Masonry Control Joints
Masonry Control Joints
(OP)
I understand that typical masonry joints are at 24' on center in a wall. However, how does that impact the rest of the structure?
ie... A 500' long building that has 12' tall masonry exterior walls for a pre-engineered metal building. There is a tie beam at the top of the wall that is spanning between metal building columns. For joints at 24' o.c., how does that impact the concrete beam? Is all of the temp/shrinkage transferring to the tie-beam? What about the Z-purlin continuous along the top of the wall?
Aren't we just preventing the stair-step crack and placing more stress on another element?
ie... A 500' long building that has 12' tall masonry exterior walls for a pre-engineered metal building. There is a tie beam at the top of the wall that is spanning between metal building columns. For joints at 24' o.c., how does that impact the concrete beam? Is all of the temp/shrinkage transferring to the tie-beam? What about the Z-purlin continuous along the top of the wall?
Aren't we just preventing the stair-step crack and placing more stress on another element?






RE: Masonry Control Joints
Regarding the steel beam at the top of the CMU wall, this is a wind/seismic beam between the mainframes that is there to support the CMU wall, and is designed to take the wind/seismic thrust from the CMU wall to the mainframes. The Z roof purlins have nothing to do with this. There should be a CMU bond beam at the intersection of the steel beam with the CMU. Is this the concrete beam you are referring to?
Mike McCann
MMC Engineering
RE: Masonry Control Joints
But more to the point, if I position the control joints at the columns (24' o.c. +/-), doesn't this just stress the concrete tie-beam as the masonry is free to expand and contract?
RE: Masonry Control Joints
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If we have any masonry structure: bearing walls with bar joists and non-composite concrete deck, bearing walls with metal roof deck or trusses, cladding masonry walls as called out above, etc...
When we create all of these control joints in the masonry, what is the effect on the surrounding elements? Is there undue tension stresses placed on the tie beam? Should we provide a control joint in the tie-beam also? If the Z-girt is continuous at the top of the wall as PEMB components usually are, but the masonry is discontinuous with control joints, is the girt in tension also?
RE: Masonry Control Joints
With your system, for global stability, there will need to be diagonal braces from the knee of the frame to the beam supporting the top of the wall
RE: Masonry Control Joints
So the intent of masonry control joints is to relieve the temp stress in the masonry? And the idea is to have small 24' sections do this, whereby reducing the amount of tension stress on the connecting elements?
Is there any detrimental effects on, say, a concrete tie beam at the top of the wall in typical bearing wall construction?
RE: Masonry Control Joints
Theoretically, nothing should cross a control joint or an expansion joint, because it will restrain movement.
In practice, due to overriding structural concerns, sometimes a bond beam will continue across a control joint, or sometimes a deck edge angle will continue across a control joint.
DaveAtkins
RE: Masonry Control Joints
In response to the original question as recommended by hokie66 use a pre-engineered steel shape with a horizontal slot at expansion bolts to attach the masonry to the steel framing with a bond beam at the connection. If the block wall is full height we brace the building is the short direction by placing horizontal wind bracing in the end bays which attach to the rigid frames and then attach the rigid frame to the wall with plates and expanson bolts.
RE: Masonry Control Joints
Anyone's idea for a more reasonable spacing? In a 500' wall, 20 control joints seems excessive.
RE: Masonry Control Joints
Each panel should be isolated. The joint reinforcement should stop at the control joint. The steel in the bond beam should also stop at the control joint. To carry any shear across the control joint or to maintain alignment, use a steel bar enbedded in one panel and allow the end on the other side of the joint to "slip" by one of the common methods.
Florida has conditions that preclude many of the nationally used details. This is the reason why no problems are seen. Cracks in masonry walls are caused by the stresses induced by temperature CHANGE/DIFFERENCE, moisture CHANGE/DIFFERENCE and shrinkage combine to cause enough length change to cause a crack. Most buildings in Florida and constructed within a relatively narrow temperature change compared to other areas. The moisture/humidity is relatively uniform and the walls do not see the drastic drying that happens in colder climates where the dew points are much lower. Because of the relatively high humidity and temperature, the carbonization of the cement in the mortar and units proceeds much sooner, increasing many structural properties. - Just some un-scientific observations based on experience.
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I have (unintentionally) gone 20m in a basement wall, with wall returns (with N12-400 horizontally) without evidence of cracking.
My company provides galvanized, greased dowels to bondbeams at cj locations. Continuing the reinforcing defeats the purpose of the joint and subjects the reinforcing to the elements.
RE: Masonry Control Joints
Or is this issue alleviated by considering a continuous edge angle bolted to the wall and considering it as the chord?
Any thoughts...
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My reference is more to tilt up construction with a roof diaphragm instead of floor diaphragm but the concept is still the same...
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Hokie, in a much earlier post you said your company provides CJ's 4m from corners. Is this for wall shrinkage or slab shrinkage? If it is for slab shrinkage say no more but if they are for wall shrinkage - i tend to think of returns as 'releases' to shrinkage rather than 'restraints'. Would you provide shrinkage joints in a wall stepping in and out every 5m?
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I can't honestly tell you why. The specification has been around for a long time, and I didn't write it. But like you, I see it as a restraint release for slab shrinkage. I think it is intended to apply only near the extremities of slabs where the restraint problems are worst, not at any steps along the way.
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As long as the step lengths are not too short or too long there should generally be no need for joints.
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For rigid diaphragms, would you try to isolate the walls, and put shear transfers at each masonry panel?
RE: Masonry Control Joints
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Typically the ties between the masonry and the structure are flexible enough to allow the in plane movement.
The fewer the joints, the more movement there will be at each joint.
RE: Masonry Control Joints
We don't seem to have problems in Florida, so I'm curious how you northerners provide that connection?
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Your reference applies to brick growth, and we were talking primarily about concrete block. But in some cases, you could get the same stiffness problems with the forces in the opposite direction.