BRIDGE AND IT’S TYPES

A bridge is a structure built over a river, seas, and so on, that allows people or vehicles to cross from one side to the other.

? Over the last several thousand years, bridges have served one of the most important roles in the development of our earliest civilizations, spreading

of knowledge, local and worldwide trade, and the rise of transportation.

? Initially made out of most simple materials and designs, bridges soon evolved and enabled carrying of wide decking’s and spanning of large

distances over rivers, gorges, inaccessible terrain, strongly elevated surfaces and pre-built city infrastructures.

? Starting with 13th century BC Greek Bronze Age, stone arched bridges quickly spread all around the world, eventually leading to the rise

of the use of steel, iron and other materials in bridges that can span kilometres.

There are several types of bridges typically their structures can be classified mainly into seven types on the basis of vertical/horizontal stresses which are

acting on the bridge and the type of the support given to the bridge.

Arch bridges:

Arch bridges use arch as a main structural component (arch is

always located below the bridge, never above it). With the help of mid-span piers, they can be made with one or more arches, depending on what kind of

load and stress forces they must endure. The core component of the bridge is its abutments and pillars, which have to be built strong because they will carry the weight of the entire bridge structure and forces they convey.

Arch bridges can only be fixed, but they can support any decking fiction, including transport of pedestrians, light or heavy rail, vehicles and even be used

as water-carrying aqueducts.

Beam bridges:

? Beam bridges employ the simplest of forms one or several horizontal beams that can either simply span the area between abutments or relieve

some of the pressure on structural piers.

? The core force that impacts beam bridges is the transformation of vertical force into shear and flexural load that is transferred to the support

structures.

? Because of their simplicity, they were the oldest bridges known to man. Initially built by simply dropping wooden logs over short rivers or

ditches, this type of bridge started being used extensively with the arrival of metal works, steel boxes, and pre-stressed construction concrete. Beam

bridges today are separated into girder bridges, plate girder bridges, box girder bridges and simple beam bridges.

Truss bridge:

? A single-span truss bridge is like a simply supported beam because it carries vertical loads by bending.

? Bending leads to compression in the top chords (or horizontal members), tension in the bottom chords, and either tension or

compression in the vertical and diagonal members, depending on their orientation.

? Trusses are popular because they use a relatively small amount of material to carry relatively large loads.

Cantilever bridge:

? A beam is said to be cantilevered when it projects outward, supported only at one end.

? A cantilever bridge is generally made with three spans, of which the outer spans are both anchored down at the shore and cantilever out over

the channel to be crossed.

? The central span rests on the cantilevered arms extending from the outer spans; it carries vertical loads like a simply supported beam or a truss that

is, by tension forces in the lower chords and compression in the upper chords.

? The cantilevers carry their loads by tension in the upper chords and compression in the lower ones. Inner towers carry those forces by

compression to the foundation, and outer towers carry the forces by tension to the far foundations.

Suspension bridge:

? A suspension bridge carries vertical loads through curved cables in tension.

? These loads are transferred both to the towers, which carry them by vertical compression to the ground, and to the anchorages, which must

resist the inward and sometimes vertical pull of the cables.

? The suspension bridge can be viewed as an upside-down arch in tension with only the towers in compression. Because the deck is hung in the air,

care must be taken to ensure that it does not move excessively under loading. The deck therefore must be either heavy or stiff or both.

Cable stayed bridge:

? Cable stayed bridges use deck cables that are directly connected to one or more vertical columns (called towers or pylons) that can be erected near

abutments or in the middle of the span of the bridge structure.

? Cables are usually connected to columns in two ways – harp design (each cable is attached to the different point of the column, creating the harplike “strings” and “fan” designs (all cables connect to one point at the top of the column). This is a very different type of cable-driven suspension than in suspension bridges, where decking is held with vertical suspenders that go up to main support cable.

Tied arch bridge:

Tied arch bridges are similar in design to arch bridges, but they transfer the weight of the bridge and traffic load to the top chord that

is connected to the bottom cords in bridge foundation. The bottom tying cord can be reinforced decking itself or a separate deck-independent structure that interfaces with tie-rods.

Conclusion:
As we can see that there are so many different designs of bridges involved and which are dependent on its applications.

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