This document discusses various earthquake design considerations for buildings. It notes that buildings with unequal mass distribution, soft ground floors, or uneven structural elements can twist during shaking. Different buildings respond differently to ground vibrations depending on the period of earthquake waves. Indian design codes like IS 13920 and IS 1893 provide guidelines for ductile reinforcement details. Proper detailing of beams, columns, joints, walls and foundations is necessary to resist seismic forces. Base isolation and damping devices can also help reduce earthquake shaking and damage.

1. Earthquake Design Considerations
By Dr. N. Subramanian
3rd Nov. 2012
Dr. N. Subramanian

2. Pounding between adjoining
buildings due to horizontal vibrations
Dr. N. Subramanian

3. More mass on
one side causes the floors to twist
Dr. N. Subramanian

4. One-side open ground storey building
twists during earthquake shaking
Dr. N. Subramanian

5. Unequal vertical members cause
building to twist about a vertical axis
Dr. N. Subramanian

6. Waves of different periods
If the ground is shaken by earthquake waves that have short periods, then
short period buildings will have large response.
Similarly, if the earthquake ground motion has long period waves, then long
period buildings will have larger response.
Dr. N. Subramanian

7. Soil condition at site may influence
damage
Different Buildings
Respond Differently
to Same Ground
Vibration
Dr. N. Subramanian

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. Longitudinal steel in Beams
Dr. N. Subramanian

10. Stirrups as per IS 13920
Dr. N. Subramanian

11. Stirrups with 135 degree hooks at the
end are required
Dr. N. Subramanian

12. Lapping of Longitudinal bars
Dr. N. Subramanian

13. Soft storey created by open GF car
park
Dr. N. Subramanian

14. Earthquakes do not kill people;
man in his role as a builder, kills
people.
Total Horz. EQ Force increases downwards along its height
Collapse of partially open GF building in Bhuj EQ, with vertical split at
the middle! Dr. N. Subramanian

15. Possible plastic collapse mechanisms
Dr. N. Subramanian

16. Strong-Column Weak –beam Principle
Dr. N. Subramanian

17. Circular spiral columns Vs Rect.
Columns in the same building during
1971 SFO EQ
Dr. N. Subramanian

18. Column reinforcement
Dr. N. Subramanian

19. Detailing of columns in seismic zones
180 links are necessary to prevent the
135 tie from bulging outwards
Dr. N. Subramanian

20. Shear failure of column
Large spacing of ties and lack of 135 hook ends caused
brittle failure of columns during 2001 Bhuj earthquake
Dr. N. Subramanian

21. Buckling of column bars
Dr. N. Subramanian

22. Confinement steel in columns
Dr. N. Subramanian

23. Correct location for column splices
Dr. N. Subramanian

24. Short Column effect
Short columns are stiffer and attract larger forces during
earthquakes – this must be accounted for in design
Dr. N. Subramanian

25. Short column effect
Dr. N. Subramanian

26. Short column effect
Dr. N. Subramanian

27. Detailing of short columns
Dr. N. Subramanian

28. Beam-Column joints should be designed
and detailed properly
Dr. N. Subramanian

29. Detailing of beam-column joints
Ties with 135 degree hooks resists the ill effects of
distortion of joints
Dr. N. Subramanian

30. Pull-Push forces cause two problems
Dr. N. Subramanian

31. Three stage procedure to provide
horizontal ties in joints
Dr. N. Subramanian

32. Anchorage of beam bars in interior
joints
Dr. N. Subramanian

33. Anchorage of beam bars in exterior
joints
Dr. N. Subramanian

34. Shear walls are to be placed
symmetrically to avoid twist
Dr. N. Subramanian

35. Detailing of shear walls as per IS
13920
Dr. N. Subramanian

36. Collapse of nominally connected
water tank
IS 1893 – Connections designed for five times the design
horizontal acceleration coefficient
Dr. N. Subramanian

37. Bare Vs infilled frame
Predominant frame action Predominant shear action
Dr. N. Subramanian

38. Effect of infill walls
Dr. N. Subramanian

39. Collapse of intermediate storey in 6
storey building, Bhuj, 2001
Dr. N. Subramanian

40. Improper Anchorage into stiff RC
elevator core walls in Ghandhidham
Dr. N. Subramanian

41. Effect of Staircases
Diagonal slabs or beams in staircases attract large
seismic forces-sliding supports limits the seismic forces
Dr. N. Subramanian

42. Brick Buildings- Horz. Bands
Dr. N. Subramanian

43. Base isolation of buildings to reduce
shaking
Dr. N. Subramanian

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. 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. Examples of Base Isolated Systems
Base Isolated LA City Hall
Base isolator being installed. during a seismic
event. Every isolator will extend in any
direction 21 inches.
San Francisco Airport International
Terminal is the World’s Largest Base
Isolated Building
Dr.N.Subramanian 46

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. 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. 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. 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. Viscous Damper
Dr.N.Subramanian 51

52. Example- Viscous damper
Dr. N. Subramanian

53. Tuned Mass Damper (TMD)
Taipei 101, the world's second tallest skyscraper is equipped with a tuned mass
damper. This 18 feet dia.,730-ton TMD acts like a giant pendulum to counteract the
building's movement--reducing sway due to wind by 30 to 40 %. Cost: $4 million
Dr.N.Subramanian 53

54. Dr.N.Subramanian 54