Corner Zone Loading at Small Outside Corners 6

[Ceinostuv]

I typically apply corner zone loading for components and cladding where any outside corner over 1'-0" occurs on a level but I'm starting to feel this is overly conservative and am curious to hear what others do. Where do you apply corner zones and what is your reasoning? Say you were working on an apartment building with recessed balconies spaced less than the corner-zone dimension (see image), would you design every stud with corner zone pressures?

Judgement-In-Training

 

[DaveAtkins]

Excellent question--I have wondered the same thing myself.

I consider corner loads only at the corners of the overall building, not at every nook and cranny like you have been doing. I believe my method is consistent with the intent of the code. With your method, the entire building could end up being a "corner."

DaveAtkins

 

[Dowels93]

I agree with DaveAtkins that corner loads should only be applied at corners of the overall structure, not every jog in the structure. My understanding of corner zones is that the additional wind pressures are present due to the stream created as the wind blows against the building and flows around the corner of the building. The wind has to go around or over the building, so the wind that blows near center has to flow around to the sides/above. This increased flow requires the wind to speed up, in turn causing higher forces at the corners. The wind cannot blow around the small corners like you have shown, so the speed up of wind won't significantly occur, meaning that there will be no increase in load (although there might be a bit of an increase due to turbulence, but that is not what the corner zones capture).

 

[brut3]

If you have a copy of ASCE 7-16 handy take a look at Figure 30.3-2 in the commentary section. It has a nice diagram identifying what ASCE considers a corner zone in irregular shaped buildings.

 

[Ceinostuv]

Thanks for the responses gents. Double thanks to Brut3 for the diagram and reference!

We once had a plans reviewer explain that corner zones were located where "X ≥ a" (essentially, Note 2 of the 7-16 image from Brut3) but we were never able to track down any literature to back it up (this was a few years back, before 7-16 was published I think), and we've been erring on the side of conservative since then; I'm happy to see a cite-able source for this information.

Judgement-In-Training

 

[txeng91]

“Wind Loads Guide to the Wind Load Provisions of ASCE 7-10” (not sure if they’ve released 7-16 yet) is also a great resource. It’s answered a lot of the questions I’ve had that are similar to this. Don’t think there’s anything in there that’s not in the commentary but it does a good job of summarizing it and has some good design examples.

 

[acbfusa]

Curiosity question here. Why does ASCE 7-16 ignore the new zone requirements for irregular shaped buildings? It seems they have not updated the diagram for C30.3-2 to account for buildings lower than 60'. Am I wrong in thinking this?