residual stresses due to welding
residual stresses due to welding
(OP)
I'm looking for a residual stress value to use for the analysis of an existing structure - a beam-column (Fy=33ksi) with plates (A36) welded to each flange. (The member was rolled, then, after 40 years of service, these flange plates were added by continuous fillet welds on each edge of the plate.)
Testing for stresses isn't an option.
I haven't found very clear guidance on the stresses caused by welding the flange plates.
Salmon and Johnston, p. 286, shows typical residual stress distributions for welded shapes, ranging from 12-40 ksi. The discussion is a little thin. Based on their info, I would use the 40 ksi tensile stress in the flange tips for my structure, but that is higher than yield, and, clearly, would render my structure inadequte.
Stability Design Criteria for Metal Structures by Galambos, p. 35, states that the max tensile residual stress at a weld is equal to or greater than the yield stress of the plates. It seems sensible to conclude that this MAY occur, but that such high stresses would be relieved, to an acceptable level (<<Fy) before the member is put into service.
So, both texts say that residual stresses due to welding can be about equal to yield, but that doesn't make sense, given the implications.
What about the good old Fr = 16.5 ksi, from Ch F in the silver LRFD manual?
Any comments/suggestions/clarifications would sure be appreciated!
Testing for stresses isn't an option.
I haven't found very clear guidance on the stresses caused by welding the flange plates.
Salmon and Johnston, p. 286, shows typical residual stress distributions for welded shapes, ranging from 12-40 ksi. The discussion is a little thin. Based on their info, I would use the 40 ksi tensile stress in the flange tips for my structure, but that is higher than yield, and, clearly, would render my structure inadequte.
Stability Design Criteria for Metal Structures by Galambos, p. 35, states that the max tensile residual stress at a weld is equal to or greater than the yield stress of the plates. It seems sensible to conclude that this MAY occur, but that such high stresses would be relieved, to an acceptable level (<<Fy) before the member is put into service.
So, both texts say that residual stresses due to welding can be about equal to yield, but that doesn't make sense, given the implications.
What about the good old Fr = 16.5 ksi, from Ch F in the silver LRFD manual?
Any comments/suggestions/clarifications would sure be appreciated!





RE: residual stresses due to welding
RE: residual stresses due to welding
http://www.welding-advisers.com/
RE: residual stresses due to welding
http://airmatic.com/content/view/50/70
BK
RE: residual stresses due to welding
Try: http//airmatic.com/content/view/50/70/
BK
RE: residual stresses due to welding
RE: residual stresses due to welding
RE: residual stresses due to welding
RE: residual stresses due to welding
RE: residual stresses due to welding
Consider:
Modulus of elasticity equals stress divided by strain.
Set:
maximum stress is the yield point of the base metal.
strain is equal to coeff. of expansion times delta T.
E = Yield Point divided by delta T times coeff. of expansion, solve for delta T
Then consider the instantanious temperatures involved when you weld a piece of plate. The temperatures between the heat affected zone and slightly beyond can easily have temperatures exceeding the delta T derived from the equations above.
The secret is the delta T between the immediate area of the weld joint and the unaffected base metal surrounding the weld. The cooler unaffected base metal acts as a restraint against the metal being heated by the welding operation. As it is being heated, it expands, but is restrained, thus the maximum force it can exert is equal to the yield strength of the base metal (at temperature). At that temperature plastic flow is experienced because the yield strength of the base metal has been reached. As the metal contracts as it cools, the compressive forces become tensile in nature. Thus the residual stresses are equal to the yield strength of the base metal.
Hope this helps to explain what happens.
Best regards - Al
RE: residual stresses due to welding
Stresses < 0.5Fy is certainly better than stresses > Fy, but it would be nice to know for sure. I just orded Welding Research Council bulletin 383 on nondestructive means for determining residual stresses, so we may use one of those methods to know for sure what's going on with this structure.
RE: residual stresses due to welding
Assuming the modulus of elasticity for all carbon steel is the same, the delta T will be influenced by the actual yield strength of the alloy selected for fabrication. Still, the delta T required to develop stresses equal to the yield point are much lower than most people would expect.
This is put to use by fabricators to camber or put sweep into beams and girders. It is also used to remove excess sweep, camber, or to straighten beams that have been damaged during shipment or erection.
Best regards - Al