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Weld fusion zone capacity

Weld fusion zone capacity

Weld fusion zone capacity

(OP)
Looking for some clarity on the necessity in checking stresses at the weld fusion zone.

Quote (Page 16.1-397 of Spec Chapter J Commentary, of AISC 14th Manual )

...Note that planes 1-1 and 3-3 are positioned away from the fusion areas between the weld and the base material. Tests have demonstrated that the stress on this fusion area is not critical in determining the shear strength of fillet welds (Preece, 1968).

Quote (Section 22.2.3 of "Welded Connections" - Blodgett and Miller, 1999)

...For fillet welds or partial joint penetration groove welds, using filler metal with strength levels equal to or less than the base metal, the theoretical failure plane is through the weld throat. When the same weld is made using filler metal with a strength level greater than that of the base metal,the failure plane may shift into the fusion boundary or heat-affected zone. Most designers will calculate the load capacity of the base metal, as well as the capacity of the weld throat. The fusion zone and its capacity is not generally checked, as this is unnecessary when matching or undermatching weld metal is used. When overmatching weld metal is specifically selected, and the required weld size is deliberately reduced to take advantage of the overmatched weld metal, the designer must check the capacity of the fusion zone (controlled by the base metal) to ensure adequate capacity in the connection.

I ordinarily specify E70XX weld material for ASTM A36 base material, which is a "matching" weld material per AWS D1.1 Table 3.1. The weld Fu = 70 ksi, which is obviously much greater than that of A36, considering Fu = 58 as a minimum. If the weld material were closer in mechanical property to A36 it is obvious to me that the effective throat governs the weld capacity, and is how I was taught a long time ago to check a PJP or fillet weld.

I will take a stab at answering my own question; I am wondering if the difference in rationale (between the above) is as simple as this:
AISC "assumptions":
1. The weld material is required to be "matching" to the base
2. The ratio of the rupture strength (filler/base) for any approved AISC structural steel, A36 for example being (70/58 = 1.23), verses the ratio of a unit effective throat width (1/0.707 = 1.41) for an equal leg fillet will exclude failure at the weld fusion capacity (this logic doesn't satisfy my concern about potential PJP weld fusion zones).

Blodgett and Miller "assumptions":
1. The authors are speaking strictly about filler/base strength ratios which are outside of those identified in the AWS D1.1, and not the precise/calculable differences (in my example above).

I can't find a pdf of that Preece document, but I imagine the answer is in there somewhere.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Weld fusion zone capacity

MG22....just an opinion, but if the weld meets the quality requirements of AWS D1.1 for steel, I would not be concerned about a separate check on the fusion zone.....

For aluminum, different story

RE: Weld fusion zone capacity

Another thought.....you can't accurately determine the strength or the area of the fusion zone. Both the strength (from solutioning of two different strengths of steel) and area (only the visible weld is definable/measurable) are inferred based on history of performance and various empirical tests over the years.

RE: Weld fusion zone capacity

(OP)
Thanks, Ron. Yeah the "critical" fusion area and post-weld chemistry of the fusion zone seem very complicated.

"It is imperative Cunth doesn't get his hands on those codes."

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