teori jembatan modern
TRANSCRIPT
BRIDGE CONSTRUCTIONBRIDGE CONSTRUCTION
DEFINITIONDEFINITION
-a structure that allows people or -a structure that allows people or vehicles to cross an obstacle vehicles to cross an obstacle such as a river or canal or such as a river or canal or railway etc. railway etc.
-is something which holds -is something which holds together without falling apart or together without falling apart or collapsingcollapsing
THE IMPORTANT OF BRIDGETHE IMPORTANT OF BRIDGE
-Bridges are built to make life easier -Bridges are built to make life easier
-Bridges are used to get people and -Bridges are used to get people and vehicles safely over obstacles that cannot vehicles safely over obstacles that cannot be crossed by foot or car. be crossed by foot or car. -We can do this by understanding which -We can do this by understanding which shapes are strong,shapes are strong,understanding how materials behave and understanding how materials behave and understanding forces which push and pull understanding forces which push and pull on structures. on structures.
Designing BridgesDesigning Bridges
• When designing a bridge, engineers take the intended When designing a bridge, engineers take the intended load, width, and height of the span into account. load, width, and height of the span into account.
• Engineers build strong structured piers that are made Engineers build strong structured piers that are made out of concrete and steel and they support the bridge.out of concrete and steel and they support the bridge.
• A bridge must be able to support themselves and the A bridge must be able to support themselves and the mass its supporting. Designing and building a bridge is mass its supporting. Designing and building a bridge is a complex task.a complex task.
• We can do this by understanding which shapes are We can do this by understanding which shapes are strong,strong,understanding how materials behave and understanding how materials behave and understanding forces which push and pull on understanding forces which push and pull on structuresstructures
Type of BridgeType of Bridge
• Suspension bridgeSuspension bridge
• Beam bridgeBeam bridge
• Arch BridgeArch Bridge
• Cable-stayed bridgeCable-stayed bridge
TYPES OF BRIDGETYPES OF BRIDGE
SUSPENSION BRIDGESUSPENSION BRIDGE
• Suspension bridges are best to use Suspension bridges are best to use across large areas because their across large areas because their span is longer than most bridgesspan is longer than most bridges
• distances from 2,000 to 7,000 feet -- distances from 2,000 to 7,000 feet -- far longer far longer
• most expensive to build most expensive to build
TERMINOLOGY OF SUSPENSION TERMINOLOGY OF SUSPENSION BRIDGEBRIDGE
• CableCablePart of a suspension bridge extending from an Part of a suspension bridge extending from an anchorage over the tops of the towers and down anchorage over the tops of the towers and down to the opposite anchorage. Suspenders or to the opposite anchorage. Suspenders or hangers are attached along its length to support hangers are attached along its length to support the deck.the deck.
• SpanSpanThe horizontal space between two supports of a The horizontal space between two supports of a structure. structure.
• SuspendersSuspendersTension members of a suspension bridge which Tension members of a suspension bridge which hang from the main cable to support the deck.hang from the main cable to support the deck.
• CamberCamberA positive, upward curve built into a beam which A positive, upward curve built into a beam which compensates for some of the vertical load and compensates for some of the vertical load and anticipated deflection. anticipated deflection.
THE IMPORTANT OF THE IMPORTANT OF ANCHORAGESANCHORAGES-solid rock or massive concrete blocks. -solid rock or massive concrete blocks. -these cables rest on top of high towers and are -these cables rest on top of high towers and are
secured at each end by anchorages. secured at each end by anchorages. -function; -function; -help to stabilize the bridge-help to stabilize the bridge . .--Most of the weight of the bridge is carried by Most of the weight of the bridge is carried by
the cables to the anchorages.the cables to the anchorages.-Inside the anchorages, the cables are spread -Inside the anchorages, the cables are spread
over a large area to evenly distribute the over a large area to evenly distribute the loadload
-prevent the cables from breaking free.-prevent the cables from breaking free.
