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silverstrike 06-15-2012 06:21 AM

Core filling a bowing wall, please assist
 
The rear foundation wall in my house is bowing inward, and looks like it has been re-supported with some steel beams years ago. But there is roughly an 8 foot span that has a major stress crack both vertical and horizontal in between two of the steal beams. Several guys have looked at it and said it isn't bowing too bad but I should fill the cores to stop it from moving more. I have spoken to a number of masons and am getting different stories for the technique of filling the cores. What type of fill should I use? Just a sand grout or include small stone too? My blocks are the old 4 core blocks (very small cores). Also, would you suggest popping holes on the inside or the outside of the wall? My intention is to remove the face of the 2nd or 3rd block down so I can shove 3/8'' or so rebar down in to the cores and then fill every other 2 cores for about a 12 foot span. What are your thoughts?

CplDevilDog 06-15-2012 06:29 AM

Might want to consider addressing the Fill on the outside of the foundation as well. Sounds like there are some issues. Maybe they back-filled with clay?

silverstrike 06-15-2012 07:24 AM

Yes, my whole neighborhood is mostly clay. And word on the street is the builders backfilled too soon as well when the house was built about 45 years ago.

21boat 06-16-2012 12:32 AM

Quote:

Originally Posted by silverstrike (Post 943838)
The rear foundation wall in my house is bowing inward, and looks like it has been re-supported with some steel beams years ago. Several guys have looked at it and said it isn't bowing too bad but I should fill the cores to stop it from moving more. I have spoken to a number of masons and am getting different stories for the technique of filling the cores. What type of fill should I use? Just sand grout or include small stone too? My blocks are the old 4 core blocks (very small cores). Also, would you suggest popping holes on the inside or the outside of the wall? My intention is to remove the face of the 2nd or 3rd block down so I can shove 3/8'' or so rebar down in to the cores and then fill every other 2 cores for about a 12 foot span. What are your thoughts?

NONE of the above will work period.

As a 35 year professional mason/creter now GC. I find many do not understand walls /weight and shear forces. The skinny on walls.

I’ve spent many of years jacking up structures and replacing foundations and footers.

Block wall integrity depends on many things for it to support a load in shear. End walls are usually the first to go because there is not much down pressure on it to (Pin the wall to the footer.) as opposed to the sidewalls that have the house weight on it. BUT the long wall for another reason “distance” also changes dynamics when its length VS weight in shear changes because the return corners are further away for support in counteracting shear/length.

Your first problem is Shear/ weight /down pressure no matter what soil you have. It’s all relative to weight mass VS mass, which brings me to soils.

Generically all loose Soils/Aggregates/ can be piled up in a pile to form a 45 degree angle at its worst/ So if you build a wall in front of that pile and backfill the wall its shear pressure comes from that 45 degree angle filled in weight pushing the wall sideways. Basic physics are it takes equal weight of mass/force to hold back opposite mass to stabilize that force

To really screw you up a smaller wall in thickness can actually support more shear pressure then a thicker wall if that thinner wall has more load in weight from above.

There’s nothing in your equation of repair to address your problem, which is horizontal “Shear” that’s moved your wall. Grouting a wall really doesn’t address Shear In your case. All your adding here is more dead weight, which at this point since the walls out of plumb that again changes that dynamics.

Secondly your block cores are way to small to do any good in grouting them.
On a side note look at your finish grade in water runoff. Generically a min distance of 10 feet from structure must slope away from that structure. Also check downspouts. That done you have a few options here. Dig out and replace wall with thicker block. You also may need pilaster laid in that wall with bar and concrete in them

Bottom line here is your screwed in trying to fill your block cores..

silverstrike 06-16-2012 06:35 AM

I am going to have to respectfully ignore your post due to the fact that you contradict yourself numerous times.

You made a comment how according to physics, a thinner wall would actually support more shear pressure, but then you say I have to remove part of my wall and replace with bigger block. I will correct you by saying a thinner wall will take on more sheer pressure per square inch due to down pressure per inch compared to side pressure. BUT that does not mean a thinner wall can support more pressure.

A thicker wall may have less down pressure per square inch, but hallow walls can bend and bow and crumble much easier than a solid wall of ther same thickness. Not to mention the fact that the "dead weight" you speak of with filled cores will actually help increase that downward pressure

Plus, sheer strength is vastly improved if the cores get filled with rebar and concrete. Have you ever tried sheer "chopping" a piece of hallow 2 inch pipe compared to "chopping" a solid 2 inch shaft of the same metal? That's sheer strength. A solid wall has more sheer strength than a hallow wall of the same or similar size.

And as far as bowing, the wall is out of plumb by roughly 1.25 inches. So its not bad.

