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Re: Bolted steel connections -- flame-cut holesl[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: NRoselund(--nospam--at)aol.com, seaoc(--nospam--at)seaoc.org
- Subject: Re: Bolted steel connections -- flame-cut holesl
- From: Rick.Drake(--nospam--at)fluordaniel.com
- Date: Wed, 6 Aug 1997 7:23:00 -0400
Nels Roselund wrote: <<I'm working on strengthening of a 1898 steel frame building. "Carnegie" is rolled into the structural steel members. The testing lab has advised that the chemistry of the steel is not compatible with the modern welding process; I've designed all connections to existing steel to be bolted. The steel is HARD; some cannot be drilled with hand-held equipment. The Contractor is using mag-drills and that is working O.K. However, some holes are not accessible to the mag-drill equipment. The contractor is proposing to flame cut the holes 1/8" undersize and to ream to the specified size; no flame-cut edges are to remain in the hole. Is there any problem with this procedure? What about using slip critical high strength bolting? Is there any advantage or disadvantage considering that the connection is secured by clamping remote from the hole rather than by bearing on the hole?>> Your solution seems reasonable. I offer the following comments: 1) Consult with a metallurgist for his opinion on whether this "hard" steel will become unacceptably brittle as a result of the flame cutting operation. 2) Make sure that all of the burrs are removed in the reaming operation to allow proper "clamping" of the connected parts. 3) Make sure that your connected parts match the requirements as specified in the AISC Spec for high strength bolts. Especially note the requirements for "Joint Assembly and Tightening of Connections Requiring Full Pretensioning". 4) Make sure that you design for the "slip critical" values as specified by AISC. Note that the AISC "High Strength Bolting" specification gives different values based on the coatings classification. The manual design aids are calculated for Class A coatings. You might have Class C coatings with higher allowables. Good luck, Rick Drake, SE Fluor Daniel, Inc.
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