STC comparison wall on concrete vs wall on floating

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Postby Paul Woodlock » Sat Feb 21, 2004 7:30 pm

Greetings

Hi Paul:

Interesting.

If the new i-beams were supported using the same way as the existing i-beam,
then effectively they'd be coupled to each other to some degree.
The existing i-beam is supported at both ends at the concrete foudnation
walls and in the middle by a round 4" support steel pole that goes into the
slab (presumably to a footing).
To keep the new i-beams decoupled from the old i-beam they would have to be
supported at both ends on the floating floor. That sounds doable.


Yes that was the idea. The 2 I-beams woudl be supported on the floated walls.

The problem is still having room for the X bracing in the existing joists.
Those X braces only have 2 3/4" (7cm) below them. To put up a 2x6 using your
I-beam idea would mean I'd have to sacrifice another 3 1/4" of room height.
The joist span is shorter, so perhaps 2x4s would do. 2x4's with a 10' 9"
span on 16" centers can support a dead load of 5 lbs / ft^2. Gypsum is 2.2
lbs / ft^2. That doesn't leave me much room to hang anything else on the
ceiling (skylines, absorbtion, polys). Although I'm not worried about the
soffits around the i-beams since that extra weight is at the i-beam where
the 2x4 joist would be strongest. The fake soffit is in the middle of that
spance and would add another 20% to the weight (1' down on both sides vs 10'
of run is 2/10 or 20%), so that's (2.2 + 2.2) * 1.20 = 5.28. That's already
over the dead load limit, so I guess 2x4's are out. It'll have to be 2x6's.
Or double the 2x4's (the X cross braces would push the 2x4's a little
lower).

Concrete slab to joist is 230cm. Less 30mm for ceiling gypsum is 227cm. Less
8cm for the floor on pads is 219cm. Less 9cm for the 2x6's on your i-beams
is 210cm. That's 6'10". With a 11" lower than that for the soffits around
the i-beams, that's 5'11". I'm 6' tall, and when I walk my head bounces to
6'3". Hmmm. (Note, your design really only costs me about an inch in ceiling
height at the soffit over my design, and 3" for the rest of the ceiling
height)

Anyway, it's an interesting idea. I'll consider variations on the theme.

I suspect Kinetics springs are expensive. I wonder how much i-beams are.

Regards
Bob


The other thing to consider....

As you're in a basement, do you *really* need a floating floor? Consider that the foundation walls and floor are quite stiff. presumably all srrounded by earth.

not floating the floor, but floating the walls and ceiling structure would still prevent most airborne sound from being structurally transmitted. I would think the ceiling is the weak point in the system. ( it must be ... flexible 1" floorboard v. stiff concrete and earth.) This would give you 8cm of room hegiht back and you could then put in thicker joists and more layers of gypsum. You could also possibly insert some strips of gypsum on the underside of the upper floorboards ( removing and re-inserting the X-bracing as you go )


I-beams ain't cheap I would imagine, but neither would the kinetics hangers.


PAul
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Postby Bob » Sat Feb 21, 2004 8:22 pm

Hi Paul:

Your drawing is now on page 2 of my http://groups.msn.com/BobGoldsHomeTheatre/shoebox.msnw

As you're in a basement, do you *really* need a floating floor? Consider that the foundation walls and floor are quite stiff. presumably all srrounded by earth.
Not having a floating floor would be much cheaper. The floor is not level, so it still needs to be leveled (6.5cm slope over 14'). There are three 8" thick concrete walls and a concrete slab floor. The two narrow 8" thick concrete walls and the concrete slab floor have earth on the other side. The remaining long 8" thick concrete wall has a neighbour's basement in it, and of course that shared foundation wall holds up the walls between our houses (e.g. living room, and next level up the bedrooms).

I have a 50db furnace, although I'm considering what an in-line fan might do for my airflow, mounted 15 feet away from the room, and leave the furnace off.

The other way, if I listen to DVD movies at 85db in the room, with the subwoofer going, I would like the neighbour and the sleepers in my home to hear very little of it.

So, as for "do I need a floating floor". I don't know. I think so, based on Eric's concrete slabs are 47db + 8db horizontally. 85db - 47db -8db is 30db. Presumably it's worse for subwoofers (17hz to 80hz).

