Cracks in Reinforced Cocrete Slab

Post pictures if you can, and wait for capt moosie to come along. He's the resident civil engineer.

As well as pictures, dimensions, reinforcing and mix proportions particularly water/cement would be useful information. Confirm that the crack is through and through and not different cracks.

not to mention base and site preparation

new slab bottom

new slab topold slab
Concrete=c20/25 laboratory tested-ok

reinforcement=pc52 diameter(10 and 14),step=10 cm, 10/10 (lower part); 14/10 (upper part) on beams sections.

slab width=18 cm

beams sections(+slab)=60x30

slab openings=6mx6m

These cracks all look like poor moisture management to me...

GA for the best comment so far.

I totally agree. It dried too quickly.

thank you very much for your answer!

Too late to edit my comment. Correction to rate of contraction:

Should be 1/16" in 10' not 1/16" in 10".

PMoon, what is a trade name or brand name for this spray on curing compound ? I am getting ready to convert by back deck to a 14' x 40' slab, and based on my location, I would sleep better if I used it.

There are two types so I looked for a better explanation than I would do. This site discusses hardeners too but you wouldn't have need of one. When you decide which type, do a search.

Laticrete

If it were me and if I were home, I might just lay some burlap down and wet it down now and again.

Pmoon is absolutely correct in his statements and earns a GA from me.

From what I can ascertain from the photos is appears to a shrinkage crack all right. It does concern me that the crack is observed going all the way through the slab, and if it is true that it has occurred at the mid-span this could be a potentially unsafe condition because maximum positive bending moment will most likely occur there as well. If the crack occurs through the entire depth there is a very high probability that NO transformed section has sufficiently developed between the concrete and the steel reinforcement, therefore the load-carrying capabilities of the slab would be greatly reduced...the tensile stresses in the rebar would be the limiting factor and none of the concrete at that section can be relied upon to aid in the load carrying. IF you can pour water through it then I'm afraid the slab would be considered inadequate.

Probably this crack was caused by a high Water-to-Cement (W/C) ratio used in the concrete mix, water added to the concrete during placement and finishing, unacceptable handling of the concrete during placement, and inadequate concrete curing and temperature control techniques.

What I am not saying is that it is NOT my opinion that this slab is structurally sound and safe. All the supplied data supplied by the OP is in Metric and I'm not about waste my time converting it all.

OP, how was the concrete curing accomplished (type and methods) and for how long?

Did a Registered Structural Engineer design this slab, and was the design followed completely? IF there is an engineer involved have he/she observed this crack and reviewed the laboratory test data, as well as accepting the construction as-is? Is this slab installation under a current building permit, and if so, has the inspector/code enforcement official observed the construction and signed off on it for Occupancy?

A little off topic, University of Wisconsin-Madison has a 50 year cement experiment that started in I believe the 19th Century. The professor that started had made so many cement samples to test, that it's now known as the 100 year cement evaluation.

-the designer is registered

-the cracks have been observe by an inspector (not a real problem in his opinion)

-the laboratory tests are ok regarding the concrete

-the cracks can be observed just in the midle of the slab (not along the slab from end to end)

-in the middle zone of the slab in the upper part (compresion) their is no reinforcement in the design plans...is that ok?

-anyway ,I repeat, almoust all slabs have cracks in the middle zone of the slab opening (ok, contraction) and also the beams have cracks in section-visible on all faces of the beam- in the middle (where the bending moment is maximum).Let-s say the concrete is good,the desing is good, why do cracks still can be observed?As I see from your opinion contraction is the main reason, like I tought ,but what about the beams?can be the same reason?contraction...

Immediately after placing the concrete, solid particles tends to settle down by gravity action and water rises to the surface. This process is known as bleeding in concrete. The bleeding process produces a layer of water at the surface and this process continues till concrete has set.

Plastic shrinkage cracks are common in slabs. In slabs due to rapid drying, the surface concrete turns very stiff to flow and then it will possess no strength to withstand the tensile stresses caused by restrained shrinkage. This causes concrete to develop cracks on surfaces.

Source of this information and more details you can read at:

Concrete Cracks (Plastic Shrinkage) on the Surface of Slab

I am not a professional in this field, but have done several small concrete projects myself. Most of what I did had too much water, but I never had cracks in any of them except one corner fell off on one (about 2 inches) when I removed the forms. I was able to epoxy glue it back, and can't tell where the joint is even after 20+ years. My guess is that it was worked too long or did not have enough cement in the mix, with the latter being the most probable.

do you ix your cement? or buy ready mix delivered?

Did you make cement test pieces?

Ready mix makers have been known to make lower cost concrete with lower cost materials. Large users of concrete always make test pieces. Once the ready mix maker knows you will be making test pieces according to a standard and testing them, you might find better stuff shows up on site. Cap't Moosie can probably be more precise

Concrete

it is a ready mix delivered concrete (their are also concrete epruvetes for laboratory testing-which are ok);

then the problem may indeed be loss of water by wicking into wooden forms or by excess water or excess working?? H

An experienced concrete person on site might help. As it is, you may have to remove the bad slab and make another one if a state or city approval process is involved.

what does this mean ?? concrete epruvetes

Without knowing the physical/constituent makeup of the concrete mix it is very difficult to ascertain why the slab is cracking as much as it did. But please keep in mind that nearly all slabs, beams, girders, columns, and walls will experience some degree of shrinkage cracking.

Getting back to the mix itself, we would need to know the following:

1. Aggregate sizes and types, and their sieve analysis distribution. This includes all rock and sand, and their compliance to various testing standards. Here in the US we use ASTM Standards. We also would need to know the total weight (in pounds) of each aggregate, as well as the maximum size of the largest aggregate used, based on standardized sieve/screening analysis.

