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Reinforcing 8" Block Wall

 
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Old 02-22-2015, 05:26 PM   #21
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Re: Reinforcing 8" Block Wall


fjn -

The moment at the base of the wall is only created if it is connected to the footing by grout and rebar. Otherwise it is simply supported wall that has horizontal resistance at the top and bottom. Usually the joists parallel to walls are blocked well between them for the first couple of spacings get the floor system to resist at the top of the wall.

If it is a wall on a strip footing with the typical basement floor cast over the footing, which is suggested/required in many ares, it is a simply supported wall that has no "moment" at the base and the moment of maximum stress in the wall is moved up to near the center of the wall area from the soil, so reinforcement can be required depending on the amount of retained soil. This stress is reduced somewhat by the vertical load from the walls and above floors and compressive strength of the masonry or concrete is usually not a factor of a home.

The bond beam on a masonry walls is just there to provide masonry continuity at the top of walls with no joists on it and a level area for bearing on all masonry walls.

In many areas where 12" masonry basements are used, a special filled top is used on the top course of the wall for good bearing and they can be grouted at down to 16" increments for anchor bolts. - A common historic term for those block is "FHAs" since they were required by the Federal Housing Authority (FHA).

Sorry for the engineering and code slant.
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Old 02-22-2015, 06:36 PM   #22
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Re: Reinforcing 8" Block Wall


I agree with concretemasonry (I think...not sure what a moment is in engineering). The major problem with block basements is soil pressure/hydrostatic pressure. reinforcement that doesn't join with the footing will still resist that soil pressure which is fairly low at the bottom near the footing. At the top where soil pressure is strongest the masonry should be tied in via the floor system so the area where it's going to be effected the most is in the middle and reinforcement every 4 cores should be plenty to deal with that. Personally I don't think horizontal re-enforcement is particularly necessary in this situation. Dead loads are pretty constant and fairly light

remember that the foundation has been doing it's job without ANY re-enforcement for 40-50 years
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Old 02-22-2015, 07:37 PM   #23
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Re: Reinforcing 8" Block Wall


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Originally Posted by fjn View Post
True,however,that gets you one bond beam. And that one is at the very top of the wall,more than likely above the unbalanced fill.....the place where it is needed the least and does the least good.
That's why you have vertical reinforcing?
Never seen horizontal reinforcing called out for at grade or an intermediate bond beam if you will at grade?
Although I would think that in conjuction with vertical reinforcing a continuous or more commonly called structural bond beam would provide more stability and continuity to the vertical reinforcing intention than none at all?
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Old 02-22-2015, 08:16 PM   #24
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Re: Reinforcing 8" Block Wall


I dont know that its not already re-inforced, I don't really know anything at this point, other than, from what I can see , it doesn't look bad, and would like to save some money by re-using the foundation.....I would say that the footing drain is a definate. I'd be hard pressed to build a new house on top of a potentially wet basement

The purpose for my inquiry, is simply to gain knowledge and prepare myself
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Old 02-22-2015, 08:20 PM   #25
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Re: Reinforcing 8" Block Wall


The foundation was built outside of California 50 years ago. It doesn't have any reinforcement. Almost a guarantee
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Old 02-22-2015, 08:28 PM   #26
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Re: Reinforcing 8" Block Wall


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I dont know that its not already re-inforced, I don't really know anything at this point, other than, from what I can see , it doesn't look bad, and would like to save some money by re-using the foundation.....I would say that the footing drain is a definate. I'd be hard pressed to build a new house on top of a potentially wet basement

The purpose for my inquiry, is simply to gain knowledge and prepare myself
PHOTO'S Would greatly aide in your request.
And I would also think the engineer
would be quite knowledgeable as that is his forte?
Seems a whole lot of brain power is being wasted? Without more information on your part?
As most some or all replies and input of knowledge may be mute?
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Old 02-22-2015, 08:45 PM   #27
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Re: Reinforcing 8" Block Wall


I'll get some photos, but the basement interior partitions have to be demoed first..... I was planning on using the structural engineer who does everything for me , for framing.... I don't know any masonry specific engineers, anyone got any suggestions.... As far as wasting knowledge/ input, I have nothing better to while my wife watches some award show, and don't incinveniance yourself on my behalf, but I do appreciate the advice
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Old 02-23-2015, 12:23 AM   #28
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Re: Reinforcing 8" Block Wall


In my experiance with block retaining most situations require specific engineering from the footings up. Footing width,amount of bars in the cages, diameter of starters, centres of starters....etc etc.
As far as retro fitting reinforcing i know theres some cool new products out there as mentioned earlier they have been used over here abit for earthquake strengthening.
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Old 02-23-2015, 05:18 AM   #29
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Re: Reinforcing 8" Block Wall


Figuring out steel requirements for a residential or light commercial block wall isn't all that tough. You need 0.002 of the gross cross section of the wall to be steel and for some to be horizontal and some to be vertical with a minimum of 1/3 in either direction.

