Stearns Bayou Bridge - Michigan

The Stearns Bayou Bridge, constructed in 1966 in Ottawa County, Michigan, is the first, fully galvanized bridge constructed in the United States. All structural members, fasteners and other steel components of the 425-foot bridge were hot dip galvanized after fabrication. The bridge has a 30-foot clear roadway with 5 ft walks on each side.

The steel work was about six feet about fresh water for most of the length of the bridge and is subject to heavy winter salting.The deck is a re-enforce concrete slab, which is supported on rolled steel beams.

A three-coat paint system was originally specified as the method of corrosion protection. However, galvanizing was investigated as an alternative. Based on this study, several design modifications in the bridge were made to facilitate galvanizing. These included

• The use of high-strength bolted splices at inflection points of the continuous sections.
• Seal welding for all attachments
• Cropped corners of stiffeners in order to allow the free flow of molten Zinc when the stiffeners were dipped on the galvanizing kettle
• Spot welding of shear developing components before galvanizing.

The first cost of galvanizing the Stearns Bayou Bridge was 8,750. The comparable paint estimate was 5,500. The bid for the paint alternative did not include surface preparation. It is estimated that, at the time of construction, this would have added about 15-20 dollars per ton to the cost of painting. This made the galvanizing and paint alternatives nearly identical on a first cost basis.

When inspected in April of 1986, 20 years after it was first placed in service. Beams and diaphragms still exhibited spangle and an absence of rust on all exposed surfaces. Coating thickness ranged from 3.0 mils to 5.0 mils with an average of 4.4 mils, still well above that originally specified. Minimum coating on bearing pads was 3.5 mils and handrails thickness of 2.0 mils.  Based on this exposure data, the estimated remaining life of the coating on the bride steel was, at the time of inspection 66 years.The total rustfree life cycle of this bridge will be 86 years.