The bridge, constructed in 1970, consists of a 9-span, composite steel plate girder superstructure with a lightweight reinforced concrete deck slab supported on seat type abutments and single reinforced concrete hollow columns on spread footings. The structure has a total length of 1,441-feet and a clear roadway width of 28-feet between concrete curbs.
MGE evaluated the capacities of the steel girder superstructure elements as well as the capacity of the deck slab spanning between girders in accordance with the current AASHTO LRFD Bridge Design Specifications. The results of the superstructure capacity analysis showed that most of the superstructure elements are adequate for legal loads based on the current code requirements with the exception of the main plate girders for negative moments and shear.
MGE also performed field observations and testing to determine the cause of deck cracking and delamination, concrete spalling near open joints in the soffit concrete, and longitudinal splitting of elastomeric bearing pads. Based on these observations, the results of the deck concrete compressive testing, and the adequacy of the deck slab design, it appears that the deck cracking is limited to the “natural sand mortar” overlay and is not a result of deck slab material or design deficiencies. Thus, it appears that the “natural sand mortar” overlay has reached the end of its useful life in the areas of direct wheel line loading which explains the extensive cracking and moderate delamination in these areas.
In addition, team members from MGE and subconsultant (Collins Engineers) performed an in-depth structural condition assessment of the bridge. The condition assessment consisted of a Level I visual and tactile examination of all accessible surfaces of: bridge deck, bridge parapets and rails, bridge drainage features, steel girders, steel framing members, concrete abutments, concrete piers above the waterline, drainage features, bearings, expansion joints, fixed joints, and approaches. Locations of all defects were referenced and notable deficiencies were measured, photographed and recorded in the inspection notes. The inspection of the superstructure and the upper portions of the substructure units was conducted by two team members with the use of a Hydra Platform Under Bridge Inspection Vehicle. All portions of the superstructure were subject to a thorough inspection.
It was found that the entire bridge deck overlay and portions of the bridge deck joints were generally in poor condition and should be replaced. Recommendation was made to remove the overlay and replace it with polyester concrete. In most instances, the bridge joint seals have also reached the end of their serviceable lifespan and no longer function properly, allowing significant water infiltration down on to the superstructure which has, in some locations, hampered the effectiveness of the weathering steel corrosion process. In combination with the joint seal replacement, it was recommended that steel angle joint nosing that was missing be replaced.