Today’s ag buildings are getting bigger than ever, and they’re requiring more sophisticated engineering. A recent mammoth Wick project is a perfect example of just how bigger buildings are requiring better engineering.
There’s an old adage in architecture that says when you’re building a skyscraper, if you want to add another floor, you can’t put it on top. You have to add it to the bottom, because the new floor has to be able to support all the floors above it.
Post frame buildings follow a similar principle. When you’re building a bigger building, you have to account for the additional snow and wind loads. That means determining the right spacing and lumber sizes, as well as how the columns are put into the ground. Bigger buildings don’t just mean longer lumber. You have to space and size things properly.
There’s a lot of engineering and knowledge that goes into making a bigger building that won’t collapse under a heavy wind or snow load, let alone its own weight. A recent ag building we constructed is a perfect example.
Putting the Knowledge Into Action
This particular ag building project is one of the biggest we’ve done in the last 20 years. Designed to hold bulk cottonseed, the building itself is 99′ x 200′ with 25′ eave height. While most of our buildings take 1 – 2 trucks to deliver all the posts, trusses, and other components, this building took nine trucks to deliver everything.
When the length of a building is more than twice the width, that means we review some of the loading principles and sheathing attachments. That’s because we’re designing the building for the wind load transfer of the roof to the end walls.
Because of its size, we made other engineering changes to this particular building, including:
* Intermediate support columns are installed between the main columns, spaced 4′ on center. These don’t support any trusses, so they’re a 3-ply column (3-2x12s).
* Columns are buried 5 feet into the ground, plus a 10″ x 24″ wide footing. That means each column is nearly 6′ below grade. That compensates for not only the extra wind load, thanks to the height, but the interior pressure from the cottonseed as well.
* Additional wind load bracing is placed in the roof line and knee braces at every truss-to-column connection. This is in addition to the heavier columns. We could also use corner bracing in the walls, but didn’t in this particular case.
* Additional wind load support also comes from the diaphragm strength of the steel. It can essentially transfer that load to the end walls. With the proper fastening, and the proper number, the end wall steel provides that extra resistance.
The Importance of Working With Professional Engineers
There’s a science to making a bigger building. You can’t just use wider lumber or place girts and purlins closer together — we have licensed professional engineers determine what the correct spacing will be, based on the size of the building and your region’s expected snow and wind loads.
In our cottonseed building, we had to calculate the internal forces of the many tons of cottonseed and compensate for the external forces of increased wind loads, thanks to a 25 foot wall height. This requires experience and expertise.
If you’re constructing a large ag building — or a building for any purpose — make sure your builder understands all that is required to construct a strong building ideally suited for your climate and weather zones.
Bigger buildings require better engineering. As in, if your builder doesn’t have an engineer on a job like the one we described above, they’d better get one!
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