Masonry Design Question

[Squirl]

Ok.  I'm a big fan of the building code.  I have been looking into designs that can use onsite building materials for construction.
The code has a section for rubble stone masonry.  It has allowable and required height, length, thickness, mortar, and almost all design specifications to pass code and are "not required to bear the seal of the architect or engineer responsible for design."

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_sec006.htm?bu2=undefined

The one thing I can't find is openings for doors and windows.  Concrete and wood walls have rebar and headers.  They are well documented and explained.  Does anyone know about them for masonry?

[Don_P]

R606.10, design required (engineered)
The contractor desk can help with lintels. Beyond that and it's an engineer if required for steel or an arch. I've seen tables of angle sizes for brick, maybe check the brick association?.

with adequate support on each side against lateral displacement and enough height above an opening the masonry over the opening forms an arch. If it collapsed from being level over the opening it would only collapse to form an arch, that volume is what your lintel or beam is supporting, the arch is a compression structure over and around the opening.

[Squirl]

Thanks for the response.  I am still getting up to speed on the terminology.

It would seem kind of silly to put in section R606.1.1 Professional registration not required, as long as there are no windows or doors.

It does say,  "When the empirical design provisions of Chapter 5 of TMS 402/ACI 530/ASCE 5, the provisions of TMS 403, or the provisions of this section are used to design masonry."  Hopefully they will shed more light on what to do about openings.

This is what I found so far. 

I could corbel an arch under R606.3 Corbeled masonry.



It is a little cumbersome, but I could fill the space wood.

You are right. If the masonry is made in running bond it forms a corbelled arch above the opening and the lintel only carries the load under the arch up to the Apex.



If the masonry is not in running bond (1/4 overlap between courses) then the weight above the opening must be supported for the full span.  Area of b x h1 in the picture.



So if I were designing random rubblestone masonry with no ashlar or mixed methods, I would probably want a lintel to support the full load to the top.  I would use a design criteria for the materials of 150 pounds per cubic foot (the IRC design guideline for concrete which is denser than masonry) for the wall alone even if there were no load from a roof or floor. 
They do make precast lintels that can take X pounds per linear foot.
http://www.fendtproducts.com/pdf/products/concrete_masonry_units/precast_concrete_masonry_lintels.pdf

That would hopefully satisfy if I ever had to run it by an inspector.

I will look more into the additional design sources accepted by the IRC.  Any more insight or comments would be greatly appreciated.

[Don_P]

The picture of the corbelled arch reminded me of something. A dome is simply an arch thats been spun around. Google tholos or the treasury of aratria and you'll see very ancient corbelled domes. They were built underground to use the weight of the soil to provide the counterweight and thrust restraint.

Depending on the depth of the arch, the parkway bridges here do have fitted stone arches and roughly coursed stonework behind that foot or so thick facing the underside of the bridge arch is reinforced poured concrete, then another stone facing on the other side of the bridge. Full stone can still be a veneer if there is structure behind it that bears or supports it.

Also google span tables for steel angles. I'm going too slow but there were some good hits.

[Davegmc]

Regarding openings in masonry structure:  Did you guys see the Nova episode on how the great cathedrals were built?  They showed how the tall thin open walls can support those massive roofs. Used a system of pointed Arch's and flying buttresses. Really interesting!

Dave

[Squirl]

R606.10 Lintels.
Masonry over openings shall be supported by steel lintels, reinforced concrete or masonry lintels or masonry arches, designed to support load imposed.

I have skimmed a few books on masonry. 

Steel lintels

I found one chart of angle iron requirements for brick veneer masonry.  I'm not expecting to find much on this, because of the load I am looking for.

Reinforced concrete or masonry lintels

I have found prefab ones to support the load I may need.

