Wind loading on roof trusses

[JohnKWR]

This is a question about design/calculation method for the MWFRS. It is in regards to post frame construction where the load path is from the trusses to a truss carrier attached to each post and then from each post to a isolated footing under each post. Each post "feels" a gravity load and an uplift load. Each post need be designed as such. My question is as follows and I hope it's clear enough:

After you calculate the design wind pressure from the wind speed and you have the coefficients for each zone of the roof, etc, how do I then apply the wind pressure in each area to the trusses that fall in those areas? I realize that if you have a pressure in PSF and you want it in PLF then multiply by the member trib. width. If a roof truss falls in multiple roof pressure zones, for example a gable end truss, I would have to calculate how much of each zone that that particular truss "feels," correct? And then I add up all the tributary pressures from those zones in the form of PLF so I can get a total force that the truss exerts on the truss carrier?

Any help or advice with this is much appreciated. It could be that I'm confusing myself by overthinking. Also, if you have advice on how to analyze the wind pressures on a Gambrel style roof, please feel free to contribute you expert advice. So far I have not found much/any information on it :/

 

[RontheRedneck]

Don't know if it's of any help to you at all, but -

When we input trusses for wind loads, there's an option for "Design all trusses for end of building loads". It comes up with something like 28 wind load cases.

You might be able to get some info from a local truss supplier about the loads, reactions for each load case, etc.

 

[DaveAtkins]

Wind loads are applied perpendicular to the roof surface. So on a gable roof, you get a vertical component of wind and a horizontal component, on each side of the roof.

Otherwise, your approach is correct.

DaveAtkins