A Look At:
These beautiful and graceful bridges are an example of a standard plan bridge that includes aesthetics as part of the plan. A casual glance might cause one to incorrectly think that these are a form of a rainbow arch bridge. However, these are basically normal through girder bridges with a bit of an arch added. The way they work in terms of engineering could be compared to the steel girder bridges that are commonly seen on railroads. Although girder bridges are an extremely common type of bridge, this concrete curved variety is something that was developed in Michigan and only used in Michigan and its neighbor, Ontario. For a discussion of Ontario, see the end of this article.
Developed by C.V. Dewart in the late 1910s, these concrete curved-chord though girder bridges were mostly built in the 1920s. When he was designing the plans for this bridge type, Dewart was looking for a standard bridge plan that was easy to follow, used simple materials and resulted in a strong bridge that did not require much work to maintain. Since no one had ever seen bridges like this before, they at the time developed the nickname "Dewart's Tunnels". Today they are known by engineers as concrete curved chord through girder bridges. People who are tired of that mouthful sometimes call them Concrete Camelback bridges.
There are several different styles of this bridge that all follow the same design, yet are each different in their own way. I will discuss the four different varieties, each of which are in the above picture.
This is the most impressive and significant style. Although the height of the arch seems to vary from bridge to bridge slightly between 70 and 90 foot plans, the top of the arch is much higher than a car. Architectural designs include the arch itself, and the inset arch. Inside the inset arch are little arched "windows" that complement the main and inset arches of the bridge. Below the windows are further inset squares running along the base of the inset arch. Viewed from the outside at mid-span, like in the above picture, these ancient bridges have a look to them that I would describe as modern. The arch is a very graceful streamlined arch. This style of bridge can be found with the usual one span, or can have two spans. There is even one three-span example that has been preserved in a park. The preserved three-span bridge is a former US-12 bridge. Finally, I should mention that although the curved-chord through girder bridge was a standard plan, there seems to be no limit to the design of the end posts for these bridges. I have seen flat end posts, box-shaped end posts, angled end posts, and even a bridge with large concrete obelisks at each corner. Some of these bridges have plaques mounted at the end posts and some look like they never had a plaque. I am unsure of why there are those inconsistencies, however, it helps make each bridge interesting in its own way. Another inconstancy is sidewalks. Only two curved girder bridges that I know of have sidewalks. This is because most of the curved girder bridge were built in rural areas.
One example of a curved girder bridge is over the Red Cedar River in Okemos, and it has no end posts.
The Wadhams Road Bridge over Pine River is a two-span example, with square end posts.
The Griswold Road Bridge, with its unique stripes on the main arch. If you are fond of this bridge, you can scoop up some and take it home, since the bridge is crumbling severely.
The Marquette Survivor is the bridge I found with obelisk end posts. Read more about this bridge in the next section.
This is the next size down of the curved girder bridge type. This style was used for the smaller spans, and lacks the windows and inset squares of its larger siblings. Inset arched rectangles take the place of the windows. These seem to be less common than the larger bridges and many of them are quite old.
The Yale Road Bridge is a skewed example that is in decent condition.
Finally, I would like to point out that I have noticed two styles of support under the deck. In one example, the Wadhams Road Bridge, there are no beams going across under the road. However, the Griswold Road Bridge has large beams under it. See the pictures below.
Wadhams Road Bridge, with no beams.
Griswold Road Bridge, with beams.
This bridge style is an unusual style, occurring in scattered locations in the state. The curve is very slight in this style. However, the girder in these bridges is not functional, it acts only as a railing. The bridge shown in the photo above, in the city of Lapeer, serves a four-lane road. A true curved-chord through girder could never be so wide. However the style of the curved girder is apparent in the concrete railings. The inset arched rectangles are gone, leaving only the inset arch and the main arch. This bridge is only a little bigger than the mini-girder style (which I discuss next), This is basically in appearance, a baby curved-chord through girder bridge. Since it is on a former trunk line road, this would have been a trunk line bridge, although it is no longer maintained by the state.
Its just a little bridge.
The top-most bridge in the picture is an example of a different bridge type that I put in here because it follows the architectural style set up with the concrete camelback bridge design. These tiny bridges were built long ago when culverts were apparently not built as large as they are today. These days, if a bridge like this is torn down, the replacement is not even a bridge, it is a culvert. Examples of these bridges can be found all over, both on country roads and busy highways. These tiny bridges were built well, and I have given them the unofficial nickname mini-girder bridges, even though the so-called girders are really just railings on these bridges.
Sure looks a lot nicer than a culvert. This bridge is in Imlay City.
Dewart designed these bridges to have a large safety margin. He succeeded. Although these bridges were built in the 1920s, at a time when steel pony truss bridges were still being built, many of these bridges still exist today with no posted weight limit. Many of these bridges are even on routes that carry truck traffic. This is amazing to me, since there are bridges on rural dirt roads, built in the 1940s, that have weight limits and are torn down and replaced. These concrete curved girder bridges are so strong that they seem able to take some erosion and still be structurally sound. Since no one seems to care about maintaining bridges anymore, the large amounts of salt that are dumped on our roads in the winter erode these bridges like acid. Since the concrete girders are above the road, and in addition, since the bridges themselves are so narrow, all that salt splashed right onto the girders. Despite this beauty-depriving erosion, these bridge continue to remain on our roads without that condemning weight limit! Another example of the might of these bridges happened when a series of damns broke in Marquette and sent water surging onto a curved girder bridge. The bridge appears to be a former highway bridge that was allowed to remain beside the new bridge to serve as part of an access road to a park. Anyhow, the flood washed out a large amount of the park road and yet the old bridge just sat right in the middle of the torrent, and came out with hardly a scratch! See the pictures below.
