Why was steel selected as the girder material instead of precast concrete?

The main reason that steel was chosen is that the end spans of the bridge are curved. Steel girders can be curved to match the curve of the roadway; precast concrete girders cannot be curved. Precast girder bridges built in short, straight segments with a pier at each “kink” in the beam line, and the bridge deck is built in a curve on top of the girders. Constructing a curved roadway on straight precast concrete girders would require at least one additional pier.

A second reason that steel was chosen is that steel girders are built in relatively short sections in a fabrication plant and then transported to the site and bolted together to make up any span length. These short sections can be designed so that they can be easily transported to the site. For instance, a 150-foot long span could be made of two 75-foot long girder sections that are bolted together at the site. Concrete girders must be built in one single piece. Concrete spans greater than 125 feet have been constructed, but it is very difficult to transport concrete girders this long. Transporting two 75-foot girders through an urban area is much easier than transporting a single 150-foot long girder.

One last reason that steel was chosen is that steel is a recycled and recyclable material. The steel used on this project will come from bridges and buildings that have been demolished, old cars, and even soup cans from your recycling bin. When this bridge has finally lived its useful life, the girders will be recycled to make other bridges, buildings, automobiles, and soup cans. When concrete girders are demolished, the reinforcing steel is recycled, but the crushed concrete is only useful as fill material.