Base Plate Design - Overstrength Factor

[Light1997]

I'm using moment frames as my lateral system. These moment frames are classified as "Steel Systems not specifically detailed for seismic resistance" since we are in class C. I've pinned base at the columns, am I supposed to design the column base plates with overstrength factored loads or not? Can someone provide an ASCE section where the requirements of overstrength factor for base plate design are there?

 

[driftLimiter]

The selection of systems not specifically detailed for seismic design is very open to interpretation. I don't think you will find any specific requirements for this system, I would suggest to review and understand the requirements pertaining to ordinary moment frames. These systems have more information in AISC 341 etc. That could be used to guide you.

 

[Light1997]

Agreed, but whatever I saw was just the requirement of Omega level forces for connection design of beam to column. I could not find any specification for column base plate design. Thus, my question that are we supposed to design the base plate and anchors for omega level force or not.

 

[driftLimiter]

Did you consider AISC 341 Part D6? I think it is a wise idea to follow these provisions even if not explicitly required for your selected seismic system.

 

[Deker]

My understanding is that AISC 341 is not applicable to R=3 design. You can design everything to AISC 360. Therefore the only elements that require consideration of the overstrength factor are those specified by other design standards, such as collectors per ASCE 7 and base plate anchorage (bot not the base plate itself) per ACI 318.

 

[driftLimiter]

I agree with @Deker that the code does not require it. My line of questions so far is an attempt to push you towards those provisions

If you check ASCE7 Chapter 14 Section 14.1.2.2.1 it plainly states that if you select 'Steel system not specifically detailed......" then you do not need to use AISC 341 for detailing etc. It refers you back over to AISC 360 which generally means that you just need to determine the required design forces from analysis.

Still good seismic design practice is to attempt to control the failure mode. We (ASCE) doesn't know the maximum magnitude of earthquake forces, the earthquake forces are a statistical approximation. You don't want the baseplate to be the first thing to go if the estimated load is exceeded.

You are essentially saying that the frame will have the same ductility as the OMF which is why I suggested following those recommendations on the connection design.