Base Isolated SMF Design

[gzdee]

Hi everyone,

I am designing a base-isolated SMF. I am confused about Strong Column-Weak Beam Criteria in codes for SMF desing. Superstructure in a base-isolated building must be essentially elastic under design earthquake. So when designing superstructure, do I need to ensure strong column-weak beam criteria for also base-isolated structure?

Thanks for response.

 

[canwesteng]

Which code specifically? Strong column weak beam is more applicable to plastic design. I might be inclined to neglect the ductility factor when figuring your base shear if you wanted the structure to stay elastic, but it's hard to say if that's approriate without more details.

 

[gzdee]

I mean it is required to ensure moment ratio at beam to column connections and strong column-weak beam criteria for highly ductile members for SMF design in AISC 341-10. ASCE 7-10 Chapter 17 is just giving R value as 3/8 of the factor that is permitted for design of conventional, fixed-base building and also that value must be maximum 2. So for SMF base-isolated building desing, I take R value as 2. But Chapter 17 doesn't mention about other ductility requirements whether if we must ensure that criterias.

 

[mike20793]

I would think that if you are outside the realm of Chapter 12, then you are outside the realm of Table 12.2-1 and your moment frame isn't actually special, but rather a typical, non-seismic moment frame with an isolated base. But I have never designed such a structure, so this is merely my first intuition when reading the problem.