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.
Compression is a force that acts to compress or shorten. (a push)
Tension is a force that acts to expand or lengthen. (a pull)
Bending An action that creates both compression and tension in object being bent. T C
What happen when the forces are too much? Snapping- too much tension/ pulls apart. Buckling- too much compression, deflects to the side.
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.
Beam Bridge Notes: - Top in compression, bottom in tension - Max span ~ 200 feet
A thicker beam bridge Still experiences compression and tension but the forces are dissipated. But a thick beam bridge is pretty heavy…
TRUSS BRIDGE Notes: - A thicker beam bridge - C and T forces are more spread out - Max span ~400 feet
ARCH BRIDGE Notes: - All parts are in compression - Max span ~ 1000 ft - VERY sturdy but labor intensive. Roman arches are >2000 years old
SUSPENSION BRIDGE Instead of supporting the deck from below, Suspension bridges hang the deck from a cable above. But the towers need balanced forces.
SUSPENSION BRIDGE Notes: - Supports (towers) in compression, - cables in tension - Max span ~ 7000 feet
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
Truss Bridge Geometry • What shape do you see a lot of?
Truss Bridge Geometry • Squares can collapse by rotating at the joints without ever breaking the members. • Triangles can only collapse if a member breaks.