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Old 11-26-2010, 04:08 AM   #1
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Concrete: Need reference to shear strenth, angle


Here is my deal, and I don't expect an engineer to stick his/her neck out on it, but perhaps could suggest where I can read to learn. I am building a 2-story addition to my house, 24x24. 60 psf snow load, etc. Nothing unusual up above. The question is in tapering/angling/beveling out the foundation wall. I need a 12" wide foundation wall for my stick walls to sit on (Riversong Truss, if you are familiar w/ them. If not, see http://www.builditsolar.com/Projects...arsenTruss.htm if interested.) I would like my 8" wide foundation wall to angle out at the top, 30 degrees for the last 8" of height. That will give me a 12" wide platform; I don't want to pour a 12" wide foundation wall if I can avoid it. I will be using ARXX blocks, and they make a Brick Ledge block that may do what I want, and save me building a form. Either way, the part that tapers out will have the load bearing wall on it, and I don't want it to shear off, obviously. Where can I read about doing this with concrete, as I am surely not the first one to do this? Drawing is neither to scale nor complete; it is a concept drawing, not a blueprint. Thanks. john
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Old 11-26-2010, 06:24 AM   #2
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Concrete: Need reference to shear strenth, angle


only suggestion i'd have is #5 bar coming out of the icf's at the proper angle for more shear support otherwise looks good to me,,, doubt if i'd have any problem having a pe/arch stamp affix'd to the dwgs,,, used reward system several times before but never the arxx. overbuilding is never going to get you in trouble,,, i forget what the dimensions for the brick ledge but like your method much better,,, good luck !

of course, jo, dan, 'scar, & dick may have other comments.

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Old 11-26-2010, 05:39 PM   #3
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Concrete: Need reference to shear strenth, angle


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Originally Posted by itsreallyconc View Post
only suggestion i'd have is #5 bar coming out of the icf's at the proper angle for more shear support otherwise looks good to me,..•• That crossed my mind, too. Thanks.

...used reward system several times before but never the arxx. •• Only used them once, in my son's basement, and they were pretty easy to work with, though we had two blowouts (not the blocks' fault, the operator of the pump truck brought the wrong vibrator...). They also looked at little more skookum than the other brand in town.

... overbuilding is never going to get you in trouble... •• gross overkill is a thing of beauty.

•• Thanks for the comments. Always good to hear from cats that do this stuff. john
see after the bullets.
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Old 11-26-2010, 07:51 PM   #4
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Concrete: Need reference to shear strenth, angle


I would flare the outside top of the concrete wall rather than the inside. I believe that would help with two things; the first layer of foam would have a place to tuck in- helping reduce the flashing width from the siding above; secondly, you would have full direct bearing on the inside wall to the basement foundation wall below. A concrete support isn't as critical in front because of the non-bearing wall above. Curious as to why would you want ESP foam instead of a close cell, that won't absorb the water and hold it next to the concrete foundation wall (another water reservoir)?
Remember to have the Engineer reviewing your plans to state the required spacing, number and length of nails connecting the floor joists to the studs as the ledger is ½ of the bearing width required by Code for floor joists. The S.E. may also add solid blocking at the floor line as a fire stop required by the Building Code. Redraw the rigid foam board to repel water as it comes sideways from the earth and from above, the laps are wrong in the diagram, letting the water through at the vertical joints. At least if you are not there while back-filling, a correct diagram may help. If you are using individual boards, installed perpendicular to rafters, for the roof sheathing be sure to add diagonal braces under the rafter faces, between 45-60°, the ones in the picture appear to be over 60° and few as well as too short to contribute much, the S.E. will know.
Don't forget to label the vapor barrier under the slab in the drawing and continue it over the top of the concrete wall and up the edge of the slab. I would use a sill sealer between the mud sill and the inside bearing wall bottom plate leaving a lap over onto the concrete to cover the mud sill completely as a thermal break to the floor covering there (unless heated slab): http://www.greenbuildingadvisor.com/...-building-code I would add 3/4 inch plywood over the top of the two exterior walls to act as a fire stop and tie them together there, especially at the gable ends.
Your ceiling joists cantilevering outside will act as thermal sinks, drawing the heat from the room span to the outside ends and their temperature. No matter how much insulation you put inside and above them, the heat would transfer through the boards along their length to their ends exposed at the soffit: fig.11: http://docs.google.com/viewer?a=v&q=...BiEiG1lHFDd9yA

