IIW devised a plan to maintain the structural stability of an existing bridge in order to keep traffic moving along one of Dubuque’s major thoroughfares during the reconstruction of U.S. Highways 52, 151 and 61. Throughout the design process, IIW’s concept re-used and recycled components of the former bridge structure to minimize environmental impacts and costs.
IIW structural engineering team worked with the bridge contractor to design the temporary sheet pile shoring for a 35-foot deep excavation alongside the existing bridge that supports the existing roadway.
The plan used steel walers to transfer the loads from steel sheeting to the tie-rods, which extend to a deadman on the opposite side of the roadway. This creates a temporary structure to sandwich the roadway. A key innovative concept is the installation of tie rods using directional boring equipment commonly used in the underground utility industry.
To conserve steel when constructing the deadman, IIW’s engineers nested wide flange beams that formerly were longitudinal girders salvaged from the demolished section of the bridge. These beams were driven vertically into the ground and then excavated on the downslope side to allow the placement of the waler, also a salvaged bridge girder. The plan placed stabilization stuts at each tie-rod location and created bearing plates using the existing bridge’s stringers.
IIW engineers minimized movement and approach pavement by placing these tie-rods with directional boring equipment through the existing embankment. The plan fastened the anchorage to the outside flange of waler beam because of difficulty in aligning beam to fasten on inside flange because of the skew angle and the necessity of lining up three tie locations at the same time.