The suspension bridges, the The suspension bridges, the roadway hangs from roadway hangs from massive steel cable, massive steel cable, which are draped over which are draped over two towers and secured two towers and secured into solid concrete blocks, into solid concrete blocks, called anchorages, on called anchorages, on both ends of the bridge. both ends of the bridge. The cars push down on The cars push down on the roadway, but because the roadway, but because the roadway is the roadway is suspended, the cables suspended, the cables transfer the load into transfer the load into compression in the two compression in the two towers. The two towers towers. The two towers support most of the support most of the bridge's weight bridge's weight
TYPES OF CABLETYPES OF CABLE
• 1.Parallel Wire 1.Parallel Wire CablesCables
- made up of a large - made up of a large number of individual number of individual wires wires
-used on monumental -used on monumental structuresstructures
TYPES OF CABLETYPES OF CABLE
2. Parallel Strand 2. Parallel Strand Cables, Cables,
-consist of several -consist of several prefabricated prefabricated Galvanized Bridge Galvanized Bridge Strands Strands
-Wood or aluminum -Wood or aluminum fillers are used to fillers are used to bring the cable to a bring the cable to a circular cross-circular cross-section section
A BEAM BRIDGEA BEAM BRIDGE
A beam bridge is basically a rigid A beam bridge is basically a rigid horizontal structure that is resting on horizontal structure that is resting on two piers, one at each end. The weight two piers, one at each end. The weight of the bridge and any traffic on it is of the bridge and any traffic on it is directly supported by the piers. The directly supported by the piers. The weight is traveling directly downward. weight is traveling directly downward.
• A beam or "girder" bridge A beam or "girder" bridge is the simplest and most is the simplest and most inexpensive kind of inexpensive kind of bridge.bridge.In its most basic form, a In its most basic form, a beam bridge consists of a beam bridge consists of a horizontal beam that is horizontal beam that is supported at each end by supported at each end by piers. The weight of the piers. The weight of the beam pushes straight beam pushes straight down on the piers. down on the piers.
The beam itself must be The beam itself must be strong so that it doesn't strong so that it doesn't bend under its own weight bend under its own weight and the added weight of and the added weight of crossing traffic. When a crossing traffic. When a load pushes down on the load pushes down on the beam, the beam's top beam, the beam's top edge is pushed together edge is pushed together (compression) while the (compression) while the bottom edge is stretched bottom edge is stretched (tension). (tension).
In its most basic form, a beam bridge consists of a horizontal beam that is supported at each end by piers. The weight of the beam pushes straight down on the piers.
The beam itself must be strong so that it doesn't bend under its own weight and the added weight of crossing traffic. When a load pushes down on the beam, the beam's top edge is pushed together (compression) while the bottom edge is stretched (tension).
• Advantages of beamsAdvantages of beams
• Because a beam rests simply on the supports, the Because a beam rests simply on the supports, the effects of thermal expansion and movements of the effects of thermal expansion and movements of the ground are fairly easily sustained.ground are fairly easily sustained. The supports can The supports can be simple vertical piers, because there is no be simple vertical piers, because there is no horizontal reaction.horizontal reaction. In principle, a beam may be In principle, a beam may be built away from the final position, and lifted swiftly built away from the final position, and lifted swiftly into place with minimal disruption of traffic or into place with minimal disruption of traffic or navigation.navigation.
• Disadvantages of beamsDisadvantages of beams• The beam maintains its shape by means of the The beam maintains its shape by means of the
opposed tension and compression, and by the shear opposed tension and compression, and by the shear forces also.forces also. This means that a beam contains forces This means that a beam contains forces which are much larger than the load, and it needs to which are much larger than the load, and it needs to be relatively massive, though truss construction be relatively massive, though truss construction reduces the mass in the larger examples.reduces the mass in the larger examples.
