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RE: Flame Cut Holes for Connections[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Flame Cut Holes for Connections
- From: carter(--nospam--at)aiscmail.com
- Date: Wed, 15 Sep 1999 13:32:59 -0500
>Are there any AISC guidelines for flame-cut holes used for bolted connections? Flame-cutting of bolt holes is permitted, but subject to the approval of the engineer of record. I've cut and pasted the following text from AISC's "A Guide to Engineering and Quality Criteria for Steel Structures: Common Questions Answered", which will give you some guidance. The numbers that precede each question relate to the numerical section organization of that document. In general, flame-cutting has been used for large-diameter holes that can't be drilled or punched, like in base plates, and field modifications. Today's equipment (mechanically guided flame cutters and plasma punches) make flame cutting very feasible and accurate. I think flame-cut holes that are reamed are essentially equivalent to a drilled hole; untreated flame-cut holes (i.e., flame-cut and left alone) are about equivalent to a punched hole, although there is a martensitic layer at the untreated edge. This differes from the punched hole, which has a different but similarly damaged rim of material. In case you are interested in getting a copy of that book I mentioned, it is AISC publication number S323 and you can order it through our website www.aisc.org or by calling 800/644-2400. Charlie Here's the pasted text: 2.4.1. What are the acceptable methods for making bolt holes? Acceptable methods for making bolt holes include: 1. Punching 2. Sub-punching and reaming 3. Drilling 4. Hole sawing 5. Flame piercing and reaming 6. Flame cutting, subject to surface quality requirements as discussed in 2.4.2. See also 5.1.3. 2.4.2. What variation in profile is generally acceptable for bolt holes? The slightly conical hole that naturally results from punching operations is acceptable. From RCSC Specification Section 3(c), "holes not more than 1/32-in. larger in dimension than the true decimal equivalent of the nominal dimension that may result from a drill ... of the corresponding nominal diameter are considered to be acceptable." The width of slotted holes that are produced by flame-cutting, or a combination of punching or drilling and flame-cutting should generally be not more than 1/32-in. greater than the nominal width except that gouges not more than 1/16-in. deep are permitted. In Statically Loaded Structures, the flame-cut surface need not be ground smooth; for Cyclically Loaded Structures, the flame-cut surface must be ground smooth. 5.1.1. Maximum hole sizes for bolts are specified in LRFD Specification Table J3.3. What if an actual hole dimension is between two of the values? AISC LRFD Specification Table J3.3 is based upon RCSC Specification Table 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 1 1/4-in. slotted hole for a 3/4-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 RCSC Specification Section 3(c) allows a 1/32-in. tolerance on these maximum hole sizes as discussed in 2.4.2 and 2.5.5. 5.1.3. Does flame-cutting of bolt holes affect connection strength and performance? Generally, no. 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 1/2-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.
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