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RE: Connection Pins in Old Steel Truss Bridges

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Steve:
	Firstly, I'm working off the digest form of the listserver, so I may
be behind in this thread.  I offer a passage from a text entitled "Modern
Framed Structures, Part 3, Design" by Johnson, Bryan and Turneaure (first
copywright 1893)regarding pin-connected trusses.

"Pins are designed with reference to shear, bearing pressure, and bending
moment.  The shear, however, rarely governs the design.  The following
articles from the specifications give the allowable working stresses, in lbs
per sq. in., to be used in designing pins.

	Bending on extreme fibres of pins..........24,000 psi
	Shearing, on pins..........................12,000 psi
	Bearing, on pins...........................24,000 psi"

As far as I can tell, the "specifications" referred to above are the
American Railway Engineering Association specs from 1910.  Where did you get
the 30 ksi yield strength of the pins?  From the above info, I'm thinking it
would have been standard practice to use higher strength steel for the pins
of a truss.  You may want to investigate further the assumed strength of the
pin steel.
	If you plan on working further with evaluations/retrofits of older
truss bridges, I highly recommend you pick up a text that is typical of
those used in the original designs, such as the one above (or others by, for
example, Hool and Kinne, Merriman and Jacoby, etc.)  Hope this helps!


Thomas P. Murphy, Ph.D., P.E.
Structural Engineer
Modjeski and Masters, Inc.
Harrisburg, PA