ASCE 7-10 Wind Pressures for Buildings with Multiple Roof Heights

[slaeng]

I am working on a project with a building where the main structure of the building has a roof height of 120' and a lower addition to the building will have a roof height of 30'. If the 30' section is connected to the main building, will it have to abide by the 120' wind pressures. If not, can someone point me to the section of the code that states this?

 

[phamENG]

I'm not sure of a location in the code that specifically says it, but if you read through the commentary and supporting documentation, you'll get a good feel for where those numbers come from. That, in turn, will give you the background necessary to make the necessary judgement call.

I'm guessing most of your issue is with the side and leeward walls, correct? If the 30' tall portion is relatively small in area, then I'd be inclined to use the pressures using h=120'. If it's relatively large in plan (say, greater than 30x30), then I'd probably consider leeward forces for h=30' when you have both windward and leeward 30' walls. If you have a windward 120' and leeward 30', use h=30'.

It mostly boils down to wind flow separation. If the primary flow separation is being caused by the 120' section, use h=120'. If it's being caused by the 30', use that. If you're not sure, then fail conservative and assume the larger load of the two.