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Block Wall Design Question

 
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Old 04-10-2016, 04:51 AM   #1
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Block Wall Design Question


In the planning stages of building a pole barn here at my place. It's an ag building with no building inspections. Dug the footprint of the building out... building is 40X64 and plan was to dig the footprint into the bank then create swales.... Long story short I ended up going deeper to make the driveway more flat and ended up with about 5' if dirt wall in the back. got me thinking about just laying block instead of moving all of that dirt.

My question is, what size block wall/footer would be recommended for the 64' long back with 5' of backfill, and no support on top of the wall? Floor will eventually be concrete. My wall would be 6', with 8' framing directly on top of it. The side walls would start at 6', and step down to grade. front would just be a footer and block up to grade.

South eastern Pa.
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Old 04-10-2016, 06:22 AM   #2
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Re: Block Wall Design Question


The city or county you are in should have a set of standards for retaining walls. Though you won't be inspected, it could give you an idea of what is required. The county standards here in San Diego CA are quite strong and would require a wide footing, probably with keyway for a wall retaining 5feet. They tend to way over-engineer out here and could be the same where you are but I would at least look at them
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Old 04-10-2016, 06:23 AM   #3
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Re: Block Wall Design Question


I dont know what you would need for a footer, but an 8" wall would fine, although you could do a 12" wall as well. It would need steel vertically, Out of habit up here most guys go 32", and I would do a bond beam with #5 in it, overlapping a good amount.

Drainage would be as important as the wall.
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Old 04-10-2016, 06:51 AM   #4
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Re: Block Wall Design Question


I would at least use 12"block because I never like back filling against 8" block.

Here locally, all retaining walls have to be engineered. I always said they don't engineer them, they just throw everything at the building supply at it.

A engineer here will make us put #5 or #6 rod every 8" vertical, ladder wire every 8" horizontal, completely fill entire wall, and bond beam on top.

A retaining wall here gets really expensive, but you only want to build it one time.

My advise to you would be, go ahead and talk to your building inspector or even an engineer and see what they would recommend.

Good luck
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Old 04-10-2016, 07:28 AM   #5
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Re: Block Wall Design Question


A sure fire design would be 24/30" wide footings below frost line with a 12" wall.

Set the wall towards the front side of the footing, dowel at 12" centers.

I'd probably use Ivany block and run horizontal bar every other course and grout solid.

Waterproof the back side and apply at least 1ft wide teabagged drainage stone backfill...drain through weeps or to grade if possible using 3 or 4" pipe.
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Old 04-10-2016, 05:46 PM   #6
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Re: Block Wall Design Question


How do you dowel every 12"? 8" multiples to my mind

12" block for sure without any floor system on top of the wall with a 24" x 6" footing (i wouldn;t go any less than 7.25 but that's me). The rule is 0.002x the amount of steel as the gross cross section of the wall. I don;t know where my charts are anymore but I would hazard that block Lok/durwall evry 2nd course and #5/(metric)#15 bar every 3rd core would suffice. I didn't read it but this link will probably help explain
https://books.google.ca/books?id=GGb...00.002&f=false
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Old 04-10-2016, 06:31 PM   #7
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Re: Block Wall Design Question


Sorry that was a typo...yes increments of 8"...typical is 16" or 32 oc.

I believe code allows 2" off center to be technical.
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Old 04-10-2016, 07:20 PM   #8
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Re: Block Wall Design Question


I believe a building was being built on top of the wall. Its not a stand alone retaining wall I dont think as I would just do a dry wall if thta wrre the case.
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Old 04-10-2016, 07:42 PM   #9
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Re: Block Wall Design Question


CMU are not in the design window for retaining walls unless there is a building on top of them.
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Old 04-10-2016, 07:52 PM   #10
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Re: Block Wall Design Question


Around here they are...ivany block in particular. many get faced with brick or stone.
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Old 04-10-2016, 08:04 PM   #11
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Re: Block Wall Design Question


Quote:
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I believe a building was being built on top of the wall. Its not a stand alone retaining wall I dont think as I would just do a dry wall if thta wrre the case.
You are correct, and just to clarify there will be no lateral support on top of these walls. I will also say it wouldn't be a big deal to cut down the unbalanced fill to 3-4' if it meant I could go with 8" block.
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Old 04-10-2016, 08:12 PM   #12
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Re: Block Wall Design Question


You can build the wall infinitely strong but it'll still push over if you don't have your footer design and connection to footer done right.
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Old 04-10-2016, 08:24 PM   #13
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Re: Block Wall Design Question


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Originally Posted by psu927 View Post
You are correct, and just to clarify there will be no lateral support on top of these walls. I will also say it wouldn't be a big deal to cut down the unbalanced fill to 3-4' if it meant I could go with 8" block.
3-4' is certainly doable with 8s, stuff it with steel.
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Old 04-11-2016, 05:53 AM   #14
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Re: Block Wall Design Question


My code says 3' max for 8" block without a floor system (laterally supported) but I've literally seen hundreds of foundations done in 8" block with zero steel that are 60 years old or older. With free draining soil I wouldn;t be too worried....if it were my place
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Old 04-11-2016, 08:32 AM   #15
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Re: Block Wall Design Question


Put some piers 10' OC and tie them in every other course go 12/8/4 block, some durawall every other course and some vertical rebar every 4' OC that will give you a structural wall
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Old 04-11-2016, 04:35 PM   #16
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Re: Block Wall Design Question


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Put some piers 10' OC and tie them in every other course go 12/8/4 block, some durawall every other course and some vertical rebar every 4' OC that will give you a structural wall
Steel requirements for block walls are dependent on height, whether they are laterally supported and seismic zone. There is not 1 structural wall design
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Old 04-11-2016, 06:22 PM   #17
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Re: Block Wall Design Question


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Steel requirements for block walls are dependent on height, whether they are laterally supported and seismic zone. There is not 1 structural wall design




Also,the diameter of the steel is an engineered thing,not a one size fits all.
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Old 04-11-2016, 06:24 PM   #18
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Re: Block Wall Design Question


thanks guys for all the input. Going to consult with a few local guys and then make a decision.
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Old 04-11-2016, 06:31 PM   #19
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Re: Block Wall Design Question


Here is what the NCMA has to say on the topic.



http://www.ncma-br.org/pdfs/5/TEK%2015-06.pdf
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Old 04-18-2016, 01:17 AM   #20
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Re: Block Wall Design Question


Don't forget the Frost depth of the footings, the side walls will of course have to have a step or down. If the garage is unheated of course the frost depth will start at the Slab on Grade height.

I'd consider laying pilasters that were entirely out side the wall line so no loss of floor space occoured. A mix of pilasters and 8" or 10" block. or even laying 12 " till the last 2 or 3 courses. plastering would add cost but add considerably to the wall's strength.

At the pilasters add "toes" that widen the footer in BOTH directions with a J hook bar, the toe under the 6 ft. of dirt restrains the wall from rolling, and the "heel" improves the footer resistance to rolling also.

I have even hand dug post hole sized-cave like toe holds into the bank every 4- 8 feet with a rebar at the footing level, just before the concrete comes...

insulation is a no-brainer, and it will protect the damproofing/drainage board.

Working drainage is essential for the long term survival of the wall and the usability of the garage space.

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