Slides Earthquake Resistant Design part2


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This second part discusses about seismic design and detailing

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Slides Earthquake Resistant Design part2

  1. 1. Earthquake Design Considerations By Dr. N. Subramanian 3rd Nov. 2012 Dr. N. Subramanian
  2. 2. Pounding between adjoiningbuildings due to horizontal vibrations Dr. N. Subramanian
  3. 3. More mass onone side causes the floors to twist Dr. N. Subramanian
  4. 4. One-side open ground storey building twists during earthquake shaking Dr. N. Subramanian
  5. 5. Unequal vertical members causebuilding to twist about a vertical axis Dr. N. Subramanian
  6. 6. Waves of different periodsIf the ground is shaken by earthquake waves that have short periods, thenshort period buildings will have large response.Similarly, if the earthquake ground motion has long period waves, then longperiod buildings will have larger response. Dr. N. Subramanian
  7. 7. Soil condition at site may influence damageDifferent BuildingsRespond Differentlyto Same GroundVibration Dr. N. Subramanian
  8. 8. Design Codes IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces 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) Dr. N. Subramanian
  9. 9. Longitudinal steel in Beams Dr. N. Subramanian
  10. 10. Stirrups as per IS 13920 Dr. N. Subramanian
  11. 11. Stirrups with 135 degree hooks at the end are required Dr. N. Subramanian
  12. 12. Lapping of Longitudinal bars Dr. N. Subramanian
  13. 13. Soft storey created by open GF car park Dr. N. Subramanian
  14. 14. Earthquakes do not kill people; man in his role as a builder, kills people.Total Horz. EQ Force increases downwards along its heightCollapse of partially open GF building in Bhuj EQ, with vertical split atthe middle! Dr. N. Subramanian
  15. 15. Possible plastic collapse mechanisms Dr. N. Subramanian
  16. 16. Strong-Column Weak –beam Principle Dr. N. Subramanian
  17. 17. Circular spiral columns Vs Rect.Columns in the same building during 1971 SFO EQ Dr. N. Subramanian
  18. 18. Column reinforcement Dr. N. Subramanian
  19. 19. Detailing of columns in seismic zones 180 links are necessary to prevent the 135 tie from bulging outwards Dr. N. Subramanian
  20. 20. Shear failure of columnLarge spacing of ties and lack of 135 hook ends causedbrittle failure of columns during 2001 Bhuj earthquake Dr. N. Subramanian
  21. 21. Buckling of column bars Dr. N. Subramanian
  22. 22. Confinement steel in columns Dr. N. Subramanian
  23. 23. Correct location for column splices Dr. N. Subramanian
  24. 24. Short Column effectShort columns are stiffer and attract larger forces duringearthquakes – this must be accounted for in design Dr. N. Subramanian
  25. 25. Short column effect Dr. N. Subramanian
  26. 26. Short column effect Dr. N. Subramanian
  27. 27. Detailing of short columns Dr. N. Subramanian
  28. 28. Beam-Column joints should be designed and detailed properly Dr. N. Subramanian
  29. 29. Detailing of beam-column jointsTies with 135 degree hooks resists the ill effects ofdistortion of joints Dr. N. Subramanian
  30. 30. Pull-Push forces cause two problems Dr. N. Subramanian
  31. 31. Three stage procedure to provide horizontal ties in joints Dr. N. Subramanian
  32. 32. Anchorage of beam bars in interior joints Dr. N. Subramanian
  33. 33. Anchorage of beam bars in exterior joints Dr. N. Subramanian
  34. 34. Shear walls are to be placedsymmetrically to avoid twist Dr. N. Subramanian
  35. 35. Detailing of shear walls as per IS 13920 Dr. N. Subramanian
  36. 36. Collapse of nominally connected water tankIS 1893 – Connections designed for five times the designhorizontal acceleration coefficient Dr. N. Subramanian
  37. 37. Bare Vs infilled framePredominant frame action Predominant shear action Dr. N. Subramanian
  38. 38. Effect of infill walls Dr. N. Subramanian
  39. 39. Collapse of intermediate storey in 6 storey building, Bhuj, 2001 Dr. N. Subramanian
  40. 40. Improper Anchorage into stiff RCelevator core walls in Ghandhidham Dr. N. Subramanian
  41. 41. Effect of StaircasesDiagonal slabs or beams in staircases attract largeseismic forces-sliding supports limits the seismic forces Dr. N. Subramanian
  42. 42. Brick Buildings- Horz. Bands Dr. N. Subramanian
  43. 43. Base isolation of buildings to reduce shaking Dr. N. Subramanian
  44. 44. Base Isolation Technology One of the most significant developments in earthquake engineering in the past 35 years. It provides the design profession the ability to design a building that is “operational” after a major earthquake Base isolated structure Conventional structure Dr.N.Subramanian 44
  45. 45. BASE ISOLATOR Base isolators may be either coiled springs or laminated rubber- bearing pads, made of alternate layers of steel and rubber, and have a low lateral stiffness. Dr.N.Subramanian 45
  46. 46. Examples of Base Isolated SystemsBase Isolated LA City HallBase isolator being installed. during a seismicevent. Every isolator will extend in anydirection 21 inches. San Francisco Airport International Terminal is the World’s Largest Base Isolated Building Dr.N.Subramanian 46
  47. 47. Energy Absorbing Devices• “Passive energy dissipation is an emerging technology that enhances the performance of buildings by adding damping to buildings.”• (ASCE/SEI 41-06, pg 280) Dr.N.Subramanian 47
  48. 48. Commonly used dampers Viscous dampers (They consist of a piston-cylinder arrangement filled with a viscous silicon based fluid, which absorbs the energy) Friction dampers (energy is absorbed by the friction between two layers, which are made to rub against each other). Hysteretic dampers (energy is absorbed by yielding metallic parts) Visco-elastic dampers (containing visco-elastic material, sandwiched between two steel plates, which undergoes shear deformation, thus dissipating energy. Dr.N.Subramanian 48
  49. 49. Other Types Of Dampers Tuned mass dampers (TMD)- They are extra masses attached to the structure by a spring- dashpot system and designed to vibrate out of phase with the structure. Tuned liquid dampers (TLD) – They are essentially water tanks mounted on structures and dissipate energy by the splashing of the water. Hydraulic activators- They are active vibration control devices and have a sensor to sense the vibration and activate the activator to counter it. - Require external energy source and are expensive. Dr.N.Subramanian 49
  50. 50. Why Use Dampers?Dampers dramatically decrease earthquake induced motion . Less displacement : over 50% reduction in drift in many cases Decreased base shear and inter-story shear, up to 40% Much lower “g” forces in the structure. Equipment keeps working and people are not injured Reduced displacements and forces can mean less steel. This offsets the damper cost and can sometimes even reduce overall cost. Dr.N.Subramanian 50
  51. 51. Viscous Damper Dr.N.Subramanian 51
  52. 52. Example- Viscous damper Dr. N. Subramanian
  53. 53. Tuned Mass Damper (TMD)Taipei 101, the worlds second tallest skyscraper is equipped with a tuned massdamper. This 18 feet dia.,730-ton TMD acts like a giant pendulum to counteract thebuildings movement--reducing sway due to wind by 30 to 40 %. Cost: $4 million Dr.N.Subramanian 53
  54. 54. Dr.N.Subramanian 54