Monday, September 21, 2009

Oregon's Bridges: Alsea Bay Bridge (2)

A bridge is considered to have a lifespan of 75 years. Some bridge become so popular or are so expensive to replace that extraordinary efforts are performed to keep the bridge in service. Of course, 75 years is somewhat arbitrary. A bridge that is not worn down by heavy traffic or inclement weather and is well-maintained can stay in service well over 100 years. In fact, there are design recommendations to give important bridges a 100 year lifespan (with more concrete cover, more deck reinforcement, etc.).

The original Alsea Bay Bridge was designed by the great Conde McCullough and built in 1936 (see posting for February 5th). It was considered to be one of the finest examples of concrete bridge construction in the United States. It became eligible to be put on the National Register of Historic Places in 1981. However, the harsh salt water environment began to cause corrosion to the reinforcement, and despite efforts to preserve the bridge, it was finally replaced in 1991.

The new Alsea Bay Bridge (designed by HNTB) pays homage to the original structure in several ways. The central arch span resembles the arches on the original structure. The pedestrian observation platforms (with dramatic pylons) were preserved from the original structure. However, the bridge also updates the style from Gothic to Modern with Y-shaped piers and a parabolic line to the arch. The bridge was also modernized with a latex concrete deck and a thicker concrete cover to prevent corrosion of the reinforcement.
Creative Commons License
Oregon's Bridges: Alsea Bay Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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