Bond breaker in masonry detail.
Bond breaker in masonry detail.
(OP)
I was reviewing some Plans and noticed a masonry detail for a block building with a flat concrete roof. The flat roof has a peripheral beam that rests on top of a bond beam. The peripheral beam has 2 no. 5s top, 2 no. 5s bottom and no. 3 stirrups at 12" o.c. The bond beam has 2 no. 5s. The block wall is reinforced with no. 5s at 48" o.c. There is a bond breaker shown between the bond beam and the peripheral beam and the vertical reinforcement in the wall does not extend into the peripheral beam. The detail calls for one no. 4 bar at each corner of the building connecting the bond beam to the peripheral beam. This basically separates the roof diaphragm from the walls of the building. Anyone want to speculate why its detailed this way? Why break the bond at this location? Does the roof slab expand and contract? Anyone have a better detail for this?
Thanks for your input.
Thanks for your input.






RE: Bond breaker in masonry detail.
I have disconnected the tops of CMU walls from the underside of the floor above for locations where I do not want the CMU wall attracting floor to floor lateral loads (I did brace the top of the CMU against the upper floor in the out of plane direction though).
RE: Bond breaker in masonry detail.
There is no support provided at the top of the wall in the out of plane direction.
RE: Bond breaker in masonry detail.
RE: Bond breaker in masonry detail.
But cripes - the walls provide the ONLY lateral stability to the building correct? From your description, you say this is simply a four-walled box with a lid and no other structural entities attach to it? And it is exterior?
Somethings wrong here. The four #4 bars in the corners probably aren't adequate to drag the lateral forces into the shearwalls. But we are going by your description only.
RE: Bond breaker in masonry detail.
As it stands with corner bars tying in the lid to the walls, there is no expansion possible as the corner bars will fight each other.
RE: Bond breaker in masonry detail.
"This seems really odd. I suppose there could be concern that there would be thermal movements over time and a desire to let the roof slide relative to the walls.
But cripes - the walls provide the ONLY lateral stability to the building correct? From your description, you say this is simply a four-walled box with a lid and no other structural entities attach to it? And it is exterior?"
My concerns exactly.
I think that the vertical wall reinforcement should extend into the peripheral beam on all the exterior walls. I will end up debating this with another engineer that has 40 plus years of experience, so I wanted to see what others had to say about it before.
RE: Bond breaker in masonry detail.
RE: Bond breaker in masonry detail.
RE: Bond breaker in masonry detail.
I agree that the situation is not good, but...
Mike McCann
MMC Engineering
RE: Bond breaker in masonry detail.
It was assumed that the sliding joint provided enough resistance for normal loads such as wind e.t.c. but would allow movement under the much higher stresses caused by shrinkage and temperature.
Sound like your designer may be using a similar philosophy.
I would definately not use it in a seismic area but for wind it may be okay (unless prohibited by code) as long as the weight of the slab exceeds the wind uplift.