Reinforced brick masonry

[bookowski]

I am looking at a free standing garden wall, the wall ranges from about 8'-10' in height. The wall will be sitting on concrete curb which in turn is on a concrete slab so the wall will be easy to anchor.

The architect is showing a 3 wythe brick masonry wall. I am not familiar with reinforcing brick masonry. I've looked at the BIA technical notes and it seems to be fairly common. I've run some initial calcs per ACI 530 and the wall seems to be easily designable (under lateral loads).

I'm not familiar with doing this and I'm wondering if anyone has any tips or can point me to some reference material. What is the best way of reinforcing the wall
- should I use hollow brick for the center wythe thus giving me a 'd' of 1/2 x t of wall?
- Some people have mentioned leaving out vertical pockets in the center wythe for the reinforcing, is this a good method?
- Can the vert bars (#3) be placed in the mortar joints thus giving me a 'd' of 2/3rd t of wall? In this method I would have to have bars on both sides - staggered I guess.
- Anything that I should be checking/thinking about in advance?

thanks

 

[JAE]

Check out the Brick Institute website:

http://www.bia.org/

Click on the Technical Notes tab at the top and you will find a list of BIA pdf documents - some of which are on reinforced brick.

Usually, the center wythe of brick is left out and grout/rebar is used within this center section to create a reinforced brick wall system. Lateral ties are required as well.

 

[hokie66]

Agree with JAE. Don't put bars in mortar joints. When you say the wall is on a curb on a slab, make sure the overturning resistance is adequate.

 

[bookowski]

As I mentioned in my original post, I had already checked out the BIA material, it's not very comprehensive. Is there a reason that you say not to put bars in the mortar joints? I've found several details showing it this way.

Are there any design guides on this? I'm not completely comfortable with the concept that the outer wythes act compositely with the inner - how is shear transfered across the collar joint? With the grout and the tied?

I'm sure this is common, I just want to make sure I'm not missing something. I also have several parapets with the same condition.

 

[JAE]

With the grout and the tied?

Yes. This is a common way to do it.

 

[concretemasonry]

JAE had the best concept. Eliminate the center wythe of brick use appropriately spaced ties to help transfer the loads between the wythes since a proper grout.event the extra heavy joint reinforcement can be sufficient when used with a grouted cell, but there are also some standard hardware items to serve the same purpose. Bars in a mortar joint will totally change the appearance of a brick wall and do little good unless there are pilasters and you design the wall as using some component of spanning between pilasters/columns.

For an 8'to 10' high free-standing wall, the problem is anchorage to an adequate foundation and flexural resistance.

Apparently, it is necessary to have brick on both sides of the wall. If not, an CMU would be more structurally efficient, since the vertical steel can be placed closer to the face of a 12" thick bonded wall(8" + 4").

I assume there are no vertical columns of pilasters.

There are many feet of privacy wall that have become sidewalks because of lack of a proper connection to the foundation or inadequate wall flexural strength.

Dick

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

 

[bookowski]

Thanks concretemasonry. There are no columns/pilasters and there does need to be brick on both faces with a max total thickness of 12", otherwise I would definitely be going with CMU.

I'm not worried about the base, I have a 10" structural slab on a 12" foundation wall, there's plenty of structure there to deal with the overturning. I'm just not too comfortable working with brick.

So you are saying to leave out the inner wythe completely, reinforce this region vertically, and tie the entire wall every so many x courses correct? In this configuration is it permissible to use standard design procedures per aci 530?

How about the hollow brick that has holes for reinforcing/grout? Is this useful/helpful?

Thanks

 

[JAE]

I don't believe that the holes in brick are for reinforcement or grout. They are there to facilitate fabrication and to provide a sort of moderate mortar key to help the mortar lock the individual bricks together.

 

[concretemasonry]

since the wall surfaces, based on appearances, seem to dictate the available brick choices reinforcing of the common cored brick and grouting those units is eliminated and grouting the space between the wythes is a way to resist the lateral loads and provide flexural strength with a low "d" distance.

There are some 6" wide brick with cores (for a 12" wall) that may be grouted to provide a wider reinforced section, but the exterior appearance choices are limited.

How long is the wall between any corners are stiffening? 6' high privacy walls are common, but the extra 2' to 4' make a big difference when it comes to lateral loads.

Dick

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

 

[bookowski]

Thanks Dick.

It's about 18' to 20' between return walls for stiffening. It's a rear yard in manhattan so realistically it will not see much wind load. I am still using the full wind load, I'm just saying that there is a bit of cushion there to sleep at night.

Are there any rules about how often to provide ties? When I draw this it feels like the outer wythe and that center reinforced potion want to separate and not act compositely. Is there a check or rule for how often the wall should be tied?

 

[concretemasonry]

If the center wythe is not used and is grouted properly after the wythes are laid, the two wythes plus the grout are normally acceptable for most codes especially with extra heavy joint reinforcement at 16" or 24" on center to bond and make the wall act as a structural element instead of separate wythes.


I have seen 15 to 30 story loadbearing buildings built with bonded, grouted 6" clay tile.

Dick

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

 

[hokie66]

I would put the cross ties in about every 4th brick course. There is ample roughness between the back of the brick and the grout to develop the shear along that plane. The ties help in that regard, but their most important function is to brace the wythes until the grout hardens. You don't want the wall to collapse during construction.