BRIDGES Beauty and Function
HISTORY 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.
ROMANS 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!
FORCES ACTING ON A BRIDGE http://www.pbs.org/wgbh/buildingbig/lab/forces.html 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
BALANCING THE FORCES A good bridge keeps all the forces in balance; if there is compression there is and equal amount of tension.
BRIDGE TYPES • 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!
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!
Your Challenges Today: Arch Bridge Challenge! Tomorrow: Start building a bridge using 100 toothpicks!