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Rigid or Flexible Diaphragm Analysis?

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I have a complex roof structure I am designing for a high end resort condominium building.  The plan configuration is irregular, being described as a "U-Shape" with 45 degree bends at the intersection of the horizontal and vertical "legs" of the building plan.  The roof consists of structural steel wide flange sections to carry gravity loads, and I am proposing to use moment frames to resist lateral forces (unfortunately no walls are available to use braced frames).  Metal deck will be used on top of the structural steel to form the diaphragm.  Because of the buildings odd plan geometry, and moment frame orientation to the orthogonal planes, I am reluctant to regard this structure as a flexible diaphragm.  I am concerned with twisting (torsion) at the 45 degree bends, and do not feel that the loads will be distributed as assumed under flexible diaphragm analysis using tributary area loading.  This project requires a lot of solid engineering judgement, and I hope to receive some comments from those of you who have designed similar structures.  Computer analysis is not possible for verification of hand calculations, as most of our programs will not perform a diaphragm (rigid or flexible) analysis on a sloped roof system.  RAM Structural claims to have this capability next year, but I will be complete with this project next month.  Comments and suggestions or leads to references would be greatly appreciated.  Thanks.
 
Bill S. Marczewski
Martin Design, Inc.
1360 S. Clarkson St.
Denver, CO 80210
bmarczewski(--nospam--at)martind.com