In this situation it would be very difficult to add any horizontal steel and since the wall is already under built those steel requirements would change but for new work that is the method
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Old 02-23-2015, 10:58 AM   #30
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Re: Reinforcing 8" Block Wall


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Although I would think that in conjuction with vertical reinforcing a continuous or more commonly called structural bond beam would provide more stability and continuity to the vertical reinforcing intention than none at all?



Exactly,that is why belts work really good around our mid sections.
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Old 02-23-2015, 11:10 AM   #31
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Re: Reinforcing 8" Block Wall


This article sheds some additional light on the subject. Of particular interest is the chart depicting the unbalanced fill,which is always a concern. The soil type is also a very large factor,I.E. clay vs. sand or gravel.


http://www.masonryconstruction.com/I...68-1374431.pdf
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Old 02-23-2015, 12:29 PM   #32
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Re: Reinforcing 8" Block Wall


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Exactly,that is why belts work really good around our mid sections.
FYI I prefer and use suspenders as I also need the vertical reinforcing they
provide.
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Old 02-23-2015, 06:43 PM   #33
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Re: Reinforcing 8" Block Wall


Just because I'm an ass...another paper saying that joint reinforcement counts as horizontal reinforcement
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Old 02-23-2015, 07:02 PM   #34
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Re: Reinforcing 8" Block Wall


You guys are all messed up...

The main concern would be if the basement walls were exposed to fire or not. If the temp of the walls went over 600 F, the mortar and block will be ruined beyond repair and require replacement. I would basically assume any burn marks are over 600 and replace those sections.

If you're digging out the perimeter for a new footer drain, then by all means check out the wall and reinforce as needed. Pins and grout will do the most for the least and personally I would not get too concerned about drilling into the footer.

Helicoil could be added to the bed joints on the outside wall for extra measure. The manufacture probably has some data on tensile strength.

Get the deck back on before back fill. If it ain't broke, don't kid yourself into thinking you need to fix it.
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Old 02-23-2015, 07:20 PM   #35
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Re: Reinforcing 8" Block Wall


I think if you read the 9th. post made after the starting thread. I most definitely made the statement your referring to? So I don't know that we're all messed up?
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Old 02-23-2015, 07:30 PM   #36
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Re: Reinforcing 8" Block Wall


If you wanted to install rebar into the wall and pour the wall solid, you would probably have to remove the top course or maybe two as these are usually poured solid or laid with semi solid block on the top course.
Unless the wall looks like it sustained very high heat, it will probably be fine if it has lasted 50 years in its present state. In Ontario, you could probably only be allowed to backfill about three feet on eight inch block. We use 12 inch block with rebar every hole, poured solid with concrete and we can only backfill about seven feet. Buttress walls on the inside are a great idea. As already stated, if the basement floor is poured a good portion up on the bottom block, it would help stop the bottom of the wall pushing in. Therefore rebar would help even if it cannot be drilled into the footing. If the floor isn't at least half way up the bottom block, the rebar will be fairly ineffective unless pinned to the footing somehow.
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Old 02-24-2015, 09:08 AM   #37
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Re: Reinforcing 8" Block Wall


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If the floor isn't at least half way up the bottom block, the rebar will be fairly ineffective unless pinned to the footing somehow.
Yes it will. Soil (same as hydrostatic) pressure increases with height. There is little to no force at the bottom. and it would need to move all that soil to swing outward
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Old 02-24-2015, 10:28 AM   #38
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Re: Reinforcing 8" Block Wall


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Yes it will. Soil (same as hydrostatic) pressure increases with height


Yes this is correct. One other important fact to keep in mind,the pressure exerted with an increase in height is exponential.Six feet of fill exerts considerably more than double the pressure of three feet of soil etc..
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Old 02-25-2015, 06:45 AM   #39
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Re: Reinforcing 8" Block Wall


Ask the local inspector if you have to retrofit reenforcement meet current codes

Cover it up before it freezes.... hope it isn't to late.....

Many CMU basements only work because the weight of house keeps both faces under compression. thus removing the weight of the superstructure will allow the basement walls to cave in.....even using 2x4 instead of 2x8 sillplates can allow the block roll more easily.

Worse case, its already cracked.... Hire a PRO, that knows masonry to inspect it.

Last edited by Fouthgeneration; 02-25-2015 at 06:55 AM.
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Old 02-25-2015, 11:28 PM   #40
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Re: Reinforcing 8" Block Wall


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Yes it will. Soil (same as hydrostatic) pressure increases with height. There is little to no force at the bottom. and it would need to move all that soil to swing outward
Why do they make us pin the bottom course to the footing if it has no benefit. Just asking.

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