wind load cases and combinations

[CTSeng]

ASCE7-05 Fig 6-9 Design Wind Load Cases state “pressures acting on the projected area perpendicular to each principal axis”. Does this mean roof pressures are not included?

In addition, while it seems reasonable to ignore side wall pressures since they counteract each other, they can be a factor in the combined directions of case 3 and 4.

Any input is appreciated.

 

[rb1957]

if you're tlaking about flat (horizontal) roofs, then yes (as the projected area is zero).

personally, i'd've thought the wind loads on the sides of buildings would apply loads to the horizontal partsof the building (roofs, floors), as these react the side loads.

 

[CTSeng]

Yes, flat roof buildings.

Side loads could apply for component cladding although unlikely but are not part of the MWFRS cases in figure 6-9, correct.

 

[rb1957]

but won't a flat roof have a different wind loading ... suction, the reduction in static pressure when you've got a 100 mph (or whatever) wind blowing outside ?

 

[CTSeng]

Yes, a flat roof will have suction or uplift. But my question is that figure 6-9 MWFRS load cases ignore it, correct?

 

[kslee1000]

How many principal axis does a rectangle has?