Support for Granite 12' Span - AVS Forum
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post #1 of 37 Old 01-03-2012, 06:40 PM - Thread Starter
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I'm building a bar behind my riser and dont want to have knee knockers.
After tossing around a few ideas and searching my life away I found a thread that shows what I'd like to do:
http://www.avsforum.com/avs-vb/showp...4&postcount=69

Upon closer inspection its seems that .25" thick steel is way overkill.

How can I figure out how thick of beam I really need?

I'm thinking 2 beams, across approx 10' 6" span, with 12' granite 1" thick and about 16" deep.
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post #2 of 37 Old 01-05-2012, 06:38 AM - Thread Starter
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Cmon forum dont let me down.
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post #3 of 37 Old 01-05-2012, 06:54 AM
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Talk to the place where you plan on buying your granite.
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post #4 of 37 Old 01-05-2012, 07:22 AM
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You can find span calculators on the internet that cover structural steel, as in steel beams and columns used in construction. Google "span calculator for steel" and you'll find some examples. However, I haven't ever seen a span calculator for the steel dimensions you're talking about, which are obviously much smaller than what would be used to support a floor in a building (or whatever).

Your design requirement that a 1" granite slab span 12' with no center support seems pretty ambitious, especially since the granite won't flex much before it breaks. I don't think you want a solution that just barely works. I would view this as a situation where overkill is a good thing.

The steel will be relatively expensive, relatively hard to find, and difficult to transport. All of which is fairly typical when an ambitious design requires robust engineering. If it was cheap and easy, everybody would do it.

It will be cool, though!

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post #5 of 37 Old 01-05-2012, 07:44 AM
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I hope your plan includes a path to get a 12' long heavy, inflexible piece of granite into the room from outside!

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post #6 of 37 Old 01-05-2012, 09:38 AM
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No kidding... I could not get that into any theater room I have been involved with. It would have to go in before putting up the walls.
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post #7 of 37 Old 01-05-2012, 09:48 AM
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Quote:
Originally Posted by calimark View Post

Cmon forum dont let me down.

Calimark,

Here you go; also check out my page 8 (from post #238)
http://www.avsforum.com/avs-vb/showt...=896895&page=2

I borrowed the same idea from "Hawkeye Josh". I used a 2" x 1/4" steel tube - I would not go with anything lighter, especially knowing you will be using a using a granite slab. I bought both the 12' long 1/4" square tube, and accompanying angle iron for around $130 (from a specialty metal/ iron seller). Drove it home in a suburban with the tailgate open (and of course a thunderstorm hit in the process .. )

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post #8 of 37 Old 01-05-2012, 04:42 PM - Thread Starter
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Thanks cuzed. I took a look. Interesting you have a middle support in there.

I have plenty of room to get the slab in there if it's a single 12' piece.
(I settled on Actual length of 10' 6")
I definitely wont go with bare minimum required but 0.25" is plenty thick. I also could not find any span calculators for this size steel hence why I was hoping for extra insight. Even hawkeye said his was designed to hold 2 peopl + the granite.

I have a quote for $127 for two bars so I guess I'll just stick with that since its easier. 2x2 1/4" thick
Big, I'm gonna ask the stone yard, but I can put good $ I'm gonna get a blank stare about it.
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post #9 of 37 Old 01-05-2012, 04:46 PM - Thread Starter
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Quote:
Originally Posted by dwightp View Post

The steel will be relatively expensive, relatively hard to find, and difficult to transport.

definitely not hard to find at least not here in Tampa Bay.
Transport not a problem in my case I have transported 16' crown easily in a f150 work van. 12' would fit easy.
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post #10 of 37 Old 01-05-2012, 06:33 PM
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50mm x 50mm x 6mm thick square hollow section. Steel. 4.0m span simply supported. Deflection = PL^3/48EI for point load at the centre of the span.

P = 50kg = 0.5kN = 500N = 110 pounds
L = 4000mm
E = 2 x 10^5 MPa
I = 3.77 x 10^5 mm^4

--> Deflection = 9mm = 11/32"

I have no idea if this would be a problem for the granite.
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post #11 of 37 Old 01-05-2012, 06:44 PM
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The above is for a 220 pound person spread over two bars.