Masonry arches

I found that there are major and minor arches. 
Major Arches are arches that support spans greater than 6 ft or more than 1000 pounds per linear foot and must have a rise/slope ratio greater than .15.  Minor arches are the arches that aren't major.  I am looking to probably use a major arch.  Most books and definitions say that a semicircle arch is the strongest and used for major arches.  I would love to find a authoritative reference that I could point to for this design and load capability. 

[Squirl]

Some maybe curious what this excercise is for.  I am looking build a stone foundation with lookout on top and I would need a door in.  Something like this.



or this



or this



or this

[Squirl]

In much, much further research I was able to find many PEs and building inspectors accept the tables of R703.7.3.1 for R606.10.

TABLE R703.7.3.1 ALLOWABLE SPANS FOR LINTELS SUPPORTING MASONRY VENEER^a,b,c,d
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_7_par050.htm?bu2=undefined
a. Long leg of the angle shall be placed in a vertical position.
b. Depth of reinforced lintels shall not be less than 8 inches and all cells of hollow masonry lintels shall be grouted solid. Reinforcing bars shall extend not less than 8 inches into the support.
c. Steel members indicated are adequate typical examples; other steel members meeting structural design requirements may be used.
d. Either steel angle or reinforced lintel shall span opening.

As long as the weight supported does not exceed code specifications it can be used.  So they can treat each wythe as a separate supported amount and increase the amount of steel accordingly.  As an example, a normal brick veneer is 4" wide, if you have 3 wythes of brick they would accept 3 wythes of lintels.  Same weight and size, just thicker.  Some comment sections in masonry designs also point to this table for steel lintel sizing.  No engineering required.

So there is an empirical safe code specified chart for masonry lintels and steel.

I would love to read a technical reference for the Arches though.  I know they are the strongest and I would much prefer them.


Comments?

[Squirl]

I would assume that this table should probably be used where there is no load bearing since, I don't believe, masonry veneers are load bearing.

For my own personal designs, I would corbel and arch and simply use these lintels to hold the masonry up to the apex of the corbelled arch.  Then they would only be bearing the weight of a small amount of the masonry and not any floor or roof loads.

[Squirl]

I also read a few places that some building inspectors will accept lintels made in accordance with concrete wall R611.8 Requirements for lintels and reinforcement around openings.

http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_6_par278.htm?bu2=undefined

[Don_P]

Those are cool buildings.

One thing I've gleaned is that the load path of an arch is a catenary, the shape formed by a hanging chain, think St Louis Arch. Effectively a catenary is a parabola. The chain can be shorter or longer and the arc formed will be a catenary... the tension force involved in forming a tight arc is telling you about the thrust when you flip that low arch over and load it, it'll shove out hard.

The roman semicircular arch works fine as long as you can inscribe a catenary within the masonry, usually you can. If the parabolic true load path falls outside of the masonry the arch is possibly unstable.

Look over lintels in old work, sometimes you'll see arches of some type. The train starion in Bristol had high and low arches and jack arches over various openings, they even stuck in a circular porthole high on one side with 4 keystones around the circular brickwork.

"simplified engineering for architects and builders, Parker/Ambrose" has a pretty good background in reinforced concrete design and construction. Very little on arches, it discusses beams and columns in some detail.

Edit;
This is how Gaudi modelled the Sagrada Familia Cathedral. Single point loaded spires and uniformly loaded wall supporting arches, cool pic.
http://1.bp.blogspot.com/-nEe_BMNS3Xo/UQBR6r4OZEI/AAAAAAAAKTQ/SKMgFNMm1ss/s1600/DSCN3990.JPG

[UK4X4]

Arches- how big would you like them ?

These are two viaducts close to my home in the UK- still used today for trains, the rear one i think is now redundant

http://www.flickr.com/photos/alwyn_ladell/7468853686/in/set-72157630350120796

[hpinson]

You might want to contact these folks and ask how they handled it:

http://www.prairiewindarch.com/award.html

I'm confused though - in all the pictures you posted, and in the ones I just did of the Judith Mountain cabin, the lintil is just a bridge of solid stone or timber, and there does not appear to be any special treatment above the lintel that is different than the rest of the wall. None of these appear to be arched?  Or am I missing something (no doubt).

