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Old 15th January 2015, 10:54 AM   #1
factory-fit
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Default Stiffeners to openings

Having to add lots of service and duct holes to a set of 16.5m primary beams, the openings sit below 200mm depth cold-formed secondary beams at 400mm centres which are inset into the top of 610 deep primaries, designed as fully restrained. Got snagged on the lack of torsional restraint despite lateral restraint being near perfect using flat plate cleats welded into the upper flange and web. Fixed that with a 45 knee brace at 2.4 pitch which when the restraint was limited to 2.4m pitches results in the same beam. Next snag was the opening had to be set low in the beam, to clear the secondaries, so exploited the larger sized hole available using stiffeners, but with the hole size reduced at the top only so the entire 'letterbox' slot was in the lower section, this gave a handy limit to how close you could cut the slot to the bottom flange, by inferring this from a centrally located larger stiffened hole.

Fabrication now want to know if the stiffeners can be 50% stitch welded as they are quite long, 1200mm or so so the welding is becoming onerous?

Hope you can help
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Old 16th January 2015, 11:16 AM   #2
Tony Bryer
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Default Re: Stiffeners to openings

I don't think there is any scope to reduce the welding as the stiffeners combine with the residual webs and flanges to form two I-sections which resist the Vierendeel moment across the opening.

The current design guide SCI P355 Design of Composite Beams with Large Web Openings is available as a free download from http://www.steelconstruction.info/in...t=SCI+P355.pdf . Stiffeners are covered on page 63ff.
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