A brief study of bridges

# A brief study of bridges

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## A brief study of bridges

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1. A brief study of bridges

2. How to talk about bridges: Span- the distance between supports Supports- piers, columns, or towers that elevate the bridge. Deck- The section that we walk or drive on Members- supporting pieces within a bridge.

3. Forces in Bridges

4. Compression is a force that acts to compress or shorten. (a push)

5. Tension is a force that acts to expand or lengthen. (a pull)

6. Bending An action that creates both compression and tension in object being bent. T C

7. What happen when the forces are too much? Snapping- too much tension/ pulls apart. Buckling- too much compression, deflects to the side.

8. Dissipation All bridges are subject to forces. The goal of designing a bridge is to dissipate the forces, that is to spread them out over a greater area.

9. Beam Bridge Notes: - Top in compression, bottom in tension - Max span ~ 200 feet

10. A thicker beam bridge Still experiences compression and tension but the forces are dissipated. But a thick beam bridge is pretty heavy…

11. TRUSS BRIDGE Notes: - A thicker beam bridge - C and T forces are more spread out - Max span ~400 feet

12. ARCH BRIDGE Notes: - All parts are in compression - Max span ~ 1000 ft - VERY sturdy but labor intensive. Roman arches are >2000 years old

13. SUSPENSION BRIDGE Instead of supporting the deck from below, Suspension bridges hang the deck from a cable above. But the towers need balanced forces.

14. SUSPENSION BRIDGE Notes: - Supports (towers) in compression, - cables in tension - Max span ~ 7000 feet

15. CABLE STAY BRIDGE Notes: - Stiffer than a suspension bridge because all points of deck connect to a support. - Much cheaper to build than a suspension - Max span ~ 5000 feet

16. Truss Bridge Geometry • What shape do you see a lot of?

17. Truss Bridge Geometry • Squares can collapse by rotating at the joints without ever breaking the members. • Triangles can only collapse if a member breaks.