What is the average life span of a road bridge?

Answer 1

Bridges design life and bridge life spans vary greatly by the type of material used in construction, maintenance carried out on the bridge and the environment in which the bridge is constructed. The following comments are limited to the superstructure (parts in the air) and deck. The biggest enemy of structures is moisture. Moisture allows for biological and chemical attack by making the materials easier to eat, chew or corrode. The design life is chose based on economic impacts and a bridge reverse engineered for a specific purpose...Freeway bridges carry more goods and people than rural bridges and will have a longer design life, a rural bridge has a design life longer than an industrial road. A wooden log bridge in a wet/damp climate with a regular freeze thaw cycle (Washington state) might have a design life of 20 years. The same bridge material might survive over 50 years in a dry climate. Expect to find them in low population density areas, low volume roads or industrial roads. A woode truss bridge is often designed for a life expectancy of 50 years - the material is carefully selected, graded and treated with preservative. If the structural wood components (heavy load carrying elements) are protected from moisture with a roof or protective covering these bridges survive indefinitely and individual components are replaced. For example, covered wooden bridges can survive for more than 100 years. These bridges are "old school" and survive because the cost of replacement and the aesthetic values are high. The majority of modern bridges are steel and concrete and began with the merger of technology, industry. The materials are inexpensive and have a good quality control process. Steel and concrete bridges are usually constructed with a design life of between 50 and 100 years. If these bridges are located in a high salt usage area these structures will require a thorough cleaning/washing program annually. The steel and concrete bridges will require a rehabilitation of areas exposed to salt and corrosion. This usually is done on a 20 to 30 year timeframe and will get a lot of these bridges to 100.