Masonry Control Joints - Rubber Gasket Shear Capacity
Masonry Control Joints - Rubber Gasket Shear Capacity
(OP)
For concrete masonry wall construction it is usually required to provide vertical control joints in the walls - perhaps at 25 feet on center.
For a wall that spans vertically from foundation to roof, the joints don't interfere with the wall's load paths.
We typically place the joints in clean areas (i.e. not near openings)
Some technical manuals recommend placing the joints off the upper corners of doors. However, if you do this, then the area of masonry above the door has no load path against perpendicular wind forces.
The joint would interrupt the ability of the wall area above the opening to shed the wind laterally to the adjacent full height, reinforced cells on that side of the door.
We've seen where NCMA and other literature imply that the cruciform shaped rubber or PVC joint gaskets (go here for a look at one: (Link) may provide lateral shear capacity to transfer shear loads across these gaskets.
The literature that we found always seems to suggest that the manufacturer should/can provide the engineer with the shear capacity of these gaskets.
We haven't found anything online - just wondering if any of you know where this sort of info might be found. Just a general shear capacity (range of values) would be adequate.
For a wall that spans vertically from foundation to roof, the joints don't interfere with the wall's load paths.
We typically place the joints in clean areas (i.e. not near openings)
Some technical manuals recommend placing the joints off the upper corners of doors. However, if you do this, then the area of masonry above the door has no load path against perpendicular wind forces.
The joint would interrupt the ability of the wall area above the opening to shed the wind laterally to the adjacent full height, reinforced cells on that side of the door.
We've seen where NCMA and other literature imply that the cruciform shaped rubber or PVC joint gaskets (go here for a look at one: (Link) may provide lateral shear capacity to transfer shear loads across these gaskets.
The literature that we found always seems to suggest that the manufacturer should/can provide the engineer with the shear capacity of these gaskets.
We haven't found anything online - just wondering if any of you know where this sort of info might be found. Just a general shear capacity (range of values) would be adequate.
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RE: Masonry Control Joints - Rubber Gasket Shear Capacity
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
Got it here: Link
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
I'm aware of smooth dowels, placement of joints, etc. Just want/need information on the gaskets.
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RE: Masonry Control Joints - Rubber Gasket Shear Capacity
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
http://www.wcrfabricators.com/masonry_brochure.pdf
BA
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
(The 0.4 is a made-up shear safety factor - could be anything I suppose - 2.0, 3.0, etc.)
That shear capacity value seems high to me (in light of Ron's suggestion to not count on them at all).
So if I had a 20 ft. tall wall with a 10 x 10 ft. door opening and a control joint on one side of the door - the wind load that I'd be trying to
transfer might be on the order of this:
25 psf (C&C Wind) x 5 ft. = 125 plf. That seems way below the 3600 plf capacity.
So the numbers here seem to suggest that the gasket has way more capacity than the applied shear.
Besides your link, BA, I can't seem to fine very much information on this so it seems the manufacturer's aren't pushing this aspect very much.
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RE: Masonry Control Joints - Rubber Gasket Shear Capacity
http://www.rcpblock.com/images/pdf/TEK-10-2C-Contr...
BA
RE: Masonry Control Joints - Rubber Gasket Shear Capacity
Although the gasket shear capacity is very high (750 lb/in / FOS), I wouldn't expect the assembled joint to possess anywhere near that capacity. Among other issues, the masonry pocket that contains the gasket shear key wouldn't be able to sustain that level of localized stress. Here's how I think that the gaskets work:
1) Unless we think that the manufacturer's are lying, shearing of the gaskets is off the table. Definitely not the limiting failure mode.
2) It's a good thing that the gaskets are not particularly rigid. Their flexibility probably protects the surrounding masonry pocket from high localized stresses.
3) Since the pertinent source of deformation is shear strain across a gap of 1/8", the joint will be relatively stiff despite the constituent material being relatively flexible.
I think that I'm a believer now. It's really quite an ingenious setup.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.