- Side view of the bridge. Unless noted, the following photos are courtesy of Jonathan Parrish, used with permission.
Author’s note: This article is in connection with the series on the Historic Bridge Conference, which took place in Indiana during the weekend of 21-23 September, 2012.
Rehabilitation. A word that is used to describe the process of rebuilding a historic bridge, but without destroying its historic integrity. What is meant by that is that some parts of the bridge are replaced with additional parts being added to the structure for safety purposes, while at the same time, the outer part of the bridge, its facade, must not have its aesthetic value compromised. There are some examples of how rehabilitation works. One is replacing the portal bracings of a through truss bridge to encourage better height clearance, as was the case with the Minnesota River Bridge at the south end of St. Peter in the 1960s. There is the widening of the truss bridge, as seen with the Checkered House Bridge near Richmond, Vermont, which occurred this summer. But it could mean just replacing the decking and other parts that are worn out, as was the case with the Cold Spring Road Bridge in Stamford, Connecticut, where the facade of the arch bridge was kept, but the decking was replaced and the arches were reinforced. That bridge was recently reopened to traffic.
St.Peter Bridge before……
…..and after the portal bracing replacement in ca. 1960. An example of rehabilitation. The bridge was built in 1927 and replaced in 1998. Photos courtesy of MnDOT
However, the definition of rehabilitation can be a bit fuzzy if it deals with a massive bridge project. Take for instance the Madison-Milton Bridge in southern Indiana. The bridge was built by the Mount Vernon Bridge Company in Ohio in 1929. Spanning the Ohio River between the towns of Milton, Indiana and Milton, Kentucky, the bridge features a cantilever through truss design, whose truss types are Pratt on the outer spans and Baltimore petit for the center span. The bridge fits perfectly into the historic landscape of the two towns, as the people of both communities take pride in them and their 3200 foot long Ohio River crossing. Despite this, there is one flaw that the bridge has: the structure is too narrow- two lanes totaling 20 feet wide with no space for the pedestrians to walk across.
Instead of demolishing the entire bridge (piers included) because of its historic significance and replacing it with a boring and bland concrete bridge, the plan is to replace the cantilever trusses on its original piers, piece by piece and section by section, while at the same time, make it wider but keep its historic value tied into the community. This is very unusual for cantilever truss bridges are becoming seldom a choice of use for bridge construction; especially in light of the Minneapolis Bridge Disaster in 2007. In addition to that, the plan has met opposition from people claiming that the bridge could have been maintained more often and incremental measures, such as deck replacement and swapping gusset plates would have been more cost effective than just replacing the truss bridge, bit by bit.
Yet by the same token, if one looks at the pictures provided by Jonathan Parish, one could think that the bridge is being rehabilitated just by replacing sections of the truss bridge, but keeping the integrity in tact. While many like me are not of the same opinion, some people would think otherwise when looking at the pictures more closely. This is where rehabilitation can be a center of discussion, with the question of whether it is really is what it is, or just a downright bridge replacement. The project is the first of its kind ever undertaken, yet there are some projects, where only one or two small sections of a bridge is replaced and the rest are sandblasted and restored to its original form. Take the Hochdonn Bridge over the Baltic-North Sea Canal in western Schleswig-Holstein in northern Germany, as an example. Built in 1920, the 4,400 foot long viaduct features deck Warren truss approach spans and a Camelback Warren through truss bridge with a main span of 223 feet long. In 2006, that span was replaced with a replica as part of the project to rehabilitate the bridge. The rest of the steel viaduct was strengthened through sandblasting and adding rivets and plates to support the structure. The project was finished in 2008 and still serves two lanes of rail traffic today, linking Hamburg and the island of Sylt. More on the bridge will come in an article coming later.
South approach to the Hochdonn Viaduct. Photo courtesy of Jan-Geert Lukner (blocksteller.de), used with permission
Camelback Warren through truss (which was replaced in 2006). Phoo courtesy of Jan-Geert Lukner (blockstelle.de), used with permission
But for the Madison-Milton Bridge, the project being undertaken has produced some questions that are posted below. Look at the pictures below and answer the following questions in the comment section:
1. Is the project an example of bridge replacement or bridge rehabilitation? Compare this project with that of the Hochdonn Viaduct and one that you know that is in your neck of the woods.
2. Will the new bridge have as high of historical integrity as the old one and why?
3. If you dislike the was the bridge is being redone, what other options should have been taken for the structure?
4. Do you think that cantilever truss bridges still have a future on all roadways in America and beyond, despite the tragedy in Minneapolis five years ago?
5. What are the advantages and disadvantages of rehabilitating a historic bridge, based on the factors of structural stability, safety as well as historic and aesthetic value?
Have a look at these photos and post your thoughts either directly or through facebook or LinkedIn.
Photos:
The original main span in the foreground and the newer main span in the background
- The portal view. Note that on the Milton side, the original approach span was demolished but not before a makeshift approach span was constructed, causing traffic to shift at a 90° angle
Close-up of the demolished approach span and the makeshift approach span (in the background)
The new span in the foreground and the original span in the background
The portal bracing of the approach span. The question is what will the portal bracing look like when this approach span is replaced?
Author’s Note: Another article with this bridge in there will be coming out soon, as there is another section of the story that has yet to be mentioned. Moving on to another Indiana-related historic bridge topic…..
The author would like to thank Jonathan Parrish, Jan-Geert Lukner and MnDOT for the use of the photos in this article.
