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Tall buildings

  1. 1. A VERY SIMPLE UNDERSTANDING By Yasaswini Laxmi.V
  2. 2. Why should we know about TALL BUILDINGS???
  3. 3. TYPES OF TALL BUILDINGS
  4. 4. WHY EARTHQUAKE RESISTANCE?
  5. 5. CASE STUDY: BHUJ EARTHQUAKE GUJARAT Date- Time : 26th January 2001 03:16:40 Location 23.41N70.23E : Magnitude : 7.7 Depth : 16 Kms : Source : USGS NEIC Death toll : 19,727 Injured 166,000 Homeless :600,000 Economic Losses : $1.3 billion
  6. 6. The earthquake design philosophy may be summarized as follows. • Under minor but frequent shaking, the main members of the building that carry vertical and •horizontal forces should not be damaged • Under moderate but occasional shaking, the main members may sustain repairable damage. •Under strong but rare shaking, the main members may sustain severe (even irreparable) damage, but the building should not collapse.
  7. 7. STEPS IN SEISMIC DESIGN: A.PLANNING STAGE: 1. Plan the building and structures in a symmetrical way both in plan (horizontal axis) and elevation. (vertical axis). 2. Avoid open ground (Soft storey) which is used for car parking. 3. Avoid weak storey and provide strong diaphragm. That is thinner slabs and flat slabs are to be avoided. 4. Provide openings for doors and windows at a distance of min 0.6 m from the column edges. Follow the IS code 4326 –page 11-for more details for masonry structures. 5. Follow the codal provisions for location of water tanks and swimming pools etc which will create a vast difference of Centre of mass.
  8. 8. 6. Conduct soil test and investigate the soil nature to avoid soil liquefactions. 7. Follow the IS codal and NBC provisions while in Planning stage which will aid more safer structures. 8. Select good materials-concrete ingredients, brick, steel etc. Specially steel having an elongation of above 14% and yield strength of 415N/mm^2. 9. The yield stress shall not be greater than 415N/mm^2. Steel having an yield strength 500 N/mm^2 may be used provided the % of elongation is above 14%. Make sure before approving it by means of lab. test results. 10. Provide plinth beam at ground level , lintel and roof band (masonry structures). 11. Do not lower the beams in RCC frames at lintel level to have financial savings since the load path will not be there.
  9. 9. 1) Building Plan Efficient Bearing of Earthquake Forces 2) Heavy mass at top should be avoided NO YES Smaller water tank at top is preferred
  10. 10. 3) Large projections not allowed 4) Floating column not allowed 5) Soft Storey at Ground Floor
  11. 11. 6) Foundation (Isolated footings) Tie Beams Similarly can have RAFT, STRIP , STRAP foundations
  12. 12. KEY CONCEPT TO EARTHQUAKE RESISTANT STRUCTURES  Ductility  Divertingthe forces of an earthquake safely
  13. 13. HOW TO INCREASE DUCTILTY?  Ductility of a section can be increased by :  Decrease the % of the tension steel.  Increase the % of compression steel.  Else provide as per steel beam theory.  Increase in compressive strength of concrete.  Increase in transverse shear reinforcement.  For ductile detailng –IS 13920- 1993.
  14. 14. How to divert the forces safely?  Dissipation of forces through reliable load paths: Primary load paths Horizontal vertical
  15. 15. Horizontal load path  Tuned liquid dampeners (TLD)  Self righting buildings  Tuned mass dampeners (TMD)  Base isolation
  16. 16. Tuned liquid dampeners (TLD)
  17. 17. Self righting buildings
  18. 18. Tuned mass dampeners (TMD)
  19. 19. Base isolation
  20. 20. Vertical load path: Sesimic resistance of building can be enhanced mainly by:  Providing shear walls .  Tubular designs(tube in tube/tube in tubes).  Providing bracing in walls.
