be where you have top reinforcing. because if you >use SFRC, after you pour concrete most of fibers go to the bot of slab >and you will get more tensile strength at bot. So I would probably like >to keep up to 70% of top reinforcements. > >AM > > >-----Original Message----- >From: Meyer, Jonathan [mailto:jmeyer(--nospam--at)webbersmith.com] >Sent: Thursday, June 17, 2004 3:52 AM >To: seaint(--nospam--at)seaint.org >Subject: Steel Fibers Replacing Structural Reinforcing? > > > >I am currently designing an industrial facility a portion of which is a >rack supported building. We designed the mat foundation to support this >building and came up with an 18" thick slab with two layers of #7 bars >@12 OCEW. One of the concrete contractors has asked a steel fiber >manufacturer to value engineer the reinforcing to determine if they can >do it with steel fibers instead of the reinforcing specified. There are >also slab on grade and elevated composite slabs in this facility. That's >the background, here is my question - Has anyone replaced structural >reinforcing with steel fibers and are there any standards related to >such a replacement? > >The steel fiber representative called me and told me that they would >have to increase the slab thickness to 19" and use 60# of fiber per >cubic yard. He invited me to use their software to "verify" the design. >I guess I am a bit skeptical about using someone else's software that >has a vested interest in the outcome of the design to produce a design. >I told the steel fiber manufacturer that they would have to take full >responsibility for the design and produce sealed stamped plans if they >wanted to change my designs to steel fiber for the mat slab of the rack >supported building. As far as the slabs on grade are concerned, I feel >that if the client wants to use steel fibers in those areas that would >be fine as long as they understand any limitations of the fibers. > >Any input would be greatly appreciated. Thanks for you assistance. > >Jonathan Meyer > >Webber Smith Associates > > ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
- RE: Steel Fibers Replacing Structural Reinforcing?
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- RE: Steel Fibers Replacing Structural Reinforcing?
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