Earthquake engineering : causes , analysis and mitigation.


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Causes , analysis and mitigative analysis of earthquakes

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Earthquake engineering : causes , analysis and mitigation.

  3. 3. What is an earthquake? An earthquake is a sudden release of energy due to shifts in the earth’s plates that has been stored in the rocks beneath the earth’s surface which causes a trembling or shaking of the ground. The energy that is released from the ruptured rock travels in waves which are known as seismic waves. There are two types of seismic waves; body waves which travel through the interior of Earth and surface waves which travel on Earth's surface. The two body waves are primary waves (p-waves) and secondary waves (s-waves).
  4. 4. The compressional (push-pull) wave will vibrate parallel to the direction that the wave is traveling up to speeds of 4 to 8 km per second (2.49 to 4.35 miles per second). The S-wave vibrates perpendicular to the direction of travel and can travel up to speeds of 2 to 5 km per second ( 1.24 to 3.11 miles per second). Love waves and Raleigh waves are known as Surface waves. Surface waves are the slowest of the seismic waves, but because they travel near the surface of Earth and contain a range of oscillating frequencies they often cause the most damage
  5. 5. World Earthquake Fault Lines
  6. 6. • Ground Shaking: Shakes structures constructed on ground causing them to collapse • Liquefaction: Conversion of formally stable cohesionless soils to a fluid mass, causing damage to the structures • Landslides: Triggered by the vibrations • Retaining structure failure: Damage of anchored wall, sheet pile, other retaining walls and sea walls • Fire: Indirect result of earthquakes triggered by broken gas and power lines • Tsunamis: large waves created by the instantaneous displacement of the sea floor during submarine faulting
  7. 7. Ground Shaking Frequency of shaking differs for different seismic waves. High frequency body waves shake low buildings more. Low frequency surface waves shake high buildings more. Intensity of shaking also depends on type of subsurface material. Unconsolidated materials amplify shaking more than rocks do. Buildings respond differently to shaking depending on construction styles, materials  Wood -- more flexible, holds up well.  Earthen materials, unreinforced concrete -- very vulnerable to shaking.
  8. 8. What is liquefaction? This residential and commerial building sank more than three feet into the partially liquefied soil.
  9. 9. Liquefaction is a type of ground failure in which water saturated sediment turns from a solid to a liquid as a result of shaking, often caused by an earthquake or even a volcanic eruption. In order for the liquefaction to occur the sand grains must be fine grain sand that are not closely packed together nor must it be held but some sort of cohesion. The intense shaking causes the strength of the soil to become weak and the sand and water begin to flow.
  10. 10. Nishinomia Bridge 1995 Kobe earthquake, Japan Flow failures of structures - caused by loss of strength of underlying soil Earthquake Destruction: Liquefaction
  11. 11. Lateral Spreading: Liquefaction related phenomenon Upslope portion of lateral spread at Budharmora, Gujarat
  12. 12. Inadequate attachment of building to foundation
  13. 13. Building design: Buildings that are not designed for earthquake loads suffer more
  14. 14. Increased water pressure causes collapse of dams
  15. 15. Cracked Highway, Alaska, 1964 Lateral spreading in the soil beneath embankment causes the embankment to be pulled apart, producing the large crack down the center of the road.
  16. 16. Lateral Deformation and Spreading  Down slope movement of soil, when loose sandy (liquefiable) soil is present, at slopes as gentle as 0.50  In situations where strengths (near or post liquefaction) are less than the driving static shear stresses, deformations can be large, and global instability often results
  17. 17. Mexico City Earthquake, 1985 8.1 Magnitude Poorly constructed buildings caused thousands of deaths
  18. 18. Northridge Earthquake, 1994 Southern California, USA 6.7 Magnitude most houses were wooden and did not collapse
  19. 19. Kobe Earthquake Japan 1995 Structures in Kobe built since 1981 had been designed to strict seismic codes. Most of these buildings withstood the earthquake. In particular, newly built ductile-frame high rise buildings were generally undamaged.
  20. 20. Northridge Earthquake Southern California 1994
  21. 21. A major cause of damage was liquefaction of the recent alluvial deposits that under laid large portions of the city. The result was excessive settlements and bearing capacity failures for countless buildings, most of which were supported on shallow foundations. This new building was not yet occupied at the time of the earthquake. Again, the bearing failure of its mat foundation was related to its relatively large height- to-width ratio. Adapazari, Turkey, 1999 Kocaeli earthquake
  22. 22. Damage due to Earthquakes Earthquakes have varied effects, including changes in geologic features, damage to man- made structures and impact on human and animal life. Earthquake Damage depends on many factors:  The size of the Earthquake  The distance from the focus of the earthquake  The properties of the materials at the site  The nature of the structures in the area
  23. 23. Damage to the Intercontinental Hotel during Mexico City's 1985 earthquake was severe even though the building was relatively new
  24. 24. Oakland Bridge failure
  25. 25. Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. The water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass, which acts under the influence of gravity, attempts to regain its equilibrium. 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 effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast and can flood a vast area. Earthquake Destruction: Tsunamis
  26. 26. Tsunami Movement: ~600 mph in deep water ~250 mph in medium depth water ~35 mph in shallow water Tsunami
  27. 27. The tsunami of 3m height at Shikotan, Kuril Islands, 1994 carried this vessel 70 m on-shore. The waves have eroded the soil and deposited debris.