  21. 21. BRACED STRUCTURES DIAGONAL BRACING X- BRACING V- BRACING INVERTED V- BRACING K- BRACING
  22. 22. TUBED  STRUCTURE • WILLIS TOWER (CHICAGO)
  23. 23. SHEAR WALL CONSTRUCTION AND DESIGN
  24. 24. What is a Shear Wall? Buildings often have vertical plate-like RC walls called Shear Walls in addition to slabs, beams and columns.
  25. 25. PURPOSE OF A SHEAR WALL Shear walls provide large strength and stiffness to buildings in the direction of their orientation, which significantly reduces lateral sway of the building and there by enhances the earthquake resistance of the structure.
  26. 26. How shear forces work?
  27. 27. Architectural Aspects of Shear Walls  Shear walls should be provided along preferably both length and width.  If they are provided along only one direction, a proper grid of beams and columns in the vertical plane (called a moment-resistant frame) must be provided along the other direction to resist strong earthquake effects.
  28. 28.  Door or window openings can be provided in shear walls, but their size must be small to ensure least interruption to force flow through walls.  Shear walls in buildings must be symmetrically located in plan to reduce ill-effects of twist in buildings.  Shear walls are more effective when located along exterior perimeter of the building.
  29. 29. GEOMETRY OF SHEAR WALLS  Shear walls are oblong in cross-section, i.e., one dimension of the cross-section is much larger than the other.  While rectangular cross-section is common, L- and U-shaped sections are also used.
  30. 30. REINFORCEMENT DETAILS  The minimum area of reinforcing steel to be provided is 0.0025 times the cross- sectional area, along each of the horizontal and vertical directions.  This reinforcement should be distributed uniformly across the wall cross-section as vertical and horizontal grids.
  31. 31.  The vertical and horizontal reinforcement in the wall can be placed in one or two parallel layers called curtains.  Horizontal reinforcement needs to be anchored at the ends of walls.
  32. 32.  Under the large overturning effects caused by horizontal earthquake forces, edges of shear walls experience high compressive and tensile stresses.  To ensure that shear walls behave in a ductile way, concrete in the wall end regions must be reinforced in a special manner to sustain these load reversals without loosing strength.
  33. 33. ADVANTAGES OF SHEAR WALLS  Shear walls are easy to construct, because reinforcement detailing of walls is relatively straight-forward and therefore easily implemented at site.  Shear walls are efficient, both in terms of construction cost and effectiveness in minimizing earthquake damage in structural and non-structural elements (like glass windows and building contents).
  34. 34. TUBED STRUCTURES
  35. 35. What are TUBED STRUCTURES?  A three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation.
  36. 36. The tube system concept is based on the idea that a building can be designed to resist lateral loads by designing it as a hollow cantilever perpendicular to the ground.
  37. 37. Where do we use tubed structures? skyscraper design and construction
  38. 38. •In the simplest incarnation of the tube, the perimeter of the exterior consists of closely spaced columns that are tied together with deep spandrel beams through moment connections.
  39. 39. ADVANTAGES  Framed tubes allow fewer interior columns, and so create more usable floor space.  It can take a variety of floor plan shapes from square and rectangular, circular, and freeform giving scope for architecture.
  40. 40. TYPES OF TUBED STRUCTURES  Bundled Tube  Framed Tube  Braced Tube  Tube in Tube
  41. 41. BUNDLED TUBE
  42. 42. FRAMED TUBE
  43. 43. BRACED TUBE
  44. 44. TUBE IN TUBE
  45. 45. References : •IS 1893 (2002) – Criteria for earthquake resistant design of structures •IS 13920 (1993) – Ductile detailing of reinforced concrete structures subjected to seismic forces •IS 4326 (1993) – Earthquake resistant design and construction of buildings •Tall Buildings by Mark Fintel
  46. 46. Web pages: •Building structure http://www.nd.edu/~tkijewsk/Instruction/solution.h tml •Fundamental rules for earthquake design http://www.samco.org/download/reports/rules.pdf •IITK, BMTPC Earthquake Tips by Prof.C.V.R.Murthy IIT Kanpur. •http://www.bstn.co.nr

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