Overstrength Factor for Light Frame Shear Wall

[adealba10]

In reference to previous post "thread507-268104" about this topic I was not able to find a definitive answer for use of the overstrength factor in ASCE 7-10 12.10.2.1 with regards to light frame shear walls.

Exception #2 states "In structures or portions thereof braced entirely by light frame shear walls, collector elements and their connections including connections to vertical elements need only to be designed to resist forces using the load combinations of Section 12.4.2.3 with seismic forces determined in accordance with section 12.10.1.1"

I am designing a soft story retrofit using a light frame wood shear wall and from my understanding should be able to design my drags/collectors and associated connections WITHOUT overstrength factor as indicated by this exception. What is confusing to me is that the table still shows an omega value of 2.5 (flexible diaphragm) for light frame shear walls. Is that only to be used in buildings with different systems (not exclusively light frame shear wall)?

 

[AaronMcD]

See 12.3.3.3 Elements Supporting Discontinuous Walls or Frames.
For a single story, sure, you may not have any use for overstrength in a light frame building except for anchorage.
Also don't forget 12.3.3.4, which increases collector loads in SDC D, E or F if certain irregularities occur. I just always design my chords and collectors for the extra 25%.

 

[adealba10]

Thank you for clarifying AaronMcD, yes that makes sense. I also include the 25% for irregularities unless it's very clear cut rectangular with no openings or discontinuities. About half the time the old buildings we retrofit are nice and square. Thanks for your reply!