Partial Moment Connection

[PEinVA]

Hi All,
I have a 6 story steel building. It resides in IBC 2003 - Seismic Zone B, Site Class D.
I am on the east coast in the mid-Atlantic region.

I have a braced frame system to resist lateral forces. However, along the exterior of my building I have a few moment connections to support areas where the columns and facade step to obtain the design "motif" that the architect desired.

However, now I have moment connections in a great position for lateral loads. I wasn't designing it this way until I realized what was going on, and now I'm trying to determine how to mesh these things together. I want to partially restrain these connections in units of a spring constant.
I've found some articles for how to do this in an unbraced frame, but how do I do this in a braced frame?
Thanks.

Rick


RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[prsconsultant]

1. IBC does not have seismic zones anymore. Do you mean seismic design category "B"?
2. SDC would dictate what kind of moment frame you may use.
3. Moment frames can hardly compete with braced frames from a stiffness point of view. I don't see why you are thinking of modeling partial fixity? Even with full fixity you may hardly see any forces in moment frames due to lateral loads.
4. If your system is not classified as a dual system, I would distribute lateral loads to moment frames based on tributory area.
5. If you are planning to utilize partially restrained composite moment connections there is a AISC design guide explaining how to design.

 

[PEinVA]

prsconsultant,
Thanks for the response, sorry for the typos on the previous post.

1. Yes I do mean design category.
2. I'm not actually looking to use a moment frame in my lateral design and I want to see with the partial fixity at those connections if the load getting into them versus the braced frames would be small enough that existing gravity controlled members would be sufficient.
3. I modeled the members as fully fixed and got some crazy results. So I wanted to model it more accurately within ETABS. ETABS only allows you to model partial fixity with a spring stiffness.
4. I am designing my system using R = 3 for a system not specifically designed for seismic.
5. I will look that up on AISC.org.

Thanks again

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[prsconsultant]

I think you may be seeing a modeling problem in your etabs. Even with complete fixity I would not expect significant forces in MF members. I don't think partial fixity would make any difference. Verify your model.

 

[strguy11]

From a stiffness point of view, I cant imagine that the much load is going to the moment frames, since the braced frames will be more rigid than the moment frames.