1. How Bridges Respond to Loads
Engineering Design
Mrs. Hodgson

2. Static Load vs. Dynamic Load
A Static Load is a load that is either constant or applied over a long period of time. All dead loads are static loads.
A Dynamic Load is a load that is variable and applied over a short period of time
Bridges (or structures in general) respond to static and dynamic loads very differently

3. Static Load vs. Dynamic Load

4. How Bridges Respond to Truck Loads
When loads (live or dead, static or dynamic) are applied to bridges, the elements of the bridge (beams, cables, roadway) experience STRESS
Stress is like pressure. It the amount of force applied on a given area
The ability of a material to resist the applied force is the STRENGTH of the material

5. Basic Response
There are four basic responses of bridge elements to load
Tension/compression
Shear
Bending
Torsion

6. Tension
Tension stresses cause cracks to open

7. Compression
Compression stresses cause cracks to close

8. Shear
Shear stresses cause two points in the steel to slide past each other

9. Bending Causes tension and compression stresses in element compression

10. Torsion Results from twisting of bridge elements
Causes a combination of tension/compression and shear stresses