6" CMU

[SteelPE]

I am working on a project where we have some interior not bearing masonry walls and an elevator shaft out of masonry. A GC was brought in to run the project and help the design team during the planning phase to help with budgeting the project. Somewhere behind my back a decision was made to switch these walls to 6" CMU. Now I'm not worried about the non load bearing walls but I am a little worried about the masonry shaft walls for the elevator. Are these blocks the same as the 8" blocks? Meaning:

I can get vertical reinforcing into them
We can obtain joint reinforcing (ladur reinforcing)
I can get bond beams into the walls
Keeping with masonry construction the dimension of the block would be 5 5/8" thick

In 17 years I have never been asked to use 6" CMU (maybe I am just sheltered here).

The issue is that all of the architectural drawings were switched to 6" CMU and the interior of the building is tight so a switch back is going to be meet the wrath of everyone above.

 

[concretemasonry]

You can do almost everything with a 6" CMU wall as an 8" CMU if you have a supplier with the necessary molds or ability to be creative.

You have been VERY sheltered.

In many foreign countries 6" CMU are very common and are the standard for structural or architectural purposes. - I have spent many trip to countries where the standard units are 6".

In South American countries (Brazil for one) the most common units for loadbearing engineered structures are 6" (150 mm). I saw one complex of 15 to 20 loadbearing partially reinforced masonry buildings that were 4 to 22 stories. The used units required by the builder/contractor/designer. The molds were supplied by a U.S. equipment supplier. When I talked to the engineer about the design, he said "We use your codes/standards (ACI 530) and used what we learned about partially reinforced masonry in California and other areas.

They used a general system based on 6" CMUs that had 2 webs that were 8" inches on center, so the webs and cores aligned completely. Since most of the buildings had many angles special units were made to be used for partially grouted construction. The strengths required from a f'm of 3000 psi to 4800 psi.

All of the joint reinforcement supplier offer 6" joint reinforcement.

Bond beam that allow use of vertical steel also are possible. The 5-5/8" unit thickness is possible.

Unfortunately, in the U.S., the use of masonry does lag behind a bit in some areas.

Dick








Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Shotzie]

You should contact a local supplier to see if they have specs for the blocks they manufacture. I know companies like Expocrete have information packages that outline each type of available block of varying thicknesses. It's important to find out what kind of molds the suppliers have (as Dick mentioned). I've seen 4" blocks that have cores of constant width and some that completely taper shut at the base of the core, not that you'd ever get steel reinforcement in a 4" block.

 

[concretemasonry]

Shotzie -

When I was involved with a block manufacturer, we actually made different 4" block. - Some had one horizontal surface that was "semi filled" and the others had totally open cores. The "semi-filled" were preferred for fireplaces and chimney construction, while the open cores were preferred for commercial construction where conduit or wiring was used.

We also made 4" bond beams that were used for lintels. We sold the block themselves and also had 4" lintels made in various lengths up to 6' long (spaghetti).

At any time we had over 1000 different sizes/shapes of CMUs in stock and sold them to our competitors and other masonry suppliers.

Just ask questions and you can find what you need.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Shotzie]

Very interesting! Sounds like there's even more you can do with masonry than I thought.

 

[JAE]

I can get vertical reinforcing into them
We can obtain joint reinforcing (ladur reinforcing)
I can get bond beams into the walls
Keeping with masonry construction the dimension of the block would be 5 5/8" thick


Yes, yes, yes and yes.



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[XR250]

I use them all the time here in central NC. Rebar is no problem. They usually make their own bond beams. Can also easily get precast lintels.

 

[hokie66]

I have used 6" (or 140mm) blocks many times. Just a couple of cautions, they don't work as well at corners and intersections as 190 blocks, and they are more difficult to fully grout.

What's the deal with "ladur" reinforcing? I presume you mean ladder, but does it really do any good? Horizontal bars, centrally located, are the go where I work.

 

[SteelPE]

What's the deal with ladur reinforcing? That's how Dur-O-Wall used to spell it, hence that is how we show it on our details.

 

[hokie66]

OK, but does anyone think it actually does anything beneficial?

 

[OldBldgGuy]

Does it do anything? Absolutely. Knock down a few walls with & without durowall & you'll soon see what the difference is.

 

[hokie66]

OK, I can see it might make demolition more tedious, but in place, I see no benefit. If reinforcement is required, do it properly.

 

[Ingenuity]

hokie: may be analogous to the 'chicken-wire' WWR/mesh that the US use in SOG, compared to what Australia uses with deformed F82 fabric mesh and the like, etc.

 

[hokie66]

Yes, I think so.

 

[concretemasonry]

Hokie -

I think the problems you may have encountered with 150 mm thick block for corners may have been for a particular supplier. In most markets (domestically and many internationally) corner units are available. In most U.S. markets, 90 degree corner units are available for 4", 6", 10" and 12" thick walls. Also, fractional length units may be available for 90 degree corners depending on the wall panel lengths.

When I was involved as a CMU supplier, we made 3/4 length 6" corner units for 45degree corners that were burnished (ground architectural face). About 10 years later, while giving design classes to engineers/contractors in Brazil/Brasil, I saw the same units with plain faces used on a development of 20 loadbearing masonry buildings up to 20 stories. These buildings were generally partially reinforced interior and exterior walls and they also had no problems with grouting. They used a 150 mm thick units with 2 webs at 200 mm on center and open ends for easy grouting - Obviously having the developer/builder/engineer/contractor combined, there were many efficiencies. The CMUs required 3 different strength levels and had the units tested and color coded or identified before delivery to the construction site. They also solved the inspection problem and eliminated clean-outs by getting random video inspections before grouting of the walls approved.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

Dick,

You have mentioned those 20 storey Brazilian buildings many times before, with 150 loadbearing masonry. Makes me tend to avoid Brazil. I know a lot about Brazilian construction companies, and it is often a case of what they can get away with.

 

[concretemasonry]

Hokie -

You are right about some contractors getting away with some poor practices and it does happen everywhere. Apparently, the ones I encountered had a large vested interest since they also were the owners of the many structures. They were from Sao Paulo and Florianoplis (not B.A.) and they also visited the U.S. several times to understand the processes used in seismic areas.

I did question their extreme concerns about the seismic to go into the details and methods taken for the severe seismic west coast of the U.S. It was refreshing to see engineers and contractors interested in learning and not just copying.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[KootK]

I've also been sheltered it seems as I've never been asked to do anything serious with block less than 8" nominal. It sounds as though the use of narrower CMU, and CMU in general, may vary with latitude, at least in the Americas. And CMU field QC in my market seems to be bad enough with 8" block that I certainly share the concerns initially expressed. Availability of the products is one thing; availability of personnel who can work with the products effectively is another.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Retrograde]

Workmanship issues aside, I would be concerned that a 6" wall would not have the structural capacity to carry the axial load from a 20 storey building.

 

[SteelPE]

My problem isn't a 20 story building, my problem is a elevator shaft and non load bearing partitions. The elevator shaft only goes up one story. My next issue is to figure out what lintel sizes to use as my standard 3.5 " leg steel angles won't be big enough. Maybe use 5" angles