By Rebecca Ebnet-Mavencamp
Opening a letter that announces the Anoka County Historical Society has once more received an award from the Minnesota Historical and Cultural Heritage Fund for a special project gives history geeks the greatest of glee. The following is an excerpt from a recently funded project providing for the research and writing of 18 new MNopedia articles (found online at http://www.mnopedia.org/) – one for each of the National Register Properties in Anoka County. We anticipate the articles to be available on the website by this summer.
Constructed in 1884, the Anoka-Champlin Bridge 4380 was the first bridge to span the Mississippi River between Anoka and Champlin and consisted of four steel spans with a wooden deck measuring 18’ wide. One of the spans could rotate and therefore allow the passage of steam boats and other large vessels.
The wood decking limited traffic capacity and individuals received a fine of $10 if they crossed at a pace faster than a brisk walk. The advent of the automobile at the turn of the century meant the bridge became inadequate. Furthermore, the War Department determined that in the event of a national crisis, the bridge was too narrow and weak to support military vehicles and would also impede the swift flow of river traffic. In 1926, assessments and proposals for construction of a modern bridge to replace the outdated bridge were made. Until a new bridge could be completed, the State Highway Department set a definite load restriction of six tons and posted signs to that effect. Yet, the signage, heavy fines, and even threats of criminal prosecution failed to deter the damage incurred by excessive loads.
During the 1920s, concrete quickly became a popular material for bridge construction – it was cheaper than stone yet similar in compressive strength. By 1929, a new bridge replaced the old steel structure and that same bridge is still in use today. The arch form and encased steel were used to compensate for the materials low tensile strength. The Anoka-Champlin Bridge’s concrete arches were built using “falsework,” a term for scaffold and wooden forms used to pour concrete. This method was time consuming, labor intensive and expensive. In the 1950s, this type of bridge construction was eventually replaced by pre-stressed girders.
In 1979 the bridge was nominated for the National Register of Historic Places stating, “[it] is a fine representative of the open spandrel concrete arch bridge which reached a high state of development in the twin cities and surrounding area in the late 1920s.” Replacement of the top half of the bridge, down to the arches, occurred in 1998-99 but the reconstruction did not alter the historic designation of the famed bridge.
Rebecca Ebnet-Mavencamp is the executive director for the Anoka County Historical Society.