Ohio Street over the North Branch of the Chicago River

Description of Project

The existing structure consists of two double-leaf trunnion bascule bridges that carry three lanes of westbound traffic and three lanes of eastbound traffic over the North Branch of the Chicago River. Each bridge consists of a variable-length west backspan, a west fixed span over the counterweight pit, two bascule leaves comprising the main river span, an east fixed span over the counterweight pit, and a variable-length east backspan. The structure has an overall length of 354’ (centerline-to-centerline fixed piers; 26’-9” / 31’-9” / 237’-6” / 31’-9” / 26’-3” spans). The overall out-to-out deck width of each bridge is 43’-10”. The movable span superstructure consists of 3” high concrete-filled metal grating supported on W18 steel stringers, built-up transverse floor beams and built-up truss members. The approach span superstructure consists of a 71/2”-thick reinforced concrete deck on W30 steel stringers and built-up transverse floorbeams and cross girders. The substructure consists of reinforced concrete piers and abutments with counterweight pits.

Description of Scope of Work

HBM performed an in-depth complex structural inspection for the Ohio Street Bridge (SN 016-0202). A hands-on visual inspection was performed, structural elements were load rated and three repair alternatives with cost estimates were provided to IDOT in a feasibility study report.In the feasibility study, the deteriorated truss gusset plates, truss members, stringers, floorbeams, and lateral bracing members were investigated. A finite element model of the movable span was generated using CSI Bridge (SAP2000) to model the structure and obtain the dead and live loads for rating the structural members. The movable leaves were also modeled in the open position to verify the adequacy of the structure under dead and wind loads.

Due to the deteriorations, it was recommended to repair one of the gusset plates. In the first alternative, it was recommended to repair two of the truss members on each leaf. The second alternative included all items from Alternative 1 in addition to plating of one of the stringer webs. The third alternative included all items from Alternatives 1 and 2 in addition to repairs to the deteriorated members of the fixed framing.

Due to the inventory rating of 0.88 for two of the floorbeams, the repairs were recommended as part of Alternative 1. Removal and replacement of deteriorated lateral bracing members was also included. Other recommended items include repairs for the cross girder front braces, counterweight pits, bearings, catwalks, and pit partition walls.

In summary, the HBM scope of services included the Phase I engineering services as described below. The Feasibility Study was submitted in May 2017, and Phase II is anticipated to follow based on IDOT recommendations.

Phase I:

• Existing document review, detailed field inspection, and preparation of field notes
• Structural Analysis and Rating for Repair Recommendations
• Feasibility Report with Repair Alternatives