STAAD.pro 2007and IBC 2006/AISC Seismic Provisions 1

[TiffanyEIT]

Dear respected Engineers,
I am designing my first pipe rack using STAAD.pro 2007and IBC 2006/AISC Seismic Provisions. I'm using the load combinations stipulated in section 1605.2 and 1605.4 which leads to section 12.4.3 of ASCE 7-05. I need some clarifications please: .

1- Is the overstrength factor used to design all members of the structure?

2 - What does 1.1*Ry (or 1.1*Ry*Fy*Ag) represent? Is it applied to all members of the structure? how would you write it in STAAD editor?

Please advice. if I missed anything or if you have any tips for modeling pipe racks in STAAD and would like to share them.


Thank you.

Regards,

Tiffany Lorenzzi
Structural Engineer (EIT)

 

[JAE]

I don't know anything about STAAD but the 1.1RyFy value is used by AISC to require the engineer to design portions of the lateral force system such that brittle failure modes are avoided.

One example is the connection of a brace at its ends. The code will require you to design the connection for 1.1RyFy of the brace member. In other words, the real yield stress is a bit higher than Fy and by designing the connection such that its capacity is HIGHER than the brace itself, ensures that the brace will yield prior to the connection failing.

 

[prsconsultant]

Below is a link to FEMA 350 document which explains in detail why we need to use a factor with Ry. Look at section 2.6.2.

http://www.fema.gov/plan/prevent/earthquake/pdf/fema-350.pdf