Slide 10 of 24
Notes:
- Force has reached the house. Now what happens at the house?
- Inertia Forces
- Inertia
- Tendency for an object at rest to remain at rest, or
- Tendency of an object in motion to remain in motion.
- Force
- The energy required to move or accelerate the object.
- Inertia forces
- Forces that move or accelerate an object
- They are proportional to the object's weight.
- Seismic forces on buildings are inertia forces and are weight driven.
- Discussion of figure
- Consider a person standing in the bed of a pickup truck.
- If the pickup truck accelerated rapidly, inertia would tend to keep that person's body in its original location and the person would be thrown backward relative to the car’s motion.
- Similarly, if the pickup truck decelerated, the person would be thrown forward
- The same reaction occurs in a building when the ground moves.
- The building moves back and forth, with the bottom of the building moving with the quake and the top tending to remain in place.
- Now imagine two persons in the back of a pickup truck: one weighing 100 pounds and the other 200 pounds.
- As the truck accelerates, the individual that weighs 200 pounds would be pushed back with twice as much inertial force as the person who weighs 100 pounds.
- Another example: Roof Weight
- Assume there are two tract homes located side by side.
- Houses are identical except for one has an asphalt shingle roof and the other has a heavy clay tile roof.
- Because clay tiles weigh more than asphalt shingles, the home with the clay tile roof will experience higher inertia forces from the earthquake and, most likely, suffer more damage.
- Roofing weight does make a difference!
