Hello fellow engineers!
I would like to get an interpretation on how to define Horizontal irregularity #5 - Nonparallel system per ASCE 7-16, Table 12.3-1.
Per the table, "Nonparallel system irregularity is defined to exist where vertical lateral force-resisting elements are not parallel to the major orthogonal axes of the seismic force-resisting system."
My question is: Which part of the vertical lateral force-resisting elements? Does it have to be the entire element on one side, or any part of the system will trigger this nonparallel system irregularity?
Please take a look at the floor plan below for a concrete tilt-up warehouse with flexible roof diaphragm. On the south side, about half of the concrete shearwall is parallel to the major orthogonal axis, the other half is skewed and not parallel.
Would you define this as nonparallel?
If nonparallel system exists here, then Section 12.5.3 and 12.7.3 are applicable.
12.5.3 tells you how the structure shall be loaded.
12.7.3 tells you how the structure shall be analyzed and modeled. For irregularity #5, a 3D model is required; the only exception is provided for a flexible diaphragm structure if it has horizontal irregularity #4.
As computer modeling becomes widely available, I do not see an issue for analyzing this kind of building using a 3D model to get a more realistic results, and I think it's a great way to learn how the building would behave in different kinds of irregularities.
Thanks!
#ASCE7-16
#Seismic
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Manhin Lee Aff.M.ASCE
Plan Check Professional
City of Fremont
Fremont CA
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