need opinion of classification of building for horizonal plan irregularity

[Engineerataltitude]

I am looking for other professional opinions as to whether or not this building should be classified as a Type 5 Nonparallel System Horizontal Structural irregularity or not per ASCE 7-16 Table 12.3-1. See attached plans

Owner wants to build with light wood frame construction and thus wants wood shear walls as the shear resisting elements.

However, if it is a Type 5 horizontal Structural Irregularity per Table 12.3-1, Sec 12.7.3 REQUIRES a 3D analysis in addition to the 100% 30% loads per 12.5.3. Not optional.

However, if it is not a Type 5 horizontal structural irregularity, no 3D analysis would be required.

As you might guess, I did not have a 3D dynamic model in my budget for engineering this house.

By the way, anyone ever heard of any successful 3D modeling of an irregular 3 story building with all wood construction and wood shear walls?

Thanks in advance for your thoughts.

 

[le99]

Table 12-3-1, 5. Nonparallel System Irregularity:
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.

In your plan, the vertical lateral force-resisting elements (the columns) ARE parallel to the major orthogonal axes (grids A-A and D-D or E-E) of the seismic force-resisting system. So, you don't have type 5 irregularity.

Edit: The above assessment is false because the shear walls are not parallel to the main grid system.

 

[driftLimiter]

It sure looks like a non-parallel system. If you check the commentary they show a structure that looks pretty similar. By my reading of Table 12.6-1 you can still use ELF for this system, and my understanding of 12.7.3 is that you need to account for the 3D effect and the coupling of shear wall forces. It doesn't mean you have to do a 3D model IMO, it means you need to determine the forces to the lateral elements based on the 3d layout. 12.7.3 uses the terms '3D representation' and '3D model' differently.

I think it just means that you need to assess the loading in each lateral element properly based on the 3D orientation and with respect to the direction of load application. Then you need to go to 12.5.3.1a and use the 100% and 30% combinations to determine the maximum effect. More accounting to do for sure, full 3D model maybe not??

I don't know any software that does a flexible diaphragm assumption on a 3d wood building properly. You could perhaps try using semi rigid and rigid approaches but the stiffness of your wood shear walls and diaphragm are difficult to asses and should be based on the code required deflection equations.

 

[driftLimiter]

In your plan, the vertical lateral force-resisting elements (the columns) ARE parallel to the major orthogonal axes (grids A-A and D-D or E-E) of the seismic force-resisting system. So, you don't have type 5 irregularity.

The axes your referring to are not orthogonal!

Basically with the shear walls identified, there would always be LFRS elements that are not parallel to a set of orthogonal axes. The 'X' and 'Y' direction of the EQ are arbitrary, but they are always orthogonal.

 

[le99]

Yes, I agree, The shear walls are not parallel to the main grid system. My negligence.

 

[Engineerataltitude]

Thank you for your help!