Steel moment frame 1

[LGARG]

Hi guys

I wanted to know if its ok to calculate all the OMF with a 2.8 omega factor(not only the connection).WE usually do that to avoid the design of the connection and the drift check. We usually use a Column to beam welded connection without plates. Is this Ok?


LG

 

[JAE]

If you beef up the beam too much you may force the hinge back into the connection. The desire is to ensure that any plastic hinges will form in the beam, and not a brittle failure in the connection.

 

[JAE]

...I'm sure some seismic gurus out there can add/correct what I just posted......Taro? Qshake?

 

[haynewp]

Sounds right to me, e.g. dogbone requirements.

 

[Taro]

LGARG, I assume from your reference to "2.8 omega factor" that you are using 1997 UBC (or equivalent California code). If this is the case, I would suggest that you consider using a more modern code. A lot of research has been done on steel moment frames in the past 13 years since the 1994 Northridge earthquake and the code provisions have changed substantially. Stricter limitations have been placed on the use of ordinary moment frames.

Also, I'm not quite sure what you mean by "avoid the design of the connection and the drift check". Connection design and drift checks apply to all systems. I assume you mean that you do not want to do cyclic testing of the connection to assure the required strength and inelastic rotation capacity. Again, I would recommend using a more modern code that provides "prequalified" connection configurations that have already been tested.

 

[LGARG]

Taro you are right i´m using the UBC 1997 code. I apologize for my bad english. What code or seismic book that contains this prequalified connection do you suggest ?
Thanks to all of you for your answers

LG

 

[Taro]

The current state-of-the-art publications are AISC 358-05 "Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications" and AISC 341-05 "Seismic Provisions for Structural Steel Buildings". Both are available as free downloads from aisc.org. These standards are also included in the AISC Seismic Design Manual.

Good background material for reference is the FEMA 350-355 series of publications that came out of the SAC research following Northridge.