bridge

A bridge is a structure built to span physical obstacles and provide passage for people, vehicles, or utilities. Bridges vary in size and form and are classified by their structural system, including beam, truss, arch, suspension, cable-stayed, cantilever, and movable types such as bascule or lift bridges.

Key components include foundations, supporting piers or abutments, the superstructure (decks and girders or arches), bearings, and expansion joints. Materials range from stone and masonry to reinforced concrete and steel, with modern bridges often using composite materials. Design considers loads, traffic patterns, environmental conditions, wind, seismic risk, durability, and maintenance requirements.

Design and construction follow engineering standards and involve geotechnical assessment, load ratings, safety verifications, and quality control. Construction methods may use on-site casting, prefabricated elements, or incremental launching, depending on site conditions. Movable bridges require mechanisms for operation and control.

Historically, bridge design evolved from simple timber or stone spans to sophisticated iron and steel constructions in the 19th and 20th centuries, followed by reinforced concrete and composites. Early bridges emphasized solidity, while modern designs also optimize lightness, stiffness, and resilience.

Notable bridges include the Akashi Kaikyō Bridge in Japan, the Golden Gate Bridge in the United States, and the Millau Viaduct in France. Bridges are valued for enabling transportation, shaping cities, and demonstrating engineering achievement, while requiring adaptation to local geography, climate, and usage patterns.