earthquake and earthquake resistant design

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  1. 1. EARTHQUAKES AND EARTHQUAKE-RESISTANT DESIGN OF STRUCTURES
  2. 2. SCOPE OF PRESENTATION EARTHQUAKE AND ITS CHARACTERIZATION EARTHQUAKE-RESISTANT DESIGN REPAIR & RETROFITTING OF STRUCTURES EARTHQUAKE ANALYSIS OF STRUCTURES ADVANCED TECHNOLOGIES
  3. 3. EARTHQUAKE An earthquake may be simply described as a sudden shaking phenomenon of the earth's surface due to disturbance inside the earth.
  4. 4. CLASSIFICATIONS AND CAUSES OF EARTHQUAKE Tectonic Earthquakes Non-tectonic Earthquakes
  5. 5. TECTONIC EARTHQUAKES Due to disturbances or adjustments of geological formations taking place in the earth's interior. Due to slip along geological faults. Less frequent. More intensive. More destructive in nature.
  6. 6. ELASTIC REBOUND THEORY
  7. 7. NON-TECTONIC EARTHQUAKES Due to external or surfacial causes such as: Volcanic eruptions Huge waterfalls Occurrence of sudden and major landslides Man-made explosions Impounding in dams and reservoirs Collapse of caves, tunnels etc. Very frequent, minor in intensity generally not destructive in nature.
  8. 8. EARTHQUAKE TERMINOLOGY Seismograms Focus or Hypocentre Epicentre Focal Depth Hypocentral Distance Epicentral Distance Isoseismal-lines of equal seismic intensity Coseismal-lines designating the affected area
  9. 9. EARTHQUAKE PHENOMENON
  10. 10. Energy is released in the form of waves and radiates in all directions from its source, the focus. What Happens During an Earthquake?
  11. 11. EARTHQUAKE WAVES P Waves: Primary waves, Longitudinal waves, etc. Speed 8 to 13 km/s S Waves: Shear waves, Transverse waves, etc. Speed 5 to 7 km/s L Waves: Long waves or Surface waves, etc. Speed 5 to 7 km/s
  12. 12. Body Waves Travel through Earths interior. Two types based on mode of travel. Primary (P) Waves Push-pull (compress and expand compressional waves) motion, changing the volume of the intervening material. Therefore, can travel through solids, liquids, and gases. Generally, in any solid material, P waves travel about 1.7 times faster than S waves.
  13. 13. Seismic Wave Motion Animation #77
  14. 14. Body Waves Secondary (S) Waves Shake motion at right angles to their direction of travel that changes the shape of the material transmitting them (shear waves). Therefore, can travel only through solids. Slower velocity than P waves. Slightly greater amplitude than P waves. Lesser amplitude than L Wave.
  15. 15. Seismic Wave Motion Animation #77
  16. 16. Surface Waves Travel along outer part (surface) of the Earth. Complex motion (up-and-down motion as well as side-to-side motion). Cause greatest destruction. Exhibit greatest amplitude and slowest velocity. Waves have the greatest periods (time interval between crests). Often referred to as long waves, or L waves.
  17. 17. Seismic Wave Motion Animation #77
  18. 18. Seismic Wave Motion and Surface Effects Animation #78
  19. 19. Sensitive instruments, called seismographs, around the world record the earthquake event. Seismographs record seismic waves.
  20. 20. Seismographs record the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape. More than one type of seismograph is needed to record both vertical and horizontal ground motion.
  21. 21. Seismographs Animation #79
  22. 22. 1. Three station recordings are needed to locate an epicenter. 2. Each station determines the time interval between the arrival of the first P wave and the first S wave at their location.
  23. 23. 3. A travel-time graph is used to determine each stations distance to the epicenter.
  24. 24. 4. A circle with a radius equal to the distance to the epicenter is drawn around each station. 5. The point where all three circles intersect is the earthquake epicenter. 6. This method is called triangulation.