I would add solid blocking above the inside bearing wall between the gable lookouts to prevent lateral displacement and shear nailing required at the full perimeter of the roof deck above.
Be sure to locate the continuous soffit venting right next to the fascia board, so as not to pick up the wind pressure coming up along the side of the house wall and blow snow and rain into the attic: pp.616: http://books.google.com/books?id=Z8a...0vents&f=false
T-braces are weak and only temporary: http://bct.eco.umass.edu/publication...n-the-outside/
Be sure to nail the rim floor joists as per Code, and not leave a 3 foot space between nails in a picture for us to catch…….. LOL.
I read the first Charlie Wing books when they first came out, very informative.

We expect to see many, many pictures.

Gary
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Old 11-26-2010, 10:56 PM   #5
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Concrete: Need reference to shear strenth, angle


Quote:
Originally Posted by GBR in WA View Post
I would flare the outside top of the concrete wall rather than the inside. I believe that would help with two things; the first layer of foam would have a place to tuck in- helping reduce the flashing width from the siding above; secondly, you would have full direct bearing on the inside wall to the basement foundation wall below. •• That was my first "plan", for the reasons you stated. However, I'd like a nice, flat face to insulate on the outside. A full, 4' wide sheet would eliminate horizontal gaps. But, structurally, that would be best. The question is, is flaring inside sufficiently strong.

Curious as to why would you want ESP foam instead of a close cell... •• The ARXX blocks are EPS. I've been reading about EPS, and according to one plastic foam site, it only absorbs something like 0.2% of its weight in water. I don't know if that "only" is a big "only", or a small one. That same site said that EPS actually outperforms XPS below grade, because its R value does not change over time. I will have to re-read that, and more, as I sort of remember it being an EPS-oriented outfit, not a foam-board-in-general outfit.

Remember to have the Engineer reviewing your plans to state the required spacing, number and length of nails connecting the floor joists to the studs as the ledger is ½ of the bearing width required by Code for floor joists. •• Am confused. Ledger is 4" wide; 2x4 is 3.5".

The S.E. may also add solid blocking at the floor line as a fire stop required by the Building Code. •• Even w/ dense-packed cellulose? Will check into that.

Redraw the rigid foam board to repel water as it comes sideways from the earth and from above, the laps are wrong in the diagram, letting the water through at the vertical joints. •• Good point. I just quickly drew them in, for kicks. Typically, only 2' wide foam board lies horizontally 2' at the footer. I doubt that the ground will be wet that far down. I've dug 1,000 holes here, and have never seen water in the soil. But, there's no sense in setting up for failure.

At least if you are not there while back-filling... •• Trust me. I'll be doing ALL of this, but appreciate anyone pointing out any potential pitfalls.

If you are using individual boards, installed perpendicular to rafters, for the roof sheathing be sure to add diagonal braces under the rafter faces, between 45-60°, the ones in the picture appear to be over 60°... •• Gary, one of us is in the wrong thread here. Rafters? Roof sheathing? I'm completely confused on this one. Are you looking at the Build It Solar page? That is Robert Riversong's job, or that of someone else, following his truss design (he modified the Larsen Truss, by, I believe, moving the band/rim joist away from the outer wall, so as to not have a big thermal bridge there. I will look at the web site and try to see of what you speak. I have not gotten into the details of the roof at all, as this will be the first time I have used the Riversong truss system. Sharp eye, dude! If I see what you are talking about, I'll ask Robert about it.

Don't forget to label the vapor barrier under the slab in the drawing and continue it over the top of the concrete wall and up the edge of the slab. •• Roger that. When I get to making more "real plans", I'll do that. The VB will be TuTuff. On the VB, I also envisioned doing that, but was discouraged from doing so. Was told to just DryLok the H out of the place, essentially.

I would use a sill sealer between the mud sill and the inside bearing wall bottom plate leaving a lap over onto the concrete to cover the mud sill completely as a thermal break to the floor covering there (unless heated slab): http://www.greenbuildingadvisor.com/...-building-code •• Will read that link. Yes, PEX in floor, and likely 6" of XPS under the slab; at least 4".

