SHEAR WALLS

We need to think about both the longitudinal reinforcing needed and the shear (diagonal tension) reinforcing required for each interior element (unit) which in our case is typically a 4.5 M X 6 M (16 X 20 ft) room.

Shear walls are vertical, interior and exterior walls that are vital to the structural integrity of a vaulted building. They act to transfer the lateral loads to the foundation -- so the walls don't fall over with the vaulted roof in one piece.

Compressive loads are easy to take care of with reinforced concrete columns (or buttresses) but shear walls are needed for the sideways loads encountered with earthquakes or high winds.
These lateral forces are best visualized by imagining your structure turned, 90 deg.,on its side and supporting it from the side. How might the building now collapse? You will need to look at lateral loads in both direction, so turn your structure 90 degrees again (keeping the bottom on the vertical plane) and look at it again. How can it fail?

You will observe that vaults are very strong in the direction of the vault, (the long side) but could tend to collapse on themselves perpendicular to the vault ( just as a curved piece of paper is very strong in the long direction, but weak in the curved direction). Each individual vault needs to be supported perpendicularly somewhere, either with walls under, and perpendicular to the vault , or under an adjacent vault. Adding lateral supports is easily done with exterior walls at each end of the vault. Penetrations in these end walls is possible (and necessary for windows and doors), as long as there is SOME wall left. If you have a series of vaults, you can transfer the shear over to the vault next door (but no further)

You should plan on leaving at least 1/3 of the end wall without openings ,assuming your vault width to length is not more than about 3:1. The longer the wall that’s left, the better. A series of 1 foot wide by 7 foot tall walls is useless. Ignore any wall section that is greater than about 1:3 (e.g. a 2 foot wide wall next to a 6 foot tall opening counts, but a 2 foot wide wall between 8 foot tall windows should be ignored.) If you must have walls of windows, reinforced vertical columns between the windows can help to gain shear strength but if your ratio is less than 1:3 (see above) you need to talk to a structural engineer.

You must also have shear walls parallel to the vaults, but this is not so fussy (since we already determined that the vaults are really strong in shear in the direction of the vault) If you have 2 or 3 vaults in series, you don’t need to have shear walls under each and every vault edge, you can just move all of the shear out to the exterior walls and leave the interior open, except for columns for vertical loads. After you get 3 or 4 vaults in series, you will probably want to include some interior shear walls parallel to the vaults since you will have more need for shear walls than can be handled by the exterior walls.

The longer your shear walls, the more effective they are, so instead of a bunch of skinny shear walls, just have a few long ones. Long walls having more capacity than a bunch of narrow ones. These need to be distributed evenly across the structure– otherwise when loaded, the building will tend to twist around the strong wall. In most cases, if 30% of interior and exterior walls are shear walls and they are evenly distributed around the room sized unit 16 X 20 ft), you won't have problems.

Shear walls can be reinforced or not, but a concrete filled, reinforced block wall will have over twice the shear strength of an unreinforced block wall.

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