how thick is a poured ceiling/floor?
I work in the basement of a four-storey medical centre (5 floors total). Before installing an x-ray machine we have to let the Ministry of Health know the thickness of the concrete around us, so I am trying to determine the thickness on the concrete floor (well, ceiling) above me. I had the original blueprints, and there is a scale (1:20 in the detail cross section). Scaling it up, I figured the floor was 6 – 8 ” thick. Is this a normal thickness for a ceiling/floor. When I scaled up the below grade walls, and the floor beneath me, the numbers made sense. But I’m just not sure if that is a normal thickness?? The flooring for the main floor is quarry tile. Building is 20yrs old. No earthquake considerations in our part of the country. (well, we have had two earthquakes [~4-5] since I’ve worked there, but e.q’s aren’t part of the code). You guys are always so helpful, I’m sure someone will be able to help me on this one. Thanks in advance
Replies
I don't know what kind of info you will get as this is a fairly unusual question but you can increase your chances by including details such as span, what's on the floor above you, are there support columns, etc. Good luck.
Here's a real low tech approach. Remove a ceiling tile or two in the basement and measure from the floor to the bottom of the deck above. Then measure from the basement floor up the stairwell with a measuring tape and a straightedge to find the distance to the top of the floor above. Should get you to within a quarter of an inch.
The best way to determine the actual thickness of the floor is to find a mechanical penetration and physicaly measure the thickness. If you are in the basement look in the closest mechanical room near you. Most concrete post pillar and grade beam construction will have been poured with the HVAC and plumbing penetrations formed in the pour. If you have a drop ceiling in your area, just pop out a ceiling tile and look up. With a little luck you will find a waste drain or water line hiding up there. Follow it untill it goes up. There will be a pipe sleeve through the floor and the line will pass through it. Locate the pipe on the upper floor and place a piece of duct tape over the edge of the opening. Now go back down stairs and use a stick rule or yard stick to push up untill it hit the duct tape. There is you thickness.
An alternative to this is to find the structural pages of the prints. It should give you a floor section with the designed thickness clearly detailed on the print. Trying to scale a print is not a good way to determine the floor thickness. A 1/16 inch difference from one set of prints to another would throw you off 3" on a 1/4 inch to 1' scale. Someone in your facility maintenace or srevic group should have a full set of prints that they will let you look at.
If all else fails find a closet upstairs some where and hammer drill a hole through the floor. A quarter inch hole is all you need. Then use the same duct tape method above and a 1/8 inch rod to guage the thickness.
I don't know about poking holes in the floor. Thought about measuring the floor to ceiling height, hmm, just wondering if I can do that one. With a ladder and a flashlight, might be able to. Guess what I was really wondering is if 6" seemed really too thick. Since the x-ray beam is never pointed that direction, it doesn't have to be much more than a piece of cardboard to stop any possibility of any ion ever affecting someone walking overhead, but I don't want to give a number that will get the government people scratching their heads and coming out to investigate.
>Guess what I was really wondering is if 6" seemed really too thick.
My house has an 8" elevated slab, so 6" isn't necessarily too much. Don't assume anything about your floor--make sure you see the entire thickness somewhere.
Cloud,
You got xray machines in your basement?
or are you parkin a D9 in you livingroom?
;)
TLayers
Onions
Have
Layers,
Carpenters
Have
Layers
If it was someone else I would have made a joke about him or wife needing a diet. But one look at us makes that silly. Nothing more than a big clear span w/ a desire for a thin floor. Thinner concrete woulda meant support beams/columns.
DaveRicheson isn't talking about making new holes in the concrete, he is telling you to find existing ones in a mechanical room and measure them. This is how we always do it. The mechanical rooms always have lots of deck penetrations that were either core drilled or sleeved when the floor was poured. Piece of cake.
carpenter in transition
Is this is really a job requirement?
Don't they have people that know how to do this stuff for real working there?
Facilities Dept maybe? Hate to be admitted to your place....maintenence crew do the x-rays after hours too?? Jeff "That's like hypnotizing chickens........."
a whole lotta NASA engineering going on here just to measure a hole that already exists. like my mom always told me, " look with your eyes, not your mouth !"
carpenter in transition
Montegon,
You are very fortunate that I have given a lot of thought to your dire dilemma and I think I have a possible solution to your problem. Taking perhaps Dave Richeson's suggestion of drilling a whole thru the concrete a step further, I suggest the following modification:
What you need is a stop watch and a rotary hammer with a long 1/4" bit. Put a piece of black electrician's phase tape one inch from the tip of the drill bit. Start drilling and time how long it takes to drill one inch deep.
