Weight versus Cost: Light-Weight Materials in Cable-Stayed Bridges

The weight advantage of light-weight construction materials such as steel or fiber-reinforced plastics is usually accompanied by the disadvantage of greater costs when compared with, e.g., reinforced concrete. This cost disadvantage makes light-weight materials uneconomical for many kinds of structures, because the advantage of reduced weight cannot efficiently be transformed into a cost benefit. For certain kinds of structures, however, weight reduction at the right locations conveys cost savings large enough to compensate for the higher material cost. Typical examples are high-rise buildings and long-span bridges, where light-weight materials can result in overall cost savings when used in the upper floors of the building or in the midspan region of the bridge. The weight-versus-cost problem is analytically investigated for a fan-type, cable-stayed bridge. A break-even point is determined that indicates the extension of the main-span center part that should be made of light-weight material to minimize overall costs. Results of example calculations are presented.