Believed to have been fabricated around 1906, the 20 Mile Road Bridge spanned the St Joseph River in Calhoun County and remained in service until its closure in 1992. There is little written documentation about this bridge, no county records on when the bridge was purchased or erected, no maintenance schedule, and no historic photographs.* There were some significant historical features of the bridge that made it eligible for the National Register of Historic Places, most of these features determined from reading the physical parts of the bridge. It is made of steel, the only one of the five historic bridges in the Calhoun County Historic Bridge Park fabricated with steel, the other four made of wrought iron.** Once the original members were shotblasted clean for painting, the embossed Illinois mill marks could be plainly seen, a clear indication that these members were milled at the Illinois Steel Company. More than likely, the trusses themselves were fabricated at another location. Another historic feature of the bridge is its all-riveted construction. The trusses were fabricated without bolted or pinned connections, unlike most bridges of this size that typically were fabricated in shop-riveted sections, shipped to the bridge construction site, and assembled there with pinned and bolted connections. Shop-riveted sections of the 20 Mile Road Bridge trusses would have been shipped by rail on flatcars to the erection site. The trusses, 64 feet in length overall, were probably fabricated in shorter sections. There was some indication during the restoration of the bridge that hand field-riveting was done at vertical and diagonal connections. Documents for the historic evaluation of the 20 Mile Road Bridge show no distinction between the different rivet methods: shop-riveting, field-riveting, hand field-riveting, all of which would have been done with different tools.

The romantic vision of a hot rivet pulled from a bed of black burning coals, grasped by iron tongs, thrown up several floors, expertly caught in a catcher's can, seized by a shorter set of iron tongs, slipped in a drilled hole of several plates, hammered round and solid with a pneumatic field rivet hammer, is often imagined as the way most riveting got done. However, that scenario actually represents only a small percentage of the driven rivets in a riveted structure. Riveted structures were fabricated with thousands of shop-driven rivets, and the primary methods used heavy pneumatic powered equipment.

The Historic Architectural Engineering Record (HAER) for the 20 Mile Road Bridge reports that " Flat steel bars are welded to the four angles to create a lattice pattern." In fact, no welding, either forged or electric arc, was made on any of the bridge members (except for later repairs). It would be decades before electric arc welding was in widespread commercial use. In the historic record, welding is sometimes confused with riveting.

In the historic evaluation of the 20 Mile Road Bridge, two other features were listed as historically significant: the concrete abutments and the concrete jack arch deck. Neither of these features was replicated on the restored bridge.

 

Restoration work began with the dismantling of the trusses. The tools used in this process were the same as those used in steel fabrication, both historic and contemporary. It was during the restoration of the 20 Mile Road Bridge that many of the metal restoration skills used later for the next three bridges were developed: the electric arc welding process adapted for the replication of bridge members, the hot rivet process for reassembling the bridge trusses, and the development of a process for removing pack rust. Future ISP Newsletters will continue to tell the story of the restoration of the 20 Mile Road Bridge, as well as the third bridge restored for the Historic Bridge Park, the Gale Road Bridge.