Viaducts

A viaduct is a bridge composed of a series of spans that carries a road or railway over valleys, lowlands, rivers, or other terrain that would be difficult to cross with a single span. The term is typically used for long, multi-span structures; a single-span crossing is usually described simply as a bridge.

Viaducts take several common forms. The arch viaduct, built with a sequence of arches, is one of the oldest and most enduring designs, often constructed in stone or brick. Beam or girder viaducts use a deck supported by parallel girders. Truss viaducts employ truss frameworks to distribute loads across multiple spans. In modern practice, reinforced concrete, steel, or composite materials are common, and some viaducts use precast elements or slab spans for efficiency. Viaducts are typically designed to maintain a consistent gradient suitable for road or rail traffic and to minimize the number of foundations required across uneven terrain.

Materials and engineering have evolved from traditional masonry to contemporary concrete and steel solutions. Early viaducts relied on durable masonry, while later projects exploited reinforced concrete, prestressed elements, and modern fabrication techniques. Design considerations include load capacity, structural redundancy, seismic performance, drainage, and foundations capable of supporting deep or soft-soil courses, often employing piles or caissons.

Function and context: viaducts enable grade separation and efficient routing in challenging landscapes, preserving local environments and reducing disruption. They are widely used along rail corridors, highways, and urban transit networks, forming essential components of regional and national infrastructure.