Lesson 5-2 Bridge Building Foundations of Technology Mr. Brooks

Objective: To familiarize students with bridge design and construction, including an understanding of the forces acting on structures.

Types of Bridges 4 types of bridges: – Beam bridges – Arch bridges – Suspension bridges – Cable-Stayed

4 types of Bridges cont. The difference is the span that each can cross. A span is the distance between two bridge supports. A modern beam bridge can span a distance of about 250 feet. A modern arch bridge can span a distance of feet. A modern suspension bridge can span a distance of 2000 to 7000 feet. A modern cable-stayed bridge can span a distance of up to feet.

Forces Acting on a Bridge The span a bridge is able to span depends on how each design deals with tension and compression. Compression is a force that acts to compress or shorten the thing that it is acting on. Tension is a force that acts to expand or lengthen the thing it is acting on. Compression and tension are present in all bridges. It is the job of the bridge designer to handle these forces without buckling or snapping.

Forces Acting on a Bridge buckling is what happens when the force of compression overcomes an object’s ability to handle compression. Snapping is what happens when the force of tension overcomes an object’s ability to handle tension.

Forces Acting on a Bridge The best way to deal with the forces acting on a bridge is to either dissipate them or transfer them. To dissipate a force is to spread it out over a greater area so that no one spot has to bear the brunt of the concentrated force. Ex: an arch bridge To transfer the force is to move it from an area of weakness to an area of strength. Ex: a suspension bridge.