Slides Earthquake Resistant design part1


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Details earthquakes and their effect on Structures

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    I'm designing a vertical column 11meter High (steel pressure vessel) for Zone 2 Addis Ababa in Ethiopia, I need to use in calculation G Loading, I need to know Longitudinal Acceleration (Gx); Lateral Acceleration (Gz); Vertical Acceleration (Gy), Can you help me? Best Regards.
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Slides Earthquake Resistant design part1

  1. 1. Earthquakes and Seismic Design By Dr. N. Subramanian 3rd Nov. 2012
  2. 2. Cross-section of EarthThough we have explored Space above ground extensively, wecould go only about 7.6 miles below ground! Russiangeologists started drilling into the Kola Peninsula, nearFinland, in 1970 and after 22 years could not proceed further.
  3. 3. Plate tectonics- Alfred Wegener , 1912 Dr. N. Subramanian
  4. 4. Plate tectonics (PT) Earlier theories assume gradual shrinking (contraction) or gradual expansion of the globe. PT is based on continental drift & developed in early 20th century Lithosphere is broken up into 7-8 major tectonic plates, and numerous smaller plates Tectonic plates move – because lithosphere has a higher strength and lower density than the underlying asthenosphere- Dissipation of heat from the mantle is the source of energy Lateral relative movement of the plates- 0 to 100 mm annually Dr. N. Subramanian
  5. 5. Three types of plate boundaries exist Dr. N. Subramanian
  6. 6. Global earthquake epicenters, 1963– 1998 Dr. N. Subramanian
  7. 7. Aerial view of San Andreas Fault in the Carrizo Plain, northwest of Los Angeles Dr. N. Subramanian
  8. 8. Earthquakes• Around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt.• Human activities that produce minor earthquakes: – Storage of large water behind a dam, – Injecting liquid under high pressure into wells (fracking to extract natural gas), – Coal mining – Oil drilling Dr. N. Subramanian
  9. 9. Recurrence of Earthquakes• Average recurrence of Earthquakes are: – Earthquake of M3.7–4.6 every year, – Earthquake of M4.7–5.5 every 10 years, – Earthquake of 5.6 or larger every 100 years.• The United States Geological Survey estimates that, since 1900, there have been an average of 18 major earthquakes (M 7.0– 7.9) and one great earthquake (M 8.0 or greater) per year. Dr. N. Subramanian
  10. 10. Aftershocks An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. It occurs in the same region of the main shock but always of a smaller magnitude. If it is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Formed as the crust around the displaced fault plane adjusts to the effects of the main shock They are dangerous - usually unpredictable, can be of a large magnitude, and can collapse buildings that are damaged from the main shock Dr. N. Subramanian
  11. 11. Earthquakes-EpicenterEpicenter is the point on the Earths surface that is directly above thehypocenter (where the Strain energy stored in the rock is first released) Dr. N. Subramanian
  12. 12. EARTHQUAKES Dr.N.Subramanian 12
  13. 13. Earthquake Prediction Instrument... from ancient China Dr. N. Subramanian
  14. 14. Seismograph is used to measure wave amplitude Dr. N. Subramanian
  15. 15. Can we predict earthquakes correctly?• Long ago, Catholic Church in Rome condemned Galileo Galilei and put him under house arrest for teaching ‘Earth revolves around the sun’!• Now, (Oct 22, 2012) an Italian court convicted seven scientists and experts for 6 years in prison for failing to adequately warn citizens before an earthquake struck central Italy in 2009, killing more than 300 people. Dr. N. Subramanian
