Earthquake Resistance planning


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  • The Earth and its Interior
    Long time ago, a large collection of material masses coalesced to form the Earth. A large amount of heat was generated by this fusion, and slowly as the Earth cooled down, the heavier and denser materials sank to the center and the lighter ones rose to the top. The differentiated Earth consists of the Inner Core (radius ~1290km), the Outer Core (thickness ~2200km), the Mantle (thickness ~2900km) and the Crust (thickness ~5 to 40km). Figure 1 shows these layers. The Inner Core is solid and consists of heavy metals (e.g., nickel and iron), while the Crust consists of light materials (e.g., basalts and granites).
  • Basic Difference: Magnitude versus Intensity
    Magnitude of an earthquake is a measure of its size. For instance, one can measure the size of an earthquake by the amount of strain energy released by the fault rupture. This means that the magnitude of the earthquake is a single value for a given earthquake. On the other hand, intensity is an indicator of the severity of shaking generated at a given location. Clearly, the severity of shaking is much higher near the epicenter than farther away. Thus, during the same earthquake of a certain magnitude, different locations experience different levels of intensity ( e.g., Figure 14).
    To elaborate this distinction, consider the analogy of an electric bulb (Figure 15). The illumination at a location near a 100-Watt bulb is higher than that farther away from it. While the bulb releases 100 Watts of energy, the intensity of light (or illumination, measured in lumens) at a location depends on the wattage of the bulb and its distance from the bulb. Here, the size of the bulb (100-Watt) is like the magnitude of an earthquake, and the illumination at a location like the intensity of shaking at that location.
    Suggestion: Can student think of any other analogies. e.g. ripples formed by dropping a stone into a pond………?
    Magnitude and Intensity in Seismic Design
    One often asks: Can my building withstand a magnitude 7.0 earthquake? But, the M7.0 earthquake causes different shaking intensities at different locations, and the damage induced in buildings at these locations is different. Thus, it is particular levels of intensity of shaking that buildings and structures are designed to resist, and not so much the magnitude. Buildings are designed as per the intensity, since intensity can vary place to place, for a given magnitude.
    The peak ground acceleration (PGA), i.e., maximum acceleration experienced by the ground during shaking, is one way of quantifying the severity of the ground shaking. Approximate empirical correlations are available between the MM intensities and the PGA that may be experienced. For instance, during the 2001 Bhuj earthquake, the area enclosed by the isoseismal VIII is thought to have experienced a PGA of about 0.25-0.30g. Now strong ground motion records from seismic instruments are relied upon to quantify destructive ground shaking. These records are critical for cost-effective earthquake-resistant design.
  • Seismic Zones of India
    The varying geology at different locations in the country implies that the likelihood of damaging earthquakes taking place at different locations is different. Thus, a seismic zone map is required so that buildings and other structures located in different regions can be designed to withstand different level of ground shaking. The seismic zone map of 1984 subdivided India into five zones – I, II, III, IV and V (Figure 12). The maximum Modified Mercalli (MM) intensity of seismic shaking expected in these zones were V or less, VI, VII, VIII, and IX and higher, respectively. Parts of Himalayan boundary in the north and northeast, and the Kachchh area in the west were classified as zone V.
    The seismic zone maps are revised from time to time as more understanding is gained on the geology, the seismotectonics and the seismic activity in the country. For instance, the Koyna earthquake of 1967 occurred in an area classified in zone I as per map of 1966. The 1970 version (same as Figure 12) of code upgraded the area around Koyna to zone IV. The Killari (Latur) earthquake of 1993 occurred in zone I. The current Indian seismic zone map (Figure 13) places this area in zone III. The zone map now has only four seismic zones – II, III, IV and V. The areas falling in seismic zone I in the 1984 map were merged with those of seismic zone II. Also, the seismic zone map in the peninsular region is modified; Madras now comes under seismic zone III as against zone II in 1984 map.
    The national Seismic Zone Map presents a large-scale view of the seismic zones in the country. Local variations in soil type and geology cannot be represented at that scale. Therefore, for important projects, such as a major dam or a nuclear power plant, the seismic hazard is evaluated specifically for that site. Also, for the purposes of urban planning, metropolitan areas are microzoned. Seismic microzonation accounts for local variations in geology, local soil profile, etc.
    Suggestion: Ask the students to indicate in which zone their birthplace is located.
  • Buildings with one of their overall sizes much larger or much smaller than the other two, or very large buildings, do not perform well during earthquakes.
  • Base Isolation
    The concept of base isolation is explained through an example building resting on frictionless rollers (Figure 6). When the ground shakes, the rollers roll freely, but the building above does not move. It remains stationary. No force is transferred to the building due to shaking of the ground; simply, the building does not experience the earthquake.
    Unfortunately, under wind load the building will move and impact against the end of the pit.
  • Seismic isolation is a relatively recent and evolving technology. It has been in increased use since the 1980s, and has been well evaluated and reviewed internationally. Base isolation has now been used in numerous buildings in countries like Italy, Japan, New Zealand, and USA. Base isolation is also useful for retrofitting important buildings (like hospitals and historic buildings). By now, over 1000 buildings across the world have been equipped with seismic base isolation. In India, base isolation technique was first demonstrated after the 1993 Killari (Maharashtra) Earthquake [EERI, 1999]. Two single storey buildings (one school building and another shopping complex building) in newly relocated Killari town were built with rubber base isolators resting on hard ground. Both were brick masonry buildings with concrete roof. After the 2001 Bhuj (Gujarat) earthquake, the four-storey Bhuj Hospital building was built with the base isolation technique (Figure 8).
  • 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
    14. 14. Prepared by CT.Lakshmanan
    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
    18. 18. Prepared by CT.Lakshmanan
    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
    31. 31. Prepared by CT.Lakshmanan
    32. 32. Prepared by CT.Lakshmanan
    33. 33. Prepared by CT.Lakshmanan
    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
    52. 52. Prepared by CT.Lakshmanan