Structures

What is a Bridge?A Structure across an obstacle to allow safe passage

The Sault Ste. Marie International Bridge made traveling across the St. Mary's River and the Soo Locks much more desirable.

Mackinac Bridge The Mighty Mac

London Bridge

Confederation Bridge

Loads: Dead or AliveTwo categories of loads try to destroy structures. They are known as:Dead loads, andLive Loads Dead loads are the permanent loads on a structure. For example, the self weight of a bridgeLive loads are all the variable loads, those that occur from time to time. For example, your weight in the classroom

Loads: Dead or AliveList LoadsDeadLive

Completion Of Bridge LoadsSelf-weight Concrete, steel, asphaltLights PedestriansBikesCars TrucksTrainsSnowWind Earthquake Dead LoadsLive Loads

Loads Create Forces Types of Forces Tension

Compression

Tension and Compression ActivityDrawings are used by architects and engineers to communicate important information. Use your sketching skills to draw the wheel of a bicycle and a step ladder.Note on the sketch which components are in tension and which components are in compression.

Types of BridgesBeam Bridge2

When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

Sault Ste. Marie International Bridge

Types of Bridges

Arch Bridge2

The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

Arch Bridge

Types of BridgesTruss Bridge2 Every bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges.

Truss Bridge

Types of BridgesSuspension Bridge2 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.

Suspension Bridge

Types of BridgesCable-Stayed Bridge2 The cable-stayed bridge, like the suspension bridge, supports the roadway with massive steel cables, but in a different way. The cables run directly from the roadway up to a tower, forming a unique "A" shape.

Cable-Stayed Bridge

Building MaterialsNeed to pick the best materialWood, plastic, concrete, steel, aluminum Compare forces that the material must resist to the properties of the materialDont forget Cost Materials Lab2

ElasticityBridges sway and flex under loads.But when the loads are removed the bridge returns to its original shape. The property that the bridge possess to return to its original shape is called elasticity.

Elasticity DemonstratedDemonstrate, to yourself, the elasticity behavior of an elastic band by gently pulling and releasing the tension in it.An eraser can easily substitute for the elastic band. But instead of pulling, slightly twist it. Did you notice how both the elastic band and eraser returned to their original shape?

ElasticityBridge members dont experience the extreme elongation or twist that you noticed with the elastic band and eraser demonstration.They experience more moderate shape changes that are not easily detected by the human senses unless you pay real close attention.Next time you are stuck in traffic on a bridge pay attention to the rocking motion of your vehicle as a heavy truck goes by in the opposite direction.

Contest InformationRefer to your handout on contest information and please feel free to ask questions. Make sure that you are clear on the following points:materials to be usedconstruction specificationsjudging categoriestesting procedure

ReferencesNova Online, Super Bridge, Build a Bridgehttp://www.pbs.org/wgbh/nova/bridge/build.html

BUILDING BIG: All About Bridgeshttp://www.pbs.org/wgbh/buildingbig/bridge/

West Point Bridge Design Contesthttp://bridgecontest.usma.edu/