Deflection due to weight of granite = 5wL^4/384EI

w = 1" x 16" granite = say 25kg/m = 0.25kN/m

--> Deflection = 6mm = 1/4" = span / 670

Again ... no idea if this is actually OK.
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post #12 of 37 Old 01-05-2012, 06:53 PM
 
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When granite is transported, it is done on a vertical plane. Best thing to do is to go to a yard that also would have remnants and talk to them. Worst case is that they may have to grove out the underside to install steel pieces, otherwise they may suggest two six foot pieces vs one twelve foot.

As long as you have some type of cabinet holding it, or if there is a one foot or greater overhang, there should also be supports on the face side as you sit. I would suggest visiting some bars in your area, preferable higher scale hotels, and let the Food & Bev or sales manager that you are just wanting to look how theirs was installed, due to you are making your own bar and want to see the makeup. They should have no problems if you call ahead and come in during the day, or on a weekend when nothing is really going on.

I have seen people use custom made steel braces vs. wood, it is just up to you what your style is.
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post #13 of 37 Old 01-05-2012, 08:37 PM - Thread Starter
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Peter thanks. That is the type of info I'm after. That I can definitely ask the stone yard about(deflection).

I found this calc:
http://metalgeek.com/static/deflection.php
Do you know what fixed vs free ends mean?
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post #14 of 37 Old 01-05-2012, 08:41 PM - Thread Starter
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Gregzol,
Im ok if it has to be 2 6' lengths .
My only req is no vertical support aka knee knocker in the middle.

Gonna go with whichever the yard is most comfy with
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post #15 of 37 Old 01-06-2012, 12:05 AM
 
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You should be able to get away with the vertical brace, as long as the yard doing the install can guarantee that you did your job in building the structure to support it. Now of course, they would be the experts and would also have books full of bars, etc, and show you how they have braced their's in their showroom. Make sure that you take pictures and plans/drawings when you visit the granite guy/gal.

Check with local Realtors also that deal with nicer homes, and see if the home owner will allow you to go in and see how their counters were installed, or better yet hit up the home shows, which usually come up in February, which ours does here, and you may be able to find one or two there hawking their wares.

Also, I would not use tube stock, I would use a extruded bar stock instead. That is if the granite place states that is the best solution to get away from the middle brace.
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post #16 of 37 Old 01-06-2012, 12:27 AM
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IIRC maximum deflection needs to be less than L/720, or 2/10" in this case. And that includes any dynamic loads (like someone sitting on it) in addition to the static load from the weight of the stone itself.

IIWY I would count on two pieces. Most stone comes in 10' slabs give or take a foot or so, by 5' or 6' or so.

You may have trouble finding 1". I think you will be looking at 20mm (3/4") or 30mm (1 3/16"). Weight varies but will be around 15# per square foot for the former, 22# for the latter.
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post #17 of 37 Old 01-06-2012, 07:25 AM - Thread Starter
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Good thanks guys. Good to have more info.

I quoted 1" so I can be in the middle of the 20/30mm.
I'm open to every aspect, except the knee knocker, so am willing to flex on the other criteria. We'll see what they say.
Once I hear them say ok "we'll gaurantee the install" I'm good to go.
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post #18 of 37 Old 01-06-2012, 08:24 AM
 
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Post pictures of the install, I would like to see how it goes, due to we are looking at a extension of our counter for our Kitchen from the last base cabinet, which will be about 40", and I am up in the air as to what we are going to use for the counter, but I want granite in there, since we went that route with our Vanity top in our bath.
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post #19 of 37 Old 01-06-2012, 03:11 PM
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Quote:
Originally Posted by calimark View Post

Once I hear them say ok "we'll gaurantee the install" I'm good to go.

I don't think you have a snow ball's chance in hell of getting that. But you never know...
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post #20 of 37 Old 01-07-2012, 04:11 AM
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Quote:
Originally Posted by calimark View Post

Peter thanks. That is the type of info I'm after. That I can definitely ask the stone yard about(deflection).

I found this calc:
http://metalgeek.com/static/deflection.php
Do you know what fixed vs free ends mean?

For a beam supported at both ends, fixed end means that it cannot rotate at the ends. In practice this is vey difficult to properly achieve. Free end (or simply supported, or pinned) means a support that resists vertical load but not rotation. You should use this one.

Your final span is very important for these calcs as for a point load deflection is proportional to span^3 and for a uniform load deflection is proportional to span ^4. I think you mentioned 10'6" above, which for the uniform weight of the stone would reduce deflection by 40% from my 12' calcs above.