The only thing I will agree on is the fact that it's going to be a pain to fill the tiny cores all the way down, bc I do not want to mix it tooo wet, in addition to trying to get the rebar all the way to the footer.

So if anyone would like to provide me with the answers to the questions I asked regarding filler type, inside vs outside cut, and maybe how many cores to fill in a 4 core block, that would be great!

Thanks!

wkearney99 06-16-2012 08:27 AM

I'm no mason but I'd have to imagine the hassle of trying to "fix" it by filling the cores is going to be a lot more work than just digging it out and replacing it properly.

And it's 'hollow' not hallow.

concretemasonry 06-16-2012 10:46 AM

The fact that there was problem years ago and the cheap, temporary steel column braces performed as expected since the real cause was the poor soil and moisture behind the wall. The best long term solution is to remove the rotten soil condition and replace with good soil and a properly partially reinforced and partially grouted wall, that does not have to be thicker. 8" is thick is very common up to 14 courses.

The existing cores are not too small to grout if you use a proper grout meeting ASTM requirements including a slump of 8" to 11", as opposed to concrete that is usually 3" to 5". High strength grout is not necessary, but a "wet" fluid mix (8" to 11" slump) is necessary to insure complete filling.

Whatever you do make sure an engineer comes up with a solution and not a "good ole boy" solution, that may not be adequate for your soil, moisture and conditions.

The weight of a house is usually minimal and has little to do with the thickness of the wall. I have seen 22 story load-bearing block buildings built using 6x8x16 partially grouted and reinforced block.

Dick

hand drive 06-16-2012 11:02 AM

maybe another vertical steel column mounted to the floor above and to the floor/concrete below placed between the two original repair columns will be needed. for inconsistencies, fill behind the steel column with a non shrink grout. would this fix the wall?

silverstrike 06-16-2012 12:49 PM

Thanks, Concretemasonry, I've been trying to find an engineer to come look, without any luck. The few contacts I found are not returning my calls, I guess they don't want the business! Haha. I don't even think the wall is moving anymore anyway (cracks are same now as a few years ago). I can fill the cores with a wet mix sand grout for pretty low cost, and will take about a day I figure, maybe 2 at most. I'm obviously not the expert, but I don't think ripping out the wall and rebuilding is needed if the current wall is not moving at all, am I correct? I just want to prevent it from moving down the road by making it stronger.

Daniel Holzman 06-16-2012 01:41 PM

To the OPS, you are correct in believing that if the wall is no longer moving, there is no reason to perform any work. The simplest way to determine if the wall is stable is to either perform careful measurements of the bow of the wall, using a laser to establish a straight baseline, or you can use a long level (like a six foot masons level) or a plumb bob along a straight baseline on the floor. Make measurements approximately once a month, and see if the wall is stable. It will take at least a year to get a reliable set of data, at the end of that time you can determine if you need to do something.

As for "fixing" the wall, you are not going to "fix" it by adding grout, rebars, or another steel beam, if by "fix" you mean returning it to a plumb condition. If your goal is to stabilize the wall, that is a totally different matter, and can be done using a variety of techniques, including steel tiebacks, vertical steel beams inside the house, removal of improper fill and replacement with granular fill, installation of grout and rebar, or several other less frequently used methods. So before undertaking a project, you need to carefully determine the goal, whether that be stabilization or return to a plumb condition, as the methods will be quite different.

Should you decide to add grout and rebar, that will not hurt anything, but is not likely to add significant strength to the wall. The reason it will not add much strength is that the grout and bars are going to be added near the centroid (center) of the block, where the stress due to the moment exerted by the soil pressure on the wall is low. Hence the steel bars will not be doing significant work (low strain means low stress), and will add little to the overall strength of the wall.

The actual mechanics of bowing of a block wall is relatively complex, and I am not going to spend any time discussing it. If you are interested, Google stresses on a foundation wall, and you will see that the analysis of a foundation wall under loading from soil, and dead weight from the house, is surprisingly complex, as the wall acts like an elastic beam under two dimensional loading, hence it is more of a problem in plate mechanics that beam mechanics. Plate mechanics is far more complex than one dimensional beam mechanics, hence the actual stresses in the wall are more difficult to estimate than for a uniformly loaded beam of similar length.

Without doing the math, let's just say that adding grout and rebar will not hurt, but will not restore the wall to original condition either. I would recommend undertaking a program of measurement to determine if the wall is moving, and base my "repair" program on the results.

silverstrike 06-16-2012 03:21 PM

Thanks for the info. At this point, all I care about is making sure the wall is stable and structurally sound.

