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RE: Remove Weld Backing Bar, ASCE 31 Review

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Sam,

There are many factors here. Is the building currently occupied? Are the
connections accessible for modification? What is the current occupancy /
intended occupancy? How much redundancy? What is the owner's expectation for
performance in the next seismic event? Any idea of type of welding process
or filler metal used to make these welds?

Backing removal is typically done by air arc gouging (fire hazard in
occupied building). Could be done by grinding (ditto on the fire hazard, but
less risk). Pneumatic chiseling another (loud) option. 

UT of existing joints would likely tell you little in this case, unless
there were gross nonconformances that were not found in the initial
inspections and testing. You have a pre-existing "crack" at the root from
the backing. If you do have UT done, make sure they are highly skilled with
these joints, and can distinguish between backing indications and root
discontinuities.

You had mentioned funding? Private? Insurance? Government assisted?

SSTC will be having our Steel Connections: Seismic Applications 2005 seminar
in late April in South San Francisco. Fresh updates for AISC Seismic
Provisions 2005, and for AWS D1.8 nearing completion. Trying to get people
off FEMA 353. We'll also be having our Structural Welding: Design and
Specification seminar and our Structural Steel Inspection seminar the same
week. Info is on our website at www.steelstructures.com .

Bob Shaw
SSTC


-----Original Message-----
From: Szuchuan Chang [mailto:szuchuan(--nospam--at)gmail.com] 
Sent: Thursday, March 03, 2005 3:17 PM
To: seaint(--nospam--at)seaint.org; Sam Chang
Subject: Re: Remove Weld Backing Bar, ASCE 31 Review

Mr Shaw,

Thanks for your infomation.  I was in your seminar many years ago at
Palo Alto, CA.  ASCE 31 is the old FEMA 310 except it cost about $30
per copy.

I have just read the chapter 2 of FEMA 351.  I am going up there (25'
high) to take a visual on the connection.  Backing bars used in those
days are pretty big.  It is not a easy task to remove them.  The
process of prying it off, may also add to the existing stresses.  The
cost starts to build up if we decided to pay for the cost of folloing
Seismic Provision recommended grinding and fillet weld per I-11.2(1).

I thought about  UT the joints.  With a backing bar there, UT may be a
problem too.

I will keep you posted.

Sam

On Thu, 3 Mar 2005 11:33:52 -0500, Robert E Shaw Jr
<rshaw(--nospam--at)steelstructures.com> wrote:
> Sam,
> 
> Take a look at FEMA 351, Recommended Seismic Evaluation and Upgrade
Criteria
> for Existing Welded Steel Moment-Frame Buildings, July 2000, esp section
> 5.4.
> 
> I don't have ASCE 31 so I do not know how detailed it gets regarding the
> issue.
> 
> Bob Shaw
> SSTC

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