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[SEAOC] Re: [SEAOC] Response to Steel Frame Question[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: [SEAOC] Re: [SEAOC] Response to Steel Frame Question
- From: "DW" <wish(--nospam--at)cyberg8t.com>
- Date: Wed, 23 Oct 1996 20:44:01 -0700
Ken, your letter amplifies the frustration that exists among many of us out there that are required to conform to the interim guidelines but are not given enough information with which to design. Recently, I designed a steel mezzanine within a concrete shell building. The mezzanine has a large cut-out in the center and therefore required lateral restraint by the plan checker from Wildan. Although the building design considered the mezzanine mass in the lateral analysis, the plan checker reasoned that the discontinuity in the "cut-out" created a need for a rigid connection and lateral restraint of the unsupported edge of the mezzanine. When I called to ask for a design guide or at least a recommendation for design, I was directed to the SAC Interim Guidelines. After reading the guidelines, I got the following basic understanding: 1. Bolted moment connections should be avoided unless proven by cyclic testing. 2. Cyclic testing is, in most cases, cost prohibitive in a small job. 3. In the design of a flange weld to flange (of column) the typical mode of failure occurred in the weld to backer plate detail. To avoid this, the Interim guidelines eliminated the backer plate and coped the beam flange enough to get the weld directly from the flange to flange. Once this weld was accomplished another flange plate was placed and subsequently full-pen welded to the column flange and beam flange. The purpose, it appears was to move the plastic hinge toward the center of the beam and away from the welded connection. I'm not full sure it this is correct, since there is very little practical information written for some of use who don't do a lot of steel moment frame design. One questions I had was the need to provide this type of detail where an ordinary moment frame is designed since we are not approaching the plastic state. I was informed by the Plan Checker that the connection must be designed as would a SMRF even though the frame was an Ordinary moment frame. The fact that the seismic reaction was increased by a factor of 3 Rw/ 8 goes without saying since this is code required. I was then informed that next evolution of the code increases the 3 Rw/8 to almost twice this value. As one solution, I suggest that some of these unresolved design issues be resolved as quickly as possible. If not, the building departments should not require the engineer to invent an interpretation for the interim guidelines., The results of each stage should be made available to all engineers free of charge (rather than to charge for a seminar and notes to learn something this important) and posted online and available through the SEAOSC (and other chapter) office for the cost of mailing. I hope that I have related the frustration I had with complying to a plan check correction that required me to obtain a copy of Modern Steel design for an appropriate design solution. Time was of the essence in completing this job and waiting for a reprint form Modern Steel was not an appropriate solution. Putting this publication on the SEAOC web would have been better, but then AISC would not earn the $2.00 for distribution of this article. It's almost like holding the information ransom - but that's another issue for a later time. Thanks again for posting your information, it was sorely needed. Dennis Wish PE wish(--nospam--at)cyberg8t.com ...
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