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LaPorte Street Bridge

   


LaPorte Street Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: March 4, 2012
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Key Facts

Facility Carried / Feature Intersected
LaPorte Street (Pedestrian Walkway) Over Yellow River
Location
Plymouth: Marshall County, Indiana
Construction Date and Builder / Engineer
1898 By Builder/Contractor: Rochester Bridge Company of Rochester, Indiana

Technical Facts

Rehabilitation Date
Not Available or Not Applicable
Main Span Length
Not Available
Structure Length
100 Feet (30.5 Meters)
Roadway Width
6 Feet (1.8 Meters)
Spans
2 Main Span(s)
NBI Number
Not Applicable

Historic Significance Rating (HSR)

Bridge Documentation

This extremely rare and highly unusual bridge is the only one of its kind in Indiana. This is a cantilever truss bridge, a rare example of both a small-scale cantilever truss and a cantilever truss foot bridge. However what is most unusual is how the cantilever is arranged. The only apparent way to categorize the truss's configuration is as two kingpost trusses, however this is somewhat misleading. The vertical member of each kingpost is actually the main post of the cantilever truss, and thus is rests on a pier. A typical kingpost truss would not have a pier at this point. Another unusual aspect of the truss is that the anchor arms of this bridge are more like eyebar stays rather than a truss. On a "normal" cantilever, the truss of the anchor arm not only serves to balance the cantilever arm, it also is the supporting truss for the bridge itself between the main post and the next pier. On this bridge however, the anchor arm is a simple eyebar that runs into the ground, where it connects to an anchorage. The anchor arm does not support the deck in this area, and is not even connected to the deck. This section of the bridge is supported by steel bents. The DHPA states that these bents are added, but if they are added, they are very old (they are riveted) and it is not clear what would have supported this deck if those bents were ever not in place. It certainly was not the anchor arm, there is no way it could have connected to support the deck. In this section of the bridge, the bridge has more in common with a suspension bridge or an eyebar-stayed bridge.

There are outriggers that appear to have been added to the bridge. Otherwise, this bridge retains good historic integrity including original railings.

Information and Findings From DHPA Historic Bridge Survey

Statement of Significance

Built by a prolific Hoosier firm, this local landmark has linked the eastside residential area with downtown Plymouth for more than eight decades. The 1898 decision to restrict this crossing to pedestrians must have reinforced the residential character of the immediate neighborhood.

The structure's design is both simple and unique in Indiana. The bridge appears to retain its original members, including its latticed guardrails. The whole has been reinforced by a series of piers.

Architectural Description

A petition in the summer of 1898 from local residents to replace the bridge at this site led the Plymouth Common Council to an unusual decision: to erect a through truss for vehicular traffic at Taylor (Garro) St. and build a pedestrian crossing at E. LaPorte Street. W. B. Bassett, agent for the Rochester Bridge Company of Rochester, Indiana, secured the contract for the two bridges which were subsequently constructed at the same time and completed by December 1898.

The 100' structure consists of two approximately 20' high verticals fabricated from pairs of laced angles embedded in caissons. Angles set inward at 45 degrees to the tower-verticals are bolted from the tower top to the lower chord; they are counterbalanced by pinned, adjustable cylindrical eyebars also set at 45 degrees and which extend outward to where the lower chord and the concrete abutments meet; and thus the whole consists of two cantilevered kingpost spans joined through an extension of their I-beam lower chords. The inner panel of the longest kingpost has been subdivided to make the top chord more rigid. Designers added a diagonal from the bottom of the pier-tower to the middle of the top chord and an adjoining vertical of a pair of angles. The lower chord supports a 6' timber deck.

Extra I beams set in concrete have been added as piers at several points.

Alterations

The bridge has been reinforced by a series of piers.

Bridge Considered Historic By Survey: Yes

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