  25. 25. MAGNITUDE OF EARTHQUAKE Related to the amount of energy released by the geological rupture. Measure of the absolute size of the earthquake, without reference to distance from the epicentre. Richter (1958) defined magnitude as the logarithm to the base 10 of the largest displacement of a standard seismograph situated 100 km from the focus. Largest magnitude of earthquake recorded = 8.9 Log E M10 4 8 15= +. . (E = Energy in joules; M = Magnitude)
  26. 26. Intensity a measure of the degree of earthquake shaking at a given locale based on the amount of damage. TheThe drawback ofdrawback of intensityintensity scales is thatscales is that destructiondestruction may not be amay not be a true measuretrue measure of theof the earthquakesearthquakes actualactual severity.severity.
  27. 27. Magnitude estimates the amount of energy released at the source of the earthquake.
  28. 28. Richter ScaleRichter Scale Based on the amplitude of the largest seismic wave recorded.Based on the amplitude of the largest seismic wave recorded. Accounts for the decrease in wave amplitude with increased distance.Accounts for the decrease in wave amplitude with increased distance. Each unit of Richter magnitude increase corresponds to a tenfold increaseEach unit of Richter magnitude increase corresponds to a tenfold increase (logarithmic scale) in wave amplitude and a 32-fold energy increase.(logarithmic scale) in wave amplitude and a 32-fold energy increase. How Are Earthquakes Measured?How Are Earthquakes Measured?
  29. 29. Destruction from Seismic Vibrations 1. Ground Shaking 2. Liquefaction of the Ground 3. Seiches 4. Tsunamis, or Seismic Sea Waves 5. Landslides and Ground Subsidence 6. Fire
  30. 30. Amount of structural damage attributable to earthquake vibrations depends on: Proximity to populated areas Magnitude Intensity and duration of the vibrations Nature of the material upon which the structure rests Design of the structure
  31. 31. Regions within 20 to 50 kilometers of the epicenter will experience about the same intensity of ground shaking. Destruction varies considerably mainly due to the nature of the ground on which the structures are built. Damage Caused by the 1964Damage Caused by the 1964 Anchorage, Alaska QuakeAnchorage, Alaska QuakeDamage to I-5 during theDamage to I-5 during the Northridge, CA Earthquake in 1994Northridge, CA Earthquake in 1994
  32. 32. Unconsolidated materials saturated with water turn into a mobile fluid. Can cause underground structures to migrate to the surface, and buildings and other aboveground structures to settle and collapse.
  33. 33. Liquefaction of the Ground Dry Compaction and Liquefaction Animation #21
  34. 34. Result from vertical displacement along a fault located on the ocean floor. Result from a large undersea landslide triggered by an earthquake.
  35. 35. Advance across oceans at great speeds ranging from ~500 to 950 km/hour (~310 to 590 miles/hour). In the open ocean, height is usually < 1 meter. Distances between wave crests range from 100 to 700 km. In shallower coastal waters, the water piles up to heights that occasionally exceed 30 meters (~100 feet).
  36. 36. As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transforms. A tsunami travels at a speed that is related to the water depth hence, as the water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed diminishes as it travels into shallower water, its height grows. Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore. http://www.geophys.washington.edu/tsunami/general/physics/physics.html
  37. 37. As a tsunami approaches shore, it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundating, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called a runup height, of 10, 20, and even 30 meters. http://www.geophys.washington.edu/tsunami/general/physics/physics.html Tsunami at Hilo, Hawaii (April 1, 1946) that originated in the Aleutian Islands near Alaska, was still powerful enough to rise 30 to 55 feet when it hit Hawaii.
  38. 38. Tsunami Animation #91
  39. 39. The rhythmic sloshing of water in lakes, reservoirs, and enclosed basins. Waves can weaken reservoir walls and cause destruction.
  40. 40. Landslide caused by the 1964Landslide caused by the 1964 Alaskan EarthquakeAlaskan Earthquake
  41. 41. San Francisco in flames after the 1906 EarthquakeSan Francisco in flames after the 1906 Earthquake
  42. 42. Short-Range Predictions Goal is to provide a warning of the location and magnitude of a large earthquake within a narrow time frame. Research has concentrated on monitoring possible precursors such as measuring: uplift subsidence strain in the rocks Currently, no reliable method exists for making short-range earthquake predictions.
  43. 43. Long-R

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