I recently had an opportunity to get a good close look at the pin truss bridge used by the Northwest Railway Museum in Snoqualmie WA. This particular bridge was built by Lassig Bridge Works in 1891 for an NP crossing of the Yellowstone River. It was moved to North Bend WA and placed in service on that NP branch's crossing of the Snoqualmie River.

It got me to wondering how many other pin truss bridges are still out there? How many are still in service? I believe there is on on the Georgetown Loop RR in Colorado.

Bridge 35

brianf425@yahoo.com

The Niles Canyon Railroad has a 1896 Edgemoor pin connected bridge on 1865 masonry. They also have a 1898 through girder bridge by Phoenix and a 1906 riveted truss by American Bridge, which both also have some 1860Â’s masonry.

Of course, the Eastern span of the San Francisco Bay Bridge, and the original Carquinez Strait bridges both have pin connected componentsÂ… but both will be replaced with new spans. Both are highway bridges, but the Bay Bridge once carried electric trains from the Key System, the Sacramento Northern and the Southern PacificÂ’s suburban red electric operation.

Randy Hees


http://www.spcrr.org
hees@ix.netcom.com

I believe the huge (and out of service) Easton & Northern bridge over the Lehigh River in Easton, PA is a pin bridge, and possibly the largest one left standing.

Rob

rdavis@rypn.org

I recall the PRR P&T Branch bridge over the Main Line at Whitford is pin connected. That's double track over 4-tracks at an acute angle.

Electric City Trolley Museum Association

The Walnut Street Bridge is a pin connected truss bridge. It once carried trolleys but now is only a pedestrian bridge. The story behind its survival is a great story to tell but too long to post here. One thing discovered during its restoration was that the pins had rusted into place and no longer allowed the necessary rotation at the joints.

If you're ever in Chattanooga, be sure to check it out. It's the long multi-span truss bridge high above the Tennessee River.

G. Mark

Tennessee Valley Railroad Museum
aw90@comcast.net

The D&RGW used lots of pin-connected through truss bridges. I think they were popular with them because they could move them around easier. Three in service examples I can think of offhand are: Chama River Bridge on the C&TS - its a two span bridge originally built in 1880 and used on the North Fork Branch out of Delta, CO, installed in the early 1920's. The D&S crosses the Animas River in Durango on a 3 span bridge with includes a wood Howe truss, a thru plate girder and a pin connected through truss. North of Antonito, the former D&RGW/SP/UP, now SLRG crosses the Conejos River on a pin connected truss. On the abandoned ROW between Chama and Durango are at least 3 pin connected trusses at Navajo, La Boca and Florida. All are used for vehicle traffic now. There are other thru truss bridges out there that are also probably pin trusses, but I've never looked at them closely.

Two more,
Uncle Pete's crossing of the Guadalupe river near New Braunfels, TX, and GSMR's crossing of the Tuckaseegee river near Bryson City, NC.
The fact that both of these locations are great places to go river toobing is ENTIRELY co-incedental!

Maybe Mark Ray can expand a bit here as to why pin connections aren't used as much anymore... with a pin, all elements in the truss (save the bed) are subject only to pure compression or tension, the pins prevent any bending moments.. certainly simpler to engineer I would think.

rudd@nospamcogdellmendrala.com

A forlorn and trackless pin connected bridge used to exist just south of downtown Cortland, NY. I believe it was part of the Cincinatus branch. I haven't been there in quite a while, so it may be gone. I imagine there are others in the NE, as it seems to me that when I learned what they were, I checked around and found others, just cannot place them at the moment.
Mike.

emd_e8s@yahoo.com

> Maybe Mark Ray can expand a bit here as to
> why pin connections aren't used as much
> anymore... with a pin, all elements in the
> truss (save the bed) are subject only to
> pure compression or tension, the pins
> prevent any bending moments.. certainly
> simpler to engineer I would think.

Then as now bridge designs are typically selected by value engineering. The objective is to select the lowest-cost design that will work in a given situation. With pin connected trusses there is a significant "weakness" inherent in the design: if just one pin fails, the entire structure can collapse. Other bridge designs are a little more forgiving. This and other design factors (such as the design is not as good for heavier trains) were recognized and pin connected trusses as a design fell out of favor by the 1920's. But because this type of bridge can be taken apart like an erector set, it was easy for RR's to move them off the mainline and onto branches. This is one of the reasons we've seen a few of them (like Brian's posting above) survive for so long when many newer bridges were long ago scrapped.


Northwest Railway Museum
rra@trainmuseum.org

> It got me to wondering how many other pin
> truss bridges are still out there? How many
> are still in service?

Three former ET&WNC, pin-connected bridges survive in Doe River Gorge - one deck truss and two through trusses. The eastern-most through truss (in Blevins) is now used for auto traffic.

Best Regards,
Glenn

christensenge@tahoo.com

Does anybody want an old truss RR bridge?
I know of three in northwestern Iowa.
M. Nix

2rivers@upstel.net