Anchor Bay Drive

Anchor Bay Drive is a scenic road along Lake St. Clair in Clay, Mich., that carries fishing boats and yachts to the marina at the end of the road. Three bridges along the route provide access to the hundreds of homes that take advantage of the spectacular views of the lake and lagoon.

County engineers recently determined that these crossings--prestressed concrete box-beam superstructures with only a 30-year service life--had become either structurally deficient or functionally obsolete. New galvanized steel press-brake-formed tub girder (PBFTG) bridges with a life expectancy two-and-a-half times as long replaced the existing structures. Combined with reinforced precast concrete deck panels, this steel solution provides a cost-effective replacement option at an accelerated construction schedule with a service life expectancy exceeding 75 years.

The St. Clair County Road Commission was able to bundle these three bridges into a collective, successful superstructure replacement project. However, the bridges provide the only point of access to the far reaches of Anchor Bay Drive, rendering a complete tear-down and rebuild impossible. In addition, space around the bridges is extremely tight, with houses packed in close to the roadway and very little dry land to maneuver on.

Luckily, the chosen PBFTG option, TEG Engineering's ConStruct Bridge System, addressed these issues. The original bridge abutments were in good shape and would not require replacement, and the Con-Struct system can be installed on top of existing substructures. In addition, the system can be delivered two ways: with the precast concrete deck pre-attached to the tub girders, or with it separated. For this project, the team did not want the girders and deck to be attached, due to the space limitations at the installation site.

The county demolished and installed the bridge one side at a time to ensure that traffic flow could continue unhindered. The installation was much quicker than other available options due to the system’s modular design. Both the galvanized steel tub girders and the decking took about half a day to set in place. The county's own crew and equipment easily managed installation without additional equipment rentals or labor, saving the county even more time and money.

Project Team

• Steel fabricator and detailer: Valmont Structures, Valley, Neb. *AISC CERTIFIED*

• Steel erector, general contractor, and owner: St. Clair County Road Commission, St. Clair, Mich.

• Engineer: TEG Engineering, Wyoming, Mich.