Saturday, September 27, 2014
How do bridge's work????
Although there are many types of bridges most bridges work by balancing compression and tension. Place a flexible object like an eraser, sponge, or small piece of bread between your thumb and index finger. Press your fingers together. One side of the object will bend inwards and shorten while the other will bend outwards and lengthen. The shorter side has been compressed, while the other side is under tension. Bridge
components experience these tension and compression stresses
ARCH BRIDGE ==>>
Arch bridge are structures in which each span forms an arch. The arch bridge is one of the oldest types of bridges. Early arch bridges were made from stone. The spans range up to about 1700 ft.
GIRDER BRIDGES ==>>
Girder bridges are made of beams called girders. The ends of the beams or girders rest on piers or abutments. The span length of girder bridges ranges up to about 1000 ft.
TRUSS BRIDGE==>>
Truss bridges are supported by frameworks called trusses. Trusses are beams arranged to form triangles.
CANTILEVER BRIDGE==>>
Cantilever bridges consist of two independent beams, cantilevers, that extend from opposite banks of a waterway. Cantilever bridges have spans as long at 1800 ft.
CABLE STAYED BRIDGE==>>
Cable-stayed bridges have roadways that hang from cables. The cables are connected directly to towers.
MOVEABLE BRIDGE==>>
Moveable bridges have roadway that is moved to provide enough clearance for boats or large ships to pass. An example of a moveable bridge is a drawbridge that tilts the roadway upward.
SUSPENSION BRIDGES==>>
Suspension bridges may be the most impressive type of bridge with their long main span and beauty. These bridges have a roadway that hangs from steel cables supported by two high towers. The difference between suspension bridges and cable-stayed bridges is that suspension bridge cables are not directly connected to the towers. The cables of a suspension bridge are not connected to the bridge - the cables pass through a hole in the top of the towers.
A suspension bridge has at least two main cables. These cables extend from one end of the bridge to the other. Suspender cables hang from these main cables. The other end of the suspender attaches to the roadway.
Suspension bridges have the longest spans in the world and are used to cross great distances. These types of bridges are used to cross deep water channels, cannons or gorges, where construction of supporting piers can be difficult. The towers can be placed far apart eliminating the need for multiple towers and piers. Some suspension bridges have a main span longer then 4000 ft. The longest suspension bridge in the world is in Japan (the Akashi- Kaikyo Bridge) and has a span over a mile long. The largest bridges have cables several feet wide which weigh thousands of pounds per foot. For that reason the cables are spun in place.
