2 votes

Hollow Brook Road Bridge


at this point in time all the diagonals have been replaced

Photo taken by Andrew Pearce in August 2012


BH Photo #238068



"The skewed 2-panel pin-connected Fink-like truss bridge bears on random stone abutments with wingwalls. There are minor welded alterations and repairs, but the unusual trusses perform like a Bollman with a floor beam hung from the diagonals. Undocumented as to original date and fabricator, the bridge dates stylistically to ca. 1880 and is the sole known example of its type in the county. It is technologically significant based on the design of the trusses.

Physical Description: The 33'-long, one-span, pin-connected pony truss bridge is a variation of the Bollman truss in which the chief characteristic is that the floor beam(s) are supported by a pair of diagonals which span from end of span to end of span, accomplished in this 2-panel bridge by pairs of loop forged eye bars. Bars in one panel are fitted with a turnbuckle for adjustments. The top chord, end posts, and one vertical appear to be original, although repaired several times. The trusses consist of vertical end posts which are a pair of channels with a full-height cover plate on the approach roadway face and a top and bottom batten plate on the span face. The top chord is made up of a pair of channels with a top cover plate and bottom batten plates. It extended beyond the end post by about 8" and is finished with a decorative cast cover. The top chord is a compression strut that holds the supporting columns (end posts) from falling in to the middle. There are no bottom chord elements. The vertical is a pair of channels with top and bottom battens. The one on the upstream side is a modern replacement. The vertical is a "dummy" member which serves only to halve the unsupported length of the top chord. The rolled I-section floor beam is supported on an inverted U-hanger which passes over the pin connecting the diagonals. The end posts are set on plates on the ashlar abutments. The steel grid deck was placed in 1962. Historical and Technological Significance: Although undocumented as to date of construction and fabricator, the span is a rare example of a Fink or Bollman truss type where the floor beams are supported by a pair of diagonals that span from end of span to end of span. Originally designed for the combination of wood and iron, the Bollman truss was developed in 1850, and while it increased the possible length of bridges of its day, it passed from favor by 1880 because it is not a rigid truss. Dated stylistically to ca. 1880, the bridge represents the most basic expression of the Fink or Bollman truss form (it is not developed enough to indicate which diagonal pattern it would have been had it been more than two panels long), and it is historically and technologically significant as a rare and fairly complete survivor of the pre-Civil War bridge technology."


Pony truss bridge over a branch of Lamington River on Hollow Brook Road
Tewksbury, Hunterdon County, New Jersey
Open to traffic
Built 1880
Kingpost pony truss
"a variation of the Bollman truss"; "a rare example of
a Fink or Bollman truss type"; maybe so. But at their core, both those rare trusses are based on king posts, and that's all that this little bridge is. A single inverted king post. I think the bridge documentation person may have been having a bit of fun with us, guessing rightly that 20 years would pass before anyone checked up on his description with a camera and a tiny bit of truss knowledge.
Sure, at some point a "whipple-ized" multiple King or Queen Post truss can grow to be called a Fink or a Bollman. But I think it would require at least 3 verticals, if not 4 or more, to differentiate amongst them.
Length of largest span: 32.2 ft.
Total length: 33.1 ft.
Deck width: 16.4 ft.
Posted to the National Register of Historic Places on December 12, 2002
Approximate latitude, longitude
+40.71719, -74.73611   (decimal degrees)
40°43'02" N, 74°44'10" W   (degrees°minutes'seconds")
Approximate UTM coordinates
18/522288/4507397 (zone/easting/northing)
Quadrangle map:
Inventory numbers
NJ 100T022 (New Jersey bridge number)
NRHP 02001510 (National Register of Historic Places reference number)
BH 25263 (Bridgehunter.com ID)
Inspection (as of 07/2015)
Deck condition rating: Very Good (8 out of 9)
Superstructure condition rating: Good (7 out of 9)
Substructure condition rating: Fair (5 out of 9)
Appraisal: Functionally obsolete
Sufficiency rating: 73.6 (out of 100)
Average daily traffic (as of 2015)

Update Log 

  • May 30, 2017: Updated by Christopher Finigan: Added category "Pin-connected"
  • August 26, 2012: Updated by Andrew Pearce: added data and pictures



Hollow Brook Road Bridge
Posted January 22, 2014, by Nathan Holth

Bridge patents are an interesting aspect of bridge history. A patent does not always imply that a particular design is innovative or unique... it just meant that someone's lawyer managed to convince the government that it was innovative or unique. Half of the story behind patents is legal in nature.