2. Cement weight, and type of cement used.

3. Were Pozzolans (fly ash) used? If so, what type as well as total weight in pounds.

4. Air entrainment admixture used? If so, what type and amount used to produce what percentage (%) Air Entrainment.

5. Total weight of the water, in pounds. Was is clean fresh potable water? Were chlorine ions present, and if so, to what degree (in mg/L)?

6. Were any other admixtures used in the mix, such as retarders and plasticizers?

7. Total volume of mix, in cubic yards.

Additionally, we would need to know the following:

a. Where you are located, so as to ascertain what concrete mix, placement, finishing and curing standards should have been followed. Same for the concrete design standards.

b. Ambient air temperature and humidity records during the concrete placement. Results?

c. Were the concrete temperatures taken throughout the concrete placement? Results?

d. Were concrete slump tests taken throughout the concrete placement? Results?

e. Were air entrainment tests conducted throughout the concrete placement? Results?

f. What was the maximum drop height from the end of the ready-mix truck's discharge chute to the bottom of the form work (like that of the cast concrete beams)? Concrete segregation can be a large contributor to concrete cracking and honey-combing, if the concrete mix is dropped too far.

g. How was the concrete moved about after it was discharged? Raked, shoveled, vibrated horizontally and vertically? Again, segregation of the mixture components is a large issue here if the concrete is moved too far or over vibrated.

h. Was water added to the mix inside the truck prior to discharge to aid in it's workability? How much (gallons or pounds)?

i. Was water added to the the concrete during it's placement (after discharge from the truck) to aid in it's workability? How much?

j. How was the top of the slab finished? Methods....

k. Were any concrete floor hardeners or chemical curing compounds applied to the top of the slab? Types and application rates?

l. Concrete curing method types used and their respective duration(s)? Inappropriate or ineffective or non-existent curing during the first 10 to 14 days is the single largest reason (outside the the use of too much water) for the development of unacceptable shrinkage cracks.

m. Were independent laboratory testing technicians and the engineer's inspector present during the entire concrete placement?

Really, the above is a shopping list to hand over to your design engineer.

To answer one of your questions (regarding the absence of reinforcement steel in the upper portions of the slab (in the compression zone) throughout the center of the span), this is normally done.....depending on the design loads, slab span, slab thickness, one-way or 2-way slab, multiple slab spans, and etc.. Generally speaking, compression steel in a slab isn't present anywhere from 1/2 to 1/3 of the middle span. Sometimes it is included if the design service loads are excessive or there's a need to limit short term or long term deflection, or even concrete creep. All-in-all, there's too many factors involved to give you a definitive answer to you question.

If you are concerned about cracking in future slabs I would look at the concrete mix design much more closely and well as QA/QC field procedures......adding additional water in the field is a big no-no + proper concrete curing is absolutely essential. I prefer to have the slab covered with at least 6-mil poly plastic sheets, duct taped at the edges and the entire slab flooded with water after initial set-up (not concrete flash...), with water depth of at least 1 inch (always maintained) for a period of not less than 10 days. Actually, 14 days is preferable, then the forms can be stripped, the water drained and a high quality chemical concrete curing compound (that can penetrate the surface to at least an inch) applied to all exposed surfaces at the prescribed rate recommended pursuant to the manufacturer's written instructions. But beware, too much of an application rate can be detrimental to the concrete, causing it it erode or even flake. Too little and it's ineffective and won't do it's intended job of preventing water wicking out of the concrete mass....thus causing excessive heat of hydration.

Last item...if you are concerned about this crack you can always inject the crack with an epoxy material selected by your design engineer that's intended for concrete crack repairs.

Good luck!

==Signed,

CaptMoosie, PhD, P.E.

Civil, Structural, and Environmental Engineer

Thank you for your proffesional answer!You are right!Their are too many unknown variables to solve the equation, anyway I made up a general opinion regarding the situation.Thank you again for your time and I hope in the future I will be more specific when I ask something.This topic can be closed...

Best Regards!

al3xino,

a beginer site engineer somewhere in Europe

I am going to be building a new house this summer and plan to start pouring concrete for it in May some time.

Got any tips on how to make sure the local ACI (Al Cheapo Inc) certified suppliers actually bring me good quality mix and in the correct volumes too?

Reason being we have far too many people who do pours that always seem to need way more concrete delivered and paid for than what the physical measurement math says could have ever possibly fit. 60+ yard pours to make 50 yard slabs and quality/batch control rivaled by that of a cross eyed mule.

have the trucks weighed before dropping and after dropping, if a truck scale is handy.

This is one way you can easily be cheated by the company.

order a full truckload, and have projects to use it all, even molds form garden gnomes to use it up. The companies have highway barrier molds at the depot to use up any left overs before the washout

I has a friend help me with a patio. He ordered the concrete and specified the slump, and they put in 5 & 1/2 bags of cement per yard. That was too much for a hot day (>90F). It set up way too fast. He had them add water to the mix until they had no more. It had no cracks for quite a few years, but now has one near the middle across the whole patio. That's better that my driveway which was done by professionals. I think 5 bags per yard is about right.

Hey TCM, what house elements are going to require the concrete? Basement walls and floor slab on grade? Or a house without a basement & first floor slab on grade?

I can provide you a very good concrete mix that I've used over the years that nearly eliminates shrinkage cracks providing you use minimum Shrinkage & Temp steel ratios and proper curing.....all depends on what is going to be constructed. I have to dig around for it in my multitude of storage boxes down stairs in the b'ment. It'll be in specification format. the last time that I used it I only had a very minor shrinkage crack......in an underground stormwater detention tank, all cast-in-place concrete, measuring 32' W x 240' L x 8.5' H with a longitudinal center wall.

