Metal carport-anchor options

[flusher]

I'm shopping for a metal carport 20ft wide x 36 ft deep x 9ft wall, A-frame style with gable ends to cover the last 36 ft of my 20-ft wide gravel driveway. Tehama Co requires a building permit and also requires that the structure and the foundation designs be certified for 85 mph wind load (exposure C), no snow load, and 1500 psf soil bearing capacity.

My initial inclination was to pour two concrete footings (16" W x 16" D x 36ft long) and use concrete anchors to attach the carport. I don't want someone with a backhoe messing up my expensive gravel driveway while digging the trenches for the footing. So if I go this way, I'll have to dig the trenches by hand--good exercise, but not that appealing otherwise.

How about ground anchors? The carport vendors offer those 36"-48" long helical mobile home anchors. Are these any good? Do the carport installers normally do a standard soil test to decide what size anchor to use? Or do they just guess?

How about rebar-type anchors? Are these any good? How long do these have to be to handle that wind load I mentioned above?

TIA for your help.

 

[whistlepig]

Dig post holes at a 45 degree angle to the ground. Fill these with concrete with an anchor attachment set into them. When you cable to these anchor attachments make sure you are pulling against the concrete the hard way. That is, if the cable is running to your carport the 45 degrees should be facing exactly opposite. I have anchored mobile homes this way.

 

[dave1949]

How about ground anchors? The carport vendors offer those 36"-48" long helical mobile home anchors. Are these any good?
TIA for your help.

Mobile home anchors do work. It might depend on the soil type, but they do hold trailers down in a wind storm.

An 85 mph wind is going to damage more than your carport, that seems excessive. It would take something like a weak hurricane or tornado to generate that windspeed in most areas.
Dave.

 

[whistlepig]

We had 84 MPH gusts when Ike came through. I lost half my roof on the house. Neighbors had vinyl siding ripped off and metal roofs on pole barns ripped off.

 

[Reg]

I don't know what they would hold down, how many you would need, what the "sail area" is, etc., but I have seen 55 gallon drums filled with wet sand used apparently effectively.
These were the kind with two 2 inch bung holes in the top and rope threaded through.
They looked OK, made half decent door frame bumpers too (-:
Anyway, they would be "standing" and that might not satisfy the spec, figure >500 lbs each, portable and CHEAP.
You could dress them up if the look offends anyone.

 

[dave1949]

We had 84 MPH gusts when Ike came through. I lost half my roof on the house. Neighbors had vinyl siding ripped off and metal roofs on pole barns ripped off.

That's what I mean. 85 mph winds are strong. I figure a strong down-draft/micro burst during a thunderstorm at maybe 60-65 mph? And that won't be sustained, although they can do damage in a hurry.

It could be the carport would be the only structure left undamaged, except for all the debris that smacks into it.

I am not sure you can attain 85 mph proof/damage free residential structures without alot of changes to standard materials and methods, a typical carport roof would not be up to it IMO. That's why the spec sounds odd to me.
Dave.

 

[forgeblast]

wow thats a lot of wind. we have the same sized carport next to our a-frame and its held down by the big rebar pins.
the house shelters the carport from a lot of wind and snow. I know we will eventually move it and use it as a firewoood cover once we get a garage.

 

[gwjd]

tust remember its no that the wind is blowing its what the wind is blowing you dont want your car port added to that. also a mini exsivator is easy to run lot easser than hand digingaround here they go for about 200 a day but half day is probably enough.

 

[flusher]

I don't know what they would hold down, how many you would need, what the "sail area" is, etc., but I have seen 55 gallon drums filled with wet sand used apparently effectively.
These were the kind with two 2 inch bung holes in the top and rope threaded through.
They looked OK, made half decent door frame bumpers too (-:
Anyway, they would be "standing" and that might not satisfy the spec, figure >500 lbs each, portable and CHEAP.
You could dress them up if the look offends anyone.

I calculate that there's about 18.5 psf of uplift due to that 85 mph wind requirement. Which amounts to 13,320 lb of uplift force on that 720 sf carport canopy. If I pour two 16"x16" x 36ft concrete beams for footings (about 4.7 cy of concrete) and use embedded concrete anchors to attach the carport, the weight of concrete will be about 17,800 lb, which should be enough to keep the structure in place on windy days.

 

[RedDirt]

I calculate that there's about 18.5 psf of uplift due to that 85 mph wind requirement. Which amounts to 13,320 lb of uplift force on that 720 sf carport canopy. If I pour two 16"x16" x 36ft concrete beams for footings (about 4.7 cy of concrete) and use embedded concrete anchors to attach the carport, the weight of concrete will be about 17,800 lb, which should be enough to keep the structure in place on windy days.

Now you've got the mass to hold it down I presume you know that all your connections from concrete to ridge need to be up to the same task. EG Hold downs at studs, hurricane ties at top plates to rafters, straps across rafters at the peak, shear panel siding or cross bracing, etc.

A 85mph wind load requirement certainly seems high, but "rules are rules" and they just seem to make them more ridiculous daily. For curiosity I'd call the local weather station and inquire when was the last time the wind got even near that velocity in your area.