Table 2.4. Hex Coupling Nut Dimensions Diameter of Rod, in.
Width Across Flats, in.
Width Across Corners, in.
Height of Nut, in.
w
18
1c
2�
d
1c
1�
2s
1
1�
1w
3
1�
1d
2x
3w
1�
2�
38
4�
1w
2w
3x
5�
2
38
3s
6
2�
3d
4�
7�
Dimensions based on IFI #128 of Industrial Fastener Institute. Material conforms to ASTM A563 Grade A.
the nut are engaged. Welding the nut to the anchor rod is not a prequalified welded joint and is not recommended. If the anchor rod is too short and the rods are used only for column erection, then the most expedient solution may be to cut or drill another hole in the base plate and install a drilledin epoxy-type anchor rod. When the rods are designed for tension, the repair may require extending the anchor rod by using a coupling nut or welding on a piece of threaded rod. Figure 2.4 shows a detail of how a coupling nut can be used to extend an anchor rod. This fix will require enlarging the anchor rod hole to accommodate the coupling nut along with using oversize shims to allow the plate washer and nut to clear the coupling nut. Table 2.4 lists the dimensions of typi-
cal coupling nuts that can be used to detail the required hole size and plate fillers. ASTM F1554 Grade 36 anchor rods and ASTM F1554 Grade 55 with supplement S1 anchor rods can be extended by welding on a threaded rod. Butt welding two round rods together requires special detailing that uses a run out tab in order to make a proper groove weld. Figure 2.5a shows a recommended detail for butt welding. The run-out tab can be trimmed off after welding, if necessary, and the rod can even be ground flush if required. For more information on welding to anchor rods, see AISC Design Guide 21, Welded Connections, A Primer for Engineers (Miller, 2006).
Figure 2.4. Coupling nut detail for extending anchor rod.
Figure 2.5a. Groove weld splice.
DESIGN GUIDE 1, 2ND EDITION / BASE PLATE AND ANCHOR ROD DESIGN / 11