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RE: Backing bar in RBS steel moment connection

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For one thing, the bottom flange backing bar is located at the most extreme location as fas as stress, at the top flange it is not.
 
AISC 358 mandates this as well.  There is a rather extensive commentary in AISC 341 which may have more information.  Both are free at the AISC web site, last time I checked.
 
Additionally they found many problems stemming from the Northridge earthquake (parking structures being another one, which may be one reason they may have mandated I=1.25 for large structures, different subject)   But there has been an inordinate amount of research done in this area.  There is a Structural Engineer from the Bay area who spoke for AISC at the steel frame seminars that had been going around the country (whose name I don't recall) who was very bright, and can speak to this issue at great length. (He was also very adept at answering a lot of design questions)  There are many engineers as well, who are on the SAC committee, for FEMA 350 etc, who can speak at great length about this issue as well.
 
I know recently AISC printed the prequalified RBS connection, someone may know of a link to that diagram.

----- Original Message -----
From: "Michel Blangy"
To: seaint(--nospam--at)seaint.org
Subject: RE: Backing bar in RBS steel moment connection
Date: Fri, 18 May 2007 12:00:04 -0700

As usual excuse my ignorance, but why only the bot. flange?
 
MB
-----Original Message-----
From: bart(--nospam--at)nbse.com [mailto:bart(--nospam--at)nbse.com]
Sent: Friday, May 18, 2007 11:47 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Backing bar in RBS steel moment connection

At the beam bottom flange, the backing shall be removed.
 
At the top flange, removing the backing is optional. (continuous attachment to the column with a fillet weld is required)
 
My opinion is that leaving backing bars in place is a poor idea, however, it is often cost prohibitive to remove them, backgouge and backweld with a reinforcing fillet.

----- Original Message -----
From: "Gautam Manandhar"
To: seaint(--nospam--at)seaint.org
Subject: RE: Backing bar in RBS steel moment connection
Date: Mon, 7 May 2007 14:55:31 -0700

List members:

 

In a RBS steel moment connection, the expected plastic hinge is at the reduced beam section.  How important is it to remove the backing bar at the beam-column connection?  I am aware that in the pre-Northridge, fracture initiated at the bottom CJP joint.   Is anyone aware of tests done with the backing bar in place.

 

Gautam

 

 



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Bart Needham, SE
Principal, nbse associates, inc.
Office 206-780-6822
Office 805-452-8152
Fax    206-780-6683
Fax    208-693-3667
Mobile 206-300-2346

Office locations:
629 State Street #230
Santa Barbara, CA  93101

205 Fairview Lane
Suite 100
Paso Robles, CA  93446

365 Ericksen Ave. NE
Suite 328
Bainbridge Island, WA  98110

Mail and Deliveries:
321 High School Rd. NE
Suite D-3 PMB 216
Bainbridge Island, WA  98110