What are Truss Bridges? Structural elements and pros and cons of truss bridgesArticles > What are Truss Bridges? Structural elements and pros and cons of truss bridges
What Are Truss Bridges?
The load-bearing superstructure of truss bridges is made up of truss. A truss is a structure of connecting elements of triangle units. These elements are of the straight form, which is stressed by compression and tension. The truss does not bend due to the tension and compression exist in the elements, because when the truss (due to load and burden) bends, the elements are exerted force onto one another, thus preventing the truss from bending. The basic types of truss bridges are simple in design. The traditions of truss bridges originated from the early 19th century. This is why the countries which had been under British rule for decades, possess hundreds of bridges, as in 19th-century British rule prevailed all across the globe. Truss bridges are economical and easy to construct. A large number of workers are not needed in order to construct a truss-bridge. Heavy machinery is also not needed for this purpose. Truss bridges are very popular because of their elastic nature and durability. In short-length truss-bridges, even the piers and abutments are also not needed. However, in longer bridges, the structure of the truss is supported vertically by the help of piers and abutments. The design of a truss is so simple that the construction mechanism can easily be understood at the very first view. The duty of the truss is to support the span of bridges. Anyhow the deck of the bridge is made like that of other types.
Structural Elements of Truss Bridges:
A bridge supported with the help of a truss is composed of the following structural elements and parts:
A truss is a systematically interconnected group of steel or iron bars and rods, which are interdependent on one another in order to create strength and turgidity in the skeleton of the truss. The elements of a truss are joined in a triangular shape. The connected elements either give tension or compression, as a result of the load and burden of the bridge and truss itself. There are several types of elements are used in truss-like beams four parallel beams of truss, struts, bracings, sway bracings, lateral bracings, and portal struts and bracings. All these elements are either compressive or tensile or both in duty.
Stingers, in a truss bridge, are used instead of beams in beam-bridges. The stringers of the bridge are firmly jointed with the lower beams of the truss, in such a way that the stringers of the bridge is hung with the stringers of the truss. Stringers, generally, are two or more than two in number. These stringers are attached to Floor beams. The deck of the bridges is placed or constructed on the floor beams. The floor beams are not parallel to the Stringers, but rather cross-sectional.
(3). Floor Beams:
A number of short length beams which connect the main stringers at different points. The purposed of the floor beams is to survive the load of a deck of the bridge. The deck can be made of different types of elements, like metallic plates, metallic hollow plates, panels made up of precast concrete and RCC.
(4). Deck of the Bridge:
The purpose of the deck of the bridge is to accommodate the traffic. The deck of the bridge is made of concrete or metallic slabs. It is the main span of the bridges. It is installed on the floor beams horizontally.
(5). Piers/ Abutments:
Piers also called abutments and pillars of the bridge. The piers are either precast or constructed within the water body with the help of caissons or cofferdams.
Material Used in Truss Bridges:
Different parts of the Truss-bridges are made of different kinds of materials. The pillars, abutments, and foundations of the bridges are generally made up of CFST, RCC, and concrete, etc. However, in many areas, keeping the environment of construction in mind the piers and foundations are constructed with steel or iron. As for as the upper portion of a truss bridge is concerned, its construction is carried out with metals like steel and iron. The elements of a truss are jointed with the help of nuts and bolts. In order to prevent the truss from rusting and oxidation, it is either painted or coated with bitumen. The bitumen coat does not allow oxygen to react with iron. The maintenance of the truss is very simple. The broken parts of the truss are rejoined by means of welding and soldering, while unbroken parts of the truss are recoated with paints or bitumen. The use of bitumen is very economical.
Pros and Cons of Truss Bridges:
There are several reasons behind the construction of truss-bridges. Keeping in view the following advantages, civil engineers prefer truss bridges.
- The construction of these bridges is less time-consuming.
- Easy to mantle the elements of the truss.
- An average level of expertise is needed to build up trust.
- These bridges can be constructed even in unfavorable weather and climate.
- Land Sliding does not damage these bridges.
- These are earthquake-proof bridges.
- The truss can also be easily dismantled at the time of need.
Apart from all these advantages, these bridges, still have some demerits.
- In the regions of the hot climate, the metallic elements expand due to heat provided by sunlight in the daytime.
- These bridges are prone to rust. In moist conditions, rusting and oxidation weaken the strength of the bridges.
- These bridges are elastic due to the nature of the material they are built.
- The vibration caused by running vehicles cracks the joints of the elements of the bridge.
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