Examining potential failures

1. Suspension BridgeCompressive forces are located in members: A&C Tensile forces are located in members: B&D

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Beam Bridge (2 spans):Compressive forces are located in members: B, D & E (piers), C (bottom of beamTensile forces are located in members: A (top of beam)

Stress occurs at

points of contact

Cable Stay Bridge:Compressive forces are located in members: A & C (towers)Tensile forces are located in members: B & D (cables)

Additional Bridge Forces: Torsion and Shear

Feel it! Gently grab your neighbors’Forearm while she grabs yours. Both of you twist in opposite directions.Can you image torsion working on a steel girder?Engineers use aerodynamic truss structures and diagonal suspender cables to mitigate the effects of torsion.

Model Sheer! Clasp a a deck of cardsSlide your hand in opposite directions. The deck will “smear” into Individual cards.Can you imagine molecules in a steel girder being pulled apart by sheer? Engineers use monitoring equipment to identify fissures caused by sheer at connection points. Using materials that reduce the propensity for sheer in bridge design is important too.

Additional Bridge forces:Resonance

https://www.youtube.com/watch?v=17tqXgvCN0E Watch as waves of sound break a wine glass

Engineers useDampers (hydraulics) to Mitigate theEffects of resonance

Weather can unleash all types of dynamic forces at once

Structural design flaws can also resultIn bridge collapse:Silver Bridge:http://www.youtube.com/watch?v=dGQfUWvP0II

Okay, Let’s do it again….

Making a human cable stay

Feel it!! You are the bridge, stand in front of, to the side of (which ever way you can think of)a fan blowing wind at you at moderately high speed.What does it feel like?What points of stress are there on you?

Crazy!!!! Would you cross?

Watch this video: http://www.youtube.com/watch?v=dGQfUWvP0II