  28. 28. Foundation failure in Kerala during Tsunami (December 26th, 2004)
  29. 29. Earthquakes sometimes cause fire due to broken gas lines, contributing to the loss of life and economy. The destruction of lifelines and utilities make impossible for firefighters to reach fires started and make the situation worse eg. 1989 Loma Prieta 1906 San Francisco Earthquake Destruction: Fire
  30. 30. What is Earthquake Engineering? Earthquake engineers are concerned with creating earthquakes resistant designs and construction techniques to build of all kinds of bridges, roads and buildings. Earthquake engineers are faced with many uncertainties and must be smart in their decisions in developing safe solutions to challenging problems. They rely on state-of-the-art technology, materials science, laboratory testing and field monitoring.
  31. 31. Shock Table Test Facility for Evaluating Earthquake Resistant Features in Buildings Table (payload 5000kg) Fund. Freq. 90Hz Masonry Building Models Pendulum (1.8m length & 600kg mass Max. swing 400) Rebound beam Research & Development  Indigenous design and fabrication of test facility  Novel earthquake resistant features for masonry buildings  Simulating failure patterns same as those observed in buildings after an earthquake Data acquisition system Table acceleration response for a swing angle of 300 Corner containment reinforcement with triangular link containment reinforcement with link Peak table acceleration 1.1g
  32. 32. Behavior of building models after 13 shocks Model 1 (ERF as per IS 4326:1993) Model 2 (ERF as per IS 4326:1993 plus additional R C band at Sill level and Containment reinforcement One fourth scale models Model 1 Response at top of cross wall Model 2 Response at top of cross wall Response after 5 shocks
  33. 33. Building Design After the earthquake in Mexico City, Mexican officials adopted a new design that can protect the buildings from earthquakes. This design was developed by some engineers at the University of California at Berkeley. Looking at the diagram below you can see that the braces form an X which are anchored in concrete blocks at the base and on the roof of the building. In diagram A we have conventional steel bracing. Under the stress of the earthquake one of the braces collapses under the stress. If all the braces begging to snap then the structural integrity of the building fails. Now in diagram B, the engineers at Berkely used a hydraulic jack to pull or stretch the rods. Once the rods are prestressed they can now be anchored to the base and to the roof of the building. The braces now have some room to contract thereby strengthening the structural integrity of the building.
  34. 34. Earthquake-Resistant Structure Building designed to prevent total collapse, preserve life, and minimize damage
  35. 35. 1.Excavation, fill placement, groundwater table lowering 2.Densification through vibration or compaction 3.Drainage through dissipation of excess pore water pressure 4.Resistant through inclusions 5. Stiffening through cement or chemical addition Types of Ground Improvement by Function
  36. 36. Other methods • Displacement piles: densification by displacement of pile volume, usually precast concrete or timber piles →Compaction grouting: densification by displacement of grout volume
  37. 37. Earthquake resistant design of geotechnical structures Geotechnical structures like, Retaining wall/Sheet pile Slope Shallow foundations Deep foundations Must be designed to withstand the earthquake loading
  39. 39. Engineers chose a hybrid girder design that combined the rigidity, noise absorption, and low cost of concrete with the precision manufacturing offered by steel. The system’s reinforced-concrete support piers are designed to withstand the seismic forces of earthquakes measuring up to 7.5 on the Richter scale. High-Speed Magnetic Levitation Rail Line Shanghai, China 2004
  40. 40. Nepal Develops Earthquake Resistant Architecture A plan for safer houses in rural areas Nepal has a history of being devastated by major earthquakes every 75 to 100 years, with the first recorded as early as 1255 AD. In 1934 Nepal experienced a deadly earthquake that resulted in the death of 8,500 people and destruction of 20 percent of valley structures, at a time when the population was far less than at present. Seismologists are predicting the occurrence of a large earthquake of this kind in the near future, which is likely to be most intense in the urban core.
  41. 41. Ninety percent of Nepalese houses are made of stone and unfired bricks. The Structural Engineers in Nepal are retrofitting current structures for about $25/home. By creating a one-meter square grid of punched holes in the stone wall covered with a 10 cm mesh of bamboo on the inside and outside the homes become earthquake resistant. This net is Secured to the wall by means of 12-gauge Gabion wire, (a form of riprap contained in a wire cage that is very useful in erosion control.), which is inserted through the holes and fastened strongly. It is covered with a stucco of mud, which is used in rural areas in order to ensure longer life for the bamboo mesh.
  42. 42. The Lefkas (Greece) earthquake resistant technique Two-story houses are built with a ground floor of rough boulder masonry and three lines of wooden posts (one along each long wall, and one in the middle of the room) support the first floor. This one is erected in wood-frame construction (Dajji). Foundations are laid on a three-layer round-poles mat, which could behave as a spring if a gap was left around. The main benefit is outspread of the foundation surface. "Dajji" is traditional in Cashmere (India). It is very efficient and affordable. A wooden frame is built without bracing. The empty rectangular or square "panels" are filled with a mesh of wood and stone cemented with mud. These panels work as bracing, but allow slight movement, and give elasticity to the whole structure. Thus, the house is able to move and to absorb the earthquake’s movement. Another advantage of this technique is to be (comparatively) lightweight, and thus being less stressed by earthquakes.
  43. 43. BIBLIOGRAPHY  State departments of various countries for images
  44. 44. THANK YOU