Overload Factor (Omega) For Light Framed Wood Structures

[TimPhillips]

Hello,
I'm guessing this question has already been asked but can't find a specific thread. I am designing a single story commercial building seismic category C with a wood roof and wood shear walls. The roof diaphragm dimensions are 110'x60'. The are 3 ft wall offsets which create reentrant corners in the roof which creates discontinuities in the diaphragm chords (the top of wall wood plates).

My question is, does the diaphragm chords and the collectors at the reentrant corners need to factored by the overload factor (omega) of 3. There are exceptions listed in ASCE 7-16 12.10.2.1 and 12.10.3.4 that seem to imply the overload factor does not need to be used.

 

[HTURKAK]

The cases in ASCE 7-16 where the use of overstrength factor is necessary are the following:
1. Design of collector elements in SDC C, thru F (Section 12.10.2.1).
2. Design of elements supporting discontinuous wall or frames for the systems with horizontal irregularity Type 4 or
vertical irregularity Type 4 of Table 12.3-2.
3. Foundations of cantilever columns systems (Section 12.2.5.2).
4. Batter piles, pile anchorage and pile splices .

Acc. to your description , Section 12.10.2.1 Collector Elements Requiring Load Combinations Including Overstrength for Seismic Design Categories C through F.s applicable and the EXCEPTION:
1. In structures or portions thereof braced entirely by wood light-frame shear walls, collector elements and their connections,including connections to vertical elements, need only be designed to resist forces using the load combinations
of Section 2.3.6 with seismic forces determined in accordance with Section 12.10.1.1.




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[TimPhillips]

HTURKAK

Thank you for your response. I am asking for confirmation of my interpretation. Since the building is light framed the exception can be applied. Therefore, i believe only the diaphragm chords are to be designed using the overload factor and the collectors are not. Is this correct?

 

[ChorasDen]

Do you have an vertical or horizontal discontinuities in this structure? If so, you need consider overstrength around those discontinuities, regardless if the entire structure is light-framed or not.

 

[TimPhillips]

Yes. There are 3 ft wall offsets. So horizontal irregularities. Where does is it stated in ASCE 7-16 the overload factor is to be used at irregularities?

 

[ChorasDen]

Table 12.3-1 has all your applicable irregularity checks and the relevant sections to review associates with those checks. From what you've indicated so far, probably want to take a look at 12.3.3.3, 12.4.3, & 12.8.4.3.