BRIDGESBeauty and Function

The first bridges were nature-made: trees that fell across creeks or rivers.

The first man-made bridges were most likely made from trees lashed, stones, or vines.

HISTORY

Designed amazing arch bridges and viaducts that could withstand nearly anything when other bridges continued to fail.

The Romans discovered the strength of the arch.

The Alcantara bridge, built in 106 A.D. is still standing today – almost 2,000 years later!

ROMANS

Compression – when material squeezes together

Tension - when material pulls apart Bending – when material gets shorter on one

side and longer on the other Shearing – when material slides in opposite

directions Twisting – when the ends of a material twists

in opposite directions

FORCES ACTING ON A BRIDGE

http://www.pbs.org/wgbh/buildingbig/lab/forces.html

A good bridge keeps all the forces in balance; if there is compression there is and equal amount of tension.

BALANCING THE FORCES

BEAM BRIDGE Made of steel, concrete, or wood Typically shorter than 250’ The longest is the Lake Ponchartrain Causeway

, at just under 24 MILES long!

BRIDGE TYPES

TRUSS BRIDGE A simple but very strong bridge type made of

connected triangle shapes, called a “truss”. The trusses can be above or below the roadbed. The World’s longest truss bridge is the Itiksuki Bridge

in Japan.

ARCH BRIDGE Arch bridges have “abutments” at each end. The weight of the bridge is forced into and

supported by these abutments. The longest arch bridge in the world is the

Chaotianmen Bridge in China. It is 5,712’ long!

SUSPENSION BRIDGE The roadbed of a suspension bridge is

supported by cables hanging down from one huge cable spanning between the vertical towers.

The road is “suspended” from these cables. The world’s longest is the Akashi Kaikyo

Bridge in Japan at 12,825 feet!

CABLE-STAYED BRIDGE Use less cable than a suspension bridge by

having taller towers and cables that connect to the roadbed beneath it.

The world’s longest cable-stayed bridge is the Sutong Bridge in China at 26,923 feet!

Famous American Bridges

Golden Gate Bridge, S.F.

Sunshine Skyway - FL

GEORGE WASHINGTON - NY

Brooklyn Bridge - NY

Real bridges rely on large nuts and bolts and very strong materials.

Model Bridge Engineering

We rely on water-based glue…

You must use smart engineering to overcome weak wood and weak glue.

Therefore…

Notice how the shorter bottom pieces cross OVER the longer bottom pieces.

Which would work for balsa bridges?

With a partner, make FOUR of the wood joints using balsa wood.

Label them. Glue them to poster board,.

Put your names on it and turn in!

ASSIGNMENT #1

Design the side, top, and bottom (roadbed) for a bridge that will meet the size requirements.

Place waxed paper over your design. Cut balsa pieces to size and glue the

JOINTS with a drop of glue. Use wood joints to strengthen your

bridge.

Assignment #2

BRIDGE TESTING