Partially Restrained (PR) Moment Connections

[peteotoole]

According to the Steel Manual in B3.3 moment redistribution is not allowed for a sections that have partially restrained moment connections. I just grabbed a picture on google but for the image would a beam fixed at one end and simply supported on the other be an example of a partially restrained moment connection that cannot have the moments reduced? (also assuming this is a W-section)

Thanks.

 

[Celt83]

AISC has a good lecture on youtube done by Louis Geschwindner on the topic: Link

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[phamENG]

A partially restrained moment connection is a moment connection with a non-infinite rigidity that has a significant effect on the system stiffness, but much more stiffness than can pass for a true pin at ultimate loads. It has nothing to do with adjacent connections.

 

[JoshPlumSE]

I'm sort of a cynic about "partially restrained" moment connections. To me they are just moment connections that don't work properly. By that I mean they are poorly detailed moment connections that aren't rigid enough to be truly classified as moment connections.

But, I've spent almost all my career in California where seismic dictates most everything and partially restrained connections aren't allowed.

All kidding aside, the AISC manual section 11 (which is a very brief section) is all about PR moment connections. But, when defining a connection as FR (Fully Restrained) or PR (Partially restrained), figure 12-1 explains it better. The moment - rotation curve for these types of connections is significantly stiffer than a single shear connection. But, not stiff enough to be treated like an FR. Therefore, there are different procedures for dealing with them.

 

[peteotoole]

AISC B3.3 doesn't allow you to reduce moments "produced by loading on cantilevers, for design using partially restrained (PR) moment connections, or for design by inelastic analysis...and then further on in the commentary

[/indent]"This adjustment is appropriate only for cases where the inelastic redistribution of moments is possible. For statically determinate spans (e.g., beams that are simply supported at both ends or for cantilevers), redistribution is not possible; therefore, the adjustment is not allowable in these cases. Members with fixed ends or beams continuous over a support can sustain redistribution."

For the picture attached then, would this beam be available for moment reduction because as I read it in the commentary the beam "Must be either fixed at both ends or continuous over a support".

Thanks for the insight

 

[JoshPlumSE]

Generally, I don't use moment re-distribution like this in design. Mostly because the concept is that you are allowing the moment connection to yield in order re-distribute the moment. That means extra damage / deflection and such.

It's great for explaining why an EXISTING beam works even though it doesn't work on paper. But, I don't use it for design.

That being said, I would interpret this as a case where the moment on the FIXED end could be partially re-distributed so that it would behave closer to a pinned connection. I don't think it's going to help you too much. But, you could do it.