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The stability of girders that frame over the tops of columns can be provided in several different ways. Typical means include: beams framing on the column line and covering at least three-quarters of the girder web, joists or joist-girders framing on the column line with bottom chord extensions to brace the tops of the columns, or stiffeners.

Regardless of how stability is addressed, this is not just a matter of calculating the concentrated force and deciding based upon that if a stiffener is required. This is a critical engineering concern and not something that any engineer should rely upon a fabricator's judgement to provide. It is easily easily addressed by any of the above-mentioned means (or other suitable alternatives) but must be addressed by the engineer.

Even if the fabricator has loads from the engineers, loads will not help here because the stability concern is not directly related to the load transfered. Rather, it is a matter of stabilizing the top of the column -- the web of a girder framing continuously over a column top will rarely have enough strength and stiffness on its own to do so.

I respectfully think that the engineer who told you that it is up to the fabricator is playing Russian roulette and probably does not understand the stability issue. He or she is probably not alone. I can show you pictures of collapses to emphasize how critical this is.

Charlie






-----Original Message-----
From: dave lowen [mailto:jatech(--nospam--at)kwic.com]
Sent: Fri 12/30/2005 8:00 PM
To: seaint(--nospam--at)seaint.org
Subject: Details
 
Comments, please.

 

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
required but the fabricator and detailer have no way of knowing this. Some
fabricators and detailers share the view that if you didn't 'call for it',
they will not 'quote it' and you will not 'get it'. Beam and column
stiffeners are a high priced item and can make or break a bid.

 

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.

 

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.

 

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?

 

Regards,

Dave Lowen

V 519 587 5797

F 519 587 5138

E jatech(--nospam--at)kwic.com

 


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