Then continue drilling and timing until you break thru. The amount of time to drill completely thru divided by the amount of time to drill thru one inch shouch equal the thickness of your floor.
Of course, there are some caveats: you must maintain a constant pressure. There may be some decrease in drilling performance as the hole gets deeper due to wear. Non-uniformity of the concrete - hitting rebar for example - may also throw off these meticulate calculations.
Peter
I'v been working on buildings such as you are in for 20 years. 6 to 8 inches sounds right. I'v seen them thiner, I'v seen them thicker. It depends on the design of the building.
This dimension needs to be reported accurately for obvious reasons.
Get one of the maintenance workers that is capeable or call the elevator company and have them send out a tech. Get in the elevator with them, have them stop mid floor, open the door and measure the floor.
If you can wait a while they will be there on a call anyway and you can hook up with them then.
I worked on a building for a university once that was going to have an accelerator or something like that. We had to form concrete walls and ceiling that were FIVE FEET THICK. The door was 18 INCHES THICK, SOLID STEEL. Thank goodnes a specialty contractor took care of that one. Just thought you might find it interesting.
Jeff
The floor may also have steel decking on the underside, which could be a benefit or a liability when dealing with x-rays. It may also be hidden by fireproofing.
If you have the original drawings you have the thickness of the slab on it. Check out the written specifications on the first sheets or the information in the column on the right hand side in the title section. Sometimes the slab thickness is standard to all floors and is just noted in one of these columns as typical.
But never the less, the information is somewhere on the original drawings. You never scale drawings for unknowns because you never assume.
Gabe
In a medical center?
Can you do a quick sonogram of the floor, that will even tell you the aggregate size.
Just a thought, Docs likely won't let you near their sonogram equipment, also, don't know enough about the medical types to know if it would work like industrial casting inspection sonograms.
Gabe,
Just by looking at the drawings, specs, as-builts or whatever and accepting the information as correct is making an assumption. A good structural engineer will always field measure for verification.
carpenter in transition
Yes your right Tim, but when he's standing in 2 feet of snow in a blinding blizzard he doesn't have to call the weather bureau for a second opinion.
I was commenting on the fact that the information didn't seem to be on the drawings.
Gabe
It's this way, guys. This really is an academic question. The room is going to be used for mammograms. The x-ray emitter is permanently attached to the x-ray receiver, and permanently coned to 10 x 12" absolute maximum or usually 8 x 10". The only way the damn thing will ever be pointed at the ceiling is if someone is standing on her head (well, ok, there's the rare exception where the tube is totally rotatated) You could stand 3 feet from the damn thing and get less radiation than you will during a 3 hour airplane flight. Yes, you get more radiation in a plane (in the air) than from a chest x-ray. But you don't see anyone wearing lead aprons onto airplanes, do you. The scatter radiation from the mammo machine, going through the ceiling, would be minute, non-existent, nil. I am not an apologist for radiation industry, I am very aware of the hazards of radiation, and we are not putting a 5 megtron accelerator in the room. Then, I would be concerned.
That's why I don't want to call in structural engineers and drill holes through the floor and all the other wonderful suggestions. I wondered if 6-8" poured concrete was reasonable for this slab. That was what I was getting from scaling the drawings.
The Ministry of Health can be rather bull-headed. I know of a clinic where they made the owners lead line the outside walls, (of a block+brick building) because there was a bicycle stand outside that was "occupied" for a few minutes at a time. Again, the radiation getting through that wall would not have lit up a watch face, let alone someone's gonads, even if theyput their bike on blocks and pedalled the whole day there. I don't want to get them all excited that they've never seen an 8" ceiling if the industry norm is 4" . I was wondering if I read it right, Thanks to the guys (Gabe esp) who read what I was really trying to figure out.
Well, ok then. I have worked in two buildings in the last 6 months that are similar to your description. Both had metal deck with poured concrete on top. One had a 4" thick slab, the other 3". Both are considered typical for the area. Hope this helps.
carpenter in transition
Thanks Tim
I've designed concrete floors on steel decks as thin as 1 1/2". Those were for residential applications and were not expected to see high design loads. Regardless of how you do it, I would make or find a penetration in the floor to determine thickness. The last Xray & cancer treatment facility I was involved with required two foot thick concrete walls and/or 30" of special sand in bags stacked to deflect or absorb emitted radiation; that and lead lined gypsum sheathing. It's not something to play with or second guess. I certainly wouldn't want to be the one working or staying upstairs not knowing I'm getting zapped every time the xray machine is flipped on.