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Earthquake Resistance planning

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Earthquake Resistance planning

  1. 1. Elementary Seismology & Earthquake Resistance Building Planning Sumanta Das SRM University, Kattankulathur
  2. 2. Seismology The term ‘Seismology’ is derived from Greek word Seismo, which means earthquake and logos means science; hence the Seismology is Science of Earthquakes Seismology can be defined in two ways: 1. The science of earthquakes and the physics of the earth’s interior 2. The science of elastic wave (seismic waves)
  3. 3. CONTINENTAL DRIFT Prepared by CT.Lakshmanan
  4. 4. Prepared by CT.Lakshmanan
  5. 5. Dipesh Rathod 1) Crust: thikness~5 to 40km Light materials (e.g basalts and granites) 2) Mantle: thickness ~2900km Has ability to flow outer core materials 3) Outer Core: thickness ~2200km In Liquid form 4) Inner Core: radius ~1290km solid and consists of heavy metals (e.g., nickel and iron) INSIDE THE EARTH
  6. 6. Dipesh Rathod Local Convective Currents in the Mantle Major seven Tectonic Plates on the Earth’s surface The convective flows of Mantle material cause the Crust and some portion of the Mantle, to slide on the hot molten outer core. This sliding of Earth’s mass takes place in pieces called Tectonic Plates.
  7. 7. Source: from internet Prepared by CT.Lakshmanan
  8. 8. Fault A fault is nothing but a crack or weak zone inside the Earth. When two blocks of rock or two plates rub against each other along a fault, they don’t just slide smoothly. As the tectonic forces continue to prevail, the plate margins exhibit deformation as seen in terms of bending, compression, tension and friction. The rocks eventually break giving rise to an earthquake, because of building of stresses beyond the limiting elastic strength of the rock. Prepared by CT.Lakshmanan
  9. 9. Dipesh Rathod  There are three types of inter-plate interactions are the and boundaries 1) convergent 2) divergent 3) transform
  10. 10. Dipesh Rathod  How the ground shakes?  Large strain energy released during an earthquake travels as seismic waves in all directions through the Earth’s layers, reflecting and refracting at each interface. These waves are of two types Body waves 1. P-waves 2. S-waves Surface waves
  11. 11. Dipesh Rathod Arrival of Seismic Waves at a Site Motions caused by Body and Surface Waves
  12. 12. Dipesh Rathod BASIC TERMINOLOGY Focus: The point on the fault where slip starts. Epicenter: The point vertically above this on the surface of the Earth. Focal Depth: The depth of focus from the epicenter.  Epicentral distance: Distance from epicenter to any point of interest Aftershocks and Foreshocks : Those occurring before the big one are called
  13. 13. Magnitude Vs Intensity The magnitude of an earthquake is determined instrumentally and is more objective measure of its size Intensity of an earthquake is a subjective parameter based on assessment of visible effects. It depends on factors other than the actual size of the earthquake Prepared by CT.Lakshmanan
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  15. 15. Dipesh Rathod MAGNITUDE : INTENSITY Magnitude is a quantitative measure Intensity is an indicator of the severity of the actual size of the earthquake. of shaking generated at a given location Measured by Richter Scale  Measured by Mercalli scale Denoted by M(number) i.e. M8 or severity of shaking is much higher near the M7.7 epicenter than farther away. Same at every places like M7 Intensity is varies at each and every place.
  16. 16. EARTHQUAKE MAGNITUDE CLASS USGS IMD M>8 Great Very great 7 - 7.9 Major Great 6 - 6.9 Strong Moderate 5 - 5.9 Moderate Moderate 4 - 4.9 Light Slight 3 - 3.9 Minor Slight M<3 Prepared by CT.Lakshmanan Micro earthquake
  17. 17. GLOBAL EARTHQUAKE OCCURRENCE Magnitude Annual Average No. M >8 2 7 - 7.9 20 6 - 6.9 100 5 - 5.9 3000 4 - 4.9 15,000 3 - 3.9 >100,000 Prepared by CT.Lakshmanan
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  19. 19. IS 1893:2002 More than 60 % area is earthquake prone. Zone V % 12 Zone IV Zone III Fig. courtesy: nicee 18 % 26 % Zone II % Prepared by CT.Lakshmanan 44
  20. 20. The Vulnerability Profile - India         59% of land mass prone to earthquakes 40 million hectares (8%) of landmass prone to floods 8000 Km long coastline with two cyclone seasons Hilly regions vulnerable to avalanches/landslides/Hailstorms/cloudburst 68% of the total area susceptible to drought Different types of manmade Hazards Tsunami threat 1 million houses damaged annually + human, economic, social and other losses
  21. 21. Hazard, vulnerability & disaster Disaster = F (Hazard, Vulnerability) Prepared by CT.Lakshmanan
  22. 22. Ingredients of Risk HxV-C=R Hazard x vulnerability – capacity = risk H - potential threat to humans and their welfare V - exposure and susceptibility to loss of life or dignity C - available and potential resources R - probability of disaster occurrence - Capacity “resources, means and strengths which exist in households and communities and which enable them to cope with, withstand, prepare for, prevent, mitigate or quickly recover from a disaster” Prepared by CT.Lakshmanan
  23. 23. Earthquake Do Not Kill People Improperly Designed Structures Do! Prepared by CT.Lakshmanan
  24. 24. • The structure is to resist minor earthquake without damage. • The structure is to resist moderate and frequently occurring earthquakes without any structural damage, but minor cracks are permissible during earthquakes • The structure shouldn’t collapse under severe earthquake.