Wanna see some pics of it? They're scanned pics from a project 12 years ago....that I'm going to use for my firm's website.

Later today I can give you some very valuable pointers to get the yields and quality that you specify to the ready-mix concrete company.

Right now I'm taking a lawn mowing break and having a tall glass if ice water.....gotta get it done before the thunder boomers hit later this afternoon.....then it's pretty much solid rain until Thursday here.

No hurry on my part!

What I am doing is a full basement with 9' walls 8" thick plus a 4" slab. I don't have ground water issues and the hill I am beside that is excavated out is hard packed clay.

The hill side where the garage end is will be about 14' from footings to top though and 32' long.

I also have a vast amount of commercial chain link type fence as well and was planning to use that as a reinforcing mat being my local concrete buddy says that if I have it its way stronger than the regular wire mesh reinforcement. 5/8" rebar is not an issue either!

Any suggestions for a basement storage space under the garage? I have loads of heavy 6" x 6" steel and a good background in welding and metal fabrication so supporting a 2" - 3" pour over a 32' x 40' garage space is not an issue either.

Mostly I just don't want to get ripped off on the concrete quality and quantity end of things.

Hey TCMTECH, I'll try to find the concrete spec that I mentioned before sometime tomorrow. I may have it on one of my really old Iomega Zip Drive disks laying about. When I find it I can email it to you if you want.

Hmmm, 9' high basement walls, 8" thick may be pushing it. Code here states for that height 10" thick basement walls are required.....unless what you meant was that the total height is 9' and you have an inside ledge to rest the floor joists on with a double 2x4 or 2x6 cleat + j-anchors.

If you find that an 8" thick wall is acceptable per code, you can use the following rebar to satisfy minimum Shrinkage & Temperature Steel requirements:

Vertical steel at a single face (inside face) would require #4's @ 12" o.c. w/1.5" minimum conc. cover. If rebar is at both wall faces (preferable to lessen cracks) then use #4's @ 18" o.c E.F.. The aforementioned steel rebar wasn't designed to resist lateral earth pressure with resulting bending moments and shears....that requirement would be highly dependent on the type of soil backfilled against the wall.

Horiz. steel for single layer (inside face) or at both faces would require #4's @ 18" o.c.. Please note that the maximum rebar spacing per ACI 318 is 18" o.c. for S&T steel.

I need some clarification about the garage: 14' wall height overall? If so, you're going to need a thicker foundation wall, most likely 10" thick minimum. Also, is there to be a basement under the garage floor slab, as in suspended slab? Keep in mind that the minimum suspended slab thickness per ACI 318 is h = span (in inches) / 20.

So, for example, you have a garage slab of 12' x 20' (clear spans between inside wall faces) the minimum slab thickness for a one-way floor slab would be:

(12' x 12 in./ft.) / 20 = 7.2" minimum [so round it up to 8" thick]. Rebar required for flexure (ie, bending) and shear would need to be determined based on the service loads outlined in your state building code (most states use ASCE -07 Standard now).

Make sure you backfill you foundation walls with a good quality clean and well-graded Run-of-Bank gravel that is free of silts and clays as much as possible. I recommend silts and clays not exceed 5% (by weight) as retained on a No. 200 Sieve. Make sure you provide some sort of perforated footing drains surrounded by washed stone with a filter fabric envelope. Make sure you run the drains @ 0.50% minimum gradient to "daylight". I would worry about the clay on your lot and the fact that you have hills next to the proposed building location, as any snowmelt or stormwater runoff (and groundwater migration) will flow towards your dwelling and flood you out. It sounds to me that you've made a great big bowl in this hard-packed clay for your house to sit in. Be very careful! You don't want the underlying clay mass to become wet, as it will most likely swell as tremendous amount thus causing all sorts of structural upheaval. Also, wet clay has very little bearing capacity (actually very crappy bearing capacity) to support building foundations. with that in mind I would strongly recommend that you construct the footings and basement slab on grade with no less than 12" of well graded and well draining stone gravel to aid in draining the entire slab subbase and the clay subgrade. Minimum compaction requirements of the subbase gravel layer should be not less that 98% Modified Proctor Density (after compaction/rolling, you should not see your boot prints in the gravel surface when it is at optimum moisture content).

Okay, storage under the garage? Are we a "prepper"? hehehehe Nothing like a bomb shelter disguised as a wine celler! Don't laugh, I once had a very rich client build a very expensive $2.7M (20 some years ago) "summer home" just outside Saratoga Springs NY that had an actual bomb shelter in the basement disguised as a wine cellar. The tip off that is wasn't a wine cellar was the two 8-inch thick ASTM A36 steel plate doors (basically a bank vault door) and 18" thick reinforced concrete walls lined with 2" thick steel plate all attached w/ 1" diameter Nelson shear studs. Big enough too, to accommodate 20 of his nearest kin....also enough food and potable water to last a year + fitted with NBC air filters and a standby generator set. It was better built than most state EMS bunkers! hahahaha

Are you suggesting that you support the garage slab with 6"x6" steel what? Tube steel? Given that most basements are damp you may run into long-term corrosion problems with that steel. You could go with two parallel lines of steel beams and columns, but my initial recommendation is to construct 2 intermediate parallel reinforced concrete walls (to make 10'-8" c/c between walls and lessen the suspended slab spans) to support the garage slab.

2" - 3" pour? As a suspended concrete garage slab? If so, it will be structurally inadequate and not conform to the building code and ACI 318. See my comments above....

