Bridges - Forces Acting On A Bridge, Dynamic Loads, Model Testing, Types Of Bridges, Cantilever Bridges
according materials moveable example
Bridges are structures that join two otherwise inaccessible points of land, such as the two shores of a river or lake, or the two sides of a canyon or deep gully. Bridges are designed to carry railroad cars, motor vehicle traffic, or foot travel by pedestrians and/or animals, or to support pipes, troughs, or other conduits used for the movement of goods and materials, such as an oil pipeline or a water aqueduct.
Humans have been constructing bridges since ancient times. The earliest bridges were probably nothing more than felled trees used to cross rivers or ditches. As civilization advanced, artisans discovered ways to use stone, rock, mortar, and other naturally occurring materials in the construction of longer and stronger bridges. Finally, as physicists and engineers began to develop the principles underlying bridge construction, they incorporated other materials such asiron, steel, and aluminum into the bridges they built.
Bridges can be classified in a number of different ways, according to their intended use (railroad bridge or pedestrian walkway, for example), according to the material of which they are made (steel, wood, or concrete for example), or according to whether they are fixed or moveable. Moveable bridges are used when the height of ships traveling on a waterway will be greater than the floor of the bridge. In such cases, the bridge is built so that the roadway can be raised or pivoted to allow marine traffic to pass under or through it. Probably the most useful way to classify bridges for technical purposes, however, is according to their structural form. There are three major types of bridges: arch, cantilever, and suspension.
Additional Topics
Three kinds of forces operate on any bridge: the dead load, the live load, and the dynamic load. The first of these terms refers to the weight of the bridge itself. Like any other structure, a bridge has a tendency to collapse simply because of the gravitational forces acting on the materials of which the bridge is constructed (i.e., the wood, concrete, steel, or aluminum). The second term refers …
Dynamic loads can present special problems for the bridge designer. A bridge has to be able to withstand not only the forces of normal, everyday traffic, but also unusual forces of unexpected magnitude. In California, as an example, bridges require special kinds of reinforcement to withstand possible earthquakes. The fact that engineers have not completely solved the problems presented by dynamic …
At one time, the only test of a bridge design was actual use. Engineers could incorporate all the scientific knowledge and technological craftsmanship they had to produce a sound design. But how well the bridge would stand up under actual use and dynamic loads could only be discovered in the real world. Today, engineers have two powerful tools with which to test their ideas: wind tunnels and compu…
The simplest type of bridge corresponds to the felled tree mentioned above. It consists of a single piece of material that stretches from one side of the gap to be bridged to the other side. That piece of material—the beam, or girder—rests directly on the ground on each side or is supported on heavy foundations known as piers. The length of a beam bridge of this kind is limited by th…
A cantilever bridge is a variation of the simple beam bridge. A cantilever is a long arm that is anchored at one
Dame Point bridge in Jacksonville, Florida, is a cable-stayed bridge. The deck is supported by cables which transmit the load to the towers. © Tom Carroll/Phototake NYC. Reproduced with permission.
end and is free to move at the opposite end. A diving board is an example of…
The strength of a cantilever bridge can be increased by the use of trusses. A truss is structure that consists of a number of triangles joined to each other. The triangle is an important component of many kinds of structures because it is the only geometric figure that can not be pulled or pushed out of shape without actually changing the length of one of its sides. By combining a number of triang…
As its name suggests, the main supporting structure in an arch bridge is one or more curved elements. The dead and live forces that act on the arch bridge are transmitted along the curved line of the arch into abutments at either end. These abutments are sunk deep into the earth, into bedrock if at all possible. They are, therefore, essentially immovable and able to withstand very large forces exe…
The longest bridges in the world are all suspension bridges. Some examples are the Humber Bridge in Hull, England, with a length of 4,626 ft (1,410 m), the Verrazano-Narrows Bridge in lower New York Bay (4,620 ft [1,298 m]); the Golden Gate Bridge over the entrance to San Francisco Bay (4,200 ft [1,280 m]); and the Mackinac Straits Bridge connecting the Upper and Lower Peninsulas of Michigan (3,80…
Traditionally, three kinds of movable bridges have been constructed. In one, the swing bridge, the deck is rotated around a central span, a large, heavy pier sunk into the river bottom. The swing bridge has one serious disadvantage. The central pier, on which the bridge rotates, is usually located in the deepest part of the waterway. Ships with significant drafts may, therefore, have difficulty pa…
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User Comments
12 months ago
Vicky
I wish to know what dynamic load allowance shall be adopted for the 260m pylon to pylon distance cable stayed bridge with two single cell box girder (with total width of c/w of 30m approx.).
about 1 year ago
Name
Body
about 1 year ago
bum but not a bum and g
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