21boat 06-16-2012 10:39 PM

Quote:

Originally Posted by silverstrike (Post 944923)
Thanks for the info. At this point, all I care about is making sure the wall is stable and structurally sound.

Then get an engineer

Quote:

Originally Posted by silverstrike (Post 944519)
I am going to have to respectfully ignore your post due to the fact that you contradict yourself numerous times. You made a comment how according to physics, a thinner wall would actually support more shear pressure, but then you say I have to remove part of my wall and replace with bigger block. I will correct you by saying a thinner wall will take on more sheer pressure per square inch due to down pressure per inch compared to side pressure. BUT that does not mean a thinner wall can support more pressure.

I did not contradict myself, you don’t understand the relation in compaction/shear/weight, call and engineer and he will tell you what I’m telling you. I work with these engineers not to mention my wife’s son is an engineer. As I said earlier many now + one don’t understand conc./masonry wall in shear and compaction in weight ratios and how that changes.

Let me try and simplify this for you on how shears can drastically change in wall thickness.

A free standing 10 ft H x10 ft L x 8in W concrete wall is 2 .46 yd in concrete, wall weight is 9,840 lb .

A thinner concrete wall 10ft H x 10L x 6in wide is 1.85 yd concrete, wall weight is 7,407lb

BUT if we add a structure above that 6’ wide wall that can handle 1,000 lineal ft of weight in compaction, The 7,407lb 6” wide wall 10,000 lb heavier now in total combined weight of 17,407lb. Its almost double in weight of the free standing wall. Look at retaining walls VS house basement walls

So if we are going to push over/shear the 8in wide wall we need to counteract in weight its combined/total weight of 9,840 to move it sideways. BUT, if we need to push over the 6” wall we need to push its combined weight of 17,407 lb. So math 101, it obviously takes MORE force /shear to push over a heaver wall at the same leverage point even though that wall is 6”wide and not 8” wide

Theirs more you need to known here which so far no mason ect pointed out.

When using rebar with Crete/grout in a wall cavity ect, for that marriage to work the rule of thumb is.

Concrete around the rebar needs to be min 3 times the thickness of the rebar. So ” bar, 1.5 inch of Crete should be around that to its outside has to be 1.5” Also know one mention you have post tension on your wall, So when you Break those block cores out to get bar. grout in it what’s to keep that wall from moving while doing the work not to mention your marriage in too small of cores when grouting will actually weaken the wall because of the method you want to apply.

Commercially we lay Bond beam block to STOP shear but it does not stop vertical tilt other then adding MORE mass in weight to the wall, not unlike the 6” wall is heavier in mass with weight above iy
http://www.oneontablock.com/bondbeam.html

To stop that wall you need inside concrete pilasters, In time any wall that has moved will eventually fail unless an external force ( your house) weight can wedge it but haven't seen that work yet in the 35 years of messing with problems like yours

concretemasonry 06-16-2012 11:28 PM

21 boat -

As Daniel said, the reaction of a concrete masonry wall is relatively complex. It can also border greater problems with unoque wall construction.

There is a world of difference between shear failures/reactions and flexural failures/reactions and this gets compounded when you are repairing and conditions that has been stable for decades.

The units shown are not the type you have seen and do not react structurally when put in a wall like a conventional current CMU. The "big hammer" approach to dumping grout into the voids that are created by the units used do not increase the strength of the wall may return the wall to near it's original condition of strength since the original wall has already failed as demonstrated by the "bowing". "Bowing" is generally a flexural problem at or near the mid-point of the wall height. Shear failures are usually very low in the wall and show as a horizontal crack and lateral displacement very low (within a foot or so of the bottom). There is also a flexural failure of the wall that results in a displacement of the top of the wall due to a lack of lateral support by the floor system or connection the floor system (inadequate anchor bolts).

Unfortunately, from your position, the movement described by the OP would not be appreciably by all the horizontal bond beams that can be used in the vertical height unless there was vertical reinforcement close to the tension side (interior in this case). You are thinking in terms of gravity walls with "make-do", quyick satisfaction and not solutions. Unfortunately, as described by the OP, the unique units do not react in the wall the same a conventional CMUs and may have been a local experiment or made by a wet-cast old process that has not survived.

If the wall is carrying the loads satisfactorily grouting of the wall will improved the performance slightly without correcting the "bowing". Vertical steel would not provide strength where needed and (despite the cost and installation problems). The post of the units available is just a listing of the minimal selection of units produced by a small local producer and does not refer to the use or strength of a wall.

I base this on 40 years experience as registered engineer, 35 years experience in C/M foundation problems and writing the ACI 530 codes that the current codes are based on and the ASTM C90 standards for concrete masonry units.

Dick


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