2. 1. Suspension Bridge
Compressive 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 beam
Tensile forces are located in members: A (top of beam)
3. Cable Stay Bridge:
Compressive forces are located in members: A & C (towers)
Tensile forces are located in members: B & D (cables)
4. 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 cards
Slide 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.
5. Additional Bridge forces:
Resonance
https://www.youtube.com/watch?v=17tqXgvCN0E
Watch as waves of sound break a wine glass
Engineers use
Dampers (hydraulics) to
Mitigate the
Effects of
resonance
6. Weather can unleash all types of dynamic forces at once
Structural design flaws can also result
In bridge collapse:
Silver Bridge:
http://www.youtube.com/watch?v=dGQfUWvP0II
7. 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?