The Hollow Brook Road Bridge is a simple form of expression of a suspension design. Comparisons to Bollman could be made... comparisons could also be made to cable-stayed bridges, where the end posts of this bridge could be thought of as the towers.

Also wanted to note that the Sherman patent bridge originally DID have a vertical member... its just gone missing on the bridge as it exists today. The vertical is shown in the patent.

Hollow Brook Road Bridge
Posted January 21, 2014, by ArtS (Aasuckewer [at] knite [dot] com)


One other thing to consider is that the 1858 Hamden Road Fink Truss was just a few miles away. Which, to me, is the likely inspiration for this bridge.

While the bridge fits within the description of the Sherman, I still don't understand what is novel in the Sherman patent over Bollman. Doesn't the Sherman patent just describe the simplest form of a Bollman? Whatever the case, all three types are in the same family of trusses: Suspension Trusses, an early concept that was superseded by what I guess are called 'true trusses.'


Art S.

Hollow Brook Road Bridge
Posted January 21, 2014, by Matt Lohry

Whoops! I didn't even notice the missing lower chord--thank you, Fmiser, for pointing it out ! *red face* With that, I'll clean the egg off my face and move aside! :)

Hollow Brook Road Bridge
Posted January 21, 2014, by Fmiser (fmiser [at] gmail [dot] com)

I don't think it qualifies as a Pratt because it doesn't have a lower chord.

The lack of sloped (batter) posts on the end is unusual for a Pratt, but as I understand it that would not exclude it.

But it better matches a Fink truss - or even Bollman.

Best match, I think, is the Sherman patent. But is this NJ bridge really built based on a OH patent? Maybe.

Hollow Brook Road Bridge
Posted January 20, 2014, by Matt Lohry

I personally would classify this as a 2-panel Pratt--the Ohio Sherman lacks a center vertical, where this has it, allowing it to act like a Pratt with respect to tension/compression forces. Without the center, I believe that this would act more like an inverted kingpost.

Hollow Brook Road Bridge
Posted January 20, 2014, by ArtS (asuckewer [at] knite [dot] com)


I see your point. Nowadays the Sherman patent would likely have been disallowed for obviousness against Bollman and Fink. That said, I read the original Bollman and Fink patents and you may be right as the Fink patent only contemplates multipanel bridges in order to differentiate over Bollman and Bollman specifies lateral bracing which these bridges probably don't have (and probably don't require).

Thinking about it further, all of these are derivatives of truss rods like those used to reinforce the floors of early, wood railroad cars. The Bollman and Fink trusses extend the concept whereas these little bridges are basically the same as the railroad cars.

I guess we'll have to leave it as 'in the family of suspended truss type bridges such as Bollman/Fink'.


Art S

Hollow Brook Road Bridge
Posted January 20, 2014, by Nathan Holth (form3 [at] historicbridges [dot] org)

Its an unusual and significant bridge, but classifying it as a Fink or Bollman I think is going a little too far. In some ways, due to its small size, it suffers from the classification problem as a four panel truss Pratt truss... which can look the same as a four panel Warren.

To me, the bridge looks similar to Ohio's Sherman patent bridge, which was classified as an inverted kingpost.


Hollow Brook Road Bridge
Posted January 20, 2014, by ArtS (asuckewer [at] knite [dot] com)


Call me an optimist, but I look at it as the smallest form of both. It is within the definition of either patent, and it is a suspension truss. Only in bridges of more than two panels can you differentiate - a Bollmam having unequal length tension members in multipanel bridges whereas a Fink trusses always having equal length tension members.

I guess that because the tension members are of equal length and since there used to be another, larger and older, one near by, If I had to choose one, I'd call this is a Fink truss.


Art S.

Hollow Brook Road Bridge
Posted January 19, 2014, by Don Morrison

I'm defiitely not in charge, but I'll try to help...

The bridge has not been given either the Fink or Bollman category, so it will not show up in a category search using those criteria.

The design comments under Facts explain why this is.

Hollow Brook Road Bridge
Posted January 19, 2014, by ArtS (asuckewer [at] knite [dot] com)

Question for those in charge: when I previously did a search for Fink and Bollman trusses, this bridge did not turn up. Why? It is the most simple form of either design of suspended truss. Did i do my seach incorrectly or do the powers that be not consider this a Fink/Bollman?