Carport Footings 3

[XR250]

I have a pretty large residential carport that is to be flagpoled off six 7x7 tube steel columns. My overturning moment at each column is approx. 12 ft-k (service).
The foundation will be isolated spread footings. To get a factor of safety of 1.5 for overturning, I need huge footings on the order of 5'-9" sq. x 16" deep. If I go deeper, to keep the excavation footprint smaller, at what point can I reasonably take into account some passive pressure on the sides of the footing to help resist the overturning?

Thanks in advance.

 

[XR250]

In my area freestanding carports usually just have knee bracing at each column. That way the moment at the footing is zero and the footing can be designed for uplift only. The only time I account for moment at the footing is if there are brick piers in which case there can't be knee bracing. Just my 2c

Anytime I have looked at kneebraces, the connection loads were so high at the ends of the brace and the beam to column connection that it was nearly impossible to make the thing work nicely. I guess if the carport is small with a low pitched roof, it may make sense. This carport is way too big for kneebraces.

 

[mike20793]

I agree with CANPRO; your footing doesn't seem that large to me, especially since the carport is so large. Wouldn't a bunch of grade/tie beams be more expensive with extra forming and concrete/rebar? I'd just make them 6 ft square and forget about it.

 

[XR250]

Sounds good

 

[dhengr]

XR250 :
I like the idea of bracing the house with the carport. That’s a twofer, you design the lateral support system for the building and you get a carport for free. What a deal. How did the house stand there before you thought of putting up a carport? Lateral bracing is supposed to resist some lateral load, at some height, without too much lateral deflection (parallelograming of everything else). Are you sure your 12' flagpoles and 12/12 pitch roof trusses, on spread footings will do that?

 

[XR250]

@Dhengr

The house is being built at the same time as the carport. It is a small 1 1/2 story guest house - barely bigger than the carport in footprint. The house has its own lateral stability system - just not quite enough. (see attached)