This is the Marquette bridge just after the flood, just before the flood washed everything out.
A helicopter shot this picture of the flood washing out the land around the bridge.
By chance, I ended up in Marquette for a vacation, a bit after the flood. This is what the bridge looked like when I visited it.
The Griswold Road Bridge has suffered severe erosion, yet still exists without a weight limit!
The only weakness to this bridge design that I can see is the fact that the design limits the width of the road. These bridges could not be built very wide, and as cars and truck got bigger and faster, the bridges became too narrow. If you get two motor homes going in opposite directions on these bridges it can be a tight fit! This is not a problem on rural roads, however it can present a problem on roads that carry heavy traffic. As a result, these bridges are being demolished at an alarming rate, despite their obvious historic and aesthetic value. Regardless of the needs of the traffic on the road, I believe there is an obligation to preserve these bridges, even if for pedestrian use, with a new bridge serving vehicular traffic on a different alignment. These bridges are an expression of Michigan and its history, and represent how ahead of its time Michigan was in developing new bridge designs. This bridge type represented a sensible combination of economics and aesthetics.
The demolished East Michigan Avenue Bridge. Photo from HABS HAER. This bridge is now replaced by a slab so ugly that I don't recommend eating within an hour of crossing it.
As I began to expand the coverage of this website into southwestern Michigan, I have learned a lot of the crimes that have gone on over here against historic bridges. By far, Kalamazoo County has been the worst offender, demolishing three grand examples of this bridge type in the 1990s. Two of them, Mosel Avenue and East Michigan Avenue, both over the Kalamazoo River, were magnificent three span structures, with a main 90 foot span and two 60 foot spans, one at each end. They offered a beautiful union of the 60 foot plan and the 90 foot plan, which have quite a different appearance. These both were the second longest example of this structure type in Michigan. Since Michigan was the only state in which this bridge type was built, they were the second longest in the United States. The only bridge that was longer was the US-12 bridge in Mottville, Michigan. It was preserved by MDOT. Finally, going back to Mosel Avenue, there was actually another 60 foot plan camelback bridge that passed over Riverview Drive. All three of these Kalamazoo County bridges have been demolished, leaving Kalamazoo County with no camelback bridges. So now, pause and consider the Mission Statement listed on http://www.kcrc-roads.com/ which is the Kalamazoo County Road Commission's website:
Our goal is to maintain a county road system that is safe and convenient for public travel and to manage the roadside environment, with a view toward preservation.
Preservation? They don't have anything left to preserve because they demolished everything!!!
With the East Michigan Avenue bridge near Galesburg, the excuse that the county gave was that the bridge was the "only bridge in the area and served the needs of many people." For a paved road, this section of Michigan Avenue is very quiet, due to its proximity to I-94 which everybody uses. Granted, Michigan Avenue is an emergency route for I-94, but if a problem occurs on the expressway, chances are it would only close one direction of traffic, and thus the narrowness of the bridge would not be a problem as most people would all be going the same way.
Feel free to peruse HABS HAER's documentation of these breathtaking bridges that you no longer have the privilege of seeing thanks to the road commission.
Mosel Avenue over Kalamazoo River
Mosel Avenue over Riverside Drive
East Michigan Avenue over Kalamazoo River
An informational plaque near the US-12 Bridge in St. Joseph County mentioned that Ontario also ended up building this bridge type in addition to Michigan. Ontario apparently didn't build very many however, and it however took me forever to find even one example of an Ontario adaptation of this unique bridge design. Cameron Bevers of www.thekingshighway.ca however had located one and was kind enough to supply me with photos of the bridge. The design is clearly a concrete camelback, however its appearance is quite different, and indeed more simple and utilitarian, than Michigan's. It is interesting however because the railings that extend from the ends of the girders show hints of the concrete bowstring (aka rainbow arch) design that Ontario would later embrace at a much larger scale. Cameron gives the following description for the bridge, which crosses Gull River: "The bridge is located on a former highway alignment on the eastern side of Hwy 35 at Minden (about 80 km southeast of Huntsville). The current Hwy 35 bridge was built in 2001, replacing an earlier structure constructed on the same alignment in 1951. It is my understanding that the curved chord girder bridge has been out-of-service to highway traffic since 1951, although it is still used by hikers and snowmobilers in their respective seasons."
Please enjoy the below photos of the bridge, courtesy of Cameron Bevers. There are five photos, available both in Original / Full Size and standard 640x480 size.
Original / Full Size
Portal view.
Original / Full Size
Portal view.
Original / Full Size
Side view.
Original / Full Size
Side view.
Original / Full Size
Distant mid-span side view.
Portal view.
Portal view.
Side view.
Side view.
Distant mid-span side view.
