Assuming I ever get clearance on my site plan and the price of concrete doesn’t hit stratospheric proportions, I hope to start on my 30×40 floor slab for my steel shop building. The building vendor supplied a somewhat generic set of engineer stamped prints that is supposed to pass the county planning office. It is for a monolithic pour with the required 2′ frost depth footers. The building used “J” bolts for the steel column uprights which have to be placed precisely, so they recommend that I find someone who has done this work before. I have yet to find such an individual, but hope to soon.
With the price of rebar shooting up and supplies tightening, I thought I would lay in a supply of steel. The plans call for only a 4″ concrete floor but the vendor reportedly I can increase the thickness and add rebar without requiring re-engineering. The supplied plans only show rebar at the bottom of the footings and for the grade beams that run across the building between the main uprights.
Before the big price boost, I had thought I would add something like #4 at 12″ for a little extra strength. However, given current prices, I would like some advice on just what spacing of rebar it would be cost effective to add – 18″ or 24″ spacing? I plan on adding at least an inch of concrete probably going to 5 1/2 thickness.
The shop will primarily be used for welding and working on old vehicles, although I will use my 9,400# forklift in it on occasion and will do some work in it on my 14,000# manlift.
Replies
Your question is why engineers can charge as much per hour as they do, LOL. It'd be easy for me to say, well, yeah, pour it this thick and stick in that much metal in this configuration, and make sure the concrete mix is rich enough--and ya might be okay with those heavy vehicles on that floor.
But you'd be a fool to listen to me, cause I'd just be guesstimating.
Pay somebody with a professional license to protect to tell you what you need. Then, if it doesn't work out as promised, you've got some recourse. You definitely don't want to be looking at a busted slab to which your steel building is bolted unless somebody else is gonna have to pay to fix it....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
The professional engineer that charged $500 for the plans (but was included in the price of the building) seems to think I don't really need any rebar. Having worked as a draftsman doing as built drawings on rebar in slabs as well as having worked as a concrete laborer some years back, I would feel more comfortable with with some steel. I don't feel like sinking another $500 to possibly be told that I really don't need any. The current wet stamped plans say I don't need any - but I WANT some. I am sure that there is some practical experience here in Breaktime that can produce some rules of thumb for typical slabs that would probably equal an engineer that does generic formulations...
With so much at stake I can't imagine why you wouldn't pay a few bucks for a phone consultation with an engineer. Tell him you have 5-ton and 8-ton equipment rolling around on your slab and you don't want it to crack.
The problem with a phone consultation is that I am deaf and can't talk over the phone. There is only one PE in our town and he inspected the foundations of a house I bought which I later found had footings that were separated in six places with one place big enough to put your fist through. Finding and consulting with a PE will be a big hassle in addition to the cost. When I was shopping for a building, I was told that the standard charge for engineering a slab was $1,100. That is why I purchased the building with the plans for the slab included.
I realize that the primary protection is good site preparation with adequate compaction. Since the PE that signed off on the slab drawings thought that no rebar in the main part of the slab is needed, I am just going for the "belt and suspenders" approach. However, since all I worked on was heavy construction with rather elaborate rebar schedules, I don't really know what the standard operating procedure is for rebar in shop slabs.
(One doesn't realize just how telephone oriented our society is until you can't use one...)
Edited 5/20/2004 12:31 am ET by CaseyR
I for one realize how phone oriented we are .
My boss must get 30+ calls an hour it is amazing how difficult it is for us to finish a 3 minute conversation.
WE hired an office manager yesterday and one of the first things I want to do is redirect our calls thru the office so that she can do some of the screening.
As far as concrete and steel I would order fiber reinforced and pour 6 inch and put steel in my footings and that should be enough but I am not an expert.
ANDYSZ2I MAY DISAGREE WITH WHAT YOUR SAYING BUT I WILL DEFEND TO THE DEATH YOUR RIGHT TO SAY IT.
Remodeler/Punchout
Not to defend the engineer, but...apparently inspecting existing houses is not his forte...maybe he works better in an air conditioned office. Why not pay him a visit, or have a friend call, and explain the situation and see what he says. An initial phone call/quickie visit should be free. Since you have the foundation dwgs and all you need are steel details, the cost might be lower.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
I realize that the primary protection is good site preparation with adequate compaction. Since the PE that signed off on the slab drawings thought that no rebar in the main part of the slab is needed, I am just going for the "belt and suspenders" approach. However, since all I worked on was heavy construction with rather elaborate rebar schedules, I don't really know what the standard operating procedure is for rebar in shop slabs.
FWIW, I ignorantly poured a 4" slab with welded wire reinforcing for my shop. It's seen 16,000# machines without cracking. There was no soil testing or compaction, only a couple inches of washed stone over the undisturbed soil. That's undisturbed except where we removed small trees. The only rebar I used was in the footing holes beneath the posts with a small extension into the slab. Probably 3500# concrete, but I don't remember. Rained the night of the pour so the finish got messed up. Didn't repair it.
