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RE: PR and FR Moment Connections

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With regard to Mark Swingle's post on various moment connections, on 1/24/99 - I
will offer the following:

The primary difference between a PR and FR connection is the extent to which
connection flexibility contributes to overall frame deflection.  In an FR
connection this is presumed to be negligible, though in reality, panel zone
deformation in many standard FR connections can be significant contributors.  In
PR connections, the flexibility of the connection is a significant contributor.
There are no hard and fast rules.  Maybe that's good - it could allow you to
exercise judgement (still permitted sometimes).

Now with regard to what it all means -

If you decide a connection is fully restrained - you can do the following:
a) Do analyses to determine story drift and design forces neglecting connection
flexibility
b) Design the structure as a special moment frame, intermediate moment frame or
ordinary moment frame
Note that details for FR connections are supposed to be qualified by rigorous
laboratory testing, per Appendix S of the 1997 AISC Seismic Specification

If you decide a connection is partially restrained - you must do the following:
a) Consider connection flexibility in your analysis for story drifts and design
forces
b) design the structure as a PR frame
c) ensure that the connection is capable of developing at least 50% of the
plastic strength of the connected beam
Note that unless the connections are designed to remain elastic connection
details for Ordinary Moment frames are also supposed to be qualified for the
intended application by testing, though the testing criteria are somewhat
different.