Collectors elements clarification

[POCliche]

Hi,
(ASCE7-10)
I am designing all my building, with seismic design categories C to F, including overstrength factor in all collectors elements, and I'm looking for a way I can reduce theses forces.

Collectors elements are required to be mostly calculated with Overstrength factor in the section 12.10.2.1.

In the exception, it say that the forces calculated above need not to exceed those calculated using the load comb. 12.4.2.3 with seismic force determined by section 12.10-3 ( F=0.4*Sds*Ie*Wpx)

In 12.4.2.3, in order to have the redundancy factor = 1.0, in 12.3.4.1 it say in 5. Design of collector elements, splices, and their connections for which the seismic load effects including overstrength factor of Section 12.4.3 are used. ( Load comb with overstrengh factor )

So it gets me back to where I need to design the collectors with overstrength factor.

Is it going full circle or I'm missing something here ? Can we really reduce the force to a maximum of F = 0.4*sds*Ie*Wpx ?

thanks

 

[JAE]

POCliche - see if I have this straight:

So you have three ways to calculate a collector force - two of which are based on your "typical" derivation of seismic demand and one based on 0.2(Sds)IeWpx.
1. Includes Ω but not ρ (12.4.3) using basic seismic demand - 12.8
2. Includes Ω but not ρ (12.4.3) using basic seismic demand 12.8 with diaphragm distribution 12.10-1
3. Includes ρ but not Ω (12.4.2.3) using 0.2(Sds)IeWpx.

You take the maximum of these three.

4. It then has an Exception where you can limit the above value to a value based on E = 0.4(Sds)IeWpx (12.4.2.3)
(Note that this upper limit includes ρ)

Section 12.3.4.1 allows ρ to equal 1.0 if you use Ω in the demand derivation per 12.4.3

So all this is saying is - you calculate 1-3 above...find the maximum.
Then compare that with the Exception.
Use the smaller of 4. va. the maximum of 1-3.




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