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Saucon Creek PBNE Railroad Bridge

Photos 

Looking NE

Photo taken by Royce and Bobette Haley in January 2018

Enlarge

BH Photo #415549

Map 

Street View 

Description 

Cantilevered deck girder with pin and hanger system

Facts 

Overview
Deck plate girder bridge over Saucon Ck/Hellertown Rd on PBNERR
Location
Bethlehem, Northampton County, Pennsylvania
Railroad
- Philadelphia, Bethlehem & New England Railroad (PBNE)
Design
Deck plate girder
Dimensions
Length of largest span: 102.0 ft.
Total length: 491.0 ft.
Deck width: 60.0 ft.
Approximate latitude, longitude
+40.60867, -75.33953   (decimal degrees)
40°36'31" N, 75°20'22" W   (degrees°minutes'seconds")
Approximate UTM coordinates
18/471276/4495372 (zone/easting/northing)
Quadrangle map:
Hellertown
Inventory number
BH 79704 (Bridgehunter.com ID)

Update Log 

  • January 7, 2018: Updated by Royce and Bobette Haley: Added category "Pin-and-hanger Plate Girder"
  • January 4, 2018: Added by Royce and Bobette Haley

Sources 

  • Royce and Bobette Haley - roycehaley111 [at] yahoo [dot] com

Comments 

Saucon Creek PBNE Railroad Bridge
Posted January 6, 2018, by Matt Lohry

I’ll attempt to add a bit of engineering sense to this connection type, as they were done like this for a couple of reasons: as Nathan mentions, one primary advantage of pinned joints is that they theoretically eliminate a force that is referred to as a “moment”. A moment is a rotating force that exists in true rigid connections, such as in the case of a street light pole bolted to a concrete foundation, where there are 3 different forces acting on the base of the pole—you have an axial (up and down) force, a shear (sideways), and you have the rotating bending moment. Changing to a pinned connection eliminates the moment, leaving only the axial and shear forces to calculate. This greatly simplifies calcs when doing them manually. The other reason for this type of connection is that the beams at the time were not long enough to allow the distances between spans that they needed, so simply placing each beam between supports wasn’t feasible. This was the solution. It was done to allow the supports to hold up the adjoining beams and to suspend intermediate beams with pins, thereby allowing greater distances between supports. Cantilever truss bridges function very much the same way. Stringer bridges these days use beams that can span much longer distances, so this connection type is not commonly used anymore. And to answer Don’s question, yes, these are effective expansion joints as well. If you remove the pinned plate, you would find a “stair-step” joint underneath that allows independent side-to-side movement for expansion. Hope this helps to clear things up a bit.

Saucon Creek PBNE Railroad Bridge
Posted January 6, 2018, by Don Morrison

Hmmm...

Curious if expansion joints exist at the "Pin and Hanger" locations.

If I understand how they connect correctly, looking at Nathan's photos that show the hanger at a slight off vertical position, it seems that it might allow a little longitudinal movement, such as in the case of expansion and contraction.

Are the cantilevered ends fixed to the abutments?

Are the pin and hangers a feature of only longer span bridges, or are there examples of shorter spans that have them as well?

Saucon Creek PBNE Railroad Bridge
Posted January 5, 2018, by George oakley (georgeoakley49 [at] yahoo [dot] com)

Royce and Bobette,thanks for replying about the pictures.I thought that was snow.I do remember the coal trains passing through Quakertown when I was at my grandmother's house on Hellertown Ave.If I'm not mistaken that whole line from Lansdale to Bethlehem was owned by the Reading Co.Makes sense though that Bethlehem steel would have a yard for storing cars.As for this bridge I've never seen this kind.

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by Nathan Holth (webmaster [at] historicbridges [dot] org)

Royce,

The riveted girders of this bridge suggest a pre-1970 bridge. The "locking mechanism" you note is called a "pin and hanger" system. This design allowed steel beams to extend (cantilever) beyond the piers, and be connected to the next beam using the pin and hanger. I am not an engineer so I might not be good at explaining how this is of benefit, but this pin and hanger connection is a "hinge" that as I understand had some sort of benefit in reducing engineering calculations needed, which was important in the pre-computer era. It made designing bridges easier. The design was popular on highway bridges from the 1950s to the 1970s. As far as I know, its uncommon on railroad bridges... at least its not something I have seen often, unless John is aware of examples that I have ignored given his greater focus on railroad bridges, since I see he called it a "standard" girder. Anyway, after the 1970s, computers eliminated any reason to use a design simply because the calculations were easier. On highway bridges, a side effect of the pin and hanger design is that the joints (which let salt and water through) are not directly over the pier, so pier deterioration is reduced. Some states have been turning pin and hanger bridges into continuous bridges by bolting up the hanger, but here in Michigan we have a lot of these bridges, and we continue to replace the pins and maintain these bridges as originally designed. Here is a good example: http://historicbridges.org/bridges/browser/?bridgebrowser=mi...

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by Royce and Bobette Haley (roycehaley111 [at] yahoo [dot] com)

George,

It is my understanding Bethlehem Steel built the railroad in order to spur competition and receive better prices from the Reading and the Lehigh Valley RRs. And yes it was snowing so I got what photos I could get as I will probably not be back in the area. Still the bridge is something I have not seen before (with the locking mechanisms and suspended span).

Royce

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by george oakley (Georgeoakley49 [at] yahoo [dot] com)

Thanks for the information,Royce and Bobette.I remember when Bethlehem Steel went under but didn't know they had their own rail line.So basically they pick up rail from Norfolk/Southern that's brought to Bethlehem on their rail.Could they be considered a short line?

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by Luke

George, it was Bethlehem Steel Co.'s own "common carrier" line, so it's been gone since 2003 when Bethlehem Steel was shuttered.

According to railfan sites it's been reorganized under the name "BethIntermodal" of Lehigh Valley Rail Management ("LVRM").

http://cs.trains.com/trn/f/111/t/188862.aspx

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by george oakley (georgeoakley49 [at] yahoo [dot] com)

Royce and Bobette,i'm from Quakertown and have travelled on Hellertown Road quite a bit.Never really paid attention to this bridge you're talking about.Was it snowing when you took some of the pictures?Also,is that railroad listed on the sign still in business?Never heard of that rail line.

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by Royce and Bobette Haley (roycehaley111 [at] yahoo [dot] com)

Hi John,

The reason I ask is if you look at pics, 5,6,7,8,14,15 20,21 they show the span crossing the roadway is locked between two spans that over hang the piers. Can see in it in the wide field photos as well if you enlarge. I have not seen these locking devices or a span hung between two other spans before in deck girders. Thought it was peculiar. Oh well, thank you

Royce

Saucon Creek PBNE Railroad Bridge
Posted January 4, 2018, by John Marvig (marvigj27 [at] gmail [dot] com)

Looks like a standard 1970s deck girder me, but I could be wrong.