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ASD load reduction and shear wall capacity reduction

ASD load reduction and shear wall capacity reduction

Table 4.2a and 4.3a require a 50% reduction in capacity for ASD loads.
asce 7-10 reduces wind load by a factor of .6 in all ASD load combinations.
So, when I design a shear wall or diaphragm, do I:
1. determine load from ASCE 7-10
2. reduce load by .6 to reflect ASD load combo
3. then use half capacity from t4.2a and 4.3a
OR is the 50% reduction for ASD actually reflect the 0.6 factor on my ASD load combos.

Also, should I use a .6 wind load to figure tension and compression on a shear wall
before choosing simpson tiedowns?

I probably shouldn't be confused by this, but lack of sleep is not helping at the moment.
Thanks in advance for the clarification.

RE: ASD load reduction and shear wall capacity reduction

You should apply the ASCE load factor to the (ultimate) wind load calculated through ASCE 7-10. Then you use the reduced capacity (nominal capacity/ASD reduction factor. The load factor accounts for the uncertainty in the demand; the reduction factor accounts for the uncertainty in the capacity. If you were to approach it from an USD you would need to do the same thing. the results are comparable: ASD - 0.6/(2.0) = 1.2 and USD - 1.0/(0.8) = 1.25.

RE: ASD load reduction and shear wall capacity reduction

To clarify, I'm using 2008 sdpws for tables 4.2a and 4.3a.

RE: ASD load reduction and shear wall capacity reduction

thanks Robert, I felt like I was reducing the load too much. A little payback to ASD users from USD users designing ASCE7.
I guess we deserve it.

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