I would add 3/4 inch plywood over the top of the two exterior walls to act as a fire stop and tie them together there, especially at the gable ends.•• Will look at whether or not a fire stop is needed w/ dense pack. I believe all the 12" x 1 x 4s between the walls is the "tie together". Were I using a double-wall, both load bearing, the subfloor on the second floor would be extended out to the outer wall, for tying them together. I would also probably install the 12x1x4; overkill is beauty.

Your ceiling joists cantilevering outside will act as thermal sinks, drawing the heat from the room span to the outside ends and their temperature. No matter how much insulation you put inside and above them, the heat would transfer through the boards along their length to their ends exposed at the soffit: •• Will look at that, too. You are way ahead of me on the wood up high.

I would add solid blocking above the inside bearing wall between the gable lookouts to prevent lateral displacement and shear nailing required at the full perimeter of the roof deck above. •• Another one to look into.

Be sure to locate the continuous soffit venting right next to the fascia board, so as not to pick up the wind pressure coming up along the side of the house wall and blow snow and rain into the attic: •• Sounds good. There will be plenty of venting, too.

T-braces are weak and only temporary: •• Not sure what you mean by T-braces, but if they are the let-in, diagonal straps, I think that is all Robert often uses, to minimize lumber usage.

Be sure to nail the rim floor joists as per Code, and not leave a 3 foot space between nails in a picture for us to catch…….. LOL. •• Roger that, Eagle Eye.

I read the first Charlie Wing books when they first came out, very informative. •• And Charlie Wing is....?? You know, I think I will zap this thread to Robert and see if he wants to comment. After all, he invented and uses this method, so we can hear from The Horse (no offense intended, Roberto).

We expect to see many, many pictures. •• As this is a bit of a novel design, and I have never seen one done in Frb ( I am not a builder, though; just a DIY nimrod), so I will be taking photos and posting them on Photo Bucket in case others are curious. I have a few little projects up there, and the grapples I built for my skid steer bucket. I always like to see how people build things, even if I never will. I love building carp. Thanks for the info!

Gary
G: See beyond the bullets, above. Thanks. john
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Old 11-27-2010, 12:13 AM   #6
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Concrete: Need reference to shear strenth, angle


Gary: Here is a response from Robert. c ya. john

"Thanks for the heads up. I don't want to register for another forum (seems each time I do more spammers get hold of my email address), but feel free to post the following in response to Gary.

GBR in WA



"Remember to have the Engineer reviewing your plans to state the required spacing, number and length of nails connecting the floor joists to the studs as the ledger is ½ of the bearing width required by Code for floor joists."



If you're referring to the pictures of my Riversong Truss house, this type of balloon framing was used successfully for more than half a century in the US. The code requires 1½" of bearing for a 1½ thick joist – that's 2Ό square inches of bearing surface. Since I use full-dimension rough-sawn lumber, my 2" thick joist is resting on a 1" thick ledger on 2 square inches of surface. In addition, each joist is side nailed to both the 2x4 stud and the 2x3 outer truss chord with several 20d nails. This frame is at least as strong as any conventional frame.



"The S.E. may also add solid blocking at the floor line as a fire stop required by the Building Code."



Dense-pack cellulose has been third-party certified as a better firestop than nominal 2x solid framing. I've built several of these in various code jurisdictions without any additional firestops required by building inspectors.



"If you are using individual boards, installed perpendicular to rafters, for the roof sheathing be sure to add diagonal braces under the rafter faces, between 45-60°, the ones in the picture appear to be over 60° and few as well as too short to contribute much, the S.E. will know."



The one's in my pictures are full-dimension 2x4s, nailed with 20d galvanized nails and set at 45° to the rafters. They are overlapped for continuity from eave to ridge in both directions on both sides of the roof. They are more than sufficient for wind bracing, except in coastal high hurricane zones.



"Don't forget to label the vapor barrier under the slab in the drawing and continue it over the top of the concrete wall and up the edge of the slab."



Yes, there must be a sub-slab vapor barrier (and should be sub-slab insulation to isolate it from both the ground and the frost wall), but there's no need to run the VB over the slab edge if there's a foam thermal and capillary break (as there should be) at the slab edge.



"I would use a sill sealer between the mud sill and the inside bearing wall bottom plate leaving a lap over onto the concrete to cover the mud sill completely as a thermal break to the floor covering there (unless heated slab)"



I'm not sure what you're describing, but if the slab is thermally and hygrically isolated there is no need for sill seal as a capillary break under the inner wall plate. There is a need, however, for an air seal (Tremco acoustical caulk or EPDM gasket), if this house is to use the Air-Tight-Drywall Approach.



