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 Post subject: Construction Question
PostPosted: Sun Feb 26, 2012 1:40 pm 
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Always Moore!
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I am currently looking at buying a house that has a garage/family room added as an addition. The family room floor/garage ceiling is concrete. The garage is about 18' deep and 24' wide. Currently there is one beam (I didn't get the dimensions) running across the 24' span and it is approximately 12' back from the wall with the garage doors.

About 6' back from the wall with the garage doors was a second beam but it had been cut out to install the garage door tracks. I do not know if this was a screw up during construction or something a previous owner did.

Should I be concerned or does one steel beam seem sufficient? I know cars and airplanes - don't know jack diddly about civil engineering rules.

I'm going to pull a copy of the permit from the local municipality tomorrow and hopefully it will shed some more light but any additional input is appreciated.

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PostPosted: Sun Feb 26, 2012 2:43 pm 
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I'm certainly no engineer but if it had a beam originally, then I think it was there for a purpose. I don't like the idea of removing a load bearing beam. I would get someone to look at it. Even just a good carpenter could probably give you sound advise.


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PostPosted: Sun Feb 26, 2012 5:19 pm 
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You cold likely tell a lot by looking for sag etc. People do f'up things sometimes to install stuff. I remember seeing at someones house that a previous owner had notched a floor joist in the basement to install a boxer's punching bag. A plumber had already cut through the joists on either side though. It had an obvious sag in the floor above. I installed a brace for them with jack posts.

It's probably hard to tell if it was done properly because the wallboard covers things. IS the ceiling really concrete or is it just cement board required for code over a garage?

Try jumping up and down on the floor above. Avoid having rave parties...

Good luck!

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PostPosted: Sun Feb 26, 2012 6:14 pm 
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Difficult for us novices to tell from out here in cyber space, especially without any detailed photos. I hope you have better luck than I had when asking about building plans. I got the dumb look and was told they don't keep them after the build is approved.

IF your floor/ceiling is truely concrete, can you tell if it is prestressed or poured in place? Is the missing beam missing in it's entirety or just notched out where the door opener goes? I'd be leary of this without an engineer's evaluation. Too much can go wrong with your $$ investment. Likely that the home insurance co wouldn't pay out in the case of a failure. Sometime ask me about my foundation that sunk 9 inches in one corner. $26,000 later..... and that is 15 years old prices..... Be very wary!!!!

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PostPosted: Sun Feb 26, 2012 6:51 pm 
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Always Moore!
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Nope its completely gone.

Attachment:
oops.JPG
oops.JPG [ 9.92 KiB | Viewed 952 times ]


I have to assume at this point that the removed beam was required without having more information. I should have taken more pictures and grabbed a few measurements while I was there.

I don't know the exact details of the floor but I'm assuming its poured concrete based on the corrugated metal.

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PostPosted: Sun Feb 26, 2012 7:01 pm 
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I was curious and ran some rough numbers using Mechanical Engineering statics methods (the laws of physics don't know if its a building or a race car right?)

Since the garage is 24’ wide (and 18’ deep), I broke the floor into 24 “beams” that were 1’ wide by 18’ long and assumed the standard floor loading of 40 pounds/square foot and 6" of concrete. Each of these 1’x18’ “beams” weighs 2,200 lbs (weigh of floor and stuff on the floor). I used an FEA program instead of hand calcs since I’m lazy and found the reaction at the forward wall, back wall, and existing beam (and severed beam for case 2). From there I assumed that each of the actual I-beam/I-beams had 24 “loads” where each 1’x18’ "beam" was. Since it was evenly distributed about the entire beam I multiplied by the number of loads and placed that load in the middle.

Attachment:
floor.JPG
floor.JPG [ 220.45 KiB | Viewed 949 times ]


Without knowing the exact beam size I can't be 100% certain. Picking some random W8 and W10 beams based on what I remember and trying to scale stuff in the pictures, I'm really thinking both beams are required (or I butchered it really bad - Civil Engineers feel free to laugh). Hopefully they poured a thinner concrete pad that what I assumed or the numbers don't look good.

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PostPosted: Sun Feb 26, 2012 8:06 pm 
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Andrew,

The beams may have been the cheapest approach (materials plus labour) to holding up the corrugated form-work during the pour - if so then the beam is probably redundant. If not .....

If the place were already yours you could sight along one end of the cut beam towards the other end, to see if there had been any sag. If none, probably no problem. If sag, then maybe bigger problem.

Immediate problem is inability to get access with a civil in tow ... but you already know that.

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PostPosted: Sun Feb 26, 2012 8:13 pm 
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Looks like a know-nothing homeowner did that work.

If the beam was no longer needed, it should have been removed. What keeps the segments from falling on your head. They are not usually hard-connected into the beam pockets.

