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Masonry - Box Shaped Wall

Masonry - Box Shaped Wall

Masonry - Box Shaped Wall

(OP)
Does anyone have good ways to design box shaped masonry shear walls such as around stair cores? I can get forces for each leg of the wall individually (as planar legs) or get them for the whole box. I have a feeling that I would need the effective flange for the wall to work and I am not sure how to approach the issue in a box shaped core. I am using ETABS to get the wall forces.

RE: Masonry - Box Shaped Wall

To date, I've always chickened out on treating CMU core walls as a composite shapes. The ones that I've looked at have always been pretty short and I've made the simplifying assumption that the load distributes based on shear stiffness alone. CMU presents two detailing issues that I worry about in a composite shaft design:

1) Detailing the reinforcing in your coupling beams.
2) Detailing your reinforcing so that shear friction works for the vertical joints connecting wall segments.

I imagine that, if you're dealing with relatively low stresses, composite behaviour should be justifiable somehow. And yeah, I realize that interconnected CMU walls aren't likely to listen to me when I tell them to behave independently. Co-dependent bastards.

As for effective flange widths, you would have to do something. In the absence of CMU specific guidance, I'd be tempted to apply concrete provisions. A question that I'd like to pose here eventually is whether or not your can ignore effective flange width provisions if you've adjusted your ETABS parameters properly to deal with shear lag. I would think so. I find effective flange widths to be a pain in the ass from a modelling perspective.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Masonry - Box Shaped Wall

If the walls are reinforced in both directions and fully core filled, I would just input them as continuous around the corners and let ETABS do its thing. It is just a reinforced concrete wall of lower strength material.

As to KootK's two issues; 1) Core coupling beams are impractical in masonry construction, and at any rate are unusual in low rise buildings. Just use the wall cees or boxes without connection between them. 2) The corner bars, in the middle of the wall, make the walls continuous, at least to the extent of the effective flanges. I don't see that shear friction is involved, but then I don't use or subscribe to that concept.

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