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Re: Rigid diaphragm question

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Mark,
 
I would look at the forces two ways.  I would determine the forces from the flexible diaphragm forces above at the wall lines, perform an independent rigid analysis of the lower level with torsion effects, and produce one set of wall design forces.  Then I would apply the roof level forces to the wall lines and perform a second rigid analysis to see if there is any redistribution at the floor level.  The design would be based on an envelope maximum of either condition.
 
 
----- Original Message -----
Sent: Monday, July 19, 2004 9:03 AM
Subject: Rigid diaphragm question

I have a two story building, roof construction is wood framed, floor construction is concrete, 1st and 2nd story walls are concrete.

 

I am considering roof diaph. flexible, floor diaph rigid.

 

When distributing floor lateral loads based on rigid diaph analysis,  would it be appropriate to bring the roof lateral forces directly down to the 1st floor walls added to the floor forces determined from rigid diaph analysis, or should I consider the roof level forces to flow into floor diaph and then be distributed to the 1st floor walls, ie: add roof and floor level forces and distribute the total based on rigid diaph analysis at floor level.

 

It seems the floor diaph would be more rigid than the 1st floor walls so the forces coming down from roof would first flow into floor before going into 1st floor walls.

 

Comments please.

 

TIA

 

Mark D. Baker

Baker Engineering