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Old Posted Feb 27, 2008, 10:46 PM
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Typical slab/floor thickness in buildings?

I'm crunching some numbers in my head with a few buildings trying to figure their heights (roughly). I'm wondering, what are the typical slab "floor" thicknesses for buildings? Are all thicknesses the same for office-residential-hotel-etc.? What about for something like parking garages that would be above ground, but under a skyscraper?
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Old Posted Feb 28, 2008, 6:19 PM
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^completely depends on the materials and engineering.

Generally speaking a concrete residential highrise is 7-8" slabs, office are 9-10" and hotels somewhere in between.

Anticipated loading requirements also play a part and change these numbers.

Parking slabs are thicker, up to 12" but have far more rebar.

however, it depends on column spacing and the such as well
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Old Posted Feb 29, 2008, 2:13 PM
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There are other types of slab construction as well - for example, post-tensioned systems where you could be a little as 6". Also, don't forget steel deck systems (used with steel frame construction), where again the steel deck and cast concrete could be as little as 3" and up.

In any system, regardless, it always reduces to the supporting arrangement: joists, beams, girders, columns, and walls (size, position, spacing, etc.). Material strengths play a lesser role but also have some effect. Ditto for loading.

In most floors, if you know the clear span between the major supports - divide that span by a factor between 20 and 30 to estimate a reasonable depth for the whole floor system including beams, joists, etc.

Also - don't forget to add your non-structural topping (a cementitious topping that that helps make a smooth level top surface), false-floors (raised floors for conduits, cables, etc.), etc.
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Old Posted Mar 1, 2008, 2:22 AM
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Thanks guys.

All of these would be concrete frame.
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Old Posted Mar 1, 2008, 5:18 AM
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Thanks guys.

All of these would be concrete frame.
building a concreat house or somthing?
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Old Posted Mar 1, 2008, 12:26 PM
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building a concreat house or somthing?
Ha, no, just wondering how tall a few skyscrapers will be that we haven't heard heights for yet in Austin.
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Old Posted Mar 1, 2008, 3:27 PM
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Ha, no, just wondering how tall a few skyscrapers will be that we haven't heard heights for yet in Austin.
ooo
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Old Posted Jan 13, 2009, 4:06 PM
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WTC floors was 4 inches thick

The WTC center had floors only 4 inches think, made of light weight concrete. I wonder if it would have been thicker and/or not made of light weight concrete, I wonder if it would have faried better on 9/11.

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^completely depends on the materials and engineering.

Generally speaking a concrete residential highrise is 7-8" slabs, office are 9-10" and hotels somewhere in between.

Anticipated loading requirements also play a part and change these numbers.

Parking slabs are thicker, up to 12" but have far more rebar.

however, it depends on column spacing and the such as well
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Old Posted Jan 15, 2009, 4:03 AM
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The WTC center had floors only 4 inches think, made of light weight concrete. I wonder if it would have been thicker and/or not made of light weight concrete, I wonder if it would have faried better on 9/11.
That was just a skim coat over the steel trusses and decking that comprised the floor. It's not like that slab was the entire structure of the floor.
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Old Posted Jan 16, 2009, 5:13 PM
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^bingo, it was merely a topping and not structural.
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Old Posted Jan 17, 2009, 12:24 AM
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I'm pretty sure the WTC used composite concrete-joist construction. It was structural and and a bit more than a "skim coat".
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Old Posted Apr 2, 2009, 1:33 AM
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I am doing a project and have been wondering this same thing for a while now. I am pretty young though and I just want to get a couple things straight. Looking at the picture below (taken by harryc) if the concrete slabs between floors are say, 9" thick, then does that make the area in between the slabs the entire living (or office, or whatever) space, or are other things added in between? (Where do the air vents and all that go?)

Sorry, this sounds confusing.

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Old Posted Apr 2, 2009, 4:43 PM
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^depends on the systems being used for mech.

Generally mechanical is in the ceiling, although raised flooring is becoming popular.

So say you have a commercial building with 12' clear between floors, take 2' of that for mech/elec. etc.

In residential buildings you will see bulkheads used more commonly as well as some with inslab venting.
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Old Posted Apr 2, 2009, 5:10 PM
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So, if I wanted to draw up a hotel with 9 foot ceilings, I should make the slabs in between floors 11 feet from each other to allow for the air vents, electrical wire, plumbing, etc?
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Old Posted Apr 2, 2009, 8:13 PM
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TFF to underside of slab would likely need to be 11-12' for a 9' open space.

but again, depends on what mech you spec, plumbing/risers, lighting, etc. etc.
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Old Posted Apr 2, 2009, 9:45 PM
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Thanks alot Coldrsx! You sound like you know what you're talking about. Are you an architect? I have some other questions I would like to ask you if that's ok? (I've been searching the internet but I can't find anyone with the info I'm looking for!)
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Old Posted Apr 2, 2009, 10:50 PM
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^i am still learning myself but i am working for an archi yes. Feel free to PM me or whatever.
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Old Posted May 4, 2009, 7:28 PM
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True. But I was reading that the old building around the WTC complex. Built in the 1920's and 30's. Held up very well from being hit by self and the fire itself. But those building. Had concertet poured around the steal beams, internal walls of block and brick,etc. But back than the skyscraper was a new technolgoy and overbuilding was the only way to make sure it work. I think it would have been a bit different that day at WTC if they would have done a bit more when being it than less.

According, to what I read. THe fireproofing level code used on the WTC was change in the city of new york right before this project begin. Made much thinner. The older building around the WTC comples that had the old code and was of newer construction faired very well. And the WTC was being upgraded as floors become open to a new level of fireproofing before 9/11.

always better to add a bit looking forward to the day when something bad happens.

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That was just a skim coat over the steel trusses and decking that comprised the floor. It's not like that slab was the entire structure of the floor.
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Old Posted May 4, 2009, 7:31 PM
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I read the WTC construction manual. It was 4 inch of light weigth concrete no skim was talked about. Each floor was 4 inches thick period of light weight cement. THe trussel was close togther to make up for this lightweight desgin and to have large open spaces in the building. That was the first time that desgin was used in a very tall bulding.


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That was just a skim coat over the steel trusses and decking that comprised the floor. It's not like that slab was the entire structure of the floor.
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Old Posted May 8, 2009, 11:16 PM
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Quote:
Originally Posted by KevinFromTexas View Post
I'm crunching some numbers in my head with a few buildings trying to figure their heights (roughly). I'm wondering, what are the typical slab "floor" thicknesses for buildings?
I'm not an engineer, though I can say with some confidence that slab thickness has little to do with the overall height of the building.

I've worked on a few high rises, and slab thickness pretty much stays the same beyond the transfer slab. What does typically change with height is the reinforcement within the columns. The size of your bars tend to get smaller as you go up, and sometimes you'll have fewer bars within the column.

It is the columns after all that support the building, not the slabs themselves.
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