2 Story 6" Masonry Bearing Wall 2

[JNEnginr]

Hey Everyone...just picking everyone's brains again...

I'm looking to construct a 2 story masonry bearing wall...Not 2 story unbraced, there is a floor diaphragm that will brace the wall at approximately the mid height.

R606.2.1 states that the minimum wall thickness for a dwelling greater than one story must be 8" min. If i grout the wall solid, reinforce, account for gravity and lateral forces, and i can get the wall to work through my design, is there any other reason that this would be frowned upon?

Thanks,

 

[jayrod12]

What about doing the first floor walls as 8" then the second floor walls as 6". It would give you a 2" bearing seat around the whole perimeter for your second floor framing.

 

[JNEnginr]

I personally would like to do the whole thing out of 8", but the architect is...well being an architect...

So is it still not allowed? Anyone know why?

 

[JAE]

It is not allowed in the IRC because the IRC is an empirical design code. If you as an engineer perform all the applicable engineering checks on it and design it thoroughly, R606.2.1 no longer applies as it is an engineered system.

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[concretemasonry]

The vertical load is not beyond a 6" CMU with the lateral support at the midpoint. In the U.S., a 6" wall somehow is mistakenly omitted from the architects vocabulary as a structural component, especially id he only speaks traditional "IRCism" when it comes to use and does not know how to handle something when it comes to engineering solutions.

Unfortunately in the U.S., the sacred 4" module of masonry is habitual because it is easy and the 8" is convenient.

8" and larger are good for taller walls. In some U.S. areas, the 8" or 12" is habitual, and many areas offer 10", 12", 14" and 16" for designers that also wear suspenders in addition to belts.

In some countries, 6" block is a standard wall thickness for loadbearing multi-story apartments up to 20+ stories. This has been done for about 40+ years using ACI 530 or the standard ACI 530 is based on. - Just takes some good engineering, details and familiarity with masonry design. The buildings are typically partially reinforced with different strength masonry units that changes every 4 or 5 stories with the upper floors only containing nominal reinforcement.

Dick

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

 

[Archie264]

>>>In some countries, 6" block is a standard wall thickness for loadbearing multi-story apartments up to 20+ stories. This has been done for about 40+ years using ACI 530 or the standard ACI 530 is based on. - Just takes some good engineering, details and familiarity with masonry design. The buildings are typically partially reinforced with different strength masonry units that changes every 4 or 5 stories with the upper floors only containing nominal reinforcement.<<<

Surely I must be misinterpreting what you wrote. You don't mean 6" block is the primary load-bearding component for such a structure, right? Do you mean that the 6" block transfers the load to other structural elements, i.e., slab-to-wall-to-beam, or something like that?

 

[XR250]

"In some countries, 6" block is a standard wall thickness for loadbearing multi-story apartments up to 20+ stories. This has been done for about 40+ years using ACI 530 or the standard ACI 530 is based on. - Just takes some good engineering, details and familiarity with masonry design. The buildings are typically partially reinforced with different strength masonry units that changes every 4 or 5 stories with the upper floors only containing nominal reinforcement"

Are these the buildings that we see on the news in a collapsed state?
6" CMU supporting 20 stories - really?

 

[concretemasonry]

The buildings were 6" load bearing masonry structures of varying heights that had a first floor (ground) level of concrete columns with some block in-fill(non bearing) to allow open areas and wide doors. Generally, the concrete was poured about 24" above floor level to act as a deep beam to carry the remainder of the structure. The second floor was fully grouted/reinforced 6" CMU construction and the above levels were partially reinforced/grouted 6" with different required masonry strengths(f'm - hollow prism), depending on the level. Block were special shapes(2 webs at 8" on center) to permit partial reinforcement. Special bond beams to allow partial grouting and allow the 4" to 8" thick interior slabs to be poured once a every 4 to 8 days.

Block were color coded for strength and sampled at the plant prior to delivery. Since the block control the f'm of the walls. The mortar was mixed on site for timing purposes and spot checked and grout was a uniform strength made at a batch plant on site. Generally, clean-out were eliminated and core spaces were randomly checked visually or by remote video cameras. Unacceptable cleanliness created more frequent inspections or even the use of actual clean-outs that were a major construction cost and time.

The important thing is that the developer/builder/contractors were dealing with units that were purchased by the public and could not afford a failure/bad name since on bad building could ruin a very large company.

There have been attempts to crudely copy the system is some other areas. The engineers that designed the various large projects in different countries I saw spent a lot of time in the U.S. and followed Jim Amhrein's history in SoCal in the 1970's and had design seminars held in Brazil before Jim's concepts showed up in ACI 530. The system was a streamlined version of the reinforce mufti-story SoCal hotels/motels.

Dick

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

 

[JAE]

Good lord - the OP asked a direct question about a 2 story CMU building related to code acceptability - referencing the IRC - and we get a history lesson on 20 story buildings in some "different" countries.




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[concretemasonry]

Sometimes an engineer needs a little background to get a better understanding of the outside world.

Dick

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

 

[JAE]

Well they weren't asking whether 6" masonry could go 20 stories.
They were asking whether the IRC provision would apply if they engineered it themselves.
It was a code applicability question.
It had NOTHING to do with 6" block wall capacity. Go back and read the post.

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[hokie66]

concretemasonry,
Let me add my objection to your continually telling this story, for several years now. Whatever they do in Brazil, it is not going to convince most of us here that it is good practice.

Now who gave him the star? Ridiculous.

 

[CELinOttawa]

I don't know guys (and the occasional gal, SLTA)... Seems pretty reasonable to talk about non-US types of construction on the Internet. I also think that if a code is called the "International Residential Code" non-US construction becomes fair game when discussing the application of said code.

 

[JLNJ]

You certainly can engineer the 6" block to work for many low-rise applications, but the architect needs to know that your fee will be very different is the design goes from simple and empirical to irregular and engineered. Maybe the fee doubles, or more.

The locations which give me fits in the design (and are exacerbated with 6" block) are bearing stress at the edges of openings and bending stresses in taller walls due to wind. The flexure gets to be hard to make work where you have small piers between large windows or overhead doors or significant width. If you get in a pinch with 8" block you can offset the bars to squeeze a little more flexural strength without increasing the wall depth, but a 6" unit is pretty narrow for bars anywhere but in the center of the wall.

I think the new masonry code is a little more generous with the allowable flexural capacity of a given reinforced section, but I have not used it yet.