BRIDGES

Great Stone Bridge in China History of Bridge Development 100 B.C. Romans 2,104 years ago 700 A.D. Asia 1,304 years ago Clapper Bridge Roman Arch Bridge Tree trunk Stone Arch design evenly distributes stresses Natural concrete made from mud and straw Clapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this. Great Stone Bridge in China Low bridge Shallow arch Allows boats and water to pass through

What is a bridge? A bridge is a structure that permits us to cross over an obstacle It can span a canyon, waterway, or road

What does a bridge need? A good bridge must have a firm foundation A good bridge must be sturdy A good bridge must last a long time

Chesapeake Bay Bridge

Sydney Harbor Bridge

Dames Point Bridge

Tower Bridge

Firth of Forth Bridge

Astoria Bridge

Golden Gate Bridge

Beam Bridge This is the oldest and simplest of the four types of bridges. Originally people used a long piece of stone or tree trunk to cross small streams. It is possible that bridges made of stone slabs found in south west England are the oldest in the world. We don’t know exactly when they were built but they are still standing. As weight is placed on the beam, and the compression force shortens the upper part. This tension causes the lower part to lengthen. The beam bends and if the pressure is too great it will break. weight

Many of the beam bridges that you see above roads are made of steel or concrete to make sure that they are strong enough to hold the weight. The size of the beam, and especially its height, controls the span of the bridge. Its possible to put more weight on the beam by increasing its thickness or height. A framework or truss is used to build high bridges and this structure spreads the tension and the compression. Examples of truss patterns

Beam Bridges A beam bridge can be one span (one beam) or multi spans (many beams)

                                                                         This type of bridge was invented by the Romans. They realized that a wedge shaped stone called voussoirs could carry heavy loads if built in the shape of an arch Arch Bridges Locking stone A wooden framework has to be built to support the stones while building the arch bridge. After putting the locking stone in place the wooden frame is removed and the arch should stand by itself.

Arch bridges Stone bridges Steel Originally Arch bridges were built using materials such as stones and bricks that can withstand compression. But many modern bridges are built using concrete or steel. Strong support is needed on each side of the arch to stop it from spreading out. Steel Concrete

Truss Basics – Overview Truss Bridges A metal truss bridge is a bridge whose main structure comes from a triangular framework of structural steel or iron.

Truss Bridge Parts Truss Bridge Parts The different parts of a truss bridge are all named. Some of the parts: Top / Upper Chord Vertical (Member) Hip Vertical (Only the verticals that meet the top of the end post) Diagonal (Member) End Post Floor beam Bottom / Lower Chord Connections Each space between vertical members and end posts is one panel. This bridge has six panels. Portal Bracing Sway Bracing Lateral Bracing

Truss Bridge Forces Truss Bridge Forces Compression Tension The chords and members of a truss bridge experience strain in the form of tension (stretching apart) and compression (squeezing together). Engineers often pick different types of materials and designs for the different parts of a bridge based on these forces. An example is shown above.

Types of Bridges Suspension Bridges This kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

Types of Bridges Forces Suspension Bridges Forces In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.