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Effective Length Factor for Truss Chord
2

Effective Length Factor for Truss Chord

Effective Length Factor for Truss Chord

(OP)
I'm reviewing the design of a (fiberglass) roof truss subject to uplift.  The designer is using an effective length factor of 0.85 to compute an effective unsupported length of the comression chord.  As the effective length is squared in the Euler buckling formula, the critical buckling force is very sensitive to this factor.  I can't find anything in the literature to support an effective length factor less than one.  Do truss designers commonly use K factors less than one in the design of truss chords?  Is there any testing/reference that supports the use of an effective length factor less than one?

RE: Effective Length Factor for Truss Chord

The development of standards regarding truss design are available from
Truss Plate Institute: http://www.tpinst.org/

RE: Effective Length Factor for Truss Chord

jmiec,

CTruax is refering specifically to ANSI/TPI 1-2002 National Design Standard for Metal Plate Connected Wood Truss Construction, specifically Chapter 7 Section 7.2.2 which states "The effective buckling length (L') for buckling within the plane of the truss shall be determined when checking compressive stress between panel points.  The minimum in-plane effective buckling length shall be no less than 0.65 times the panel length, except for interior panels of continuous chord members spanning at least five panels, for which it shall be no less than 0.55 times the panel length."

You can download this publication.

I hope this helped.

Jordan

RE: Effective Length Factor for Truss Chord

(OP)
Yes, thank you both.

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