8 th Grade Applied Technology Mr. Giannone

In this unit we will study structures and the forces that affect them.

Structures include a wide range of stationary things that are built or constructed. Bridges, dams, stadiums, homes, and building of all shapes and sizes are typical structures.

People live, work, learn, and play in a variety of different structures. Engineering Structures even deals with the construction of roads for transportation and power plants for power. What structures do you know of? What kinds have you seen today?

Some structures have highly specialized functions while others can serve a variety of needs. What specialized structures can you think of?

There are many forces that act on structures. Some of these forces wind, water, snow, and earthquakes. Forces that act upon structures are called loads. There are two types of loads: Dead Loads Live Loads

Dead Loads Do not change Includes weight of structure itself (beam, floor, walls)

Live Loads Will change over time Include people, animals, or vehicles

Materials will change in shape when subjected to stress There are five types of stress.

Compression Shear Deflection Tension Torsion

Compression is a squeezing or crushing force

Shear is a force that results from a pair of forces acting on the same object in opposite directions.

Deflection is a bending force

Tension is a stretching force

Torsion is a twisting force

A bridge is a structure that carries people, cars, trucks, and trains across obstacles such as a ravine, river, road, or railroad. Bridges have different designs. Each design has its advantages and disadvantages.

Compression bridge structures rely on continuous compression to transfer the load to the ground Includes Beam, Truss, and Arch bridges

Tension bridge structures rely on continuous tension to transfer the load to the ground. Include Suspension bridges

The Triangle shaped truss is used in many structures to add strength and stability.

Made of horizontal beams supported at either end. The deck of the bridge rests on the beams. The strength of the bridge can be increased by using a truss structure above or below the beams.

Beam bridges are the simplest, most common type of bridge. They are very economic for short spans Beam bridges rarely have spans longer than 250 feet.

This bridge has supports that curve upward from both ends to meet in the center of a span. The curved supports form an arch which spreads the weight of the bridge evenly to its ends, called abutments.

The arch shape is very strong and can be used to make spans of 1,500 feet or more. Arch bridges are more expensive than beam bridges to construct.

Suspension bridges uses two very strong cables that rest on towers and are anchored at both ends. Smaller cables, called hangers, are attached to the main cables. The deck hangs, or is suspended, from the cables.

Suspension bridges can be used to make very long spans of 5,000 feet or more. Suspension bridges are not economical for short spans.

Lanes accommodate the flow of cars and trucks in one direction. Lanes are a minimum of 11 feet wide. As the amount of lanes increase, the amount traffic decreases while the negative impact on the environment increases.

A span is the part of the bridge between two supports. Different bridges are best suited for different span lengths. For example, beam bridges are well suited for shorter spans, where suspension bridges are better suited for longer spans.

A complete bridge may contain more than one span. A pier is used to support the beginning/end of a span. A bridge with many spans is generally more expensive than a bridge with fewer spans, especially if the piers must be built in a river or deep ravine.

Building a structure will have many different impacts, both positive and negative, expected and unexpected. Unexpected negative impacts are a problem because you can’t plan for them. It is important to study the impact of structures before they are built so that you may make wise decisions. Galloping Gertie