Disasters & Failures - Bridges

History of Bridges - Ages

Stone Age, The Romans, Iron Age, Steel Age

Caravan Bridge

located in Izmir, Turkey; built ~850 BC, the world’s oldest bridge still in use

Basic Bridge Requirements

handles the traffic, meet economic needs, withstand its expected environmental load (routine, potential), be aesthetically pleasing

Special Bridge Requirements

its required dimensions, its traffic load, the body of water it spans, other environmental issues

Ways to Address Special Requirements

understand the art, science, and engineering, choose the best material for the job, select a bridge design type that supports

Bridge Physics Equation

F (force) = m (mass) * a (acceleration)

F = mg (acceleration of gravity at the Earth’s surface

Newton’s Law of Universal Gravitation

Fgraw = [ g ( m^1 * m² ) ] / r²

Equilibrium

when all the forces acting on an object are balanced, all of the forces do not have to be equal to balance; implies - net force = 0 N & acceleration = 0 m/s²

Static Equilibrium

static = stationary/at rest; when an object is in a state of equilibrium and at rest; net force = 0

Gravitational Force

holds together the universe at large, including the atmosphere, water, and us to Earth

Electromagnetic Force

governs atomic-level phenomena, binds electrons to atoms and atoms to each other

Strong Nuclear Force

strongest of all the forces, holds the nucleus of an atom together (nuclear fusion)

Weak Nuclear Force

responsible for certain types of nuclear reactions

Gravitational Force

gravity is the most important force affecting bridges because essentially we are putting mass where it doesn’t normally go

Compression

static force that tries to squeeze a material together to make it shorter; buckling occurs when the force overcomes the strength of the material

Tension

static force that tries to stretch or pull apart a material to lengthen it, opposite of compression; snapping occurs when the force overcomes the strength of the material (think “tug-o-war”)

Shear

static forces that try to slide the material apart in opposite directions

Torsion

static force that tries to rotate the material in opposite directions, main issue = wind load (like ringing out a towel)

Beam Bridge

oldest type still used today, modeled after natural bridges, forms basis for all other types, easiest to build, one or more beams (decks) span the area between abutments (supports at end) or piers (supports between abutments mid-stream); as the live load moves over the beam: top of beam is compressed, bottom of beam is stretched, if beam can’t handle forces it will fail; usually for short distances, the longer the beam the weaker

Truss Beam Bridge

simplest modification to the beam bridge, easily secure strong piers to overpass, stream bed, or canyon floor, wood or steel, uses a triangle-shaped design above the deck to redistribute the forces; distributes the compression and tension forces under the live load, deck is in tension and tension travels along the beam and into the supports - diagonal beams in tension and vertical in compression

Cantilever Bridge

structures that are anchored at only one end while the other end projects horizontally into space, combines the truss with the concept of a lever and balances one side of its truss with the other, has two cantilever arms extending from opposite sides of an obstacle that has to be spanned and they meet at the center

Arch Bridge

first large-scale, always located below or through the deck (never above), abutments have to be built very strong because they will carry all of the weight and forces, reduces the ability of the beam to flex, distributes compression across and down arch

Flat Arches

Romans used, flat arches with “hanging” masonry supporting the arena floor of the Colosseum, used no mortar, central keystone has held the bricks in place since the 1st century A.D.

Cable-Stayed Bridge

bridge’s deck is directly suspended from cables that are under tension from the dead load, cables run directly from the tower to the deck forming a fan-like pattern, cables connected to a tower (pier) which is under compression, any additional forces from the live or environmental load is transferred by the cables to the tower, often used for spanning medium to long distances that are longer than cantilever bridges but shorter than suspension, steel or concrete

Suspension Bridge

like cable-stayed but cable from beams are connected to another cable, long cable is strung over the towers and anchored on both sides, smaller cables are hung from the main cables and connect to the deck, towers handle the compression and tension is transferred completely off the bridge, can be very long

Dixon, Illinois 1873

worst vehicular bridge disaster ever, iron truss bridge designed by Lucius Truesdell, May 4 1873 ~200 ppl lined bridge to be baptized, bridge twisted/splintered/fell killing 46 ppl/injuring 56, city engineer said design lacked uniformity/strength, few weeks prior another Truesdell bridge collapsed was repaired and collapsed again, “Truesdell Traps,” pastor saved 15 ppl, Truesdell blamed everyone but himself, American Society of Civil Engineers stated main causes of collapse are: incompetent/corrupt builders, neglects during construction, excessive loads

The Tay Bridge Disaster 1879

near Dundee Scotland, cross ~2 miles of River Tay estuary, built between 1871-78 (longest spanning at the time), truss beam bridge w/ iron beams sitting on iron/masonry piers, elevated center for ships to pass, 20 lives lost building bridge, Dec. 28 1979 @ 5pm storm w/ winds ~78 mph, @715pm bridge’s center span collapsed under weight of passenger train carrying 75 ppl, train fell into center and all 75 died, columns upwind failed under tension, columns downwind failed under compression, iron used wasn’t tested properly/contained numerous defects, later determined possible for train to derail, designer Sir Thomas Bouch did nothing to ensure bridge was inspected, trains ignored. speed limits

Tacoma Narrows Bridge, Washington 1940

3rd longest suspension bridge, 5,000’, narrows over 800’ deep, Clark Eldridge designed $4.6 mil over budget, design given to Leon Moisseiff who decided too heavy, ended up way too light and would sway so had to be routinely closed, Nov 7 bridge tore apart in 42 mph wind, rebuilt correctly 1950 and still in use today