Lateral Wind Design for C-shape structures (such as a garage) 1

[Joe O]

This comes up a lot in residential design...Considering lateral wind loading, when looking at a garage (or open structure) where there are little to no framed walls on either side of the door/opening, my go to has always been to add a steel moment frame to take the wind loads coming from the adjacent side walls. A fellow engineer I talk to sometimes mentioned there are methods to design a "C-shaped" structure for lateral loads, but he didn't have any information available, nor can I find anything in IBC or ASCE about it. Does anyone have any resources to evaluate this type of structure for wind loading? I would love to help my clients avoid the cost of a steel frame whenever possible, but obviously want to do that in a responsible manner. Thanks in advance.

 

[driftLimiter]

Try searching 3-sided diaphragm design.

Good references for this are Malone, and NDS SDPWS. Not a big fan of this approach is seismic areas and for multi story. But they are used fairly often, and have their place.

 

[80PercentTruth]

@Joe O

You run into this issue also with commercial storefronts in which the front wall provides little to no resistance so often neglected. Personally I'd avoid the moment frame unless you can get a 3-sided diaphragm to work. Here is a design example for some:

https://www.woodworks.org/wp-conten...gn-Example-of-a-Cantilever-Wood-Diaphragm.pdf

Given the fact that this is a garage, you'll want to make sure you can get the load from your roof into the shear walls with the blocking.

"Engineers only know about 80% of the truth, the next 10% is very difficult to achieve, and the last 10% impossible. If we are bound to be wrong, we may as well be wrong simply and conservatively."

 

[hokie66]

A moment frame is my preference every time.

 

[JedClampett]

Simpson makes a system (Stongwall) specifically for this case. You need a little space (at least 12 inches), but the track needs to go somewhere.

 

[ChorasDen]

These situations are usually referred to as "open fronted" or "3-sided diaphragm". These can be designed fairly easily using a torsional approach. ASCE 7-16 and 2015 SDPWS 4.2.5 are all you really need to achieve the design.

 

[dik]

A few years back I was involved with a large addition to a small existing building. New framing was CFS for fire rating reasons. There was absolutely no information about the existing building. Lateral load for the new addition was resisted by a rigid frame on the end and CFS and X-bracing on the side walls. I analysed the forces using a lateral load spreadsheet, written decades back. I then use the forces to design the rigid frame. The rigid frame was used because there was a stip of windows in the end wall that prevented the use of X-bracing.

I generally use X-bracing because of stiffness.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik