Featured Article Summary #104

A bridge is a structure built to cross obstacles like rivers or railroads so vehicles, pedestrians, and other loads can pass over. It usually has a deck supported by beams, arches, or cables, and it sits on a foundation designed to spread the bridge’s weight into the ground. Bridge designs vary widely depending on where they are built, what they are used for, and the construction methods available. Over time, advances such as better concrete and mass-produced steel have allowed longer spans and more complex bridge types, including suspension, cable-stayed, truss, cantilever, and movable bridges. Engineers must design bridges to safely handle their own weight, traffic loads, and harsh forces from weather and earthquakes, often using limit-state design and computer modeling. Bridges are also important to communities and culture, acting as landmarks and symbols, while sometimes bringing trade-offs like higher pollution and greenhouse gas emissions. Early bridges were simple wooden crossings over wetlands and streams, while pilings were used in Switzerland around 4,000 BC to support stilt houses. Later, many civilizations built more complex stone and arch bridges and aqueducts, including Mycenaean corbel arch bridges, Assyrian aqueduct bridges near Nineveh, and a Euphrates crossing in Babylonia, with bridge building also described in works from India and China. The Romans then created especially durable bridges and aqueducts, using semicircular arches and cement or mortar (often waterproof when mixed with volcanic ash), including the very large Trajan’s Bridge over the Danube. The Anji Bridge in China, built between 595 and 605 AD during the Sui dynasty, is the oldest surviving stone bridge in the country and the world’s oldest open-spandrel stone segmental arch bridge. Rope bridges were also used earlier by the Inca in the Andes before the 1500s. After Rome fell, bridge-building skills in Europe declined, but improved again in the High Middle Ages in places like France, England, and Italy, with surviving examples including Ponte Vecchio, Old Exe Bridge, and Monnow Bridge. In 15th- and 16th-century Europe, Renaissance thinkers focused more on science and engineering, writing detailed building treatises and developing designs like truss bridges and stone segmental arches. This led to major bridges such as Florence’s Ponte Santa Trinita, Venice’s Rialto Bridge, and Paris’s Pont Neuf, while in other parts of the world the Mughals in India and the Asante Empire in Africa built bridges using materials like stone, wood, and timber beams. In late 1700s Europe, engineers like Jean-Rodolphe Perronet and John Rennie redesigned arch bridges with flatter shapes that were faster to build and better for water flow, leading to bridges such as the Pont de la Concorde and New London Bridge. The Industrial Revolution then introduced iron, and later steel, which helped create bigger rail bridges and new designs like suspension, truss, and cantilever bridges; examples include several major British railway bridges built between 1849 and 1864. By the late 1800s, mass-produced steel made bridges lighter and stronger, and improved Portland-cement concrete became the main material for foundations, including reinforced and prestressed concrete with embedded steel for beams and box girders.