Commercial grade chain link fence would be more than adequate for the basement slab on grade as long as it have no vinyl or PVC coating. Galvanized steel is okay. Make sure that the fence is flat sheets only, and not from a roll, as it'll be a real bitch to keep the C-L-F under the wet slab....it'll bow up out of the slab. also, provide 18" minimum lap joints. Now, if you do go for a 4 inch slab, make sure it's actually 4" minimum slab thickness, and not 3 1/2" (based on 2x4 casting forms). 3.5" thickness just won't cut it for durability and not enough mass to prevent "slab creep". You may also experience slab curl at the corners and edges due to insufficient slab thickness.

I'll get back to you with that specification....it'll show you how to avoid bad concrete quality and short-changing on the quantity.

The wire mesh fencing is standard commercial heavy gage galvanized and lays down flat without problems.

The beams are 6 x 6 galvanized H beam with a roughly 3/8 web. I think I have around 2000 linear feet of them so doubling up to make 6' x 12" is what I had planned and I can also get more if needed. I also have loads of 1/4 - 3/8" steel plate I can get cheap as well so as far as supporting the concrete thats not problem either.

I have no problem with having 10" thick walls either! Around here its rare to see a full depth basement poured with anything more than 6" walls and a 2" - 3" slab. Many homes here are sitting on basic 2" x 6" treated wood basements!

No I am not a prepper! I just want lots of storage space and a unique house design. Although the thought of having my own secret lair under the garage is appealing! (Much evil laughter in the background.)

The side wall of the garage would be roughly 14' from the base in the sub garage area to the top of the main garage wall. As far as drainage and proper landscaping goes I am familiar with that as well. Same with getting all the clean sand, gravel and whatever other material. Its not hard for me to get those around here either.

TCM,

Do you know what the (H?) beam AISC designation is, as well as the Yield Strength? They may be either a Wide Flange (W6x?), Misc. (M6x?), or even a HP (HP6x?) beam.

Wide flange beams are the most prevalent, misc. beam not. Ditto with HP beams since they're mostly used for piles. Yield strength more than probably is ASTM A36 steel (Fy=36 Ksi), or another ASTM grade steel with Fy=50 Ksi). Are there any mill stamps or marks on any of the steel sections?

Anywho, you need to do accurate measurements (within a 1/16") of the beams, such as:

1. Overall depth (d),

2. Flange width (bf),

3. Flange thickness (tf),

4. Web thickness (tw).

After you give me those dimensional measurements I can narrow down what the actual ASTM beam designation for you as well as it's sectional properties to determine what their load carrying capacities are.

I have strong doubts about a single 6" deep beam carrying much load, especially when you have to support a rolling or static vehicle + the dead load of the slab and the steel plate. Possibly one beam welded atop of another will work, but that's going to be a lot of welding work for you.....lots of slotted plug welds where the beam flanges are in contact with one another. A lot depends on the span of the individual beams as well as the slab spans between the rows of beams + concrete thickness.

IMO, the steel plate will not aid much in load carrying capacity of the garage slab because there's not much concrete bondage to the steel to produce a true transform section where the steel and the concrete interact sufficiently. More than anything else, the steel plate will act like a concrete bottom form. For the steel plates to properly interact with the concrete above the plates (like rebar) have to be totally surrounded by concrete to form what is called a composite transformed section.

A slab thickness of 2" or 3", even with steel plate underneath, is going to be structurally insufficient to carry the vehicle loads on your garage floor slab. Trust me on this as I've designed many parking garages over the years, even ones for residences and to support EMS ambulances, etc. The slab thickness IMO will have to be over 6" minimum, depending of what the slab spans are from beam row to beam row or beam row to inside face of the foundation walls.

Here's some pics of large parking garages in Albany NY that I've designed in the past:

The bottommost pic is of the 950 car parking garage constructed for NYSOGS circa 1999-2000, located just east of the New York State Empire Plaza in downtown Albany. the other two are for the City of Albany Parking Authority. I have many more that I could post, but I won't because of the pic sizes & download times....

The 14' high foundation wall would have to be at least 10" thick with #5's @ 10" o.c. vertically is the wall is constructed with 3,000 psi (f'c) concrete and ASTM A615 Gr. 60 rebar (fy=60ksi). 4,000 psi concrete would be better, but it will not really decrease your rebar sizes and max. spaces all that much because of the wall height and the lateral earth pressure created by wall backfill. You'll also need to have sufficient structural floor slabs top and bottom of the wall to resist the lateral reactions. I haven't even discussed the footing requirements here, but with underlying clay it'll be wider than the usual house footing, just to carry the gravity loads and the the garage slab and vehicle LL reactions.

The thing is I am not building a commercial parking garage structure or fallout shelter here.

I had planned on setting the H beams on top of each other in the standard H type configuration with a structural pylon at the mid point of the 32' span. Spacing wise I had figured a 36" on center spacing at most.

Welding is not a problem. I have two commercial wire feed units and a 105 amp plasma cutter(and a few friends who owe me favors) so the actual cutting and welding aspects are not a big deal.

Same with setting things I have a Case 1150 bucket dozer and two tractors that can pick up up to 2500+ pounds each. Anything over that I have access to a pay loader and a 10K Telaboom machine.

tcmtech, yes I do understand that you're not building a commercial parking garage or fallout shelter. I was just pointing out that I do have experience in designing those types of structures. I'm trying to help you here, not condemn you, nor make you over- design the house.....I'm trying to steer you in the right direction because I don't think that you're looking at the long term consequences of winging this design be yourself. In effect, I'm trying to save you future hassles down the road, such as building a garage floor structural system that may have inherently insufficient structural capacities built into it. Don't forget, whatever you build has to be for the life of the house. You have to take into account the sale of the house to others in the future and the legacy that you leave to the next owner and subsequent homeowners. Most banks (for mortgages) and the future buyers will want certification of the structural integrity (and design) of the garage structural elements, to insure that it was designed properly as well as constructed properly. Do it right from the get-go and you'll not have to worry later on. Just a word of advice, that's all.

