Willett, Hofmann & Associates was hired as a subconsultant to Civil Constructors to provide a tied arch erection plan for the Morgan Street Bridge. The bridge superstructure is a three-span bridge with composite welded plate girder end spans and a parabolically-shaped steel tied arch middle span supported on concrete abutments and piers. The length of the structure is 503’ – 3 1/8” back-to-back of abutments. The width of the bridge is 73’-2” out-to-out of deck, which includes (4) 12’-0” lanes, (1) 5’-0” sidewalk, and (1) 12’-0” multi-use path. The contract Special Provisions required a detailed erection and procedure, including but not limited to the sequence of girder and tied arch element erection and bolt tightening, and provisions for the stability of girders and tied arch elements and blocking of the bearings during erection and until the concrete deck has reached its design strength; and calculations to show temporary loads, stresses, and deflections at each stage of erection on both the temporary and permanent members. Additionally, contract plans required verification of deflections, camber, and laydown dimensions shown in the plans.

Several site constraints warranted installation of temporary erection towers to construct the Tied-Arch Span over the Rock River. Upon coordination between WHA and Civil Constructors, a comprehensive 3D model of Spans 1-3 of the Morgan Street Bridge and all temporary erection towers was compiled in RISA-3D. WHA and Civil Constructors developed a two-part Erection Plan consisting of construction of the erection towers and picking/rigging of members showing all loads, stresses, and deflections during 34 pre-defined stages.