1940's Unreinforced Masonry Building
1940's Unreinforced Masonry Building
(OP)
Just talked to a client who wants me to determine the feasibility (he really wants to save the structure) of bringing up to code this structure to support two additional stories of apartments in the future. The structure is currently 2500 square foot, 8" unreinforced masonry with a wood roof. Adding footings is no prob.
Obvious problem is future code changes, but I can deal with that. What my son has suggested though is using the existing 8" CMU as a veneer architecturally with the proper lateral anchorage, and building an interior bearing/shear resisting system inside the exterior CMU wall shell. This sounds more cost effective than reinforcing the wall vertically, grouting, and coating with an FRP finish.
Anyone have any experience with the two options cost-wise that they can share?
Obvious problem is future code changes, but I can deal with that. What my son has suggested though is using the existing 8" CMU as a veneer architecturally with the proper lateral anchorage, and building an interior bearing/shear resisting system inside the exterior CMU wall shell. This sounds more cost effective than reinforcing the wall vertically, grouting, and coating with an FRP finish.
Anyone have any experience with the two options cost-wise that they can share?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask






RE: 1940's Unreinforced Masonry Building
Where is this project? (wind/seismic)
8" URM is still pretty stiff, so you would have to have compatibility with your backing system to ensure proper lateral load transfer. I wonder if using brick institute type support standards would apply here. Are you thinking steel stud and steel frame structure inside the CMU walls?
The other thing is even though its cladding, you are buying it now with your modification. So any poorly done window or door openings, cracks in the wall, deteriorated mortar, etc. may have to be addressed. You may end up needing to do some repairs and retrofitting even to make it work as a cladding and be sure everything is OK to current codes.
I am curious as to what is more economical: using it as a cladding vs tearing it down (if you are not going to use it as a structural system).
I have had lots of projects where they have had to add dowels and grout via slot cutting holes in the CMU. One was an old warehouse (several buildings hodge-podged together) that was converted into a print shop and it went from URM circa 1930s to current FBC requirements. We did not do an economic analysis of other choices as the roof stayed, but nobody batted an eye at this method as far as cost goes. But this was for 110 mph wind loads only in Florida. If you have special seismic criteria the reinforcing and grouting can get pretty heavy, and the shear walls and mass of the walls become an issue...
RE: 1940's Unreinforced Masonry Building
I have not been to the site yet, but will be going tomorrow. it is in North Seattle from what I understand from the client, near where he had me design another building for him a few years ago that was never built due to the economic downturn - that was new construction and this is adjacent.
Teardown is not an option at this point as he wants to save it to preserve the local architectural flavor of the area.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: 1940's Unreinforced Masonry Building
RE: 1940's Unreinforced Masonry Building
Brad
RE: 1940's Unreinforced Masonry Building
Yea, I thought of that, but then there is the problem with developing the horizontal shear, and having to use an internal/external FRP wrap, or some other means. We are in a high seismic area, so this is a real concern.
There is the thought that if no further weight is added to the walls via grout infill, undoubtedly a major contributor the Seismic component of the design, then the lateral forces will be reduced. Just have to see I guess.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: 1940's Unreinforced Masonry Building
RE: 1940's Unreinforced Masonry Building
In years past, as you might remember, "K-web" was used instead of the horizontal steel bars, usually every third course in the mortar joint. This is the steel that would be impossible to install, but necessary to emulate some other way.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: 1940's Unreinforced Masonry Building
BA
RE: 1940's Unreinforced Masonry Building
RE: 1940's Unreinforced Masonry Building
To quote from page 203, section 4.2.3 of the third edition of the Masonry Design Manual by Amrhein and Kesler:
"Masonry has a capability to resist shear forces, however, many times it is necessary to exceed the shear capability of masonry. When this occurs, the beam or shear wall must be reinforced with stirrups or horizontal steel to resist these high shear forces."
These horizontal bond beams with reinforcing, or the "K-Web" of years ago, serve just that purpose for shear walls. Due to the high seismicity of our area, it is just common practice here to always use bond beams. I always do, regardless of the stress level seen. That's the way I was trained years ago by the then President of the State Board.
By the way, I guess the K-Webbing was placed every other course, not every three. On page 136 of the third edition of Amrheins "Reinforced Masonry Engineering Handbook", it depicts the two types of interstitial joint reinforcing. The one with the diagonal elements is the K-Web. I do not use either any more - only 8" reinforced bond beams at 4' centers.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: 1940's Unreinforced Masonry Building
Merry Christmas to you and yours!
RE: 1940's Unreinforced Masonry Building
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask