Double Wythe Brick Wall

[jonathanwilkins]

I've got a customer who wants to build the bottom of his garage out of a cavity wall (2 bricks). Gives a "look" he's trying to achieve. Brick on the outside and the same brick on the inside. The wall will sit directly on a footing, be approximately 48" tall and support the floor above and the roof. The detail he provided me (one he drew) showed a 2x8 sill plate on top of both wythes.

I'm trying to find references on how to design this wall. I've read through the brick industry's tech papers and read some of ACI 530 but I'm having trouble figuring out the correct way to design it.

Thanks for any references. JEW

 

[concretemasonry]

It all depends on the connection between the two masonry wythes to determine if they function together or separately (shear and connections) and can resist horizontal loads.

A properly bonded wall can be extremely valuable, strong and stable, but if it acts like two individual 4" wythes the properties are very different.

A 2x8 does not always give a uniform load distribution, especially if the upper portion of the wall is not symetrical (physically and load-wise) with the lower portion.

Dick

 

[dik]

Thermal transfer? also use a hard fired brick if subject to de-icing salts and freeze-thaw...

Dik

 

[jonathanwilkins]

Thanks for all the responses. My main question is do I consider both wythes? I think this is the best way to go. Most of the load, though, will be on the exterior wythe. I've attached a very basic sketch of what a section will look like. Bricks will be tied together @ 8" or 16" o.c. vertically, whichever is required. Hemis...that reference is helpful, thanks. Are there any references using US standards?

 

[dougantholz]

Use truss horizontal reinforcement of No 9 wire and treat as a cantilevered wall for design for out of plane loads. Add rebar in the cavity if you have cross sectional tension.

 

[dik]

You might want to parge the brick surface below grade, and use mortar to provide a bit of a slope to the top of the footing adjacent to the brick (aka wash).

Dik

 

[concretemasonry]

The wall should be built with a solid collar joint (between the wythes) as the courses were laid at the same time. If you do not bond the wythes properly all the load will go to the single exterior wythe.

You will be hard pressed to really count on normal joint reinforcement (even extra heavy)to provide real structural bonding of the wythes without a solid collar joint. That concept could work if you could find something in ACI 530 and the cheat a bit to get a reasonable area/width for rebar and grouting. It appears you have load bearing wall and cannot take chances iif that is the case.

Your sketch looks a little out of scale since a tradition double wythe brick wall is made up of 2 - 3-5/8" wythes with a 3/8" joint giving a 7 5/8" overall thickness and is about the width of a 2x8 laid flat.

There are some "cheater" face brick that are actually 3" thick that could be fudged enough to get more space for rebar/grout, but they are not available in all colors and textures if there is an attempt to match a selected brick appearance.

Dick

 

[hokie66]

This wall should be reinforced. You can place vertical bars in the collar joint to make the wall act as a cantilever. Otherwise, the reaction of the bottom of the timber framed wall is only resisted by flexural tension in the mortar joints.

 

[jonathanwilkins]

I was thinking that the collar joint should be solid. Trying, though, to see if it could be done without. The drawing I attached to my previous thread just looks unstable to me. I also agree that the way the drawing currently is, all load is carried by the outside wythe. Thanks for all the input!! JEW

 

[JAE]

I agree with hokie66.

This partial masonry wall will have to support all the lateral wind loads.

The thing to do is provide a minimal space between the wythes to allow proper placement of vertical rebar, doweled into the footing and extended up the center of the wall. The whole space between the wythes should be filled with grout. Anchor bolts can then be set in the grout for the 2x wood plate (treated of course)...so the bolts should be galvanized properly for resistance to the wood treatment.

 

[jonathanwilkins]

Question about gap between the wythes. Read here 3/8" also read minimum joint. No need for any cover around the rebar? I'm figuring #3 @ __ o.c. Pretty easy calc, just want to make sure it's designed right & practical to build.

 

[hokie66]

I don't know why you would restrict the width of the cavity you are going to fill. Make it 1.5 or 2 inches wide, enough to grout. Make sure you have enough ties built in so the grout doesn't spread the wythes apart.