"I would add 3/4 inch plywood over the top of the two exterior walls to act as a fire stop and tie them together there, especially at the gable ends."



Again, no need for any firestop except the borate-treated cellulose, and the inner and outer framing is tied together 24" oc by wood or plywood gussets and needs no additional tie."

"Your ceiling joists cantilevering outside will act as thermal sinks, drawing the heat from the room span to the outside ends and their temperature. No matter how much insulation you put inside and above them, the heat would transfer through the boards along their length to their ends exposed at the soffit."



You mean thermal bridges. But this frame has less thermal bridging than any other framing system except perhaps SIPs. The thermal bridge you're concerned about requires heat transmission through 12" of hemlock, which at R-1.25/inch presents R-15 of thermal resistance and only through a 2" x 8" cross section every 24". This is insignificant compared to the R-45 of the rest of the wall and less of a thermal bridge than the doors and windows, which occupy much more area.



"I would add solid blocking above the inside bearing wall between the gable lookouts to prevent lateral displacement and shear nailing required at the full perimeter of the roof deck above."



I don't know what you mean by shear nailing at the perimeter, and I suspect your concern is about rolling of the lookouts. But they are full-dimension 2x6, nailed to the 2x8 common rafter and fly rafter with 20d nails and tied at the top from ridge to subfacia with a flat 2x4 in the line of the load-bearing gable wall. They cannot displace or roll.



"Be sure to locate the continuous soffit venting right next to the fascia board, so as not to pick up the wind pressure coming up along the side of the house wall and blow snow and rain into the attic."



My overhangs are 18" wide and with a soffit vent centered in the soffit there is little concern about wind-driven snow or rain. The real issue is that most shingle-over ridge vents have no exterior wind baffles to prevent both wind-driven moisture and positive pressure. No ridge vent operates properly in all wind conditions without external baffles, like the AirVent ShingleVent II or the Lomanco OR-4.



"T-braces are weak and only temporary."



Simpson TWB bracing meets IRC requirements for shear bracing if installed from plate to plate, in opposition at a 45° angle. They are code-certified for permanent installation as an alternative to shear panels or let-in wooden bracing.

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Old 11-27-2010, 07:37 PM   #7
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Concrete: Need reference to shear strenth, angle


I would use better shear resistance than minimum code allows. 1x4 let-in braces or “T”-braces from Simpson are minimum. With 8’ ceiling height and a T brace you get 160# shear resistance, the 9’ ceiling brace = 190# rest. Plywood or OSB gives you 3120# resistance times two corners = 6240# compared to two “T”s at 320#. This may work if you don’t live in a high wind or seismic area, more drywall fasteners would also help. Have a local S.E. check for your area, as mentioned. Page 12: http://www.strongtie.com/ftp/coderpts/rr25725.pdf

Actually, those T-braces are only for 16”o.c. framing, not 24”o.c., if Simpson brand.
And the 2x4 inside bearing walls as pictured are now required to be 16”o.c. OR 2x6, 24”o.c.
Be sure to use bracing on the upstairs gable end house wall (omitted in picture), as per minimum code for wall bracing, if under the IRC. Your Country may not require the bracing for “Basic wind speeds” and “Seismic areas” the U.S. is required to follow (scroll down): http://publicecodes.citation.com/ico...001_par004.htm

Just to build to the basic “90mph wind speed” requires uplift hold-downs and special roof diaphragm perimeter nailing (above the exterior walls) required by IRC: http://www.awc.org/pdf/WFCM_90-B-Guide.pdf

Work along with your local Inspector to get at least the minimum safest house possible. Thanks for taking time to answer, Robert. The U.S. Codes are apparently stricter than yours, that's what my concerns were. I think it's a great way to cut down on energies, keep up the good work!