When you say that the "Spacing wise I had figured a 36" on center spacing at most", are you referring to the spacing between the row of beams (the typical span of the garage concrete slab from beam line to beam line?

Just to let you know that ASCE 7-05 "TABLE 4-1 MINIMUM UNIFORMLY DISTRIBUTED LlVE LOADS, Lo, AND MINIMUM CONCENTRATED LlVE LOADS" stipulates that your garage floor slab would need to support a design Uniformly Distributed Live Load of at least 40 psf as well as support a concentrated vehicle wheel live load of at least 3,000 pounds. In addition, since your car or truck moves, a Live load Impact Factor has to be considered in the design. Most likely your local Code Enforcement Officer is going to follow this spec as part of the State Building code. You may well argue that your vehicle(s) don't weight much and those loads don't apply to you.....but, keep this in mind as this garage floor system must support vehicle loads (and any stored materials and equipment) for the life of the house. Future owners of the house may in fact have heavier vehicles than you currently have.

Professionally, I have serious doubts that a thin 2"-to-3" concrete slab overlay atop steel plate will be structurally sufficient to carry the Design Concentrated Live Load when you have spans of 16 feet. Same goes for your doubled-up 6" "H" beams, whatever they may be. Even with a total depth of the sections welded together, the cobbled together beam will have insufficient Moment of Inertia (to resist excessive deflection) and Section Modulus (to resist Bending Stresses induced by Bending Moments).....IMO, I firmly believe that you are going to have to reduce the spacing of the supporting columns (along each beam line) down to at least 8'-0" o.c. or 10'-8" o.c.. The maximum spans will be wholly dependent on how the math works out, based primarily on the actual Sectional Properties of those 6" "H" beams.

Trust me on this, as I know what the hell I'm doing here on structural design and construction matters: I've been doing this for 35 years and have been a NYS Licensed/Registered Professional Engineer the past 17 years. Just FYI, outside of Calif. (because of the seismic design requirement), New York State has the toughest PE Licensing Requirements of any state in the nation, and that even includes IL with Chicago's strict SE requirements.

Okay, I understand that you have the welding equipment and can weld. So do I and I can weld as well, but I'm not AWS certified.

[I really don't go to this level of engineering advice for peeps who visit the CR4 Forum, especially one-timers and newbies that are looking for FREE design services, but I am making an exception in your case because you've been a long term member and are a good skate....I do like you and have never had a problem with you in the past. Consider yourself "lucky". LOL.]

I am not questioning your credentials and I do appreciate the help but what you are describing is no where close to what I have personally seen used around here for the same setup that passed code inspection as I am planning.

I am not sure what our building codes are here in ND but every house I have ever been in that had a poured concrete basement had at most 8" walls, most are 6", and the few garages with storage space under them had far less structural support than what I am planning thats all.

I have a good friend who's mothers house has a good sized two stall garage with a storage area under it and I will see if I can get a look at that some time soon and possibly get pictures of it as well for reference.

I will also talk to the guy, good friend of mine also, that I am having help with my concrete work and see what he has done in the past. He is a certified contractor with a great reputation and has done several setups like this as well and I trust his work more than anyone else.

As I said I am not questioning your work or experience and I do appreciate the input rather its just that what you are saying does not match what I have come to see as standard concrete design practice around here for homes and private construction.

Up to you tchmech how you want to build it. I'm just glad it isn't my house.

Whatcha seeing is what the last guy got away with. IMPO, if they were designed (doubtful by the sounds of it) and built conforming to the ND Building Code, then the Code and Code Enforcement is way too lax. No way in hell would that degree of construction ever be allowed to be built here in New York State.....

Just sayin'.....Good luck!

I understand completely. Its just that whats acceptable in one area and works well there often times is not adequate else where.

If whats considered normal heating capacity and insulation values for a house in this part of the country was applied to a house being built in south Texas the locals would consider that nuts and gross over kill.

The thing is we have had many structures here designed by out of state people who applied their regions specs to things and stuff got way over built and ran way over budget for no reason. We had a commercial building built near here a number of years ago that that was designed by a company out in California to California earthquake specs. (We don't have earthquakes here let alone a need for structural design specs intended to cope with an 8.0 quake.)

I will be consulting people on what our local building codes require and will most likely be going above that being thats how I prefer to build things but I wont be building to specs that do not apply to our region, conditions or personal application. I just cant afford or justify it.

Now if you have advice on how to keep from getting cheated on my concrete in delivered quality and quantity I am all ears!

Ask the ready-mix company supplying the concrete to provide "BATCH TICKETS" for each and every load they deliver. If they don't have 'em then turn them around. The tickets should depict the computer printout of the weights for each aggregate, the cement, the water and the fluid measurements for all admixtures. Also demand that the Cubic Yardage (ie, YIELD) delivered is on the tickets. The delivered amount should be well within a percentage point of what is on the ticket. If it's way off they're ripping you off bigtime......triple check your measurements and calculations to determine Cubic Yards needed + add 5% for waste and losses.

Errr, not overkill on those loads I gave you.....cars and trucks weight the same around the country and world, w/ no regional differences.

Actually I considered your 3000# vehicle numbers to be rather low. The lightest car I own is well past that and my two work trucks are in the 8000+ range empty.

As I said before I trust you knowledge and skills its just that past personal experience with seeing things like what I am planing on never came anywhere close to the dimensions and design you are suggesting.

The first design I ever saw of a garage with a basement had been in place for around 40 - 50 years and supported two full size 3/4 ton pickups plus a garage full of junk and was built to about half what I planned on building mine. If I remember right I think there were upside down rail road track sections running lengthwise about where the vehicle wheels ran and a pair of 3" round steel pipes for center column support under them. The rest of the structural integrity was what ever rebar was put in the slab which was probibly no more than 2" - 3" thick at most.

