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RE: 2002 aisc seismic provisions

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Title: 2002 aisc seismic provisions


It is my understanding that Em and the “maximum force that could be delivered by the system” are two different things. Em is a code prescribed over-strength load that attempts to approximate the maximum load but is solely dependent on the system type. The building configuration, member sizes and material over-strength all contribute to the actual over-strength of the structure. The “maximum force,” therefore, is the actual load at which some component will fail, preventing the lateral resisting elements from seeing a load higher than that. An example would be the lateral load that would cause the foundation to uplift.


The commentary to the 1997 NEHRP has some good information about the Em load if you’re interested.



Matthew O. Hood, E.I.T.

-----Original Message-----
From: David Adie [mailto:DavidA(--nospam--at)]
Sent: Thursday, March 10, 2005 10:14 AM
To: 'seaint(--nospam--at)'
Subject: 2002 aisc seismic provisions


the commentary for part 1 - special concentrically braced frames - bracing connections - required strength (c13.3a) pg. 118 states "the minimum of two criteria, (i.e. the nominal expected axial tension strength of the bracing member and the maximum force that COULD be generated by the overall system) determines the required strength of both the bracing connection and the beam to column connection if it is part of the bracing system".

question #1 - how many of you design the connection per the nominal expected axial tension strength?

question #2 - how many of you are using the maximum force that COULD be generated?  that's also know as "Em", right?