Or are you wanting to build an arched entrance?

[Squirl]

I don't know about the other ones I posted, but I am familiar with the one you posted.

The few I posted are fire tower lookouts probably in areas and from times long before code enforcement.  They were probably built by masons who had a lifetime of experience in the limitations of their materials and the design capability to know how to distribute the weight.  For an amateur (myself and probably anyone reading this) I could not justify my design to a third party (building inspector) without some clear widely accepted and published definitions and charts. 

I also don't want to fall into the trap of  "I saw a picture on the internet so I copied it."  Even if I didn't have to justify my positions to a third party, I still would have to justify them to myself.

The first tower lintel has a pretty clear violation of code.  It is made of wood.  If the door rots out, no big deal.  If the wood lintel rots out, it can lead to catastrophic failure.  Big deal.
http://www.masonrydesignmagazine.com/index.php?option=com_content&view=article&id=276:minimizing-masonry-litigation&catid=28:columns-a-departments&Itemid=38

The others appear to be a solid stone lintel, but you never know.  They could have steel angle iron or rebar behind them or in the mortar.  The lintel could be of a harder stone.  They could also have a


The one that you had posted, was designed by a licensed architect, and IIRC, also an engineer.  It has been pretty extensively written about in the NY times and many cabin/small home books and sites.

Also most of them have very little stone work above the opening.  If I were to build a taller or load bearing stone wall, I would want to be sure it could bear the weight.  I do know that a semi-circle arch is the strongest and would hold the most weight.  With the help of posters, I think we fleshed out the basics of how to build some lintel openings in a masonry wall. Its not perfect.  Although I may be able to get away with designs from other parts of the building code, I am still trying to find citations for, and understanding of, all the ways to create an opening in masonry walls according to code guidelines.

I like the article I posted.  The summary is the first place to start, is by building to code, and if not to code, use an engineer.  If many contractors built to the basics of the building code, it would stop a lot of litigation before it begins.

[hpinson]

That was a facinating read. Too bad Scott Nearing is not still alive, and participating in this forum. He built a lot with stone, though I wonder if it was up to code standards - a lost art no doubt.  I was just reading about the Mad Arch Builder of Elm Tree, Texas, in John Graves' excellent "From a Limestone Ledge" book.

[UK4X4]

Being that we still build most of our houses in Brick

we have standard lintels for most designs- as the UK is predomently 2 story brick built houses

Ie if I hit the home depot for a standard door opening size- theres only 1 choice- not multiples

If I have a cavity wall, you run 2 one under each set of bricks

http://www.wickes.co.uk/bricks-blocks+lintels/concrete-lintels/icat/lintconcrete/

We also have steel ones which hide up into the cavity you could use a large stone in front of it or even below it knowing the steel was actually supporting the wall above and the large stone just for looks

These for example

http://www.lintels.co.uk/galv_cat/Galvanised_cat_24_25.pdf

All code certified- just the UK Code !

[Redoverfarm]

Not really sure if this is code compliant as the hoops I jump through are different here.  I used a concrete precast lintel in the cabin.  It was two pieces steel reenforced cast to simulate standard cement blocks.  Set on the wall blocks previously laid on either side of the doorway opening. 



The veener stone was later applied and is non-load bearing.

[Squirl]

UK, the prices are great too.

With a little guidance from that article I was able to find them.  Easy to read charts of load bearing capability of major arches.  They even have examples of how to read them. Yeah!!!

http://www.gobrick.com/Portals/25/docs/Technical%20Notes/TN31C.pdf

All you could ever wanted to know about brick and concrete masonry.
http://www.gobrick.com/TechnicalNotes/LinkstoTechnicalNotes/tabid/11294/Default.aspx
http://www.ncma.org/etek/pages/TEKList.aspx