People began to use suspension structure to manufacture bridges very early. As early as 1000 years ago, Chinese ancestors had built suspension bridges with bamboo cables and iron chains, and Jihong Bridge had been built with iron chains by the Ming Dynasty. Tents like yurts are regarded as prototypes of suspension structures.
Modern suspension bridges use high-strength steel cables, which make full use of the tensile properties of steel, and are popular because of the advantages of the bridge, such as large span, small dead weight, low material consumption, and convenient construction. Therefore, it is an ideal long-span structure. The larger the span, the more significant the economic benefits.
Modern suspension bridges are composed of towers, cables, suspenders, anchors, etc. The bridge building method is clear at a glance: high towers are erected on both sides of the river, and cables are hung on the top of the towers; After the two ends of the cable cross the tower top, they are anchored on the ground on both banks. Many suspenders are vertically hung on the thick and tough cable to suspend the bridge deck structure. The tower has been changed from the early stone tower to the current steel tower. Sometimes the tower is made of reinforced concrete, and the lower end of the tower is fixed on the pier.
At present, steel wire ropes are usually used to form thick cables. Interestingly, when the span of the bridge body is large (such as more than 750 meters), the steel cables are mostly made in situ by "aerial cable weaving method". This is because the steel cable is very heavy. If it is prepared in advance and lifted to the tower, it will bring great difficulties to the construction. For example, the Golden Gate Bridge in San Francisco, built in 1936, has a span of 1280 meters and a steel tower of 227 meters high. After being twisted, its cable has a diameter of 92.7 cm and a total weight of about 11000 tons. It is of course very difficult to lift it to a height of more than 200 meters, which can be solved by "aerial cabling". This method was invented by Roblin, a famous suspension bridge design engineer in early America.
The thick and heavy suspension cables are used to have enough bearing capacity to lift the huge bridge deck. The cable is not fixed on the high tower, but across the tower and fixed on the ground on both sides of the bridge. Dig holes or tunnels in the rock layers on both sides of the bridge, and then place the components of the fixed cable into the tunnel before pouring concrete; Or pour huge concrete blocks when there is no rock layer, and "pull" the cable by its gravity and friction.
Large span buildings such as stadiums, exhibition halls and hangars also widely use suspension structures, which is to form large indoor space without columns to meet the needs of accommodating aircraft, large-scale exhibitions and competition venues. The classic example of a long-span building with suspension structure in China is the Beijing Workers' Stadium, which was completed in 1961, when it was built to hold the 26th World Table Tennis Championships. The building is circular in plan, with an area of 40200 square meters, and can accommodate 15000 visitors. The roof adopts a spoke type double-layer suspension structure, with a span of 94 meters and 144 suspension cables in total. After renovation, the hall has become the main boxing arena for the 2008 Beijing Olympic Games and the judo arena for the blind for the Paralympic Games.
The suspension structure of the building can also form a strong sense of sculpture. For example, the Tokyo Yoyogi National Stadium, designed by the famous Japanese architect Kenzo Tanshita, has two relatively misplaced crescents and a spiral shape, like a big snail. Both pavilions adopt suspension structures, creating large internal spaces and unique external forms full of tension and flexibility. This work is known as one of the most beautiful buildings in the 20th century.
