Tallest CMU walls

For open, large/wide projects, cables on both sides of the wall offer a lot of flexibilty when you are working and just make sure the walls are plumb and the cables have equal tension when you are not around anfd the wind comes up. Make sure you have a transit available to insure plumbness of the walls.

Pallets of block are great temporary anchors for the cables and they can be moved easily if it is a long or wide building.

Make sure you have high quality block and use grout that is not too strong for the specs. The block are probably cured enough before you get to lay them. The grout just bonds the rebar to the loadbearing portion of the wall. Block with one central core and "ears" (equal to half the central core) work best for grouting and rebar placement.

If it is a very large project, look into getting permission/waiver to using a video camera to inspect randomly selected grout cavities and avoid the problems and costs with clean-outs and and do high lift grouting with fewer splices. I have seen this many times on 20 story 6" block load bearing apartments (10 to 20 buildings each site) with no real onsite inspection problems since the block (4 different strngths and color coded) were certified before delivery and the inspectors/engineers recognized the the firm could build good masonry. All mortar wa the same strength since mortar strength is really not important, and usuallt the grout was the same since ther were limits on the maximum strength of the grout to make it compatible with the other materials and the building.

For high walls, planning and pre-approvals is very important even if you are called a "flatlander" in MI.

Is it infill or structural? What size block and what is the grout schedule? Are there serious production limitations/scheduling issues?

Is this building completely open on the inside?

For your bracing needs I would check out a system called Hog Legs. We use this system for free standing walls like in warehouse construction. I do not remember off hand what the wall height limitations are on the sets we have are but I know they do make extension kits for taller walls. One nice thing about this set up is that it all pre engineered. Look up the wall height on the provided chart and it will give to anchor location and angle of brace in relation to the wall.

For anchoring the legs at the ground, drilling a hole in the concrete floor and epoxying a piece of all thread in is the easiest way. If the floor is not in place yet we use concrete blocks like the supply yards use to make sand/stone bins, similar to jersey barriers. Place a piece of all thread into the concrete block the same way you would in the floor.

http://www.ezgrout.com/pages_products/wallbracing_systems/products_wallbracingsystems.php

If you are using a mechanical scaffold the manufacturer should have tie in devices. If there is no place to attach the manufacturer tie ins you could tie #9 wire around a rebar in the wall and let it hang out of the wall. Rake most of the bed joint around the wire out so you can cut the wire out deep enough and point in after you are done. Or your supplier of wire should have metal tabs you can lay right in the wall to tie to. The tabs will break off by bending back and forth when you are done and you can point in then.

NJ Brickie
I am familar with the hog leg system, but never on walls near this height. A "pipe" brace for a wall of this height would need to be about 83' long. Even getting a brace of that length to the top of the wall would be a pain.

Yes we will be using mechanical scaffold and yes the do have brackets to tye them to the wall. That is not the problem. The problem is having the wall strong enough to support the scaffold if it needed to.


CJKarl
Yes it is completely open inside until 70'. Eventually there will be some stage rigging in there, but it will attach at that height as well.


Tscarborough
It is structural. The specs on the grout are pretty standard for this area; 4,000 psi (a little higher than normal), no calcium, 8 - 10 inch slump, poured in 4' lifts ect... The block are 12" l.w. that have some 2' x 16" pilasters on the inside built out of 8" l.w. approximately every 25 linear feet. The are tied to the 12s with 2 "Z" anchors that are .250" x 1.50" every other course. In the center of these pilaster ( not inside the block) are 4 pieces of #7. These also get filled with concrete, 3,000 psi with 1.5" rock I think (I'm not 100% certain on those specs off the top of my head).
The production/scheduling limitation are soley based on us. As with the plan we have right now, we will be able to build the wall to 40' and stop until the grout has reach 80% of 4,000 lbs. My guess is that will be somewhere between 16 - 22 days. Then we will be able to use the wall to adequately support the load it could incure from the scaffold bracing.
With that said we can build half the wall and let it sit for 3 weeks, then finish it. It is deffinately good for production.


concretemasonry
We are required (by our engineer) to have the cables anchored to something weighing 6,500lbs.

Explain to me your high quality block. Without having something special produced and shipped in, my options on block are lmited. I don't know if I have ever seen a block like you are describing with one central core and ears. Is that a specialty item or possibly a regional thing. All of my work has been in the southeast area and haven't run across that one.
Also why do you say not to use a stronger grout than spec'd?

High lift grouting would help somewhat. If we could over come the biggest problemof having to build the wall in 2 pieces we might try to get that approved.

It will hit 80% within 3 or 4 days or it never will. Hog legs are a great system, but not designed for 70' walls. I don't have an answer for you other than to say that I can not really imagine any system for a free standing 70' wall that would work without extraneous structural support or a whole lot of luck.

edit- anything over 2000psi grout is pissing in the wind, and, in addition, is giving up flexural strength for (unneeded) compressive strength.

In my exp., and it is not vast, I noticed a 50% strength in 3-5 days and about 75 % in 2 weeks. Maybe I am mixing my grout up wrong.

I wish we could get some of the people over here to recognize that 3,000 plus is over kill. The only job I have ever done that spec'd less was in OK. and it was at 2,500. Our standard is 3,000 sometimes 3,500 and once in a blue moon 4k.

Ward -

You are in Michigan and I lived there for 7 years and know much of the typical production and plants.

