AISC


8.3. Fillet Welds

8.3.1. Are fillet welds stronger when loaded transversely than when loaded longitudinally?

Yes. This long known variation in strength as a function of load angle is recognized in the 2005 AISC Specification Equation J2-5. The maximum strength increase permitted therein is 50 percent, which occurs for a load perpendicular to the fillet weld. When the load angle is intermediate between longitudinal and transverse, the strength increase will vary between none and 50 percent, respectively.

last modified 1 January 2006

8.3.2. Does the fusion zone along the leg of a fillet weld need to be checked in addition to the theoretical throat to determine the strength of a fillet weld?

No. As long as a matching electrode strength is used (see also 8.7.5) as required in the 2005 AISC Specification Table J2.5, the weld throat will always be more critical than the fusion zone (base metal) at the weld leg.

last modified 1 January 2006

8.3.3. When fillet welds are oversized, what corrective procedures are required?

Acceptable and unacceptable weld profiles are specified in AWS D1.1:2004 Section 5.24. Such profiles are subject to misinterpretation when a fillet weld has been inadvertently oversized. AISC recommends that either or both legs of fillet welds may be oversized without correction, provided the excess weld metal does not interfere with the satisfactory end use of the member. Attempts to remove such excess weld metal may cause shrinkage, distortion, and/or cracking. The profile of fillet welds shall be in accordance with AWS D1.1:2004 Section 5.24.1.

last modified 1 January 2006

8.3.4. Are corrective procedures required when fillet welds are undersized?

From AWS D1.1:2004 Table 6.1, A fillet weld ... shall be permitted to underrun the nominal fillet weld size specified by 1/16 for 3/16, by 3/32 for 1/4, and by 1/8 for welds equal to or greater than 5/16 in. without correction, provided that the undersize portion of the weld does not exceed 10% of the length of the weld. If this limit is exceeded, additional weld metal can be deposited on top of the deficient area to increase the size as required.

last modified 1 January 2006

8.3.5. How should fillet welds be terminated?

This topic is thoroughly covered in the 2005 AISC Specification Section J2.2b and corresponding Commentary.

last modified 1 January 2006

8.3.6. Why is a fillet weld size generally limited to 1/16-in. less than the material thickness when placed along the edge of a connected part?

As explained in the 2005 AISC Specification Commentary Section J2.2b, "For plates of 1/4-in. (6 mm) or more in thickness, it is necessary that the inspector be able to identify the edge of the plate to position the weld gage." Note that this requirement is qualified in AISC Specification Section J2.2b: the weld toe is permitted to be less than 1/16-in. away from the edge of the base metal, provided the weld size is clearly verifiable. Additionally, the weld size can match the thickness of the plate edge for plates that are less than 1/4-in. thick.

last modified 1 January 2006

8.3.7. Is the weld-all-around symbol acceptable when a fillet weld must be continued out-of-plane?

No. Use of the weld-all-around symbol at conditions that would require the weld to be continued out-of-plane calls for a condition that is specifically prohibited in the 2005 AISC Specification Section J2.2b and AWS D1.1:2004 Section 2.8.3.5. Instead, when an out-of-plane transition occurs, the welds must be interrupted at the corner common to both welds.

last modified 1 January 2006

8.3.8. What constitutes acceptable fit-up in fillet-welded joints?

From AWS D1.1:2004 Section 5.22.1, a root opening not exceeding 1/16 in. is permitted without modification. A root opening not exceeding 3/16 in. is generally permitted therein if the weld size is increased by the amount of the root opening or it is demonstrated that the required effective throat has been obtained. For plate thicknesses greater than or equal to 3 in., a 5/16-in. root opening is permitted if suitable backing is used.

last modified 1 January 2006