Gary
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Old 11-27-2010, 11:17 PM   #8
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Concrete: Need reference to shear strenth, angle


Gary: (1) Thanks again for your input, and I will forward this to Robert. (2) I will have to digest all of that; am pasting all this into a document for myself. I will be using 1/2" CDX on my exterior shell wall, and will likely have a 2x4, 12" OC inner bearing wall with the in-let bracing, and/or some diagonal 1x4s in the corners. I know all that is probably unnecessary, but I just feel better that way. "If you don't know, overkill." I will be DIYing this, so a little bit of extra materials here and there don't mean stink. (3) Looking at my original concern, I don't really see any danger now. As drawn, the slab will bear 3 1/2" on the 8" concrete wall directly, so it looks to me like I'd have to shear the slab and the flair simultaneously. I'm not building a sky scraper here. That said, I'll still try to find proven designs. ARXX Co opinion? Coming up. john
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Old 11-28-2010, 10:05 PM   #9
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Concrete: Need reference to shear strenth, angle


John, No doubt you will be fine as you have it drawn. I would certainly look into the brickledge option from the ICF manufacturer though. It's similar to what you have drawn, my even be more aggressive of an angle from what I've seen.

I don't even think you'd have an issue keeping the wall at 8" wide the entire way. As long as you get 2" of slab bearing, you should be fine. Far heavier point loads are brought down on slabs all the time in residential construction. For example, most often posts on stoops bear on the stoop rather than directly over the foundation.

Whatever you do, make sure to have direct concrete floor to concrete foundation contact with NO INSULATION sandwiched between. This is becoming an ever increasing detail that I see to try to combat thermal bridging, but it has a drastic adverse effect to the integrity of the foundation and floor system. I've trouble shot that exact failure before, and I can tell you what ensues isn't pretty.....
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Old 11-29-2010, 12:26 AM   #10
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Concrete: Need reference to shear strenth, angle


I've found further info on the gable end wall bracing; is not required ---if the floor sheathing is continued across 60% of the wall length, good to go-- pp. 7 and pp.33, Explanation #4 on installation.
Good you are going with ply corners: "In 1977, Roger Tuomi and David Gromala, engineers with the Forest Products Laboratory (FPL) in Madison Wisconsin studied let-in bracing. Tuomi and Gromala learned that much of a braced wall’s racking strength is owed to the interaction of board sheathing and let-in bracing. No such interaction occurs with non-structural foam sheathing. Later, in 1983, FPL researcher Ronald Wolf studied the contribution made by off-the-shelf No. 2, 1”x4” let-in braces in unsheathed walls and found they provided only 600 pounds of resistance to horizontal loads like wind. Tests conducted by Simpson Strong-tie a leading manufacturer of metal bracing and fastener systems yield similar results. So using 1Χ4 let-in braces may not be an automatic solution when building foam-sheathed walls" From my site earlier: http://bct.eco.umass.edu/publication...n-the-outside/

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Old 11-29-2010, 12:59 AM   #11
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Concrete: Need reference to shear strenth, angle


Quote:
Originally Posted by jomama45 View Post
John, No doubt you will be fine as you have it drawn. I would certainly look into the brickledge option from the ICF manufacturer though. •• I would love to use a pre-made flair, if at all possible, for sure. I only saw one listed on the ARXX web site for blocks narrower than I'd like to use. It seems that the 12" blocks ( approx 7.5" inside) are the most common here.

As long as you get 2" of slab bearing, you should be fine. •• That is what my gut says. I have no numbers, but it seems that a 2" catch would take a lot more than a house to shear it, if reinforced w/ rebar. That said, I want more support than my gut feeling.

Whatever you do, make sure to have direct concrete floor to concrete foundation contact with NO INSULATION sandwiched between. •• That is interesting, because that is how it seems to be here, primarily. I am searching for why you shouldn't or don't typically float a slab w/ the 2" XPS thermal break up here. Some very knowledgeable cats on another forum can not believe me when I tell them about tying the slab to the foundation wall w/ rebar. They say you HAVE to float it, adding a thermal break for warmth, or the slab will crack. Two engineers did the rebar connection in houses they designed for me (30 and 2 years ago) and another thought I was crazy last week when I called to get his opinion on "floating a slab-on-grade so that I can thermally decouple it from the foundation wall." I'm confused on this now, and have thought it was "normal" until recently.
See after bullets. Thanks for the reply.
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Old 11-29-2010, 01:09 AM   #12
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Concrete: Need reference to shear strenth, angle


