Gas station Canopy Footing 2

[knadia]

Hi,
The gas station canopy is 102'x30' and supported by 4 HSS columns. I am designing only the footing and making sure it is sized for a moment as well as axial load provided by canopy manufacturer. Below the canopy is a slab on grade. The bottom of each of the four footings will be 4'-0" below the finished grade. There is also a slab on grade for cars and trucks to drive up to fill up. Do I need to take into consideration any impact for loads from these vehicles onto my column footings?

 

[Ron]

TJ...you might be right...I didn't read it that way, but makes sense. In any case, the traffic loading is likely not going to be directly over the footings and most would be dissipated by the slab and the distance between them. In short, I would not consider a traffic load on the footing, either.

 

[knadia]

Thanks guys! I am only designing the 4 footings. The columns and superstructure are designed by the canopy manufacturer who didn't take into account an impact load but the columns are HSS 15x6 or something big like that. My area of expertise is buildings not these small structures and my experience says those columns are good. As for spread foundation, I think I will take into account an addition 50 psf. My footing is already large due to moment so I don't think I will need to resize it by much more. I really appreciate your input. This is my first time posting here. And I am impressed. I don't usually get this much feedback even at work.

 

[LonnieP]

Although you didn't ask about it, remember to check against wind uplift.

LonnieP

 

[ToadJones]

as I alluded to before, and Lonnie has pointed out, do not include surcharge in all cases, such as uplift.
Again, I am probably just stating the obvious.

 

[knadia]

wind uplift - check
traffic surcharge to check for downward pressure - check
Thanks so much for all your input.
love this forum.
nadia

 

[hokie66]

Regardless of whether the columns are protected by bollards, I would design the footing only for gravity loads from the roof and wind uplift loading. Traffic surcharge and impact would be incidental and would have little effect on a footing founded 4' below the surface. If the footing were at a higher level, I might consider the impact as a momentary overturning moment. But if something hit a column hard enough to displace the footing, the whole thing would have to be rebuilt anyway.

 

[hokie66]

Oh, and of course there is lateral load from the wind also, the moment from which would doubtless exceed the impact moment.

 

[Ron]

hokie66...exactly

 

[frv]

That's a good point, hokie..

I guess it's just a check I've been accustomed to do whenever I have anything exposed to vehicular impact.. but I think you're right.. In this particular case, it's quite obvious by observation that wind loading would control both overturning moment and probably shear on the footing..

So on second thought, I change my answer to "No."