Video “Bridges”
Part 1
Early Romans were first bridge building nation.
Built post and beam bridges
Lashed boats together (pontoon)
Stone Arch bridges.
The key to arch bridges are: key stone to lock arch together, built up sides to keep
arch from pushing out, Compression is the force on a stone arch bridge.
200 A.D. there were 7 bridges across the Tiber River
1779 England first Iron Bridge built.
This was easier and cheaper to do and using stone.
Iron bridges failed due to excess weight, Cast iron has flaws (tiny cracks in
material) to much tension would cause cracks to open up.
Truss bridges use compression and tension to keep structure in balance. Each
member will go from one force to the other.
Cantilever Bridges use tension for upper portion of bridge, lower is in
compression.
Suspension bridges cables are in tension towers are in compression bridge deck
supported from above anchorages at both ends of bridge.
Tension pulling action. Compression is the pushing together action.
Brooklyn bridge longest suspension bridge for that time Washington Roebling
chief engineer 1869. Was 34 years old when he began working on bridge. Dad
died because of hydrotherapy because of injury to foot when making calculations
for Brooklyn Bridge.
Part 2
Case on air tight wood box that rested on bottom of river. Men worked in
temperatures at 80 to 100 degrees. Compressed air pumped into case on. Air
locks were developed to keep compressed air in case on.
Case on disease which is the Benz. People coming in and out of case on to fast.
Nitrogen bubbles in blood causing extreme joint pain.
Took 14 years to build the Brooklyn Bridge.
Golden Gate Bridge 4200 feet span built during the Great Depression. Paid for by
selling bonds. Original design was ½ cantilever and ½ suspension bridge. Ugly
design many law suits. Tallest tower at the time 780 feet. Cables were 27,000
individual wire rope put in strands of 100. 19 men fell into net to save their lives.
12 men died when platform fell into net couldn’t hold weight. Bridge estimate for
every million dollars spent on man would die. Bridge painted International
Orange. 60 million pounds pulling on cables at anchorages. Enough wire rope to
go around equator 3 times. 1937 Golden Gate Bridge opened.