Ordinary, Intermediate, Special

[CTW]

In ASCE7's table for 'Design Coefficients and Factors for Basic Seismic-Force-Resisting Systems', Ordinary, Intermediate, and Special are used to described basic seismic resisting systems. Could someone please explain the difference between Ordinary, Intermediate, and Special?

thanks

 

[JAE]

If you are talking about steel - these systems are defined in the Seismic Provisions for Structural Steel Buildings (go to AISC's website to order.) Basically, they each have varying degrees of detailing requirements that ensure different levels of ductility....special being the highest level of ductility and therefore offers a larger R factor.

 

[Taro]

In short, Ordinary elements are expected to withstand minimal inelastic behavior, Intermediate elements are expected to withstand moderate inelastic behavior, and Special elements are expected to withstand significant inelastic behavior. The stringency of the detailing requirements is related to the expected behavior.

 

[rlflower]

I think Taro is on track. It's the detailing of the connections that is the bugger. "Ordinary" is the way it is usually done. The "Special" designation came about because the "Ordinary" was not good enough.

But technically, it boils down to just what requirements you choose to - or are required to - adhere to.

If you wish to investigate this further, purchase a copy of FEMA-350: "Recommended Seismic Design Criteria For New Steel Moment-Frame Buildings", published by the Federal Emergency Management Agency, dated July 2000. This is now recognised and required by many local jurisdictions.

 

[erkansamhal]

Dear CTW,

You will find the comprehensive details and examples on the steel and concrete ordinary/intermediate/special moment frames in the "'SEISMIC DESIGN OF BUILDINGS AND BRIDGES" by ALAN WILLIAMS and "SEISMIC DESIGN OF BUILDING STRUCTURES"by MAJID BARADAR...

See You,
ERKAN