OBC or NBCC Wind Load on Canopies - Uplift and Lateral

[puszka]

Hi All,

I'm designing my first entry canopy as an EIT and I'm a bit confused how an entrance canopy would be analyzed for wind according to the OBC or NBCC.

The canopy projects about 15 feet from the facade of the residence (to which it is attached at the level of the second floor) and is 24 feet wide.

As I'm looking for my lateral and uplift forces, I've seen some conflicting information. Would you consider the projected area of the edge of the canopy and analyze the wind force using the method for components/cladding? Or use the typical CpCg values given in the 4.1.7.6 diagrams considering a very short 'wall' in the projected area of the overhang...

I'm also curious about uplift. I know the suction at the upper surface but in an open structure is it still considered to have an internal pressure per 4.1.7.7. (+0.7 Cgi for open building) and then use that to size my post footings and anchors? I've seen some people/research pointing to the uplift force on the soffit being tantamount to the lateral wind force on the wall below.

Nothing seems as clear in the Canadian documents as what I have heard reference to in the American (is there an overhang section in OBC?). Any guidance is gladly recieved

 

[puszka]

Oh, and please if you happen to know of any good references, videos, documents, texts yada yada yada I am all ears. I'm working towards this to become second nature!

 

[puszka]

 

[puszka]

I posted this too late yesterday let's see if I get a bite once I push it to the top this morning

 

[MotorCity]

I am not familiar with the Canadian codes, but per ASCE 7, you will have main wind force resisting system (MWFRS) loads and component and cladding loads (C&C). The canopy will need its own lateral system to resist wind and seismic as well as overall stability. For canopies, the lateral system is usually cantilevered columns or moment frame depending on the size and configuration of the canopy. It most likely qualifies as an open structure.....although, ASCE 7 has come up with a few more definitions of enclosed, partially open, partially enclosed, open, etc that make it a little more convoluted. In general, you'll have uplift, possibly downward wind load but it'd be negligible, and lateral wind load on the soffit and columns.

 

[JLNJ]

Can't help you with the NBCC, but ASCE 7 has a whole section on "free roofs" - flat, sloped, or gabled. Figure 30.8-1 in ASCE 7-10.

I design these very conservatively. It seems that canopies are tied with PEMBs for "most failures under windy conditions".

Don't forget to brace it well in the cross direction and add in your snow drift.

 

[canwesteng]

I'd use C+C since it should be conservative and the canopy is a small part of the roof. Otherwise I would use ASCE 7 but you will need to rationalize the two methods, since NBC provides hourly wind pressures and ASCE 7 uses 3 second gusts.