Bridges Lesson

Bridges!

Three main types of bridges

Simple structure made of horizontal, rigid beams.

A truss system​ is a combination of triangular units. It's based on the geometric rigidity of the triangle.

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Beam/Truss

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Defining characteristic: semicircular structure.

Abutments at each end of the semicircular arch are extremely important.​

Arch

Defining characteristic: bridge deck suspended from cables (or ropes or chains)

Conventional suspension bridges have a distinctive elongated M shape​

Suspension

Multiple Choice

Which type of bridge relies on the geometric stability of triangles?

• Truss bridge (a type of beam bridge)

• Arch bridge

• Suspension bridge

Multiple Choice

Which bridge has a semicircle structure?

• Arch bridge

• Beam bridge

• Suspension bridge

Multiple Choice

Which bridge has a distinctive elongated M shape made by the cables/ropes/chains?

• Suspension bridge

• Arch bridge

• Beam bridge

Tension and Compression

Difference in distance

Beam: up to 200ft

Arch: 130-500ft

Suspension: 2,000-7,000ft

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Why? Tension and compression forces​

Compression: acts to compress or shorten a thing

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Tension: acts to expand or lengthen a thing​

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Two main forces acting upon a bridge​

Multiple Choice

When I push both ends of a spring together, am I compressing it or putting tension on it?

• Compressing

• Putting tension on it

What happens if those forces are not dissipated or transferred?

Buckling: when compressive forces overcome an object's ability to handle compression.

Snapping​: when tensile forces overcome an object's ability to handle tension.

To dissipate or transfer

Dissipate: spread it out over a greater area

Transfer: move it from an area of weakness to one of strength.​

Arch - dissipates

Suspension - transfers​

Multiple Choice

What type of bridge is this?

• Suspension

• Arch

• Beam/Truss

Multiple Choice

What type of bridge is this?

• Arch

• Suspension

• Beam/Truss

Multiple Choice

What type of bridge is this?

• Arch

• Beam/Truss

• Suspension