EQ L5: Engineering for Survival Flashcards
Magnitude of 1995 Kobe, Japan earthquake? Cost of damage and lives?
Mw = 7.2, $2.7 billion, 6 425 lives.
Magnitude, damage, lives cost of 1964 Good Friday earthquake? Where did it occur?
Mw = 9.2 (2nd biggest earthquake on record), $300-400 million, cost 116 lives in Alaska.
When in 2002 a pair of ‘quakes hit Alaska, why was the pipeline not damaged?
Because of its engineering design. The fault was already known to exist, so the pipeline was mounted on rails parallel to the fault. When earthquake occurred, the earth moved the rails under the pipeline ~2.5 m but didn’t damage the pipeline.
How does ground motion break a structure?
By applying a force to it. Moving ground causes structure to accelerate.
Structures are built to withstand acceleration in the ______ direction.
vertical (they withstand acceleration of gravity. small deviations from that value
For structures, why does a change in horizontal acceleration represent a significant change from normal?
Structures aren’t built to withstand horizontal acceleration. Normally they don’t experience any at all.
Which of these waves cause the most significant side-to-side motion at surfaces?
Rayleigh and Love waves.
Which waves cause most damage?
Waves with the largest amplitude of motion. Rayleigh and Love waves.
Magnitude vs. Intensity?
The amount of energy at the source describes the magnitude (wattage of the light bulb), whereas the experience felt as a result of that energy is the “felt intensity” (amount of light at the place it is used).
(i.e. magnitude is fixed, intensity is local)
Factor that influence intensity?
- Earthquake magnitude.
- Duration of shaking. Longer shaking causes more damage.
- Distance to/depth of epicentre/hypocentre. Closer to there, more likely for larger intensity.
- Ground type. Harder rocks are stiffer, generally experience smaller motions. Softer rocks in the same location are likely to experience larger motions. Higher frequencies tend to decay faster in softer rocks.
- Building characteristics. Stronger buildings suffer less than poorly constructed ones. Another important factor is resonance. Buildings have resonant frequency. If building is made to shake at exactly its resonant frequency, motion will increase rapidly, causing it to break faster than if not moving at a rate close to its resonant frequency.
Larger earthquakes have higher capacity to be catastrophic. However, this is only true if…
they occur near human activity.
Where in Vancouver area are rocks hard? Where soft?
Think in terms of rock and mountainous regions vs. regions that are flat and filled with recent river sediments.
What is dynamic compaction?
Blasting and dropping large weights. Causes soil layers to settle and become dense. Dense layers will not flow when the Earth shakes.
What general approaches to making buildings better able to withstand side-to-side stresses?
- Static methods (make it stronger) with cross brace, shear wall, shear core. Avoid soft storeys (weak bottom floor)
- Dynamic “active” methods:
- absorb energy (damping); uses springs and shock absorbers/dampers
- add mass (change resonance); adding mass at correct location within building so it will not be shaken to pieces when the expected ground motion occurs
- isolate the building from ground; allowing earth to move w/o dragging the structure with it. (this method isolates the Trans Alaska pipeline)
What are some aspects engineers must consider in employing good general construction practices?
Firmly attach cosmetic brick facing to buildings so they don’t fall off during shaking.
Use reinforced concrete properly. (i.e. not have weak at the joins.)
Use of shear wall. (gives it side-to-side strength)
Hillsides can be dangerous especially if they slip when shaken.
