What is a unique feature of curved bridges?

Curved bridges have unique structural properties that allow them to efficiently manage forces acting on their curvature. One of the reasons that steel box-girders are particularly well-suited for these types of bridges is their ability to provide high strength with a relatively low weight. Steel box-girders can efficiently handle bending moments and shear stresses that occur due to the curvature of the bridge, enabling designers to create safe and effective structures that maintain integrity under load. This design is advantageous as it allows for longer spans and a more aesthetically pleasing appearance that harmonizes with the surrounding landscape.

Other options suggest features that do not accurately reflect the characteristics of curved bridges. For example, saying they always use simple spans is misleading since curved bridges often utilize continuous spans to better distribute forces. The notion that curved bridges do not require any support systems overlooks the necessity of providing adequate supports at various points, as they still need to transfer loads effectively. Lastly, while there may be a variety of materials used in bridge construction, saying that curved bridges commonly utilize materials other than steel does not capture the fact that steel remains a frequent choice due to its advantageous properties.