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RE: Re-entrant Corner Question

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Thanks Scott – this answers a question that has been troubling me for a while now. I am sorry not to have responded sooner – a death in the family has had me occupied most of the week as I tried to help my second cousin in Wisconsin arrange the funeral preparations from California (could not afford to fly back but expected the passing of my cousin who was 85 years old). I am just starting to get caught up and wanted to work on Multi-Lat™ and this issue related to plan irregularity needs to be considered for how the use of Omega (Overstrength Factor) and with Rho (Redundancy factor) is to be considered.


Thanks again,



From: Scott Maxwell [mailto:smaxwell(--nospam--at)]
Sent: Sunday, July 06, 2008 6:47 PM
To: seaint(--nospam--at)
Subject: RE: Re-entrant Corner Question


I would say that you care about the re-entrant corners of the diaphragms.  If it is a one story building and the roof is rectangular even thought the outline of the buidling is L shaped or U shaped, then I would not consider it a plan irregularity typically.  If it is a multiple story building and the only the roof is rectangular (thus "regular") but other floors (thus diaphragms) at other levels are U shaped or L shaped (i.e. irregular), then you have a plan irregularity potentially.  It will also depend on if you have flexible diaphragms or not...and where the shearwalls are relative to the whole system.  I would argue that a U shaped building with a bunch of flexible diaphragms with appropriate shearwalls at the edges of the simple, flexible diaphragm might result in you realistically having a bunch of simple, rectangular flexible diaphragm segements which could result in the ability to treat it as a regular building.  To me, it is REALLY a matter of the specifics of the particular situation.





Adrian, MI

-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)]
Sent: Sunday, July 06, 2008 6:04 PM
To: seaint(--nospam--at)
Subject: Re-entrant Corner Question

When determining a plan irregularity such as a re-entrant corner do you judge the irregularity by the geometry of the resisting walls or by the geometry of the roof? For example, if you have a “U” shaped structure with a rectangular roof that covers the entire lower floor, do you define the irregularity from the roof shape of walls in plan? If the roof is square or rectangular in plan over a building that is “U” shaped then what difference does it make if the courtyard entry to the building is set back so long as the roof does not lend itself to rotation. Hope this makes some sense.


Please let me know if you have any questions to answer this properly. TIA!


Dennis S. Wish, PE


Dennis S. Wish, PE

California Professional Engineer