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Re: Increasing Kl/r

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Great scheme!  Depending on wall thickness of the existing webs, you may have to make sure that the gap between the two halves of the casing member is small, or that the tension in the bolts is not excessive so as not to crush the web member, possibly inducing local buckling.  I'd go for snug tight bolt installation, personally.

>>> "Paul Feather" <pfeather(--nospam--at)san.rr.com> 05/07 6:18 PM >>>
I would like to bounce some thoughts by you.


I am looking at some existing trusses (wide flange chords, pipe webs) with a 130 foot span.  For the new loading condition, everything checks out OK except one diagonal compression element at the third panel from each end (section changes at two end panels).

The sections have sufficient area to carry the required forces if the Kl/r could be reduced.  The area is sensitive to welding, and we would like to create a bolted solution if possible.

The concept is to split a larger diameter section, add interior ribs at approx. 24" like a plane fuselage and bolting flanges, and encapsulate the existing member for the full length minus a foot ea. end.  The two halves would be attached with high strength bolts pulling the ribs uptight against the existing member (design would allow sufficient gap to ensure the interior member is clamped).

The resulting section would then be viewed as the original section only for stresses, but as a combined section for buckling resistance. An r value would be calculated for the combined section with both the existing and new parts contributing.

What opinions do you have?  Do you see something I am missing?

Paul Feather


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