AISC LRFD 1.pdf

Comm. J2.] WELDS 2332b. LimitationsTable J2.4 provides a minimum size of fillet weld for a given thickness of the thickerpart joined.The requirements are not based upon strength considerations, but upon the quencheffect of thick material on small welds. Very rapid cooling of weld metal may resultin a loss of ductility. Further, the restraint to weld metal shrinkage provided by thickmaterial may result in weld cracking. Because a 5 16-in. (8 mm) fillet weld is the largestthat can be deposited in a single pass by SMAW process, 5 16-in. (8 mm) applies toall material 3 4-in. (19 mm) and greater in thickness, but minimum preheat andinterpass temperature are required by AWS D1.1.* Both the design engineer andthe shop welder must be governed by the requirements.Table J2.3 gives the minimum effective throat of a partial-joint-penetration grooveweld. Notice that Table J2.3 for partial-joint-penetration groove welds goes up to aplate thickness of over 6 in. (150 mm) and a minimum weld throat of 5 8-in. (16 mm),whereas, for fillet welds Table J2.4 goes up to a plate thickness of over 3 4-in. (19mm) and a minimum leg size of fillet weld of only 5 16-in. (8 mm). The additionalthickness for partial-joint-penetration groove welds is to provide for reasonableproportionality between weld and material thickness.For plates of 1 4-in. (6 mm) or more in thickness, it is necessary that the inspector beable to identify the edge of the plate to position the weld gage. This is assured if theweld is kept back at least 1 16-in. (2 mm) from the edge, as shown in Figure C-J2.1.Where longitudinal fillet welds are used alone in a connection (see Figure C-J2.2),Section J2.2b requires the length of each weld to be at least equal to the width of theconnecting material because of shear lag (Freeman, 1930).By providing a minimum lap of five times the thickness of the thinner part of a lap* See Table J2.4.Fig. C-J2.1. Identification of plate edge.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION