ASCE 7-10 Figure 28.4-1

[ash060]

I am looking at the low-rise envelope method in ASCE 7-10, and I am confused about it. They changed the cases from longitudinal and transverse to Case A and Case B. Case A does not include any sidewall pressures and Case B does. It seems to me that Case A is nothing more than Case B without sidewall pressures. Is that right? If it is what is the point of Case A.

Also, there is nothing showing the 2/3 roof zone boundary when the wind is along the ridge, but the Note 8 is still there defining that transition, but the pictures don't show it. Am I missing something, or is there a mistake? The latest errata I have is from January 2011, and I can't find anything more up to date.

Does anyone have a resolution for this?

Thanks

 

[PicoStruc]

I don't have the reference with me... but if i remember correctly,

Case A perpendicular to the roof apex generate global shear

Case B parallel to the roof apex generate no shear, just local pressure on wall that must added to interior pressure.

Case B is important in moment frame design.

 

[PicoStruc]

What i meant is that in case B the pressure cancel each other...thus no global shear.

Of course it depend of the geometry of the building (width of each frame side)

 

[JAE]

No global shear? Case B zones 5 and 6 values are not equal. Nor are zones 1 and 3.
There will be global shear since both opposite faces are of different signs (i.e same direction).

 

[ash060]

I think I made a mistake. I am used to 5 and 6 being side wall pressures, but in case B they are windward and leeward instead.

 

[PicoStruc]

What i meant is that for the Lateral force resisting system resisting lateral force perpendicular to the ridge :

- Case A generate a global Shear,
- Case B generale no global shear. See Pressure 1 & 4.

Of course Case B generate shear but in the other direction lateral force resisting system.