  16. 16. Can we predict earthquakes correctly?• Scientists generally cannot predict the time, location and magnitude of EQ - But they did it once!• On Feb. 4, 1975, seismologists issued a warning to residents of Haicheng in northeastern China, prompting people to seek safety outdoors. – A M7.3- EQ struck that evening, killing more than 2,000 people and destroying more than 90 percent of the city. – Without the warning, about 150,000 people would have died! Dr. N. Subramanian
  17. 17. Characteristics of an Earthquake Dr. N. Subramanian
  18. 18. As the “quality” of the sediment decreases, the amplitude of the waves increases Dr. N. Subramanian
  19. 19. Magnitude: Richter scale- Californian seismologist Charles F. Richter, in 1930s Dr. N. Subramanian
  20. 20. P and S waves and Magnitude• P waves are the first to arrive due to their high displacement speed,• Followed by the S waves. Two parameters that determine magnitude:• The time delay between the arrival of the first P waves and S waves(proportional to the distance between the seismograph and the hypocentre of the earthquake), and• Their amplitude. Dr. N. Subramanian
  21. 21. P and S waves Dr. N. Subramanian
  22. 22. Graphical solution of the mathematical formula fordetermining magnitude on the Richter scale Dr. N. Subramanian
  23. 23. Intensity of earthquakes• Modified Mercalli Intensity scale (MMI) and MSK scale (Appendix D of Draft IS 1893)• Initially developed early last century by Giuseppe Mercalli.• Both have twelve levels of intensity – Level I – least perceptive – Level XII – most severe Dr. N. Subramanian
  24. 24. Factors Influencing Seismic DamageThe following factors influence theseismic damage:Peak Ground Acceleration (PGA) Amplitude, Duration and frequency of ground vibration, Magnitude, Distance from epicenter Geographical conditions between the epicenter and the site, Soil properties at the site and foundation typeBuilding type and characteristics. Damage to a Steel building in Dr.N.Subramanian Mexico City, 1985 24
  25. 25. Lateral Force Resisting Systems Dr.N.Subramanian 25
  26. 26. Better Performance in Earthquakes Have simple and regular Plans Dr.N.Subramanian 26
  27. 27. Collapse of L-shaped building in Ahmedabad, 2001 Dr. N. Subramanian
  28. 28. Avoid Irregular Configurations Dr.N.Subramanian 28
  29. 29. Avoid Novel Structural Features(If their EQ behavior is not known) Dr.N.Subramanian 29
  30. 30. Geometric vulnerabilities - CCTV Tower, China Dr. N. Subramanian
  31. 31. Response Spectra for Different Strong Earthquakes Dr.N.Subramanian 31
  32. 32. Response Acceleration coefficient as given in IS 1893 (Part 1)-2002 Smoothened Elastic Design Acceleration Response Spectrum (SEDRS) for 5% damping. For Steel structures use 2% damping Dr.N.Subramanian 32
  33. 33. SEISMIC ZONES OF INDIA Dr.N.Subramanian 33
  34. 34. Probabilistic Seismic Hazard Map (PSHM) of India• The National Disaster Management Authority, Govt. Of India, New Delhi has also developed a Probabilistic Seismic Hazard Map (PSHM) of India• e/India-psha-finalreport.pdf Dr. N. Subramanian
  35. 35. Equivalent Lateral Base Shear Force ProcedureEquivalent Lateral Base Shear Force :Where Z= zone factor, I = importance factor, and R= Response reduction Factor I = 1.5 for largely crowded and imp. Buildings, and equal to 1.0 for other buildings. Dr.N.Subramanian 35
  36. 36. Approximate Fundamental PeriodThe approximate fundamental natural period of vibration for amoment resisting frame without brick infill panels is :Ta = 0.085 h0.75 in secondswhere h = height of the building in mFor all other buildings, including moment resisting framebuildings with brick in-fill,Ta = 0.09h / √d in secondswhere d = base dimension of the building at the plinthlevel, along the considered direction of the lateral force, inmeters. Dr.N.Subramanian 36