  25. 25. Planning Parameters for EQRB • Planning should be based on seismic IS codes i.e. IS 1893-2002, IS 13920-1993 • The base soil should be strong and compacted. • The zone should be free from seismological hazards. • Important heavy structures like dams, nuclear power plant etc. should be planned for higher level of earthquake protection. • The weight of building should be as less as possible. • Building height and width ratio should be maintained. • Reinforced structure should be planned. • All parts of buildings like columns, beams, roofs should be well connected properly
  26. 26. • Shear walls, ductility of buildings with greater quality should be provided for more safety. • Avoid corners, soft stories at ground floor, short column. • Good materials, modern engineering technologies, skilled engineers and labors, fund and construction methods should be maintained. Prepared by CT.Lakshmanan
  27. 27. Dipesh Rathod What are the seismic effect on structures? 1. Inertia force in structures: Earthquake causes shaking of the ground. So a building resting on it will experience motion at its base. From Newton’s First Law of Motion, even though the base of the building moves with the ground, the roof has a tendency to stay in its original position. But since Effect of Inertia in a building when shaken at its base the walls and columns are connected to it, they drag the roof along with them.
  28. 28. Dipesh Rathod Effect of Inertia in a building when shaken at its base
  29. 29. Dipesh Rathod Modes and patterns of failure of Buildings (1) Soft/weak stories A soft or weak storey is created when the lateral stiffness and/or strength of a storey is markedly more flexible than the floors above and below. Soft story This often occurs at the ground floor when it is left open for parking, a shop front, or other reasons. Most of the deformation is concentrates at this level and results in large rotation demand in columns.
  30. 30. Dipesh Rathod A typical soft storey collapse In this case, after the first storey failed, this added force of impact at each floor subsequent collapse. Typical soft storey collapse in Bhuj caused stories to
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  34. 34. Earthquake Design Philosophy Prepared by CT.Lakshmanan
  35. 35. IMPORTANT CONSIDERATIONS TO MAKE A BUILDING EARTHQUAKE RESISTANT 1. Configuration 2. Ductility 3. Quality control 4. Base Isolation Prepared by CT.Lakshmanan
  36. 36. 1. Configuration A terminally ill patient , however effective the medication, may eventually die. Similarly, a badly configured building Cannot be engineered for an improved performance beyond a certain limit. Prepared by CT.Lakshmanan
  37. 37. Regular Configuration • Regular configuration is seismically ideal. These configurations have low heights to base ratio, symmetrical plane, uniform section and elevation and thus have balanced resistance. Prepared by CT.Lakshmanan These configurations would have maximum torsional resistance due to location of shear walls and bracings. Uniform floor heights, short spans and direct load path play a significant role in seismic resistance of the building.
  38. 38. Irregular Configuration Buildings with irregular configuration Buildings with abrupt changes in lateral resistance Buildings with abrupt changes in lateral stiffness Prepared by CT.Lakshmanan
  39. 39. Re-entrant corner Prepared by CT.Lakshmanan
  40. 40. Out of plane Offsets Shear Wall Out-of-Plane Offset in Shear Wall Non-parallel system Prepared by CT.Lakshmanan Shear walls
  41. 41. ELEVATION IRREGULARITIES 1) Soft-Storey/Pan-caked 2) Set-backs Prepared by CT.Lakshmanan 3) Connections
  42. 42. ELEVATION IRREGULARITIES 4) Pounding 5) Breaks in Columns or Beams 6) Staggered Levels Prepared by CT.Lakshmanan 7) In-fills
  43. 43. Right or Wrong…? Prepared by CT.Lakshmanan
  44. 44. Ductility Let us first understand how different materials behave. Consider white chalk used to write on blackboards and steel pins with solid heads used to hold sheets of paper together. Yes… a chalk breaks easily!! On the contrary, a steel pin allows it to be bent back-and-forth. Engineers define the property that allows steel pins to bend back-and-forth by large amounts, as ductility; chalk is a brittle material. Prepared by CT.Lakshmanan
  45. 45. The currently adopted performance criteria in the earthquake codes are the following: i. The structure should resist moderate intensity of earthquake shaking without structural damage. ii. The structure should be able to resist exceptionally large intensity of earthquake shaking without collapse. Prepared by CT.Lakshmanan
  46. 46. The strength of brittle construction materials, like masonry and concrete, is highly sensitive to the 1. quality of construction materials 2. workmanship 3. supervision 4. construction methods Prepared by CT.Lakshmanan
  47. 47. Quality control special care is needed in construction to ensure that the elements meant to be ductile are indeed provided with features that give adequate ductility. Thus, strict adherence to prescribed standards of construction materials and construction processes is essential in assuring an earthquakeresistant building. Prepared by CT.Lakshmanan
  48. 48. Elements of good quality control 1.Regular testing of construction materials at qualified laboratories (at site or away) 2. Periodic training of workmen at professional training houses, and 3. On-site evaluation of the technical work Prepared by CT.Lakshmanan
  49. 49. IS CODES IS 1893 (Part I), 2002, Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision) IS 4326, 1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision) IS 13827, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Earthen Buildings IS 13828, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Low Strength Masonry Buildings IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces Prepared by CT.Lakshmanan
  50. 50. Base isolators Prepared by CT.Lakshmanan
  51. 51. While Hazards Are Inevitable, Each Hazard Need Not Convert Into A Disaster… As What Comes In Between Is The Culture of Safety And Prevention Let us Work Together to Build a Culture of Prevention ! Prepared by CT.Lakshmanan
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