bridges
DESCRIPTION
types of bridges, introduction to bridgesTRANSCRIPT
700 A.D. Asia700 A.D. Asia
1,304 years 1,304 years agoago
100 B.C. Romans100 B.C. Romans2,104 years ago2,104 years ago
Clapper Bridge
Tree trunkStone
Arch design evenly distributesstressesNatural concrete made from mud and straw
Roman Arch Bridge
History of Bridge DevelopmentHistory of Bridge Development
Great Stone Bridge in China
Low bridgeShallow archAllows boatsand water to passthrough
History of Bridge DevelopmentHistory of Bridge Development
Truss Bridges
Mechanics of DesignWood
Suspension Bridges
Use of steel in suspending cables
1900 1900
1920 1920
Prestressed ConcreteSteel
2000 2000
Compression Tension
Basic Concepts Basic Concepts
Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.
Compression –
Tension -
Force -
Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?
Basic Concepts Basic Concepts
Beam - a rigid, usually horizontal, structural element
Pier - a vertical supporting structure, such as a pillar
Cantilever - a projecting structure supported only at one end, like a shelf bracket or a diving board
Beam
Pier
Load - weight on a structure
The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.
Types of BridgesTypes of BridgesBasic Types:
•Truss Bridge•Beam Bridge•Arch Bridge•Suspension Bridge•Floating Bridge
Truss Beam ArchSuspension
Floating
Truss Bridge
All beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.
Types of BridgesTypes of Bridges
Beam BridgeBeam Bridge
Consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.
Forces
When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.
Types of BridgesTypes of Bridges
Beam BridgeBeam Bridge
Arch BridgesArch Bridges
The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.
Types of BridgesTypes of Bridges
Forces
The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.
Types of BridgesTypes of Bridges
Arch BridgesArch Bridges
Suspension BridgesSuspension Bridges
This kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.
Types of BridgesTypes of Bridges
Forces
In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.
Types of BridgesTypes of Bridges
Suspension BridgesSuspension Bridges
•Pontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads.
•While pontoon bridges are usually temporary structures, some are used for long periods of time.
•Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers.
•Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.
Types of BridgesTypes of Bridges
Floating BridgeFloating Bridge
How do the following affect your structure?Ground below bridgeLoadsMaterialsShapes
Bridge Bridge Engineering Engineering
To design a bridge like you need to take into account all the forces acting on it:
•The friction of the earth on every part
•The strength of the ground pushing up the supports
•The resistance of the ground to the pull of the cables
•The dead weight and all vehicle loads
Then there is the drag and lift produced by wind and water
•The turbulence as fluids pass the towers
SummarySummary
Bridge EngineeringBridge Engineering
Need to use appropriate materials and structural shapes in the cheapest way, yet maintaining a certain degree of safety.
To account for natural disasters, engineers design bridges with a factor of safety: usually around 3 or 4.