I also poured part of my driveway, again 4" (4000#) but without reinforcement, that later was frequently traversed by loaded concrete trucks, considerably heavier than 16,000#. No problems. Would it work for you? Beats me. This a mountain. The reason there's a mountain is: there's rock underneath. I'm pretty sure that's a main reason for my success.PAHS Designer/Builder- Bury it!
Don't want to hijack the thread here but an alternative to your phone problem would be sprintrelayonline.com. Kind of a high powered TTY that is internet based and free of charge to boot!
Rookie -
Thanks for the link. I haven't been deaf long enough to learn all the tricks. Oregon has had a similar service using a TDD (Telephone Device for the Deaf - sometimes referred to as a TTY) for a number of years. My mom tried it and decided that with all of the misspellings and miscommunications, it simply was useless for her. Oregon now has a system that uses a telephone that has a text display panel on it for receiving the typing from the relay service. A deaf user such as myself who can speak, uses it to talk normally to the recipient and the relay operator (I think it is Sprint) then types the response. I will be getting one of the phones soon but probably not before I need to have my slab in place. Oregon provides the phones free to deaf Oregon residents. I think the cost of the phone is actually around $450. It is called a CapTel phone and is by Ultratec.
Link: http://www.captionedtelephone.com/index.phtml
http://www3.sprint.com/PR/CDA/PR_CDA_Press_Releases_Detail/0,3681,1111995,00.html
Funny you should mention the CapTel phone. I use one now as part of a test for Sprint (my wife works there). It is great for those that need assistance. I wear a hearing aid and whether or not I can hear on the phone depends on the phone. With the CapTel phone the words appear almost as they are spoken so it is kind of like closed captioning that you have on television. For me it is great becasue I still hear the conversation but if I'm not sure what is said I can look on the screen. Best part is that on your end you speak as if it were a normal phone and the other party has no idea you have a hearing handicap unless of course they know you personally.
The building used "J" bolts for the steel column uprights which have to be placed precisely, Make up some 3/4" plywood templates, one for each set of j-bolts. Put the bolts into the plywood, with a nut on each side to keep the bolts in place, add some form release oil to the plywood and wrap the threads with duct tape, and fasten the plywood in place to the formwork. Set the plywood so its bottom surface is the same as the finished surface of the slab. Bake at 350 degrees for 1 hour...enjoy!
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Have you checked out the glass or polypropylene fiber that is added to concrete for tensile strength? I have built several warehouses with slab on grade, no re-bar, forklits and no problems. It's a lot cheaper than steel and extra concrete. You don't trip on it during a pour either. Site compaction and drainage are very important on any concrete slab.
Casey,
Think of your concrete slab as a piece of plywood laying on a flat surface. If the surface is strong, you can park a loaded cement truck on it without and problems. If the surface is swamp mud, you can't even stand on it without it bending in the middle.
The most important thing you can do for your slab, better than steel, better than more cement in your concrete, way better than fibers. . . Well compacted Engineered Fill (EF.)
During excavation, you will, of course be removing all topsoil from under the slab area. Go ahead and excavate 10" under the bottom of the slab (BoC), compact the undisturbed (meaning, has never been disturbed) soil. This process may lower the soil EL by 2"±, add 6" EF, compact that, add another lift of EF to about 1" above BoC and compact it. Check elevations and shave or fill to the correct El. Compact any fill you had to add.
Make sure the finished EF is flat, smooth, and level. Perform all compaction with a jumping jack style compactor (Whacker).
Make sure the mix is not too wet when you pour, think really stiff mashed potatoes in appearance.
If you want to use steel, #4 24" OC will work.
Will you be doing most of the slab work your self? If so I can give you detailed instructions for accurately setting the hold down bolts.
SamT
Sam
I will be doing the preparation and laying the rebar. For the actual pour, I will hire as good of a concrete contractor as I can find. Hopefully someone who has had experience in this specific type of slab. Pouring and finishing a slab is not something I would want to do single handed... I would guess that I can get the "J" bolts close enough but I would like to hear your method.
Thanks
Ok Casey, just remember, you asked.
First, you will need to draw a plan like below, but with all details needed and all dimensions filled in. All dimension are to the centerline of the column footpad (Boltpad). All you will work with is centerlines.
Check your blueprint detail sheets carefully, do not assume that it calls out to center of steel. Check also with the steel fabricator and use his As-Built drawings. Check with the erectors to be sure they have no surprises for you.
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After you have verified the bolt pattern for each individual column, You can create bolt plans for them.
When you know whether the columns will be plumbed with shims or by adjusting the nuts under the column footpad, you can determine the installed heigth above concrete and know if the plywood patterns will float above the concrete or if the bottom nuts will be buried.
You will have to create a method to hold the patterns proud.
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When you fabricate the plywood patterns, keep the boltholes as small as will allow the bolts thru. Layout the center lines on the patterns first. Check your detail drawings to determine the dimension from centerlines to the holes. Do not assume that they are symetrically aligned.
The centerlines of the column plan and of the bolt plan must be the same!!!!!!!!!!!
ReBar sidebar;
You have to think ahead. I would place at least 1 @ #4 laying in the lower Ell of the outer J-bolts, this means that the rebar is in the hole when you place the patterns, the Ells are turned in to the center of the stemwall. I really like to use rebar on the inner bolts also. Tie the steel to the bolts so it doesn't roll off during the pour.
If you can't achieve 1 1/2" clearance between the inner and outer bolt Ells, turn the inner Ells parallel with the side of the building.
Tape or grease the bolt uppers and upper nuts. If they plan to plumb the columns by adjusting the lower nut, tape it with electricians vinyl tape or grease (vaseline or axle or whatever,) otherwise allow the bottom nuts to be buried in the concrete. Some specify that the bottom nuts not be buried. Make sure the bolt threads extend to the finished concrete.
As soon as the mud sets up enough (30 mins??) remove the patterns and wirebrush the threads and nuts. Remove the nuts to insure their cleanliness. Do detail finishing around the bolts.
Sorry If I'm being too basic, but I really don't know what you know. Besides, I figure I might as well C&P it into my how-to manual.
All right, we're almost ready to set the patterns in or on the form.
You will need batterboards at each end of a run of patterns and a pair for across each end of the slab. You will use these batterboards to set a stringline on the centerlines of the columns and across the two slab ends. These end strings must also be set on centerlines.
Be sure to adjust the diagonals and strings untill you have a square with parallel sides. Adjust till you can't adjust no mo'. This is the most critical check.
Set the patterns to the centerline, doublechecking the dimensions between each pattern center and the end crosstring. Double check everything, for tomorrow it will be set in stone.
Squareness. Parallelity. Bolt Elevations. Bolt Plumbness. You hold the dumb end while someone else checks.
Drypack under the columns after they are set.
SamT
My concern is to keep the "J" bolts vertical when the mud starts flowing around them. I don't know if I really trust just wiring them to the rebar, I might decide to weld them.
I like your custom "center line" font...
Thanks again,
Casey,
The j-bolts must be firmly clamped to the patterns with a nut and a washer top and bottom. The wired is to hold the rebar in place on the bolt ells, incidently it will help hold the bolts more rigid.
SamT
Gotcha - thanks
May I respectfully suggest:
All that measuring, spacing, clamping, forming, etc., is way too much work for a simple steel structure.
If you're getting the best concrete guys you can then you will have a proper, flat slab to erect your frame. Don't forget to cure the slab.
When the frame is in the proper position, drill your clearance holes in the concrete right through the bolt holes in the frame base, clean out the holes and set your bolts in epoxy. Let the epoxy set the required time and add washers and nuts. You're done. Sheet the building frame.
I think that because I like things easy, I'd go Ralph's method, all other things being equal. It would be a lot easier to finish the slab to a glassy finish using the big mechanical trowel with no bolts to work around, and the possibility of a bolt being mis-templated or moving during the pour and finish would be eliminated. I could probably drill and set straight bolts as fast or faster than laying out the j-bolts.
Sam is absolutely correct about the need for compacted fill. There have been numerous discussions here about slab construction and the need for excavation and fill that's appropriate for the soil conditions where you're building. Casey, since you bought engineered plans, do you know if they take into account the soil conditions you have?
I have checked out another steel building of the same dimensions but with somewhat less massive columns that uses the drill and epoxy method. This was after I put the deposit down but before they raised the price of the building by 8% so I may change vendors. However, the vendor that supplied the plans seems to like the "J" bolts in the concrete but I will discuss it with them again as the figures I have seen give some pretty substantial withdrawal forces for the epoxy method.
Although the plans were signed by a PE, they seem to be pretty generic. No one came to my place to check the soil and I sent them no specifications on soil type or density. My soil is pretty run of the mill loam, but the PE would have no way of knowing that. I assume that they just over engineered the plans enough to take care of most eventualities.
(Actually, almost all of the soil in the Columbia River Gorge and even the Willamette Valley was washed in here about 10,000 years ago by what is termed the "Missoula Flood". A large lake was formed in the Missoula, Montana area by glacier melt and then the lake cut loose in a rather cataclysmic flood washing much of the top soil in Eastern Washington down the gorge and depositing much of it in the Willamette Valley. We just keep hoping that E. Washington doesn't demand it back...)