Moment Frame - Rigid & Pinned connection

[ronstruc]

I am designing a special steel moment frame building with 2 bays in one direction. Due to the wide flange column configuration I cannot do a moment frame with fixed ends at each column. Looking at a bay I have two beams connecting with a pinned connection to the outer columns and connecting rigidly (moment) to the center column, thus two half frames. I am designing this under the 06' IBC and the AISC 341-05 seismic provisions for SMF (special moment frame) conditions.

Does anyone know if there is a code violation of not using a frame fixed at both ends?
Thanks in advance.

 

[csd72]

I have seen this done in other countries (non-seismic) where a big column is used in the center and small pinned ones on the outside walls. It seemed to work fine.

Under lateral load it works kind of like outriggers in a high rise, one external column goes into tension and the other into compression.

I wouldnt use 2 half frames though it is virtually a mechanism.

csd

 

[prsconsultant]

If you are using an SMRF, what you are doing is not acceptable. All the AISC pre approved connections assume plastic hinges to form at certain location at both ends of the beam.

 

[LGARG]

I think that you should model this frame with some software like ram advance or risa 3d. For this kind of structure the R factor should be very low Lets say 2.2 or 2(like a cantilever column). You should be conservative and show the plan checker that this structure really works. The main problem would be the ductility of the structure that is unknown because you don´t have any test that could prove the really ductility of the sistem.


LG

 

[ronstruc]

I modeled the building in ETABS, and it appears to work fine. Drift significantly controls the design of the frames. I couldn't find anywhere in the seismic provisions (AISC 341) nor in FEMA 350 where you had to have two plastic hinges, one at each end of the beam. They address the connection and the beam and column relationship. The connection satisfies SMRF requirements. Are you aware of anywhere in the codes that specifically suggests that this is not allowed?

RC

 

[csd72]

Doesnt it have two hinges - one on each side of the middle column?

 

[ronstruc]

Yes it has two hinges, one on each side of the middle column. However each beam only has one hinge.