Prescriptive Light Frame Construction

[Engrman]

I have a 2 story (25'-0" mean roof height) wood framed apartment project with 144'-0"x60'-0" plan dimensions. 1997 UBC, Seismic Zone 1, 85 mph wind, Exp. C. All upper and lower level exterior walls with the exception of the north lower level longitudinal (144'-0")wall meet the prescriptive requirements of Division IV - Conventional Light Frame Construction. The northern lower level area is where the garages are located. Therefore, the north wall is a series of 2'-2" wall panels with 9'-0" garage doors between. Floor-to-floor height is 10'-6" with 18" deep floor structure. The transverse walls, both exterior and interior all conform to Div. IV, although the garage separation walls are out as much as 6'-0" with the unit speration walls above (this may not be a requirement with prescriptive design but it still bugs me). Can I use the APA Portal Frames on the north lower level wall and still conform to Div. IV or is an engineered lateral-force-resisting system required?

 

[AlohaBob]

I usually use a 2 tier approach to this. Under normal everyday loading, I see to it that deflection is kept to a minimum imperceptible amount. At design load, I ensure enough strength in the pier panels. For life safety, I ensure a backup torsion diaphram system is detailed and in place. Never had one come back or be questioned.

 

[Engrman]

Mahalo plenty AlohaBob. Events beyond my control (read architect) made the use of the APA Portal Frames impracticable. Without the portal frames the building official made me do an engineered system. I ended up with a series of 3 sided (torsion) diaphragms. Your answer, much appreciated, will be filed away in my wittle brain for future reference.