ABSTRACT
The Mississippi DOT’s plans to widen northbound I-55 at the interchange with I-220 near Jackson, MS were impeded by various geometric constraints, the most challenging being the limited vertical clearance under an existing CIP multi-cell box structure. Shallow depth steel plate girders were found to be the only viable solution to accommodate the maximum span length within the limited structure depth. An in-depth analysis using 3D FEM methods was conducted to assess the interaction between the existing and new structures. The relatively flexible steel structure was found to deflect and twist away from the existing resulting in large bending stresses within the slab. Further analysis demonstrated that the use of haunched plate girders would limit stresses in the deck to acceptable limits while maintaining minimum clearance to the roadway below. This solution allowed the DOT to overcome the impasse and proceed with their plans to widen this important transportation corridor.
