1940s Brick Masonry 1

[David Deck Guy]

I am installing a roof deck on a Chicago building built in 1942. I have about 13.3 kips of allowable load that I need to dump on a brick wall. I'm trying to ascertain the lower bound f'm of the material. 11.2.3.10 Default Properties of ASCE 41-17 says that if I can scrape the mortar away with a metal utensil, I need to consider it to be lime mortal and will have to use a compressive strength of 285 psi. Yikes. When I go back to the site to confirm thickness of wall and scrape at mortar, even if it doesn't easily scrape away, I'll still be hesitant to use anything higher because I assume that the walls have been tuckpointed in the last 80 years. Does anyone have any tips on how to eek out a few hundred more psi from this brick? Right now I'm looking at a 24" x 8" bearing plate for my pocketed beam, and that assumes the wall is 12" thick which is not guaranteed.


Also, if I have to use f'm=285psi, I assume this means I'd have to scale my capacity for post installed dewalt or hilti anchors, which means I probably should give those companies a call tomorrow.


Finally, in searching the forums for past posts on this topic, I came across references to the book "Structural Analysis of Historic Buildings: Restoration, Preservation, and Adaptive Reuse Applications for Architects and Engineers." Is there anyone that has this book and recommends it?

https://www.amazon.com/gp/product/0471315451/ref=ewc_pr_img_1?smid=ATVPDKIKX0DER&psc=1

 

[phamENG]

Honestly, I try to keep stresses in historic masonry down closer to 100psi. But the brickwork here in Virginia can be older by a couple hundred years. So 285 might be okay. 1942 is unlikely to be lime exclusively...you may have a blend. But short of having testing done on a prism you're best bet is to assume a conservative value.

I have heard of that book and have heard good things, but don't have it and can't speak to it from experience.

 

[David Deck Guy]

Thank you. I'm currently the only SE at a design build firm, and this will at least give me more confidence in holding my ground when I tell the construction guys they need to go with a monster plate.

Bearing Stress equation and knowledge factor puts me at 70.5 psi, which is more in line with the values you recommended.

 

[kipfoot]

I like to detail this with a cast in place padstone (which is a UK term that I haven't heard used in the US). This way, you distribute your load over a wider surface area on the brick, but have a material with properties you specify directly under your bearing plate. It also gives the contractor some flexibility with the depth of the concrete bearing block: the bottom can be placed in conjunction with the brick coursing and the top can be struck with precision to a beam bearing elevation that may not match coursing.

13 kips isn't too much; did you type the right bearing plate size?

 

[dik]

Really unlikely... since about the 30s (maybe the 10s, depending on the area), lime has been so pure that it lacks pozzolans... it has to be blended. There used to be a clay brick design manual (about 2-1/2" thick) about 50 years back that had design info. I don't recall the title, but it was a common text; it had a 'greeny-gray' fabric cover. You may be able to find a copy.) I remember using it for a 14' high gravity stone retaining structure I did in Georgia about 50 years back.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[bones206]

Brick and Tile Engineering by Plummer is a good reference for this time period. Link:

https://archive.org/details/BrickAndTileEngineering

The compressive stresses listed range from 50 to 400 psi.