Steel Solutions Center
5.1. Bolt Holes
5.1.1. Maximum hole sizes for bolts are specified in the AISC Specification Table J3.3. What if an actual hole dimension is between two of the values?
AISC Specification Table J3.3 is based upon the RCSC Specification Table 3.1 and contains the maximum dimensions of standard, oversized, short-slotted and long-slotted holes. If an actual dimension exceeds the tabulated maximum, it must be treated as the next larger hole size. For example, a 13∕16-in. by 1¼-in. slotted hole for a ¾-in.-diameter bolt must be treated as a long-slotted hole because it exceeds the maximum short-slotted hole size (13∕16 in. by 1 in.). Note that the RCSC Specification, in the footnote of Table 3.1, allows a 1∕32-in. tolerance on these maximum hole sizes as discussed in 2.4.2 and 2.5.5.
5.1.2. Alternative calculations of bearing strength at bolt holes with deformation considered or not considered are provided in AISC Specification Section J3.10. What is the philosophical difference between these options?
When deformation is a design consideration, the design strength is limited to the force at which the hole edge has deformed by a maximum of ¼ in. When deformation is not a design consideration, larger hole ovalization is permitted as the material attains its maximum bearing strength.
Generally, flame-cutting of bolt holes does not affect connection strength and performance. Iwankiw and Schlafly (1982) investigated the performance of double-lap joints with holes made by punching, punching with burrs removed, sub-punching and reaming, drilling, flame-cutting and flame-cutting and reaming. The comparison of 18 samples using ½-in.-thick ASTM A36 steel plates with standard holes indicated that there is no significant variation in connection strength according to the method of hole formation under static load. Additional considerations may be warranted for much thicker plates, steel grades other than those tested and cyclically loaded structures. Iwankiw, N.R. and Schlafly, T.J. (1982), “Effect of HoleMaking on the Strength of Double Lap Joints,” Engineering Journal, Vol. 19, No. 3, (3rd Qtr.), AISC, Chicago, IL.
5.1.4. AISC Specification Section J3.8 requires that bearing limit states be checked for slip-critical connections. Why is this check necessary? If the bolts go into bearing, hasn’t the connection failed?
Although slip-critical connections are designed to resist slip, a target reliability is established similar to that used in main member design, as opposed to the higher reliability associated with most connection-related limit states. This is allowed and not considered a connection failure since slip would not result in the loss of the connection between the elements. The language in AISC Specification Section J3.8 is to preclude a rupture failure that could result in the loss of the connection between the elements if slip were to occur. In other words, it is intended to provide a consistent level of reliability against a rupture failure.