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Obed Bridge

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From Historic Bridge Inventory By Clayton B. Fraser

Construction History

In April 1912 a citizens' group petitioned the Navajo County Board of Supervisors for a vehicular bridge over the Little Colorado River at St. Joseph. Typically, the board deferred the matter. In February 1915 another group requested the bridge, but the board again deferred. Finally, in the wake of the Lyman Dam disaster, Navajo County voted a $63,000 bond issue in January 1916 to finance construction of seven bridges damaged or destroyed when the dam broke. The St. Joseph Bridge was one of these. In June the board advertised for the bridges' construction. The following month the county received proposals and designs from eight bridge companies: the Monarch Engineering Company, Miller Construction Company, El Paso Bridge & Iron Company, Canton Bridge Company, Midland Bridge Company, Omaha Structural Steel Works, Mesmer & Rice, and B.Y. Duke. Nebraska-Omaha Structural Steel Works was awarded the contract for the St. Joseph bridge and five other smaller structures for $36,863. For this crossing, Omaha Structural Steel engineered a series of six rigid-connected pony. trusses, supported by concrete-filled steel cylinder piers and flanked on both ends by Umber approaches. The 83-foot trusses used a Pratt configuration, with steel stringers, concrete deck and steel lattice guardrails. Using steel rolled by Lackawanna and Illinois, Omaha Structural Steel fabricated the medium-span trusses, shipped the pieces to the site by rail and erected them the following spring. The St. Joseph Bridge was complete by June 1917. It has functioned as a county-road bridge since. The bridge has more recently been altered by the replacement of its substructure.

Statement of Significance

Before creation of the Arizona Territorial Engineer's office in 1909, vehicular bridges were built either by the counties or by private entities such as toll road operators The state began building bridges immediately after its formation in 1912. Following passage of the Federal Aid Highways Act in 1916, the Arizona Highway Department standardized bridge design and construction, concentrating more on concrete construction than on steel. But in the early years before the highway department controlled bridge design and construction in Arizona, the counties continued to build bridges from their own designs. The St. Joseph Bridge is one of the larger county-built structures in the state-designed, fabricated and erected under contract by a nationally prominent bridge company. The bridge is significant as one of the few multiple-span vehicular trusses remaining in Arizona. Although its substructural replacement has diminished its physical integrity, the St. Joseph Bridge remains an important early example of vehicular truss construction.

Technical Facts:

Dimensions: Roadway Width: 12.6 Feet; Structure Width: 16.1 Feet; Structure Length: 500 Feet; Main Span Length: 83 Feet.
Substructure: concrete abutments, wingwalls and corrugated steel piers with concrete caps
Floor/Decking: Timber deck with asphalt wheel tracks
Truss Composition: upper chord: 2 channels with cover plate and lacing;
lower chord, vertical and diagonal: 2 angles with batten plates; lateral bracing: 1 angle; floor beam: I-beam; steel lattice guardrails.
Alterations: Substructure replaced and superstructure raised in 1978.

Facts 

Overview
Lost Pratt pony truss bridge over Little Colorado River on Obed Road
Location
Navajo County, Arizona
Status
Replaced by new bridge
History
Built 1912; rehabilitated 1978, replaced 2010
Builder
- Omaha Steel Works of Omaha, Nebaraska
Design
Six span Pratt pony truss with riveted connections.
Dimensions
Length of largest span: 82.7 ft.
Total length: 500.0 ft.
Deck width: 12.5 ft.
Recognition
Posted to the National Register of Historic Places
Approximate latitude, longitude
+34.94134, -110.32383   (decimal degrees)
34°56'29" N, 110°19'26" W   (degrees°minutes'seconds")
Approximate UTM coordinates
12/561746/3866746 (zone/easting/northing)
Quadrangle map:
Joseph City
Average daily traffic (as of 2016)
160
Inventory number
BH 45861 (Bridgehunter.com ID)
Inspection report (as of September 2016)
Overall condition: Good
Superstructure condition rating: Very Good (8 out of 9)
Substructure condition rating: Very Good (8 out of 9)
Deck condition rating: Good (7 out of 9)
Sufficiency rating: 74.7 (out of 100)
View more at BridgeReports.com

Update Log 

  • November 4, 2011: Updated by Craig Philpott: Corrected location.
  • August 11, 2010: Essay added by Nathan Holth

Comments 

Obed Bridge
Posted November 5, 2011, by Nathan Holth (form3 [at] historicbridges [dot] org)

It wouldn't help.

Obed Bridge
Posted November 4, 2011, by Tony Dillon (spansaver [at] hotmail [dot] com)

I'm sorry...but to me these rusty welded spans are just hideous. A new truss is better than a slab...but not by much.

Perhaps if they would paint these things in some nice bright primary colors it might help...maybe.

Obed Bridge
Posted August 11, 2010, by Anthony Dillon (spansaver [at] hotmail [dot] com)

........And a National Register listed bridge at that!

Just goes to show you that NR listing really mean nothing as far as protection goes!!

Obed Bridge
Posted August 11, 2010, by Nathan Holth (form3 [at] historicbridges [dot] org)

A six span pony truss demolished in Arizona. That's a headline you won't ever see again. Not because Arizona has decided to preserve its truss bridges, but because I doubt there is another such bridge in the state.

The demolition of this bridge is ridiculous. The NBI report shows it wasn't even structurally deficient! At the very least, the bridge should either have been rehabilitated for continued vehicular use, or bypassed with a new bridge and left in place for pedestrian use. There is absolutely nothing around this bridge... plenty of room for a bypass.

Arizona is not exactly teeming with pony truss bridges with six or more spans. Actually, Arizona has one of the lowest numbers of surviving truss bridges (both per square mile and total number in state) in the entire country. The preservation of even a single span pony truss in Arizona should be considered important. The preservation of a six span pony truss should be of the highest priority.