CompressionCompression
The force of compression manifests The force of compression manifests itself on the top side of the beam itself on the top side of the beam
bridge's deck (or roadway). This causes bridge's deck (or roadway). This causes the upper portion of the deck to the upper portion of the deck to
shorten. shorten.
TensionTension
The result of the compression on the The result of the compression on the upper portion of the deck causes upper portion of the deck causes
tension in the lower portion of the deck. tension in the lower portion of the deck. This tension causes the lower portion of This tension causes the lower portion of
the beam to lengthen.the beam to lengthen.
ExamplesExamples
Take a two-by-four and place it on top of two empty milk crates -- you've just created a crude beam bridge. Now place a 50-pound weight in the middle of it. Notice how the two-by-four bends. The top side is under compression and the bottom side is under tension. If you keep adding weight, eventually the two-by-four will break. Actually, the top side will buckle and the bottom side will snap.
TYPESTYPES
• Howe TrussHowe Truss
• Through trussThrough truss
• Deck trussDeck truss
• WarrenWarren
• PrattPratt
ADDITIONAL BRIDGE FORCESADDITIONAL BRIDGE FORCES
• TorsionTorsion
• Deck-stiffening trussesDeck-stiffening trusses
• ResonanceResonance
• DampenersDampeners
• WeatherWeather
Beams
Beams used in buildings may vary in cross sectional shape. Some may be solid or hollow. Below are three different shaped beams. The first beam is a box section, the second an I section beam and the third an L section beam. Solid beams are heavier than hollow beams. Beams like the one's below are given a special cross section for strength and rigidity. They may be as strong as the solid beams but are a lot lighter. We may describe them as having a good strength to weight ratio.
ARCH BRIDGEARCH BRIDGE
• Arch bridges are one of the oldest types of bridges and Arch bridges are one of the oldest types of bridges and have been around for thousands of years. have been around for thousands of years.
• have great natural strength. have great natural strength.
• originally built of stone or brick but these days are built of originally built of stone or brick but these days are built of reinforced concrete or steel. reinforced concrete or steel.
• The introduction of these new materials allow arch bridges The introduction of these new materials allow arch bridges to be longer with lower spans.to be longer with lower spans.
• Instead of pushing straight down, the load of an arch bridge Instead of pushing straight down, the load of an arch bridge is carried outward along the curve of the arch to the is carried outward along the curve of the arch to the supports at each end.supports at each end.
• The weight is transferred to the supports at either end.The weight is transferred to the supports at either end.• These supports, called the abutments, carry the load and These supports, called the abutments, carry the load and
keep the ends of the bridge from spreading out.keep the ends of the bridge from spreading out.
HOW THE LOAD TRANSFERHOW THE LOAD TRANSFER• The load at the top of the The load at the top of the
key stone makes each stone key stone makes each stone on the arch of the bridge on the arch of the bridge press on the one next to it. press on the one next to it. This happens until the push This happens until the push is applied to the end is applied to the end supports or abutments, supports or abutments, which are embedded in the which are embedded in the ground. ground.
• The ground around the The ground around the abutments is squeezed and abutments is squeezed and pushes back on the pushes back on the abutments. abutments.
• For every action there is an For every action there is an equal and opposite reaction. equal and opposite reaction. The ground which pushes The ground which pushes back on the abutments back on the abutments creates a resistance which creates a resistance which is passed from stone to is passed from stone to stone, until it is eventually stone, until it is eventually pushing on the key stone pushing on the key stone which is supporting the which is supporting the load.load.
• Arch Bridge: ForcesArch Bridge: ForcesThe arch is squeezed The arch is squeezed together, and this together, and this squeezing squeezing force force is is carried outward along carried outward along the curve to the the curve to the supports at each end. supports at each end. The supports, called The supports, called abutments, push back abutments, push back on the arch and prevent on the arch and prevent the ends of the arch the ends of the arch from spreading apart.from spreading apart.
