MWFRS 1

[MAeng]

Somehow - despite years of doing this, I've become confused. I believe that in determining the MWFRS loads for a building, one compiles the windward wall forces, considering the + and (-) GCpi forces and the then figures the leeward wall forces, again with the + and - GCpi for that wall,and then adds the windward and leeward forces together for the load that the diaphragms at each respective level must be designed to resist and transfer to the shearwalls. Do I have this right?

 

[JAE]

Well - you add these two conditions:

Positive internal pressure condition
(where the internal pressure decreases windward and increases leeward pressures)
(Windward - internal) + (Leeward + internal) = total lateral

Negative internal pressure condition
(where the internal pressure increases windward and decreases leeward pressures)
(Windward + internal) + (Leeward - internal) = total lateral

In both of these conditions the total lateral is the same.

 

[MAeng]

Thanks JAE - that is exactly what I thought. The confusing element has been a program I am using that gives the base shear and the moment of the windward force only. I cannot understand why this would be the only info given as it really tells one nothing. Am I missing something here?

 

[JAE]

Without actually seeing and using the program I can't comment. Have you tried contacting the author of the program?

 

[MAeng]

Yes - I'm waiting for a reply on this question. I had first asked him if the base shear.moment was for the total load but he replied that it was only for the windward load. Seems like a strange result to give if not giving the leeward side results as well. We'll see what he says. Should I let you know?

 

[JAE]

If it is a fluke in the program - no. If it is a design theory/assumption/concept then it might be helpful put it up here for comment.