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Originally Posted by GBR in WA View Post
I've found further info on the gable end wall bracing; is not required ---if the floor sheathing is continued across 60% of the wall length, good to go-- pp. 7 and pp.33, Explanation #4 on installation.
Good you are going with ply corners: .... •• I'm not sure I will plywood the corners on the inner wall, but if I can get rock wool batts in Anchorage to fill the inner wall in the corners, I will. They will at least have 1x4's though. I was just told that sheet rock provides a conservative 100 lbs/ft, and likely more realistically about 200 lbs. I have no idea what I should have, though; I will have to research that. Thanks again.
See after bullets. j
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Old 11-29-2010, 02:34 PM   #13
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Concrete: Need reference to shear strenth, angle


Here is a good drywall site for the shear resistance: http://gypsum.org/download.html

Remember the 1x4 requires going from the top plate to the bottom plate, as does the T-brace by Simpson. That is where the required nail length is so important, at the ends. It wouldn't hold as much nailed to a stud at the top end rather than a continuous plate or with 3/5 as many studs (24"o.c.) or without the board sheathing added. The roof sheathing boards may tie it all together, a S.E. would know. I'd check to be safe.

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Old 11-30-2010, 01:11 AM   #14
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Concrete: Need reference to shear strenth, angle


Roger that. Once I get things a bit more pinned down, I will try to run this by a SE. I don't know how looking piece-meal at a house will rest with one, as opposed to doing the whole design. I can understand that, but maybe I'll catch one in a wild, live-on-the-edge mood. I did find out that the ARXX ledge will support up to 22' of bricks, so I know something now. I just can not imagine, with two inches of slab over the solid 8" wall (surely that load will be felt by more than the 2" directly under the slab???), that a house will shear the slab and the brick edge simultaneously. Surely??? j
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Old 11-30-2010, 08:01 AM   #15
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Concrete: Need reference to shear strenth, angle


Originally Posted by jomama45
John, No doubt you will be fine as you have it drawn. I would certainly look into the brickledge option from the ICF manufacturer though. •• I would love to use a pre-made flair, if at all possible, for sure. I only saw one listed on the ARXX web site for blocks narrower than I'd like to use. It seems that the 12" blocks ( approx 7.5" inside) are the most common here.

I'd contact them directly to see if they manufacture said brickledge block, or if you can modify on site. Another simple option that we use fairly often in strange circumstances is to merely lay 4" block haunches on the interior every 4-8'. Fast, simply and effective. Depending on how the interior is backfilled, drystacking the block may be an option as well.

As long as you get 2" of slab bearing, you should be fine. •• That is what my gut says. I have no numbers, but it seems that a 2" catch would take a lot more than a house to shear it, if reinforced w/ rebar. That said, I want more support than my gut feeling.

It's been done sucessfully for many years in residential construction. I've witnessed many, many garage floors that were completely undermined below held up simply by a 2" perimeter ledge.


Whatever you do, make sure to have direct concrete floor to concrete foundation contact with NO INSULATION sandwiched between. •• That is interesting, because that is how it seems to be here, primarily. I am searching for why you shouldn't or don't typically float a slab w/ the 2" XPS thermal break up here. Some very knowledgeable cats on another forum can not believe me when I tell them about tying the slab to the foundation wall w/ rebar. They say you HAVE to float it, adding a thermal break for warmth, or the slab will crack. Two engineers did the rebar connection in houses they designed for me (30 and 2 years ago) and another thought I was crazy last week when I called to get his opinion on "floating a slab-on-grade so that I can thermally decouple it from the foundation wall." I'm confused on this now, and have thought it was "normal" until recently.

You can go either route typically, but in this case where you have direct load being transfered to the slab via the interior bearing stud wall, it needs to bear directly on the foundation with nothing with less compressive strength than minimal concrete between. I really don't see a need for a thermal break here as you have 4" of foam on the exterior to grade already.


Quote:
Originally Posted by jklingel View Post
Roger that. Once I get things a bit more pinned down, I will try to run this by a SE. I don't know how looking piece-meal at a house will rest with one, as opposed to doing the whole design. I can understand that, but maybe I'll catch one in a wild, live-on-the-edge mood. I did find out that the ARXX ledge will support up to 22' of bricks, so I know something now. I just can not imagine, with two inches of slab over the solid 8" wall (surely that load will be felt by more than the 2" directly under the slab???), that a house will shear the slab and the brick edge simultaneously. Surely??? j
Again, that design is just fine. The heaviest element in the equation will still be the concrete floor at 50-55#'s per sq. foot (assuming a 4" thickness). The load bearing wall and subsequent roof load is bound to be a fraction of the floor weight/load.

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