  37. 37. Equivalent Static Method (seismic coefficient method)Total design seismic base shear if determined by VB = Ah WAh = Design horizontal acceleration spectrum valueW = Seismic weight of the building Dr.N.Subramanian 37
  38. 38. Fundamental natural periods of structures differ over a large rangeAdapted from: Newmark, (1970), Current trends in the Seismic Analysis and Design of HighRise Structures, Chapter 16, in Wiegel, (1970), Earthquake Engineering, Prentice Hall, USA. Dr. N. Subramanian
  39. 39. Distribution of Base Shear to Different Levels of the Building After the base shear force VB is determined it should be distributed along the height of the building (to the various floor levels) using the following expression: After the Base shear is distributed, the frames may be analyzed by any standard computer program to get the internal forces! Dr.N.Subramanian 39
  40. 40. Dynamic AnalysisThe dynamic analysis methods are grouped into:Response spectrum method (multistory buildings, irregular buildings, overhead water ranks and bridge piers are often designed using this method) Time-history response analysis (most important structures such as nuclear reactors, large span structures or very tall buildings are designed using this method). Dr.N.Subramanian 40
  41. 41. EARTHQUAKE DESIGN PHILOSOPHYThe seismic design philosophy as per IS 1893(part 1) is: Minor and frequent earthquakes should not cause any damage to the structure Moderate earthquakes should not cause significant structural damage but could have some non-structural damage Major and infrequent earthquakes should not cause collapseHence design is done for much smaller forces than actual seismic loads.Note that this approach is different than that adopted in the case of wind, dead, live and other loads, where the structure is designed for the actual loads. Dr.N.Subramanian 41
  42. 42. Earthquake design philosophy Dr. N. Subramanian
  43. 43. Seismic Design PhilosophyThough the structure is designed for reduced earthquake loads, thefollowing contributing factors will prevent the collapse of the structure:Over-strength,Redundancy,Ductility Dr.N.Subramanian 43
  44. 44. Ductile and Brittle performance Dr. N. Subramanian
  45. 45. CURRENT DESIGN CODESExpected Performance:The design requirements primarily are intendedto safeguard against major failures and loss oflife, NOT to limit damage, maintain functions, orprovide for easy repairs. Dr.N.Subramanian 45
  46. 46. Performance Based Design (PBD)Future (PBD) Codes will be based on:Desired performance chosen by owner.Reduced business interruptionReduced damage costsCurrent Performance based design documents: Vision 2000 FEMA 356/273 ATC 40 FEMA 310 Dr.N.Subramanian 46
  47. 47. Load CombinationsIn general consider the 8- load combinations:(1) 1.5 (DL + IL) + 1.05(CL or SL)(2) 1.2 (DL + IL) + 1.05(CL or SL) ± 0.6(WL or EL)(3) 1.2 (DL + IL ± WL or EL) + 0.53 (CL or SL)(4) 1.5(DL ± WL or EL)(5) 0.9 DL ± 1.5 (WL or EL)(6) 1.2 (DL + ER)(7) 0.9DL + 1.2 ER(8) DL + 0.35(IL + CL or SL) + ALWhere, DL = Dead load, IL = imposed load (live load), WL = wind load, SL = snow load, CL = crane load (vertical / horizontal), AL = accidental load, ER = erection load and EL = earthquake load. Dr.N.Subramanian 47
  48. 48. Loading Combination for Non- orthogonal buildingsEight additional possibilities should also be considered.(1) ELx + 0.3 ELy(2) 0.3ELx + ELy(3) ELx – 0.3ELy(4) 0.3ELx - ELy(5) – (ELx + 0.3ELy(6) (0.3ELx + ELy)(7) – (ELx – 0.3ELy)(8) – (0.3ELx – ELy) Dr.N.Subramanian 48
  49. 49. Dr. N. Subramanian
  50. 50. Dr. N. Subramanian
  51. 51. Seismically Active regions in India Dr. N. Subramanian
  52. 52. Past Earthquakes in India Four Great earthquakes (M>8) occurred in a span of 53 years from 1897 to 1950; the January 2001 Bhuj earthquake (M7.7) is almost as large Dr. N. Subramanian
  53. 53. Past Earthquakes in India Dr. N. Subramanian
  54. 54. Dr. N. Subramanian