Diagonal Bracing

Pole Barn FrameIn yesterday’s article I alluded to one more thing I looked at on the building in question which appears to be an unnecessary expense. Check out yesterdays photo..

In the plane of the walls of the pole building running at an angle are diagonal braces.

Diagonal bracing provides lateral stability in buildings which do not have adequate shear strength in their skin (e.g. roll formed steel siding or products like T1-11) to be able to transfer lateral loads from the roof to the ground.

Picture, if you will, a conventionally framed stud wall. Most commonly it will be around eight feet in height and composed of 2×4 or 2×6 vertical members 16 or 24 inches on center. The studs are attached to a bottom member (or plate) and usually a double top plate which run horizontally. Nailed all together, stood up and nailed to the floor, it appears as if it might be reasonably strong to support a load placed upon the top of the wall.

Now vision going to the end of the wall and leaning against it in the direction the wall runs – poof, the wall folds upon itself and becomes kindling.

There are many ways to resist these lateral shear loads. Provided there is the ability to adequately end nail – diagonal bracing of either wood or steel strapping might be used. Steel strapping affords the ability to wrap the ends around the columns to provide a greater nailing surface. The challenge of lumber bracing is very few nails can be placed into each end – it would only be effective in buildings with very low walls and a very small wind load.

Post frame buildings with wood diagonal bracing usually indicate a lack of understanding of how shear forces work and are most likely not buildings which were designed by a Registered Design Professional (RDP – engineer or architect). Experienced design professionals understand diaphragm design and the ability of wood or steel sheathing to carry forces and utilize them for proper and prudent design.

Talking to a post frame building kit provider or builder who utilizes wood diagonal bracing? My prudent suggestion would be to require them to provide engineer or architect sealed plans for the building, as it is more than an educated guess there was no structural professional involved.

And if an RDP did not design the building – who did?

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