Collins provided girder erection engineering for three curved ramp structures connecting I-355 to I-55 in Illinois. The ramps include a two-span, 353-foot ramp with a 750-foot radius; a 2,650-foot, sixteen-span ramp with a 1,050-foot radius; and a 1,883-foot, twelve-span ramp with a 1,050-foot radius.
A finite element model of each structure was developed and member stresses and deflections checked at each erection stage. Individual girder segments were analyzed for lifting effects. Shoring towers were designed where needed, and partial girder deflections at intermediate stages were allowed to reduce loads. The ramps were also analyzed for the deck placement.