Design brick lattice wall

[jturley]

I've got a project where I have to design a brick lattice wall to match an existing wall for a Church addition. Its an exterior site wall with brick pilasters in between the lattice work. See the attached pic. How in the world do I run a number on the lattice work for out of plane forces. There's no steel that I can put in it because there is only enough room on the overlapping bricks for a small bead of mortar.

 

[XR250]

"Lattice by others" would be my choice. You are pretty much stuck constructing the lattice the same as the existing. My suspicion is it would pass if you check flexural tension on a vertical section.

 

[jturley]

Thanks! That's Exactly what I'm going to do. I'll just keep widening the vertical section until I get enough to make it work for the f_rupture of the mortar. I can do like a transformed section except I'll be condensing it instead of the typical expansion when transforming steel. Then just sigma=M/S and done!

 

[XR250]

Not sure if that is a beam (wind girt) on top but if not, you would have to either design one or treat the lattice as horizontally spanning which I would not know how to do off the top of my head.

 

[hokie66]

That type wall is dangerous, and no matter how much calculating you do, it won't work. There should be zero allowance for flexural tension in the bed joints. Children around churches are just as likely to be injured or killed by falling unreinforced brick walls as children anywhere else.

 

[XR250]

There should be zero allowance for flexural tension in the bed joints

Isn't that how most un-reinforced masonry is calculated? Why do you feel this is dangerous?

 

[hokie66]

XR250,
I think it is dangerous based on knowledge of several people who have been injured or killed by toppling masonry walls.

I think you are right that most of us don't allow flexural tension in bed joints, but the OP indicated that he would try that route.

 

[XR250]

I think it is dangerous based on knowledge of several people who have been injured or killed by toppling masonry walls.

I feel it is safe as long as the columns and beams are reinforced. Not much load on the lattice and it is a pretty small area.

 

[hokie66]

My interpretation of the OP's posts was that he did not intend to use reinforcement.

 

[XR250]

I think he was referring to the lattice section.

"There's no steel that I can put in it because there is only enough room on the overlapping bricks for a small bead of mortar."

 

[hokie66]

Yes, but look at his second post where he talks about widening the solid part, rupture of the mortar, M/S, done.

 

[XR250]

There's no steel that I can put in it because there is only enough room on the overlapping bricks for a small bead of mortar.

Ah yes, you are correct.

 

[hokie66]

You grabbed the wrong line for the quote. Tricky, that bit.

 

[dhengr]

Jturley:
The base wall height is about 2'-6" high, and each of the screen panels (lattice work) appear to be about 5' high and about 9' long. I would hope that the walls are not side by side, so I could change some dimensions a bit, but maintain the same overall affect and general detail and appearance. Most people won’t see the difference, if you don’t bring it to their attention. I would hope that the wall is at least 3 or 4 brick wythes thick ( the thru dim.). I would want to be able to reinforce the brick pilasters vertically, so I would like the two end brick pilasters to be a little wider (in the direction of the length of the wall). I would like to be able to get some rebar and conc./grout in the top/header/cap beam, so I would like it to be a bit deeper/higher than the existing cap beam appears, so it would take some lateral loads to the pilasters. The pilasters might be grouted and then post tensioned down to the conc. pier and footing, not just built with mild stl. rebar and grout. You want to introduce some compression into this wall system and cantilever it off a wide footing. You could also make a full height and length steel framework on conc. piers, and then just put a brick veneer around the pilasters and grout them full. Then build the brick lattice work and the cap beam as in-fill and a topping/cap beam. I would detail a copper, rubber or lead cap flashing right under the sloped cap bricks at the top of the wall to keep all water out. These are like the sill bricks at a wall opening, sloped full/flat bricks or sloped header/rowlock bricks, with very tightly tooled mortar joints, to shed water. Very careful detailing and dimensioning will really help to simplify the building of this wall and minimize the brick cutting and messin around.

I would build the brick screen panels with a 4"+/- wide stl. beam above and below the screen brick work, and extending 6 or 8" beyond the brick at the ends of the panels. I would camber the top beam so it finally distributes a fairly uniform compressive load to the brick lattice work when the two beams are drawn together. I would drill 2 holes in each end of these beams, one each side of the web, add heavy flat pl. washers, for vert. post tensioning bars, btwn. the top and bot. beams, so the panels are each a single unit.

It is somewhat unfair.... but, good old builders and mechanics, be they carpenters, masons, metal workers, etc. could do some wonderful, amazing things, and they stood for hundreds (thousands?) of years and certainly withstood the tests of time. But, according to the/our complicated, convoluted codes of today, we just can’t justify them. From experience, they knew it would work, but they sure couldn’t put numbers to it. We are more conservative in our loading requirements today, and we certainly live in a much more litigious society today. Once we as P.E’s. touch it, our liability and responsibility is much different than that of most others on the project. So, be careful with your design, and in that respect I completely agree with Hokie, I’ve seen a number of masonry walls fail over the years. I’d try to put this design responsibility off on the Landscape Arch., as XR250 suggested.