Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Engineers position on E70T-4

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I am responding to your Email to the SEAOC list server in my role as 
Project Director for the SAC Joint Venture.  SAC is a ;jv of SEAOC, 
ATC and CUREe, formed specifically to address the fracture damage 
that occurred to steel moment frames in the Northridge earthquake.  
We were the authors for the FEMA-267 document which has been used as 
the basis for desing of welded steel frames in the last 18 months.

The concept of "critical" weld is not well defined - even for 
engineers, let alone the people who actually have to do the work.  
There is no formal position.  However, I believe you can use the 
following guideline-

The basic problem is one of fractures (cracking) initiating in full 
penetration groove welds that are subjected to large tensile stresses 
(either cyclic or otherwise).  For moment connections
this would inlcude beam flange to column flange welds,
 continuity plate to column flange welds and column splice welds.  
Depending on the design details, it may also include certain welds of 
gusset plates in braced frames to columns and beams.  The basic 
problem is that because E70-T4 material has low toughness, they are 
brittle.  Minor imperfections within the welds (even those permitted 
by AWS D1.1) can initiate unstable cracking under large applied 
tensile stresses, due to the stress concentrations that occur locally 
around the imperfection.  Other types of weld materials, for example 
E7018, E70T8 have a higher toughness and rather than fracturing, 
yield at these local areas of high stress.

In general, fillet welds and partial penetration groove welds will 
not require the notch tough material.  However, these types of welds 
are inherently poor in resisting tensile stresses and should not be 
used where large tensile demands are anticipated.

It is not really the welder's responsibility to determine which welds 
are critical.  This is really the responsibility of the Engineer of 
Record, who should designate on the drawings and/or specifications, 
those specific welds that require special processes.  Some engineers 
may wish to specify that all welds used on a project have rated notch 
toughness.
Ronald O. Hamburger
Project Director for Product Development
SAC Joint Venture