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[SEAOC] Re: I-90 Partial Collapse / Gusset Plate Analysis

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> From:   DvRinehart(--nospam--at)aol.com[SMTP:DvRinehart(--nospam--at)aol.com]
> Sent:   Saturday, June 15, 1996 6:42 PM
> To:     seaoc-ad(--nospam--at)seaoc.org
> Subject:        I-90 Partial Collapse / Gusset Plate Analysis
> 
> It has been suggested that you might have some thoughts or ideas concerning
> the following.....
> 
> Late in the morning of 24 May 1996, four gusset plates buckled on the
> westbound Interstate 90 bridge over Grand River, east of Clevland, Ohio.[...details deleted for brevity...]
> If anyone has a rational method for calculating stresses in truss gusset
> plates, I would be very interested in knowing it.  Our most honest
> references,
> the "old" books, recommend sizing gusset plate thicknesses by finding a
> similar structure and using their thickness!  We have evaluated the
> various gusset plates on the structures by various methods:  a) cutting
> free-body diagrams at several locations and evaluating the cut edge by
> conventional beam theory;  b) evaluating the "end bearing" of the member,
> over a line defined by a 30 degree line from the first rivet/bolt on the
> outside lines of connectors to the end row of connectors (according to one
> research report in ASCE's Structural journal, this is appropriate for
> tension; according to another paper in the Journal, it is terribly
> unconservative in commpression, but no alternative is offered);  c) shear
> in the connectors;  d) bearing of the connectors on the gusset plates.
> 
> We have settled (so far) on the stresses defined under a) and b) above,
> comparing them to an allowable compressive force defined by the Euler
> buckling load divided by the 2.12 factor of safety AASHTO uses in their
> column allowables.  To determine the Euler buckling load, we used a column
> of unit width the thickness of the gusset plate, with a length measured
> along the line of action of the member in question from the last row of
> connectors on the member to the first line of connectors in the chord
> member.
> 
> If you have any thoughts on our method of analysis, I would appreciate
> your input.
> 

Couldn't you do a FEM analysis of the gusset plates (including buckling 
behavior)?  It appears that the seriousness of the problem would justify this 
effort.  You could easily find an academic type well qualified to help you on 
a consulting basis.

John Bryan

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