Roof Wind Pressures in Wall Flexural Design

[LearningAlways]

It is apparent to me that we would need to design walls for out-of-plane (weak axis) flexure due to applied loads from roof wind pressures. It only makes sense, C&C pressures define roof wind pressures and these pressures are applied to the roof system which is then picked up by the walls.

I am designing tilt-up. I am relatively new at it. I am used to designing concrete garages. In garages, the applied vertical load from live load is always more than roof wind pressures on a FLAT roof which is the reason we don't consider roof wind pressures in a garage (1.2D + 1.6L > 1.2D + W + 0.5L), especially on a flat roof where minimum or near minimum wind pressures govern. For tilt-up, the roof wind pressures and roof live pressures are almost equal and it would seem that roof wind pressures need to be taken into account.

But...

In none of the design examples in ACI or the TCA manual do they consider roof wind pressures as part of their design.

Am I missing something here? Or is accounting for the roof wind pressure in the wall flexural design too conservative?

 

[phamENG]

I'm guessing by flexural design you really mean axial design, unless your roof to wall connection is eccentric. If it's eccentric, you're right - it would induce a moment in the wall. But yes - you should always include wind and live loads in your analysis per the load combinations in the applicable code.

The design examples are just a means of demonstrating their method. They are not meant to be exhaustive.

 

[Agent666]

Agree with phamENG, you need to apply all the applicable loads based on the load combinations in your codes.

If that roof load is applied to the face of the walls, then it will create some bending in the walls as you've realised (in addition to any additional axial loading).

Also, often for medium sized structures, even though the gravity loads might offset any wind uplift effects. There is often load combinations that require consideration of internal suction loads combined with downwards wind pressures (which usually develop on longer roofs).

Sometimes these downward wind effects are more critical than gravity loading, especially if the structure has dominant openings which can generate internal suction pressures as high as the external pressures. For example, an open door on the leeward side of a structure might be considered a dominant opening, allowing a greater internal suction to develop than a typical 'sealed' or 'equally permeable' building.