# RE: Design Moment For Semi-Rigid Connections - see AISC Seismic P rovisions for OMF

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>, "Rick Fiedler (E-mail)" <fiedlera(--nospam--at)stvinc.com>
• Subject: RE: Design Moment For Semi-Rigid Connections - see AISC Seismic P rovisions for OMF
• From: "Haan, Scott M." <HaanSM(--nospam--at)ci.anchorage.ak.us>
• Date: Tue, 24 Apr 2001 11:09:34 -0800
```Keith:

I had a hangover the day they covered partially restrained connections and
inelastic analysis but I will stick my neck out a little bit here.

The AISC Seismic Provisions Section 11.2a has criteria for PR OMF and one of
the criteria is that the connection has a nominal flexural strength at least
50% of the lesser of the column flexural strength or the beam flexural
strength.

A general rule of thumb for seismic design is that you normally want
connections to be as strong as the members or the maximum force that can be
delivered to the connection by the system, because you want the members to
dissipate seismic energy and not the connections.  This is the concept of R
and OMEGAo.  By thier nature partially restrained connections dissipate
energy in conjuction with the members and make me feel violated when I
review storage rack permits.

For an elastic wind loading or gravity loading it is a rule of thumb that it
is ok to design the connections for design forces.  When you say 6 times my
wind moments are you saying considering your connection stiffness? There are
formulas for adjusting your beam moment of inertia considering connection
stiffness so an elastic analysis can be done.

Peter can tell you how to do a wind-frame analysis.

Respectfully,

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://www.muni.org/building
<http://www.muni.org/building>
Development Services Department
Municipality of Anchorage
phone:907-343-8183  fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us <mailto:haansm(--nospam--at)ci.anchorage.ak.us>

-----Original Message-----
From: Hyndman, Keith [mailto:KHyndman(--nospam--at)engineeringsi.com]
Sent: Tuesday, April 24, 2001 10:03 AM
To: 'seaint(--nospam--at)seaint.org'; Rick Fiedler (E-mail)
Subject: Design Moment For Semi-Rigid Connections

In the Design of Semi-Rigid Connections in Steel Frame buildings I have
typically used moment magnitudes generated by Wind or Seismic Loading.  This
follows the guidence given in the "Big Red Book" Engineering for Steel
Construction Chapter 4.

I was thrown for a loop when I read "Design Tables for Top and Seat Angle w/
Double Web Angle Connections" by Yosuk Kim and Wai-Fah Chen in the
Engineering Journal 2nd Quarter.

In the design example they used 1/2 the Plastic Moment of the beam as the
design moment for connection.

This is resulting in moment values "6" times my wind moments.

Is this a Limit State Criteria?

Should I redesign my connections based on this?

Is this approach overkill for buidings less then 35' high and in low seismic
regions?

Your comments and opinions are greatly appreciated.

Keith Hyndman, P.E.
Exton, PA

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