Overhang, open building, or partially enclosed building? 1

[AaronMcD]

I'm working on a mountaintop house with supported overhangs on all sides. One side extends 35 feet beyond the wall.

I have a large topographic factor and some huge uplift loads. If I design as overhang, my C&C pressures will be 45-131 psf depending on zone and tributary area. I took a glance at open building coefficients and it looks like I'd have 31-61 psf if designed that way. For partially enclosed, it is closer to the overhang pressures (32-115 psf).

What would you do?

http://www.hellodwell.design

 

[KootK]

The argument that you're hoping to make is that your 35' cantilever is really more like an open building than a true overhang, right? If so, I'm inclined to agree based on the aerodynamics. As I understand it, the main reason that overhangs see so much load is that they tend to be located at points of airflow constriction as air is forced up and over the building locally. I don't feel that the same could be said of an overhang that is, itself, the size of a small building.

One thing that I would keep an eye on with this is the vibrational response. Rich folks don't like it when their dining room chandeliers dance a jig during wind events. And rich folks can afford quality legal representation.

 

[AaronMcD]

As it turns out it doesn't make a huge difference. The details and components at the "overhang" are similar to the ones at the house and near the house, except fewer and simpler so I used the same/similar details (and being a bit conservative is good). For MWFRS, as an open building, it is obstructed in 2 directions anyway so the loads are on the same order as an overhang. All in all I'm getting some pretty large foundations to hold some of these columns down.

I'm not sure how to analyze vibrational response without wind tunnel testing. Do you have any references? Is the concern mainly resonant frequency?
My main concerns would be a 22'-6" span with 6'-9" tributary (timbers), and a 14 ft cantilever with 17 ft tributary (glulam).

http://www.hellodwell.design

 

[KootK]

Is the concern mainly resonant frequency?

Yup.

Do you have any references?

Nothing other than very complex books on general wind dynamics. For things not fancy enough to get the wind tunnel or fancy math, I'll typically limit the natural frequency to:

1) 5 HZ minimum for first mode, non-aeolian wind vibration.

2) 20 HZ minimum for second mode, aeolian wind vibration (poles and signs with vortex shedding).

I'm sure that there are plenty of situations in which this would not be sufficient though.