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This bridge is one of several truss bridges on the Calumet Sag Channel that date to the 1960s. They are noted for having built-up beams held together by rivets but having all connections being bolted. There also are some welded details. While not very old or overly significant, they are more visually attractive than any modern bridge could hope to be. In addition, these bridges are quite important in conveying the final chapter in the story of the historic metal truss bridge. The use of rivets only on the built-up beams in these 1960s bridges represents the final years of the use of rivets in metal truss (and any type of metal bridge) construction. Already at this time, historical techniques like using lattice and v-lacing on built-up beams had been largely abandoned. By the 1970s, rivets were abandoned completely. After around 1970, metal truss bridges might be built occasionally for specialized situations, but were largely abandoned as a bridge type considered for a new bridge project. In addition, any truss bridges built after approximately 1970 no longer used rivets, ending a historical construction method that had been used essentially since the beginning of metal bridge construction in the United States. The elimination of this final historical construction technique by 1970 is largely why HistoricBridges.org has set 1970 as the general cutoff date to consider a bridge for historical significance and inclusion in the Bridge Browser.
The National Bridge Inventory lists this bridge with a 1967 construction date while the plaque says 1970. This suggests that for some reason it took an unusually long three years to build this bridge.
Like other Calumet Sag Channel bridges, this fixed truss bridge was designed such that, as indicated in the original plans for the bridge, the structure could be converted to a vertical lift bridge by the addition of towers in the future if increased clearance for boats was ever needed in future years. This need has never presented itself however, so these changes have never taken place. The plans for this bridge also highlight how narrow the Calumet Sag Channel used to be in terms of width, and how much wider the channel is today. Both the original and current dimensions of the channel are shown in the plans. The construction of this bridge most likely was required to accommodate the construction of this much wider channel.
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Main Plaque RIDGELAND AVENUE BRIDGECALUMET SAG CHANNEL BUILT 1970 BY COUNTY OF COOK [REMAINDER OF PLAQUE UNREADABLE] |
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