An environmental comparison of bridge forms

The embodied energy and carbon dioxide emissions from the use of construction materials are among the concerns engineers must consider when planning, designing and constructing a bridge. Previous studies have been carried out on building structures to assess both the energy consumed and the CO2 emissions in their construction and use but less information is available to bridge designers. This paper outlines the range of embodied energy and CO2 emissions for materials commonly used in bridges and the variability of these values is discussed. A study is carried out for a moderate length river bridge of energy use and CO2 emission during construction. A number of different bridge forms and materials are considered. The primary forms are girder, tied arch and cable stayed. Three broad material groups were investigated, namely concrete, steel and steel-concrete composite. The study also estimates the continuing CO2 emission throughout the life of the structure from maintenance and repairs. From the study a number of broad trends are discussed and some design guidance offered for those wishing to provide more environmentally responsible bridges