In late summer 2009, James McHugh Construction and their erection sub-contractor, Danny’s Construction Company, approached Collins Engineers, Inc. (Collins) to evaluate the feasibility of designing a temporary erection and launching runway structure that could be used to support the erection of a 1,100-ton bridge span and allow it to be moved into place. The work would be part of the replacement of CN Railway’s existing movable span at Bridge No. 552 on the Illinois River south and west of Joliet, Illinois.
Working with McHugh and Danny’s, Collins developed preliminary concepts for the runway structure that could be used for the purposes of bidding the work. The temporary runway structure would be located about 40 feet downstream of the existing bridge. The design would have to provide for movement of the new truss parallel to the existing bridge, as well as allow the new span to be translated laterally into place. Collins’ concepts utilized materials that McHugh had salvaged from a previous job for the erection runway and new pile bents to support the runway. Pile bent spacings were preliminarily established as were pile lengths so that bids could be prepared. An early decision included consideration of using the existing dolphins on either side of the river channel for the launch bents. The use of these dolphins could significantly reduce costs by eliminating the need for design and installation of temporary structures strong enough to support the launch loads.
After award of the bid to McHugh/Danny’s, Collins met with the team to review assumptions and begin design. Collins worked closely with the contractor team to verify the loads that needed to be carried by the runway structure not only during the launch but during erection as well. The system used to launch and move the span resulted in discrete moving loads applied along the length of the temporary runway structure. These loads varied as truss supports were added and removed during various stages of the erection and launch. Where issues of constructability arose, Collins worked with McHugh/Danny’s to modify the design to accommodate their customary means and methods. Collins also assisted McHugh/Danny’s in reviewing balance calculations for the new lift span which was critical to ensuring that the span could be made fully operational within the closure window provided.