movement of the web with respect to the flange). Excessive hold-back dimensions may result in localized buckling. The final example cited in the AISC Specification wherein welds must be terminated short is in the case of welds on opposite sides of a common plane, as shown in Figure 3–22. The reason for such interruption is again a workmanship issue; melting away of the edges is highly likely. Further, the short welds on the edges must be made out-of-position, and changes in welding procedure parameters will likely be required for these short welds. 3.5.11
Figure 3–21. Hold-back dimension.
Under ideal circumstances, the two members that constitute the T-joint should be brought as closely into contact as possible before those members are joined with a fillet weld. Along the length of a T-joint, perfect fit is never possible, and so some small gaps will exist. As the size of the gap between the two members increases, and if the fillet weld leg size is kept the same, the actual weld throat decreases (Figure 3–23). Externally, the weld may look identical to that of a properly prepared joint, but an increased stress level results from the applied load on the decreasing throat size. AWS D1.1 addresses this issue by requiring that the fillet weld size be increased by the amount of the gap if the fitup gap is greater than z in. (AWS D1.1, Provision 5.22.1). This principle is illustrated in the final schematic of Figure 3–23. AWS D1.1 also limits this option to gaps of up to x in. on materials less than 3 in. thick, and up to c in. for thicker materials. For larger gaps, other options are possible, but have not been addressed in a codified manner. 3.6
Figure 3–22. Welds on opposite sides of a common plane.
Fillet Welds and Fitup
Plug/Slot Welds
A plug weld is a weld made in a circular hole in one member, fusing that member to another member. A slot weld is similarly defined, but involves a slot versus a circular hole. Both are uniquely applied to lap joints. Neither is particularly
Figure 3–23. Effect of gap on weld throat.
42 / DESIGN GUIDE 21 / WELDED CONNECTIONS—A PRIMER FOR ENGINEERS