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Thebes Bridge

Thebes Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: November 2, 2013

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Key Facts

Facility Carried / Feature Intersected
Railroad (Union Pacific) Over Mississippi River
Thebes: Alexander County, Illinois and Scott County, Missouri: United States
Structure Type
Metal Cantilever 22 Panel Pin-Connected Baltimore Through Truss, Fixed and Approach Spans: Concrete Closed Spandrel Deck Arch, Fixed
Construction Date and Builder / Engineer
1905 By Builder/Contractor: American Bridge Company of New York, New York and Engineer/Design: Ralph Modjeski and Alfred Noble

Technical Facts

Rehabilitation Date
Not Available or Not Applicable
Main Span Length
671 Feet (205 Meters)
Structure Length
3,817 Feet (1,163 Meters)
Roadway Width
Not Available
5 Main Span(s) and 12 Approach Span(s)
NBI Number
Not Applicable

Historic Significance Rating (HSR)
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Bridge Documentation

View A Historical Biography of Alfred Noble

View A Detailed Historical Discussion of the Bridge's Construction

View A Historical Article About This Bridge

View A Detailed Report About This Bridge By Its Engineers


This bridge is among the earliest surviving cantilever truss bridges in the United States. It was a major engineering achievement when completed, and one of the earlier examples of a bridge designed by Ralph Modjeski who went on to become one of the greatest bridge engineers ever known, who also specialized in the design of cantilever truss bridges like this one. Modjeski teamed up with another engineer, Alfred Noble for the design of this bridge. Alfred Noble should not be confused with Alfred Nobel after whom the Peace Prize is named after. The bridge includes a substantial series of concrete arch approach spans, which are also notable as somewhat early surviving examples of large-scale concrete arch bridge technology. The main cantilever truss system is arranged in a rare manner. Rather than the traditional three-span format consisting of two anchor arm spans and a single span with two cantilever arms and a suspended span, this bridge features a five span cantilever truss system. It has a central span consisting of cantilever arms holding a Pennsylvania through truss suspended span. The end spans are quite interesting, as they include what could be called a "half-suspended span" where a Pennsylvania truss rests on a pier at the far end and on the interior end, is held by a cantilever arm. Between the end spans and the center span are anchor spans (also called "fixed" spans) which act as anchor arms for both the center and end truss spans. Among cantilever through truss bridges, this example is of the less common variety that does not feature any "pointy towers" that define the appearance of many cantilever truss bridges.

The piers of the bridge consist of an ashlar stone facing with concrete behind. The stone is a limestone from what were described as the Romona quarries near Indianapolis, Indiana and was called Indiana Oolitic Limestone. This type of stone was quarried in a manner that the surface was smooth and prior to installation on the bridge the stone was textured to make it look like a more natural rock face.


Photo Galleries and Videos: Thebes Bridge

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