6 - 220
2b.
CONNECTIONS, JOINTS, AND FASTENERS
[Comm. J
Limitations Table J2.4 provides a minimum size of fillet weld for a given thickness of the thicker part joined. The requirements are not based upon strength considerations, but upon the quench effect of thick material on small welds. Very rapid cooling of weld metal may result in a loss of ductility. Further, the restraint to weld-metal shrinkage provided by thick material may result in weld cracking. Because a 5⁄16-in. fillet weld is the largest that can be deposited in a single pass by SMAW process, 5⁄ -in. applies to all material 3⁄ -in. and greater in thickness, but minimum preheat 16 4 and interpass temperature are required by AWS D1.1.* Both the design engineer and the shop welder must be governed by the requirements. Table J2.3 gives the minimum effective throat of a partial joint-penetration groove weld. Notice that Table J2.3 for partial joint-penetration groove welds goes up to a plate thickness of over 6 in. and a minimum weld throat of 5⁄8-in., whereas, for fillet welds Table J2.4 goes up to a plate thickness of over 3⁄4-in. and a minimum leg size of fillet weld of only 5⁄16-in. The additional thickness for partial-penetration welds is to provide for reasonable proportionality between weld and material thickness. For plates of 1⁄4-in. or more in thickness, it is necessary that the inspector be able to identify the edge of the plate to position the weld gage. This is assured if the weld is kept back at least 1⁄16-in. 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 the connecting material because of shear lag (Fisher, et al., 1978). By providing a minimum lap of five times the thickness of the thinner part of a lap joint, the resulting rotation of the joint when pulled will not be excessive, as shown in Figure C-J2.3. Fillet welded lap joints under tension tend to open and
* See Table J2.4.
Apparent edge of plate
Apparent weld throat
Actual edge of plate before welding
Actual edge of plate is distinguishable
Actual weld throat Fig. C-J2.1. Identification of plate edge. AMERICAN INSTITUTE OF STEEL CONSTRUCTION
Actual weld throat is distinguishable