Of the newer designs I recall they used a similar design but with something like 4" x 12" I beams under the locations where the vehicles parked and the steel sheeting supporting the concrete looked like standard heavy gage ribbed galvanized sheeting like what is often used on comerical grain bins. As far as slab thickness goes I seriously doubt they were more than 3" - 4" thick either.

Regardless of what I have seen so far I plan to look as a few others now more closely and see whats considered standard around here and intend to plan my designs around that.

tcm, that 3,000# live load that I quoted to you is for a single wheel load if the event that one side of the vehicle is jacked up.....now it'll make sense to you. I've seen peeps (mostly Contractor friends) on several occasions over the years jack-up their huge pickup trucks (you know the ones with the 4 rear wheels) in their garages, and the result is one of the front tires (where most of the vehicle load is because of the engine and cab, etc) is the only one in contact with the garage floor slab. Then they bitch later over beers that they busted their way too thin slab on grade. LOL

Remember if you're going to install rebar of any type in that garage slab you have to have sufficient concrete coverage top and bottom for it to even work. A 2" thick slab and Chain-Link-Fence acting as rebar isn't going to have enough concrete around it. trust me on this....no one is THAT GOOD at laying C-L-F absolutely flat. I don't care if you're the best damn Concrete Contractor in the world....it just isn't gonna fit Bro! Plus you need to raise it off of your steel plate at least 3/4" to be effective, and if you don't have a heated garage 24/7 you will need at least 1 1/2" concrete coverage atop the C-L-F to prevent concrete spalling, popping, and other detrimental affects cause to exposure to the elements, which are mainly freezing of the concrete because it is porous and sucks up water like a sponge.

That galvanized sheeting may have been commercial corrugated steel floor deck, right? Usually it's used for supporting concrete floor slabs in buildings (and bridges) while the concrete is being placed and is wet. It acts as a permanent form. Depending on its gage and sectional properties it may or may not have formed a "composite section". A lot depends.

Yeah, I could see steel railroad sections possible working under the vehicle wheel loads if they were supported at the mid-span or 1/3 spans. Again, a lot depends on the spans, spacings of the steel RR members, vehicle loads, and the concrete slab thickness. But those are hard to come by and not cheap.

Okay, let's look at this problem from a QUICK number crunching standpoint:

LOAD CASE CONDITION A: Uniformly Distributed LL = 40 PSF (per ASCE 7-05 Standard/Code); a 4" thick normal weight concrete slab atop a 1/2" steel plate; maximum beam row spacing = 36" o.c; and max. Beam span = 16.0', simply supported both ends. Assume that you have W6x15 ASTM A36 steel beams.

WLL = 3.0' x 40 psf = 120 plf applied to the beam line. (=10.0 pli)

WDL (steel plate) = [((0.5"x12"x12")/1728)x490pcf] x 3' = 61.25 plf applied to beam line.

WDL (slab) = 4"/12 x 150 pcf x 3' = 150 plf applied to beam line.

WDL (beam) = 15 plf

therefore, WTL = 346.25 plf (use 348 plf = 29.0 pli)

L = 16.0' = 192"

Max. MTL = (29.0 x 192^2)/8 = 133,632 in-# = 133.632 in-Kip at midspan

max. design fb = 133.632 / 9.72 in^3 = 13.75 Ksi < Fb = 0.66 Fy = 23.76 Ksi (o.k. if each side of top flange of beam welded to steel plate above less than 24" o.c....for lateral support)

max LL deflection = (5x10x192^4)/(384x29E6x29.1) = 0.21" downwards @ midspan

LL Limit = L/360 = 192/360 = 0.53" (O.K.)

LOAD CASE CONDITION B: Concentrated Live Load (wheel) = 3,000# at midspan in lieu of Uniformly Dist. LL of 40 psf. All other construction detail remains the same as above.

P=3000# (without any Impact Factor)

Sum of WDL = 226.25 plf (use 228 plf = 19.0 pli)

Max. Design MTL (at midspan) = 231.552 in-Kip

max Design fb = 321.552 / 9.72 = 33.08 Ksi > Fb = 23.76 Ksi EXCEEDS ALLOWABLE BENDING STRESS BY 39.3%......THEREFORE, UNACCEPTABLE & N.G.

max LL Deflection = 0.93" downwards. THEREFORE, EXCEEDS LL DEFLECTION LIMIT OF L/360....UNACCEPTABLE & N.G.

You may or may not have a heavier W6X beam section there, but I seriously doubt it will be sufficient...the numbers won't be much different that what i have demonstrated above.

You could stack the beams atop one another.....it may or may not work. You may also have to decrease the beam spans considerably. Also, I haven't the foggiest what your beams actually are. Okay, I haven't the time to run those calculations, as I have a Special Planning Board Meeting (yeah I sit on our Village PB) to attend this evening and I must prepare for it.......lots on the Agenda.

Thanks. It makes more sense when I have actual numbers to look at.

I am quite good with applied engineering math but I am weak at the terms and definitions applied to areas outside my normal interests so when you define something in more detail it makes sense to me.

I didn't plan on using the wire fence material for anything other than the basement slabs and the slab in front of the garage in this project.

Relating to my beams I have no issues with moving to a 8' spacing opposed to a 16' one for the supporting columns.

As far as heavy loads go thats what I have the shop for and thats going to be a 6" slab when it gets poured. The garage is just a garage and wont be the primary work place for anything. (Wife most likely wont allow it.)

Being I have access to lots of different structural steel beams and related materials what would you recommend I look for?