You could also possibly insert some strips of gypsum on the underside of the upper floorboards ( removing and re-inserting the X-bracing as you go )
That's already in the BobCeiling1.jpg that you were looking at yesterday. Doing that was why I had to add extra joists (green). My existing joists are only good for another 2 layers of gypsum of dead load, and I used that up where you just said.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
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Postby Bob » Tue Feb 24, 2004 2:11 am

Hi Paul:

I stopped looking up i-beam things when I realized that I couldn't get it into the basement (i.e. through a wall, or down the stairs).

But this morning I realized I have a tiny basement window, and I should be able to feed a beam through that into the basement.

Since i'm thinking of floating my floor on kinetics pucks, and a beam puts half the weight of the ceiling on less than 2' of floor under the walls floating on the floor, do you think that'll be an impossible problem for the pucks? I presume I'll either have to build that part of the wall out of more vertical i-beam welded to the horizontal i-beam, or with vertical solid wood (4"x18"). It would have to support
a) the two i-beam (20')
b) a bunch of 2x4's (14' on 8" centers - actually two 2x4's on 16" centers)
c) half of 14'x20'x1" of gypsum. (the other half being supported by the outside walls)
d) two 20'x2'x1' soffits
e) assorted ceiling treatments.
f) the wall (2x4's three layers of gypsum)

It seems like a lot of weight for a square foot of pucks.
It's up in the range where I'd wonder if the concrete slab floor can take that much concentrated weight.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
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Postby Paul Woodlock » Tue Feb 24, 2004 3:33 am

Bob wrote:Hi Paul:

I stopped looking up i-beam things when I realized that I couldn't get it into the basement (i.e. through a wall, or down the stairs).

But this morning I realized I have a tiny basement window, and I should be able to feed a beam through that into the basement.

Since i'm thinking of floating my floor on kinetics pucks, and a beam puts half the weight of the ceiling on less than 2' of floor under the walls floating on the floor, do you think that'll be an impossible problem for the pucks? I presume I'll either have to build that part of the wall out of more vertical i-beam welded to the horizontal i-beam, or with vertical solid wood (4"x18"). It would have to support
a) the two i-beam (20')
b) a bunch of 2x4's (14' on 8" centers - actually two 2x4's on 16" centers)
c) half of 14'x20'x1" of gypsum. (the other half being supported by the outside walls)
d) two 20'x2'x1' soffits
e) assorted ceiling treatments.
f) the wall (2x4's three layers of gypsum)

It seems like a lot of weight for a square foot of pucks.
It's up in the range where I'd wonder if the concrete slab floor can take that much concentrated weight.


You'd be a suprised. I bet an elastomer block a foot square ( 300 x300mm ) could hold up a lot of weight.

It depends on the stiffness of the elastomer, but as an example my walls, stud, and 5 drywall layers, plus half the weigth of the ceiling, is being help up by 2 x 4 blocks spaced about 15 " apart.

IN yuor case the central point of the otherwise non supporting walls would have to hold up a 1/4 of the total ceiling weight. I'm sure 4 x 4 structural grade timber posts would hold that up, with crossbracing. Or make it 4 x 6 if the studs are 6 deep. but you'd have to check.

Presumably you've calculated the ceiling weight thus far?

The pucks would obviously populate more densly around theis area. Again requiring calculation. But you can easily get pucks to hold up this kinda weight.

You could always do a vertical X-brace between studs to spread the load over a wider area.


Paul
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Postby Scott R. Foster » Tue Feb 24, 2004 12:29 pm

Bob wrote:It seems like a lot of weight for a square foot of pucks.
It's up in the range where I'd wonder if the concrete slab floor can take that much concentrated weight.


Talk to an engineer that does calcs for residential projects [signs off on roof truss, foundation designs and such]. If I was you I'd get him to review the whole design for structural integrity.

As to the floor load, if you need to increase the strength of the plinth you could cut holes in the floor at the location for each column base larger than the column cross-section - dig a cavity in each hole - build a reinforcing steel basket on chairs in each cavity - and fill em with high strength concrete [hardware store concrete mix is usually pretty strong stuff – just read the label]. This will give you enormously strong piers at the bottom of each column. The engineer should be able to give you a good minimum spec for dimensions and materials [though he will probably want to know about soils].

Alternatively, perhaps you could spread the load with a steel plate at the bottom of each column?
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Postby Bob » Tue Feb 24, 2004 5:26 pm

you could cut holes in the floor at the location for each column base larger than the column cross-section - dig a cavity in each hole - build a reinforcing steel basket on chairs in each cavity - and fill em with high strength concrete

Yep. That'd do it.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
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