Cheers,
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post #21 of 37 Old 01-07-2012, 05:06 AM
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I'm trying to solve the same problem over on my thread. Unsuccessfully. Click my link and you'll see photos on my poor effort. I like the direction you're heading and will likely follow suit.

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post #22 of 37 Old 01-07-2012, 07:13 AM - Thread Starter
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Quote:
Originally Posted by Peter M View Post

For a beam supported at both ends, fixed end means that it cannot rotate at the ends. In practice this is vey difficult to properly achieve. Free end (or simply supported, or pinned) means a support that resists vertical load but not rotation. You should use this one.

Your final span is very important for these calcs as for a point load deflection is proportional to span^3 and for a uniform load deflection is proportional to span ^4. I think you mentioned 10'6" above, which for the uniform weight of the stone would reduce deflection by 40% from my 12' calcs above.

Cheers,

Yes I'm set on 10' 6" now and I have changed the title to reflect this.
I was tossing around the idea of using a 'S' iron bracket, welding the 2 bars to it and attaching that to the frame. Does this qualify as fixed end?
If that is a not a good idea I can also attach the bars directly to the framing and double up the top support of the frame.
Still didnt make it to the yard yesterday as planned and its not happening this weekend either. Oh well.

For reference I attached a photo to show what I was thnking for the welds.
Also atatched is a photo of the bar mine is modeled after, except I am using full wood framing.

Also for the front most support(as viewed in photo), I could attach to the vertical framing to assist with load dispersion.



tony, I took a look at your thread. In my kitchen the installers used that approach for a 6" overhang 30mm granite. I have seen that approach used a lot but not for a big overhang as yours. In my search I also saw the unistrut approach(photo attached), but I could not easily locate a dealer in my area + steel is easier for me.
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post #23 of 37 Old 01-08-2012, 12:08 AM
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Quote:
Originally Posted by calimark View Post

Yes I'm set on 10' 6" now and I have changed the title to reflect this.
I was tossing around the idea of using a 'S' iron bracket, welding the 2 bars to it and attaching that to the frame. Does this qualify as fixed end?

Unfortunately no. I'm really not trying to be negative, but your chance of achieving a fixed end if you're attaching to timber framing is nil. Having said that, every bit of extra rigidity helps, and you'll probably end up somewhere between pinned and fixed, but to achieve the full fixed end effect would require 'heroic' efforts. As an example, how does a 12" high end plate from 1/2 inch steel, gussets in the right angle between the tube and the end plate, with anchors near the top and bottom into 6' concrete sound ??!! Thought so !!

I suggest you assume you're going to end up with the 'free end' deflections.

Cheers,
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post #24 of 37 Old 01-08-2012, 12:12 AM
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I should also add that extra depth in the tubes would make a huge difference. If you can go with 3" square tube you'll reduce the deflections by roughly a factor of 3.

Cheers,
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post #25 of 37 Old 01-08-2012, 08:03 AM - Thread Starter
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Understood, so the 'fixed end' term is used in the strictest terminology.
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post #26 of 37 Old 01-08-2012, 06:18 PM
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Quote:
Originally Posted by calimark View Post

Understood, so the 'fixed end' term is used in the strictest terminology.

Exactly. Assuming they've used normal structural eng calcs, fixed end means ZERO rotation at the point of attachment.

Cheers,
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post #27 of 37 Old 05-09-2012, 06:34 PM - Thread Starter
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Just an update to this if anyone cares.
It has to be 2 piece stone. As prev mentioned stone come up to 10'.

The stone fabricator/installers said no more than 1/4" deflection to be safe. With 2 pcs he said it would never crack and if anything happened it would be the joint separating.

He also mentioned if it were a 10' *15" piece they would use 1 L brace in the middle and call it a day...even for 3 cm granite.
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post #28 of 37 Old 05-10-2012, 07:39 AM
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Interesting. I'll be curious to see how it works out for you
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post #29 of 37 Old 05-10-2012, 08:41 PM
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Still here ... still interested ... but we need PHOTOS !

Cheers,
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post #30 of 37 Old 05-10-2012, 09:05 PM
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Peter,

What is your profession? You are reminding me of Strengths and Concrete classes back in engineering school!

I havent used any engineering formulas in quite some time but as soon as I saw your posts it was instantly back in my head! I really enjoyed some of my classes as the professors were very hands on and most of the problems were actually interesting because they made tests out of problems of actually building things enstead of just giving problems.
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