It would probably fail a pre-sale property inspection done by the municipality (if required) or a private inspection you would request.

To prove it's not required you would need to know the slab design; conc compressive strength, amount of steel reinforcing, etc. A problem best avoided unless you get a serious price reduction. Then replace/restore it yourself.


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PostPosted: Sun Feb 26, 2012 10:07 pm 
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I won't pretend that I can confirm any of your calcs. However, if it were intended to be a temporary support only functional until the concrete was cured, then I would think it would have been cut into the walls but have a temporary support that would have been totally removed. Besides an I beam that large is expensive and would have been used over and over again.

I think You'll find it was cut by the proverbial DPO.

BTW, I had to really look at that photo for a while before I realized you merged 2 photos into one.

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PostPosted: Sun Feb 26, 2012 10:28 pm 
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I don't know if this will be any help to you or not. I hope it is. I have spent most of my adult life working as a full time Realtor and it is my experience that situations like yours require a structural engineer,NOT a home inspector. This is the sort of defect that should send you running away but what happens more often than not, is you have fallen in love with some other aspect of the property. It could be location, price, features of the house itself and you are trying , against your better judgement to justify the purchase. Structural engineers are expensive but not anywhere near as pricey as repairing the building when it all goes wrong. Make your offer conditional upon the seller providing a structural report from an engineer of YOUR choice and should a defect be found to exist make it the responsibility of the seller to have repairs made to the satisfaction of the engineer. If the seller refuses to go along with that you then have two options,1) run away 2) pay for it yourself. Most people get emotionally attached to a property at a time when they should be anything but that. Then when the floor falls in later on it is always someone else that should have spotted the problem. Successful commercial real estate investors never get attached enough to overlook potential problems. Good luck


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PostPosted: Mon Feb 27, 2012 2:55 am 
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I really wasn't picturing something like that. It seems unusual construction in a house. Common enough for commercial buildings.

Does that steel ceiling just hold the slab duringhte pour or is it also the tension part of the slab? Usually you have rebar which takes the tension and it is lower down in the slab and the upper part of the slab is in compression. Concrete is good in compression.

When they pour the slab the rebar is held up with little metal wire feet to the correct height. Recently a parking garage was built and two of the floors had the wrong height of wire feet for the bars. it collapsed and some construction workers died.

It seems to me when I look up in commercial buildings with that type of steel support under the slab, you see those metal rod stringers spaced closer then 12 feet apart. Check a Home Depot ceiling next time you're in one.

All of this is no help at all, sorry... Warren had a good idea to check for sag..

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PostPosted: Mon Feb 27, 2012 2:14 pm 
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You may not even see much sag, concrete does flex, but it fails quickly in bending unless properly reinforced.
You wouldn't want your '70s Disco party to fall into the garage suddenly.
I agree you need a structural evaluation, but I'd either walk away or expect to fix it.
If the beams weren't needed except to support the formwork, they would have used a lot less expensive supports, or tken them with them at the end of the job.

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PostPosted: Mon Feb 27, 2012 5:20 pm 
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Official disclaimer, I am NOT an architect or civil engineer..... but I've worked on tilt up and PIP concrete buildings enough times to remember what I've seen in the past.
In my experience a concrete ceiling OVER an occupied space (at least in the last dozen years) is "lightweight" concrete using some form of filler, styrocrete or similiar, typically a 2-4 inch thick slab out here on the left coast.
I've never worked on parking structures, just commercial buildings and apartment complexes with large open areas. Stick welding pockets overhead, 30 feet in the air such a joy :roll:
Having said that. . DUDE THAT SCARES THE BEJESUS OUT OF ME!!!!!
Most definitely get a real engineer to look at it and run the numbers, think of it as inexpensive insurance, no engineer worth their salt will sign off on something if they aren't completely comfortable because it could come back years later and bite them in the buttocks should it fail "in normal and customary use".
Remember the shopping center balcony failure maybe 15 years ago? The decision was made to go off-prints and make unapproved modifications.... a bunch of people died because someone was cheap or lazy or both.
The only reason that I can think of for someone to use iron (expensive method even years ago) rather than a gluelam on a residential structure is that it was required for load bearing. ......

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PostPosted: Mon Feb 27, 2012 8:24 pm 
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WOW! That is scary looking. I have stressed a number of structures and it simple, almost isn't worth using a computer. Keep in mind the material can be as heavy as the per sq ft loading and if you are talking about a garage floor I would use 100 lb/sq.ft. Structures are usually designed using deflection not stress. I use 1/360 or if I want it hell for stout 1/480, Some more drawings or pics would be helpful. It is possible what looks like grossly over designed beams are what they had. Construction techniques can vary so much it is hard to guess.


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