Steel Special Moment Frame with hinged one end 1

[jy4661]

I am designing seismic force resisting frames and have a question about steel special moment frame. If only one end of moment frame beam utilizes a pre-qualified connection per AISC 358 but the other end uses simple beam connection (pinned connection), Is it possible to treat this system as a special moment frame (R=8)? If not, why? For example, the bay between column line 1 and 2 or column line 3 and 4 on the attached sketch.

 

[JoshPlumSE]

No one else responding? Well, my take is that you can do it. Now, I haven't reviewed AISC 341/358 to look for specific provisions that might exclude it. But, off the top of my head, I cannot think of any.

The main challenge, in my opinion, would be that you will have to understand the code intent much better. It's not enough to follow examples because some of the canned formulas in the AISC 358 design procedures won't exactly apply. The concepts will be the same, but the configuration will be different enough that you need to thoroughly understand each step.

 

[johnbridge231]

Which software do you use for such analysis types?

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[JoshPlumSE]

The AISC 358 calculations are largely done with hand calculations. Especially for the strange case scenarios like this.

Some programs (like RISA-3D) will perform the basic AISC 358 calculations for you. But, my belief is that these programs will be built on the assumption that any beam in a SMF will be moment connected at both ends. Certainly, this is a case where you should not trust the program calculations without doing a detailed hand calculation to determine if the results are in the right ball park.

Disclaimer:
I work for RISA, so I can't really speak to what the ETABs and RAMs of the world do. But, I tested out a frame like this in RISA and the program will refuse to do AISC 358 calculations on the Fixed-Pinned beam. The column which supports it on the moment connection side looks like it gets designed nicely.... Though, it looks like the beam shears the program assumes for that connection are based on an assumption of a hinge at both ends of the beam. My belief is that this would always be a conservative error. Even so, you'd want to follow through the calculation by hand to make sure this doesn't cause other issues down the line.