How are Arch Bridge BuiltHow are Arch Bridge Built
• Building an arch bridge Building an arch bridge isn't easy, since the isn't easy, since the structure is completely structure is completely unstable until the two unstable until the two spans meet in the middle. spans meet in the middle.
• For years, engineers used For years, engineers used a technique called a technique called centering, in which a centering, in which a wooden form supported wooden form supported both spans until they both spans until they locked together at the locked together at the top.top.
• A newer method supports A newer method supports the spans using cables the spans using cables anchored to the ground on anchored to the ground on either side of the bridge. either side of the bridge.
Advantages of archesAdvantages of arches
The entire arch is in The entire arch is in compression. The compression. The compression is compression is transferred into the transferred into the abutments, and abutments, and ultimately resisted by ultimately resisted by tension in the ground tension in the ground under the arch. The under the arch. The absence of tension in absence of tension in the arch means that it the arch means that it can sustain much can sustain much greater spans than greater spans than beams can achieve, beams can achieve, and it can use and it can use materials that are not materials that are not strong in tension.strong in tension.
Disadvantages of archesDisadvantages of arches
An arch cannot stand An arch cannot stand until it is complete. until it is complete. Therefore it must either Therefore it must either rest on false work rest on false work (centering) until it is (centering) until it is complete, or the two complete, or the two halves must be halves must be cantilevered from the cantilevered from the springing, using cables. springing, using cables. The cantilever method The cantilever method cannot be used for cannot be used for masonry arches or masonry arches or concrete arches. The concrete arches. The thrust of a big arch has thrust of a big arch has a horizontal component, a horizontal component, which the abutments which the abutments must withstand without must withstand without significant movement. significant movement. The pictures below show The pictures below show the results of the results of movement.movement.
Masonry arch
Concrete arch
Metal arch
Cable-stayed bridgeCable-stayed bridge• A type of suspension bridge in which the A type of suspension bridge in which the
supporting cables are connected directly to the supporting cables are connected directly to the bridge deck without the use of suspenders bridge deck without the use of suspenders
• Cable-stayed bridges may look similar to Cable-stayed bridges may look similar to suspensions bridges suspensions bridges
• Both have roadways that hang from cables and Both have roadways that hang from cables and both have towers.both have towers.
• But the two bridges support the load of the But the two bridges support the load of the roadway in very different ways. roadway in very different ways.
• the cables are attached to the the cables are attached to the towers, which alone bear the load.towers, which alone bear the load.
• The cables can be attached to the The cables can be attached to the roadway in a variety of ways. roadway in a variety of ways.
• In a radial pattern, cables extend In a radial pattern, cables extend from several points on the road to a from several points on the road to a single point at the top of the tower. single point at the top of the tower.
• In a parallel pattern, cables are In a parallel pattern, cables are attached at different heights along attached at different heights along the tower, running parallel to one the tower, running parallel to one otherother
classifications for cable-stayed classifications for cable-stayed bridges bridges
In some cases, only the cables on one side of the tower are In some cases, only the cables on one side of the tower are attached to the girder, the other side being anchored to a attached to the girder, the other side being anchored to a foundation or other counterweightfoundation or other counterweight
Advantages of cable-stayed bridges
•The two halves may be The two halves may be cantilevered out from cantilevered out from each side. There is no each side. There is no need for anchorages to need for anchorages to sustain strong sustain strong horizontal forces, horizontal forces, because the spans are because the spans are self-anchoring. They self-anchoring. They can be cheaper than can be cheaper than suspension bridges for suspension bridges for a given span. Many a given span. Many asymmetrical designs asymmetrical designs are possibleare possible
Disadvantages of Disadvantages of cable-stayed bridgescable-stayed bridges
•In the longer sizes, In the longer sizes, the cantilevered the cantilevered halves are very halves are very susceptible to wind susceptible to wind induced oscillation induced oscillation during construction. during construction. The cables require The cables require careful treatment to careful treatment to protect them from protect them from corrosion.corrosion.
