Bridges A bridge is like an aerial road. It lets our traffic be capable of striding across natural obstacles such as straits, rivers, valleys… In some big cities, bridges are used frequently as an overhead road to reduce traffic jam and raise transportation efficiency.
The load mainly acts on the desk of the bridge. The bridge must be deigned to pass the load to the ground efficiently. Different designs of bridges are applied under different conditions.
Arch Bridge the vertical force acted on the desk would pass to the supporting points on both sides of the bridge through the designed arch-shaped curve The desk can be either under or above the arch. The entire arch bridge structure is under pressure. Therefore, materials that can bear high pressure, such as natural rocks, are the best materials for building arch bridges.
eg. Anji Bridge, built at Zhaozhou in China in the 7th century (Stone Bridge)
eg. Sydney Harbour Bridge in Australia (Steel Bridge)
Continuous Bridge the bridge desk was supported by many bridge piers. Continuous bridge is usually built over shallow water areas or places where large ships cannot pass through. eg. Seven Mile Bridge (Florida , U.S.) The Island Eastern Corridor (Hong Kong)
eg. Seven Mile Bridge (Florida , U.S.)
Cable-Stayed Bridge Pylon/Bridge towers are built on the bridge pier. Cables from both sides of the pylon/bridge tower are suspended to the bridge desk. The load is passed to the pylon/bridge tower through the cables and then to the ground through the pylon/bridge tower. Steel cables with high tensile intensity are chosen as they have to sustain strong tension. The length of the cable-stayed bridge is usually between 160 and 900 meters. eg. Kap Shui Mun Bridge (Hong Kong)
eg.Kap Shui Mun Bridge (Hong Kong)
Suspension Bridge The main suspending cables are hung on the pylon/bridge towers. Then connections are made between the main cables and the bridge desk with vertical steel cables. The ends of the main cables are anchored to the ground by concrete to hold against the great tension acting on it. The span can reach to more than 2000 meters. eg. Tsing Ma Bridge (Hong Kong) Golden Gate Bridge (San Francisco, California)
eg. Tsing Ma Bridge (Hong Kong)
Golden Gate Bridge (San Francisco, California)
NOVA Online | Super Bridge http://www.pbs.org/wgbh/nova/bridge/
Acknowledgment： Hong Kong University of Science and Technology (HKUST) Dr. Christopher K.Y. LEUNG Associate Professor, Department of Civil Engineering, Hong Kong University of Science and Technology