Infrastructure generally refers to the basic physical structures and facilities, often government-owned, needed for the effective operation of a society or economy. They include the critical assets that are essential to enable, sustain, or enhance societal living conditions. More specifically, infrastructure facilitates the production of goods and services, the distribution of finished products to markets, and provision of basic social services such as schools and hospitals. Public works and public capital are common terms for government-owned infrastructure. Examples of such infrastructure assets and facilities include the following:
A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century. Bridges without vertical suspenders have a long history in many mountainous parts of the world. This type of bridge has cables suspended between towers, plus vertical suspender cables that carry the weight of the deck below, upon which traffic crosses. This arrangement allows the deck to be level or to arc upward for additional clearance. Like other suspension bridge types, this type often is constructed without falsework. The suspension cables must be anchored at each end of the bridge, since any load applied to the bridge is transformed into a tension in these main cables. The main cables continue beyond the pillars to deck-level supports, and further continue to connections with anchors in the ground. The roadway is supported by vertical suspender cables or rods, called hangers. In some circumstances the towers may sit on a bluff or canyon edge where the road may proceed directly to the main span, otherwise the bridge will usually have two smaller spans, running between either pair of pillars and the highway, which may be supported by suspender cables or may use a truss bridge to make this connection. In the latter case there will be very little arc in the outboard main cables.
The main forces in a suspension bridge of any type are tension in the cables and compression in the pillars. Since almost all the force on the pillars is vertically downwards and they are also stabilized by the main cables, the pillars can be made quite slender, as on the Severn Bridge, on the Wales-England border. In a suspended deck bridge, cables suspended via towers hold up the road deck. The weight is transferred by the cables to the towers, which in turn transfer the weight to the ground. Assuming a negligible weight as compared to the weight of the deck and vehicles being supported, the main cables of a suspension bridge will form a parabola (very similar to a catenary, the form the unloaded cables take before the deck is added). One can see the shape from the constant increase of the gradient of the cable with linear (deck) distance, this increase in gradient at each connection with the deck providing a net upward support force. Combined with the relatively simple constraints placed upon the actual deck, this makes the suspension bridge much simpler to design and analyze than a cable-stayed bridge, where the deck is in compression.
Li Guohao (Chinese: 李国豪; Pinyin: Lǐ Guóháo; 1913--2005), Chinese structural engineer, China's celebrated bridge engineering expert, earned his nickname of "Suspension Bridge Li" from his German counterparts. His method of calculation, with a high degree of precision although of extreme complexity, can cut down the cost of engineering and promote bridge stability. Due to his outstanding achievements, Li was rated as one of top 10 world famous bridge experts by the International Bridge and Structural Engineering Association in 1981.
Li, born in Mei County, Guangdong, once studied in Germany. In 1946, he assumed the position of president of Tongji University after he returned to the China. In view of the structure of reinforced concrete bridge in common use, Li broke with convention to tackle a key problem related to calculation. This became known as Li's Theory, and has been widely adopted in the design of international bridges.