In your area, you would need a special order for high performance block. If a local producer does not have the molds, they can be rented from other producers anywhere in the country since shipping costs are not high in comparison to making a single run or two. I had a salesman come in with and order for 40,000 colored split units and the plant superintendent asked what he should make the next day - it is a volume business. These "special shaped" block are made in other areas. The trick is the gradation of the aggregate in the block and the curing of the block, so not everyone has the experience or background.

The purpose of the grout is to transfer the tensile loads in the rebar into the block, so it is not necessary to have strong grout since the laps lengths are no changed. A good engineer will place a maximum strength on the grout.

I had hollow 8" block prisms (face shell bedding) made using 8750 psi net area block and 2500 psi mortar that tested 4750 psi (f'm) and the ones with 1900 psi mortar were almost as high (4500 psi), so it is obvious that the block strength is the major factor. This was after they fixed the testing machine that failed for the first tests. the block shape is just a matter of what is efficient and works for the layout. - It was fun seeing the technicians hiding behind the tipped over steel top lab tables with protection and pressing the start button with a stick.

It is unfortunate that U.S. engineers are in the "Dark Ages" when it comes to design and practical/application of engineered masonry construction. Just a typical old "belt and suspenders" concept without knowing what is possible.

Thanks for the insight. I feel lucky, with the supplier/producers we have here, if I get square block. I'm not sure I'd feel confident in their ability to produce anything that required more attention than a monkey can give.

MS is Mississippi. I live in a burb of Memphis TN.

Sorry about the MS & MI mix-up.

There is one in MI with a slightly different spelling (South Haven) that pronounces the same to the ear.

Glad I could be of a little help.

We are required (by our engineer) to have the cables anchored to something weighing 6,500lbs.

You can possibly use Helical Anchors for your dead men based on your soil conditions and then when you’re done just unscrew and move

WARD said:

Out of curiosity, what are the tallest freestanding cmu walls you have seen or built?
We (our company) has a couple jobs in the works right now with some rather tall walls. One specifically has been a nightmare to plan on building. From the footing to the joist bearring is 70' with nothing in between. This is the tallest freestanding wall we have ever built and has thrown us some challenges we are not used to. Bracing is the first. We sent it to our engineers for bracing design. They came up with a series of pipe braces at two different heights attached to large deadmen and then some cable bracing attached to embeded plates even higher.
Scaffolding is another issue. We are using our mechanical scaffold, but bracing those on a green wall is very difficult. They will freestand up to 40' with no bracing, but above that it is every 20'. Which causes you to wait for accurate curing of the grout/wall. Conventional scaffold wouldn't require the same amount bracing for he scaffold, but keeping stocked becomes an extermely labor intensive project.

Any ideas we are over looking???

Click to expand...

Have you tried using a crane to get your block up that high, or would it not be cost effective?

Do it in concrete cheaper and faster

But not better.

Nac, what kind of Helical Anchors are you talking about? The soil doesn't look very good, clay and LARGE rock, but I am no dirt expert.

A crane is not very cost effective for us. The hoist on our mech. scaffold are free. A crane to get 2,000lbs 70 feet up and any distance from the center pin wouldn't be cheap. That was an idea we kicked around though.

You are trying to build a high CMU wall without a high lift on site?

How do you plant to get the block up above the 30' level or so?

You always need a lift on-site for a higher wall. If you do not have the equipment, you should not be bidding or planning. You can always rent a good lift or get one on trial from a good dealer. The labor cost for the lift is about the same.

We all know the height of the wall, but how many hundred feet is the total wall length?

All you really need is a double height stack of pallets of the right type (high percentage block) or 3 pallets high (10-12' lift) for the 6500# weight even if you use the wrong type of block then move the block and anchors.

The cable ideal is good and flexible to allow anchoring on the wall at different heights during construction. if you choose the anchor for used during/overnight the and possibly the scaffold support. High strength grout is really meaningless and the key is the temperature of the wall and the temperature of the grout. Forget about the meaningless spec idea of 28 days since that is for laboratory controls and does not really recognize real construction.

Like all construction, the faster you can build with proper materials, the more profit.

No we have multiple lifts on site just not a crane. But there isn't a lift available, that I know of (in the U.S.), that can lift a pallet of block to that high. There are a couple 1268s five, I think, but even with 68 foot of stick they are till to short. We have a 1055, but its obviously way to short. A crane is what I said we didn't have and is not cost effective for us to rent. We have hydrolically opperated hoist on our scaffold to lift material.
The wall are 75' long on two sides and 150' on the other two.

Are there any chemical accellerators o increase the amount of time it takes for the grout to cure totally? I know som affect the intial curing rate, but I don' know of any that affect it over the long term. Will heating the wall have a drastic affect on the curing rate? Any place on the web to back up a yes answer?

We will be using cable bracing.

Nac, what kind of Helical Anchors are you talking about? The soil doesn't look very good, clay and LARGE rock, but I am no dirt expert.

Here is a link to http://www.meadowburke.com/documents/tiltup/7%20MBT%20Bracing.pdf this is a whole tilt up manual for bracing. Also you can look into AB Chance for helical anchors.

You can also grout as you go with a specmix grout silo and mixer or can pump a grout with a small tagalong pump with an super p and 2% non cloride add mixture

Here is a lift that might work http://www.us.manitou.com/publicservlet/DownloadMedia/media-53516.pdf