I have an existing masonry structure that has a wood roof. The structure is quite old. I seem to remember a code requirement that does not allow for the use of a plywood diaphragm to resist seismic loads from masonry but I can’t seem to put my finger on it. The local jurisdiction is using IBC 2009.
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Masonry and wood construction? 1
- Thread starter SteelPE
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- Thread starter
- #2
MiketheEngineer
Structural
I think the old code forbade supporting masonry with wood - a fire problem. I think new code does not address this and local code officials are allowing it.
But as noted - you will probably not be able to show it good!!
But as noted - you will probably not be able to show it good!!
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- #5
Well, I can't say that it is really old. It's older than I am because it is made out of URM. With the building we actually have to deal with IEBC 2009. I just seem to remember a problem with plywood diaphragms/masonry walls/seismic loads. Maybe I am mistaken.
SteelPE:
There used to be a prohibition or strong caution against carrying masonry on wood framing, for deflection, long term creep and fire reasons. I believe that has been relaxed or eliminated in the latest Eds. of the codes, but still with cautions re: the above and cracking of the masonry.
We’ve been using roof diaphragms, both 2 & 3x T&G, and plywd. sheathing for years, with both unreinforced, grouted and reinforced masonry. Obviously, older construction will not comply fully with today’s codes, but adding a plywd. roof diaphragm, or improving an existing diaphragm can still be a significant improvement. The nailing and blocking of an existing diaph. would have to be reviewed, the shear connection btwn. the two would have to be reviewed and likely improved. Conc.blk. cores at opening jambs, and corners, and the like, would have to be reinforced, and you might get pretty close without a whole new building. If you are working on the roof so you can open it up and get at the walls from above, this may not be to difficult. The rods go in from the top, you can clean out the cores in the process; and then cleanouts at the bottom so you can epoxy in some dowels, and lap the vert. reinf’g. may work.
Actually, there are methods for tensioning the vert. reinf’g. if you can get an adequate doweled connection into the footing or whatever is down there. You might also consider applying FRP (Fiber Reinforced Polymers) to the URM to pick up part of the lateral loading.
There used to be a prohibition or strong caution against carrying masonry on wood framing, for deflection, long term creep and fire reasons. I believe that has been relaxed or eliminated in the latest Eds. of the codes, but still with cautions re: the above and cracking of the masonry.
We’ve been using roof diaphragms, both 2 & 3x T&G, and plywd. sheathing for years, with both unreinforced, grouted and reinforced masonry. Obviously, older construction will not comply fully with today’s codes, but adding a plywd. roof diaphragm, or improving an existing diaphragm can still be a significant improvement. The nailing and blocking of an existing diaph. would have to be reviewed, the shear connection btwn. the two would have to be reviewed and likely improved. Conc.blk. cores at opening jambs, and corners, and the like, would have to be reinforced, and you might get pretty close without a whole new building. If you are working on the roof so you can open it up and get at the walls from above, this may not be to difficult. The rods go in from the top, you can clean out the cores in the process; and then cleanouts at the bottom so you can epoxy in some dowels, and lap the vert. reinf’g. may work.
Actually, there are methods for tensioning the vert. reinf’g. if you can get an adequate doweled connection into the footing or whatever is down there. You might also consider applying FRP (Fiber Reinforced Polymers) to the URM to pick up part of the lateral loading.
- Thread starter
- #7
dheger
The thought process of the architect was to only change the structure enough to make my life miserable. ha
We advised the client not to mess with the existing URM. Of course they had to make new openings so we gave the option of reinforcing the existing (I have yet to have someone actually do this option) or providing a new section of properly reinforced masonry.
With the new section of masonry we will need a new "drag strut" to bring the loads out of the diaphragm and into the wall. We will do this with blocking and new steel members.
I guess I was mistaken by an interpretation of 2104.6.1.
The thought process of the architect was to only change the structure enough to make my life miserable. ha
We advised the client not to mess with the existing URM. Of course they had to make new openings so we gave the option of reinforcing the existing (I have yet to have someone actually do this option) or providing a new section of properly reinforced masonry.
With the new section of masonry we will need a new "drag strut" to bring the loads out of the diaphragm and into the wall. We will do this with blocking and new steel members.
I guess I was mistaken by an interpretation of 2104.6.1.
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1
- #8
You are not mistaken.
I am looking at the 2006 IBC section 2305.
Specifically section 2305.1.5 which prohibits the use of wood shear walls, diaphragms, horizontal trusses and other members from being used to resist horizontal seismic forces contributed by masonry or concrete walls in structures over one story in height. (There is a list of exceptions.)
I do not have the 2009 IBC in front of me, but I would imagine a similar section would be in that edition as well.
I am looking at the 2006 IBC section 2305.
Specifically section 2305.1.5 which prohibits the use of wood shear walls, diaphragms, horizontal trusses and other members from being used to resist horizontal seismic forces contributed by masonry or concrete walls in structures over one story in height. (There is a list of exceptions.)
I do not have the 2009 IBC in front of me, but I would imagine a similar section would be in that edition as well.
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- #9
msquared48
Structural
ASCE7-05 has a list of chapter comparisons between the 02and 05 editions (Table C11-1). Perhaps you could contact the IBC producers and see if such an addition could be made to future editions of the IBC. It is very helpful for ASCE7.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
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