Collins provided construction engineering services to Walsh Construction for the Wells Street Bascule Bridge Reconstruction project.
During the reconstruction of the 90-year-old bridge, vehicle and pedestrian traffic were detoured. Rail traffic continued uninterrupted with two exceptions. As part of this project, two nine-day windows were established during which all Chicago Transit Authority (CTA) rail traffic would be shut down over the bridge while portions of the old truss arms were removed and the new truss arms were put into place. Collins worked with Walsh to develop the plan that successfully fulfilled Chicago Department of Transportation (CDOT) and CTA’s requirements to minimize the duration of the bridge closure and reduce impact on CTA commuters.
The original design called for only partial assembly of the new truss arms offsite and the remaining members built in place. The Collins/Walsh plan involved the offsite pre-assembly of the new movable truss arms with all bracing, floor beams, and stringers. The new replacement truss was then floated up the Chicago River to the project site on a barge. The existing truss was floated out and the new replacement truss was floated in on barges. Collins extensively modeled the truss in STAAD to determine the loads on the truss members during various stages of erection. Collins reviewed the truss-carrying barges for stability, as well as the barges used by the large support cranes needed for the work.
During the two closures, work on the bridge went around the clock until completed with Collins providing continuous engineering support on-site to ensure that decisions were made expeditiously to meet any contingency. Collins’ staff served as an extension of Walsh’s field staff and was responsible for all decisions regarding truss alignment, bolt-up, and acceptance of the work.
Collins’ role on the rest of the project also included providing engineering analysis for bridge balance, temporary shoring, and change-out of various chord members under CTA rail traffic.