GIRDER BRIDGES

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GIRDER BRIDGES

• Oldest and most common bridge type known. (Fallen
  logs were used)
• In modern girder bridges, steel I-beams are used,
  but they are subject to twisting and are not
  good for bridges with any curve to them.
• Box beams are stronger and used for curving or
  longer bridges.

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ARCH BRIDGES

• Second oldest bridge type.
• Unlike girders, can be built from stone.
• Because no center pier is required, can be used
  to cross valleys and rivers without interfering
  with river traffic.
• Considered the most beautiful of bridge types.
• Many ancient arches are still standing today!

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CABLE-STAYED BRIDGES

• Really just a continuous girder bridge with
  towers above piers
• The cables are flexible and affected by the wind.
• Longer spans require very complex computations
  and analysis.

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SUSPENSION BRIDGES

• Of all the types of bridges used today, the
  suspension allows for the longest spans.
• Similar to a cable-stayed bridge except there is
  one main cable that runs between the towers with
  hanger cables below it.
• The girder and roadbed are not resting on the
  piers as with other bridge types, but is hanging
  from the hanger cables!
• Vulnerable to wind

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TRUSS BRIDGES

• Because of the use of the triangular shape,
  trusses only sustain compression and tension
  forces and not bending!
• Can be built in small sections so are ideal in
  areas where large machinery wouldnt have access.
• The most common type is the Warren Truss
• For longer spans and for a stronger Warren Truss,
  vertical members are added. Notice that the
  roadbed can be above or below the truss.

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Tacoma Narrows Bridge

• Suspension Bridge that connects Tacoma and
  Seattle, Washington.
• On the morning of November 7, 1940, the Tacoma
  Narrows Bridge twisted violently in
  42-mile-per-hour winds and collapsed into the
  cold waters of the Puget Sound.
• Caused by self-excited vibrations the bridge
  took over the wind and destroyed itself.

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TERMS OF BRIDGE CONSTRUCTION

• TORSION- THIS IS A TWISTING FORCE
• SPAN- A DISTANCE UNSUPPORTED BETWEEN 2 POINTS
• LOAD-THE WEIGHT SUPPORTED BY THE BRIDGE
• TENSION- STRETCHING A STRUTURAL MEMBER

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• DECK-THE ROAD BED OF A BRIDGE SYSTEM
• SUSPENSION- A BRIDGE SYSTEM THAT USES CABLES TO
  SUPPORT THE DECK
• COMPRESSION-DOWNWARD PRESSURE ON A STRUCTURE

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• GIRDER- A SUPPORT BEAM OF A BRIDGE
• BEAM- A BRIGE TYPE THAT USES A SOLID GIRDER AS A
  DECK
• TRUSS- A STURCTURAL SYSTEM THAT USES TRIANGLES TO
  EQUALIZE COMPRESSION AND TENDSION

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• WHICH COLOR REPRESENTS COMPRESSION AND TENSION?

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Need to know

• All 5 types of bridges (identify and sketch)
• All 10 terms (define match explain)
• Compare and contrast 2 types of bridges with AT
  LEAST 3 different UNIQUE qualities!!! (you choose
  the 2 types)
• Questions- T/F, M/C, fill in the blank, short
  essay, Venn diagram