Hey tcm, I did some really quick number crunching for you this morning regarding what you're going to need for that garage of yours. I made some assumptions first, such as:

6 parallel rows of steel beams (sp. @ 36" o.c.) if you have a 20 foot wide garage with 12" thick foundation walls. You'd have a column in the center of each 32' (+/-) long steel beam, therefore making it a 2-span continuous beam. In essence, each span would be 16'. I'm also assuming that you have a 4" thick 3,000 psi (f'c) concrete slab cast atop a 1/4" ASTM A36 steel plate. I'm also assuming that you are not heating your garage during the winter months.

First, I didn't figure in the effect of the underlying steel plate. Doing those calculations is time consuming, so I figured ONLY the rebar requirements for positive moment (tension at the bottom of the slab) in the middle 2/3's of each slab span (between beam rows) in reinforced concrete slab w/o the steel plate with an applied wheel load of 3000# and impact factor. You'd need at least #5's @ 10" o.c. (ASTM A615, Gr. 60 bars) running parallel to the beam lines. I didn't calc. the rebar requirements of the slab in the negative moment regions of the slab (over the beams & the outer 1/3 of each span.

Note: You probably could reduce the bar sizes and spacings if you construct the slab with 2 layers of rebar (top layer and a bottom layer.). This is what we refer to as a "Doubly Reinforced" member. Constructing this type of member has a whole host of advantages. Also, a big problem is when you don't heat the garage the concrete is considered "exposed" to the elements, according to ACI 318. Therefore, you would need to provide at least 2" of concrete cover atop the upper bars. You can get away with 3/4" concrete cover underneath the bottom bars (between the underside of the bottom bars and the top of the steel plate) since your basement will most likely receive some sort heat from the house above. These cover requirements are to prevent the concrete from spalling and popping due to moisture freezing in the surfaces of the concrete member. As you can see, if you go with a thinner slab you'll have insufficient concrete coverage for any top bar placement and insufficient rebar depth (as measured from the bottom of the slab to the middle of the top layer of rebar) to produce a proper concrete transformed section (strength developments/interaction between the rebar and the concrete.) in the Negative Bending Moment regions of the slab as I previously commented upon above.

You need to have each steel plate installed to run over 3 successive slab spans. Make sure you stagger each plate joint, just like you would do with installing a plywood floor sheathing. This helps with continuity, and the multiple spans reduce the bending moments (distributes the applied live load(s) to the other adjacent spans instead of a single span taking all of the load). Make sure the plates at welded to the top flange of each beam where a joint is formed.

If you install the beam rows (each 32' long) like I mentioned above, with a single steel column at the center, then I estimated that you must likely could get away with W12x14 steel beams (ASTM A36 steel). You'll need to provide a steel bearing plate and at least 2 anchor bolts where the ends of the W12x beams rest on your foundation wall (in a wall pocket or an interior support ledge). You'll also need to install some sort of clip steel angle in the upper part of the beam web here to help prevent the beam from rotating on you once it's under load....a A36 Clip L3x3x 5/16 with 5/8" ASTM A325-F bolt (or you can weld it to the upper region of the beam web....your choice) and a 5/8" expansion anchor is all you'll need.

Most likely you can use those 6" steel beam sections that you have as the center columns, providing that they're as least a W6x15 ASTM A36 section. You'll need a steel cap plate at the top of each column with 4 - 5/8" A325-F bolts. this is to prevent "web crippling" of the beam section under load. You'll also need column baseplates w/ 4 - 1/2" or 5/8" expansion anchors. Based on the clay conditions found on your property, I would use anything less than a 30" x 30" x 12" min. thick concrete footing cast atop a 12" minimum compacted gravel subbase under each steel column. You can get away with either 5 -#4's Each Way or 3 #5's E.W.....providing that you provide at least 3" minimum concrete bottom cover (between the top of the gravel subbase and the underside of the rebars).

DISCLAIMER: I did this on the back of an envelope really quick like. Actual construction should not be based on these preliminary design estimates.....

In a nutshell, this should point you to where you need to go. What you do with it is all up to you, but IMPO I really think you need to hire a Structural Engineer to finalize any design of your garage structural elements.

Getting closer! I don't mind doing a 4" slab if that whats required. The garage is attached to the house and may have a upper level as well so it will be heated year round and will never be subjected to full freeze up conditions.

The dimensions are either going to be 32' x 40' or 30' x 36' and the three doors will be coming in from the long' side. Given your estimations I am leaning toward going with a 10' spacing on my lower level support columns.

I cant find any numbers on my 6"x 6" H beams but I do have three sizes, 1/4", 3/8" and 7/16". Most of its the 3/8" and 7/16" stuff.

In all I think I have enough to do a 24" or 30" spacing without problems opposed to the earlier 36" spacing.

Relating to the rebar in the concrete I was thinking of using 5/8" on 8" centers in just a single layer although I can easily change that to 1/2" in a double layer with a 4" offset from one layer to the other as an option.

Will running 1/2" PEX for hot water heat in the slab change things much? I have hot water heat coming from my shop boiler to the old house and I plan to use that in the new house as well.

I really do appreciate the rough estimate advice so far!

tch, sorry for the delay getting back to you on this, but I was extremely busy yesterday.

