Earthquakes and Earthquake Loading

Geology

• Plate Techtonics
• Faulting
• Mechanism = Release of Energy
• Radiation and Propagation
• Last Week's Quakes with plate boundries
• Top 10 recent quakes

Site Influences

• National Seismic Hazard Maps
• Where is the nearest CA fault hazard?
• Soil interfaces and wave reflection/refraction
• Liquifaction
• Slope Stability
• Soft soil amplification of waves
• Tsunami

Quake Assessment

• Four generic types:
  • Single shock
  • moderatly long, extermely irregular motion
  • long ground motion with pronounced periods of vibration
  • ground motion with permanent deformation
• Modified Mercalli Intensity Scale (1902, modified in 1931) UBC referrs to this
• Impacts of Earthquakes on Buildings [READ THIS]
• Richter Magnitude based on maximum amplitude (1935)
  relates to the energy which is released at Epicenter and has values from 3 to 9. Each unit represents an increase of about 32 times more energy. Hiroshima atomic bomb was about a 6.4, Alaska 1964 a 8.4 = about 1000 times more energy released!
• The Wave Form
• Shake = Push/Pull = Primary = FAST
• Rattle = Shear = Secondary = SLOWer
• Roll = Ground Swell = Variable speed

Effects on Buildings

• Forces:
  Inertial: F= mass x acceleration
  Elastic : F=[stiffness] x deformation
  
• Total effect depends on the Earthquake's acceleration, duration and period
• Buildings tend to act like springs
  Haronic motion
• Amplitude = displacement from neutral position
• Period = time elapsed for one complete cycle
• Frequency = number of cycles per second
• Damping
  
• Modes
  Fundamental = Natural Period
  (0.5 for low to 7 or 8 for tall)
  Multiple depending on structure's weight, stiffness, size, etc.
  

  Mode	Freq (Hz)	Period (s)
  1	0.298	3.356
  2	0.346	2.893
  3	0.620	1.614
  4	1.066	0.939
  5	1.547	0.646
  6	1.862	0.537
  7	2.107	0.475

  Now let's see some....

And now to the SO WHAT?

• Cyclic destruction
• PDEltA Effect - Soft Story problems
• Drift
• Configuration Considerations - regular vs. irregular
• The "L"
• Optimal according to the AIA booklet
• What I want you to remember!
  • Design a crush zone.
  • Design controlled failure points
  • Think of automobiles in a collision
    what crushes?
    what would happen if the trunk was totally stiff?
    what is the intention of the design?
    survival!
    
  • Do not try to armwrestle with Mother Nature - she WILL win

As Prof. Kirk Martini, UVa says

"There is good damage and bad damage."

LEARN from previous failures!

Design for weakness - plan for failure!

• Bolt, Bruce. Earthquakes: A Primer.
  excellent explaination of ground motion.
• Arnold, Christopher. Building Configuration and Seismic Design.
  excellent discussion of the way a building behaves in an earthquake and how to design for this behavior.
• Ambrose, James. Siomplified Building Design for Wind and Earthquake Forces.
  Is to a designer what "The Joy of Cooking" is for a chef - full of the basics when you need them.