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- To: seaint(--nospam--at)seaint.org
- Subject: Re: Details
- From: ad026(--nospam--at)hwcn.org (Paul Ransom)
- Date: Sat, 31 Dec 2005 19:11:18 -0500
> From: "dave lowen" <jatech(--nospam--at)kwic.com> > When designing 'big box' buildings, engineers sometimes (at least in this > area of North America) do not indicate that web stiffeners are required for > beams that cantilever over columns. In many cases, stiffeners are not > In discussion with a local engineer, I find his position on the matter is > "it is the fabricators responsibility to determine if stiffeners are > required and supply them, if needed". His position on this matter is similar > to beam/column moment connections; the design of column flange and web > stiffeners is also the fabricators responsibility. His thinking is that this > area falls under the scope of connection design. I think that you have to consider the purpose of the stiffeners. If they are strictly for point load resolution to prevent web buckling/yielding, then it is within the requirement of the fabricator if they provide connection design services in their scope. If the stiffeners are required (and adequate) for torsional restraint at the bearing location of the cantilever, this is a more general structural consideration. Stiffeners are not the only torsional restraint method that can be used at cantilever-over-column locations. The design engineer should provide additional guidance where it is intended that stiffeners provide torsional restraint. The design engineer must either: 1) identify that the connection must consider torsional "moment" restraint (e.g. it is NOT a simple pinned bearing connection) and provide the required resistance, or 2) provide the connection design. In either case, give the fabricator enough information to know what is required to be quoted, designed and fabricated in their scope. > If the engineering drawings provided loads, I would be inclined to agree > with this position but most engineers don't supply them so it is impossible > to any calcs. Also, the majority of engineers around here will not provide > any loads when asked. I think their insurance providers tell them not to. The engineer must provide enough information to permit the structure to be fabricated and erected according to the structural intent. How could witholding adequate information be good for the insurance company? The insurance companies could take the position that an engineer should not provide any design, of anything, and limit their liability to zero! > In many states, connection design must accompany the contract documents but > for those jurisdictions that do not, what are your views? Do you leave these > tasks up to the bidder or fabricator? The fabricator will generally quote exactly what they see on the structural drawings. They will attempt to qualify limits of their supply based on what is visible to them. They MAY question aspects if there are obvious errors or omissions. If there is missing information that is required to properly design "connections", they will not quote the connection according to the intent of the design engineer. Nobody will know the difference until the details are submitted for review, much later. Extras. The fabricator will not attempt (and should not attempt) to assess the general structural intent of the design engineer - the fabricator fabricates steel. The connection design role is a service that is convenient to provide and frequently subcontracted. They will design connections for the forces that are provided (explicitly by numeric value or by reference such as 50% of section capacity U/N) which must include torsional stability forces where that is required. Fabricators become familiar with the habits of local engineers and may adjust their quotes accordingly. It is a commercial choice that they make which may cause them to be uncompetitive in certain projects. Better to lose a problem project than to lose money on a problem project. -- R. Paul Ransom, P. Eng. Civil/Structural/Project/International Burlington, Ontario, Canada <mailto:ado26(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html> ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********