One thing you may want to consider for you garage slab is using what is referred as a galvanized "Composite Steel Floor Deck". It is certainly much more lighter and easier to install than those very heavy steel plates that you have. Also, you can eliminate the overhead welding of the underside of the steel plates to each top flange of whatever beam section that you install; that is a very difficult welding position, and even more difficult to obtain adequate fillet welds. Instead with the corrugated floor deck all you have to do is provide "puddle welds" at the top flanges of floor beams. A downward weld is always preferable. With a 36" slab span (c/c of the steel beams) you may be able to get away with possibly 22 or 24 gage deck sections, but you may also need to thicken up the total slab thickness to maybe 4.5" or 5" in able to carry the superimposed wheel Live Load. Using this deck is industry standard worldwide. It also acts as a concrete form. Please keep this in mind, but by using this deck your concrete volume won't increase a huge amount because of the corrugation flutes. Also, by deepening your slab thickness and increasing the concrete compressive strength to 4,000 psi (f'c, at 28-days age) slightly you may be able to reduce your overall reinforcement steel requirements. Additionally, if you install this deck make sure you install it over at least 3 continuous spans + provide at least 6" laps at the ends with the next section of metal deck. Using this deck will ease your installation headaches and ease your back pains! Just make sure you have a Structural Engineer design this composite slab section, okay. Use too thin of a steel deck and too thin a slab thickness and too little rebar and it will spell disaster....failure of the slab under load.

You may want to strongly consider this option.....one of the benefits of using the metal floor deck is that you can prime and paint all of your steel beam surfaces prior to erection, except the topside of the top flange (which you'd be welding the deck to).

I really don't see the need to go to a lesser beam spacing (ie, lesser than 36" o.c.). That is really overkill IMO. You need to balance the overall design better. Depending in the actual slab spans and how they are designed you may be able to increase the beam line spacings to 42" o.c......a lot of IF's, but possible! Some structural calculations are required!!!!

Now, don't start guessing the rebar requirements! LOL The rebar sizes and spaces are highly dependent on how you want to construct your slab: concrete compressive strength; slab thickness; composite floor decking or steel plate; and rebar size, spacing and steel Grade all are interactive and come into play, so it is important that everything be calculated to ensure that the slab is able to be structurally sufficient.

Sure, you can run PEX tubing in your slab to keep it heated! If you use the garage on a daily basis, all day long, to do work in it would make sense, but do you really want to incur those extra energy expenses throughout the future (with ever increasing energy costs) just to save a little on the minimum required concrete coverage at the top reinforcement steel layer? Seems to me that overall that isn't very economical and just shaving the skin off the end of your nose to save a little money upfront.

I think you would be best served to use a doubly reinforced slab (two layers of bars). You get a decease in overall rebar tonnage, gained strength of the composite slab section, possible increase of the slab spans (meaning a marked decrease in the overall steel beam requirements and tonnage).

Here's the URL link for one manufacturer of the "Composite Steel Floor Deck":

http://www.corrugatedmetal.com/corrugated-floor-deck/

You can also visit the Steel Deck Institute website:

http:/www.sdi.org

You and I should really talk on the telephone about this and the necessary garage floor design. Posting through this Forum is a PIA, and highly inefficient! PM with your name and phone # and time you're available, if you want to talk directly about particulars. Central Time, correct? I am, for the most part, available many evenings and the weekend......just keep in mind the time difference as it's ET here.

ps: If you want to use those 6" steel beam sections for columns you really need to accurately measure them, so that I can determine exactly what they are......referenced back to the AISC Steel Manual; as to make sure they're adequate for use as columns. A lot of load is going to be placed on them, and if they're too slender they will buckle.....they're overall height is "getting up to their safe limits". I'd need to know the (1). overall depth, flange top to flange bottom, (2). the flange thicknesses, (3). the flange widths, and if possible (4). a good approximation of the web thickness. If you do the measurements with a caliper or micrometer that ensure better accuracy, which would ease my pain trying to figure out their AISC Designations and hence, capacities as columns.

I will be meeting with my concrete guy some time in the next few weeks so I will see what he says and if it does not appear to add up I will certainly give you a PM and a call!

Thanks for the advice so far. It has been greatly appreciated.

Not an problem tcmtech! I'm glad to have helped you out and given you some pointers.

Good luck with the Contractor!!!

i'm not sure if i understand the situation. are the floor beams stong enough to support wet concrete?

Arlette, all I get with your posted link is a French massage website.....

i would have calulations done concerning the floor beams strength once the concrete has set. re-inforcing the floor beams with false work was needed to be done. that leads me to believe you are not experience at this type of work and you did/nt hire an engineer. i think you,re in deep shit now, because is't's an unfixable problem. have the calculations done and hope for the best.

Actually, the calculations must be completed before the steel is even ordered, fabricated, and erected. It and the suspended reinforced concrete garage floor slab + the steel columns & footings must be design properly.......first, for construction loadings when the concrete is in it's plastic state (ie, wet) before it's initial set-up; the slab deck or plates, and the beams & columns must be able to be able to safely support this load. Secondly, the beams, columns and slab must be designed properly to safely carry the total superimposed design Live and Dead Loads.

It's all spelled out in the AISC Steel Manual, whether it's the Unified Steel Design, LFRD, or ASD design philosophy....

Professionally, I really think it's a very bad idea to just wing this based on what a "concrete contractor" or what the other guy(s) have done in the past and gotten away with it. That is pure recipe for a future disaster.....possibly resulting in a catastrophic structural collapse with personal injuries, maiming, or even death(s), not to speak of property damage. Think of it this way: you don't obtain the Professional Services of a SE/PE to design this sucker and your experience a failure etc, do you really think that your Homeowner's Insurance Company is really going to cover you, especially when they investigate and determine that no PE was involved in the design process or oversaw the construction? No way in hell they would! Over my career, I have sat on the Witness Chair in civil proceedings as an Expert Witness (at $250 per hour rate + incidentals by the way),and I have yet to see an insurance company lose that type of legal battle. where the homeowner and their contractor had skipped the proper design completed by a PE and the construction oversight. BTW, the Insurance companies hire some of the best legal minds in the country......they're providing policies to MAKE MONEY, not lose it to fools who think they know it all.

SOME FOOD FOR THOUGHT......HOPE YA DON'T CHOKE ON IT!