A truss bridge is a kind of bridge based around different tensions in wood or metal pulling together when weight is applied to the bridge. The bridge does not have many lower support elements, and a lot of the support comes from the placement of different pieces of metal over the top of the bridge. The bridge is designed to support itself when weight is applied by each piece straining against each other, causing the bridge to hold.
Truss bridges are one of the oldest types of large bridges in the United States. The first truss bridges were built around the 1820s. These were made of wood in many cases, and were used to transport heavy carts. When the railroad became popular in the 1880s and 1890s, the truss bridge started to be constructed of iron and other strong metals. This enabled trains to go many places they otherwise would not have been able to go. Many famous bridges, such as The Bridge over the River Kwan and the Garden Bridge in Shanghai, are truss bridges.
Truss bridges are all constructed on the same basic principle. A flat bridge is laid over the opening; supports in horizontal and diagonal layout are added to each side of the bridge to cause it to have support. Then a structure is constructed above the bridge in the same horizontal and diagonal pattern to support the bridge from above. This way when weight is applied, all of the parts of the bridge hold together, which causes the bridge to support almost any weight.
The purpose of truss bridges is to enable bridges to be built over places that have unstable ground. When ground supports are unable to be constructed, the bridge has to be supported some other way. This is where the truss bridge comes in. A truss bridge is also able to support larger amounts of weight than a traditional bridge.
Truss bridges can be almost any size. There are some that are just a few feet long, covering a small opening in the ground or helping to get over an unstable patch of ground. However, there are some truss bridges that are quite long. There is one truss bridge in Japan used as an overpass that is almost a mile long. The longer the bridge, the more support necessary.
Truss bridges have added a lot to the way that the world is run today. Railroads still commonly used truss bridges for trains to pass over. Without the invention of the truss bridge it is unlikely that the train would have become so popular. This would mean that transport would be slower, and goods would stay much more localized. Truss bridges are also used for car traffic. While many other types of bridges are used for cars, the truss bridge is still a popular choice because of its strength and ability to be placed nearly anywhere.