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Floor Truss Chase

Floor Truss Chase

Floor Truss Chase

(OP)
When press plate floor trusses are manufactured with a chase at mid-span does the truss act like a vierendeel truss at that location.  

I recently looked at a 60' glulam parallel chord truss where the structural engineer wanted to create a square opening in the truss at mid-span.  His argument was that the shear is low at that location so that you don't need a diagonal web.

I thought that if you designed a truss assuming that all the webs were pinned at the panel points, that you would create an unstable truss by removing one of the diagonal webs.

However, I have seen press plate floor trusses with chase in the middle.  Are the truss designer's relying on joint rigidity to make this work?

RE: Floor Truss Chase

Maybe not joint rigidity, but chord continuity.  Your top and bottom chords can be assumed pinned in the analysis of many trusses, but for this case, perhaps the assumption is that the chords are truly continuous across the panel points and thus span past the rectangular openings.

RE: Floor Truss Chase

Metal-plate connected are analyzed using matrix analysis.  The webs are modeled pinned and the chords are modeled as semi-rigid.  This is also how we are able to design attic trusses.

woodengineer

RE: Floor Truss Chase

(OP)
woodengineer: What is a semi-rigid joint? And how do you model one?  The program I use in analysis is the orginal Purdue Plane Structures Analyzer.

RE: Floor Truss Chase

This is realy a fairly simple analysis.

Calculate what is the maximum shear transfer required at this point due to uneven loads.

This load gets transferred over the opening by double curvature bending(as if it was fixed each end).

Check the chords under this bending combined with the axial chord force for this load case.

This method is also useful for penetrations in concrete beams.

csd

RE: Floor Truss Chase

Semi rigid joints use the combined properties of wood and steel to model the plates ability to transfer moment.  Most truss software utilizes semi rigid joints at heels, pitch breaks, and at splices in top/bottom chords.  

RE: Floor Truss Chase

See abstract:  link.aip.org/link/?JSENDH/129/1546/1

woodengineer

RE: Floor Truss Chase

(OP)
I want to thank every one for the information they posted.

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