1. EARTHQUAKE EFFECTS ON TALL BUILDINGS Dr. Ravindra Nagar M
EARTHQUAKE EFFECTS ON TALL BUILDINGS Dr. Ravindra Nagar M.tech(IIT Delhi),PhD(Liverpool) Professor Department of Structural Engineering Malaviya National Institute of Technology Jaipur (India)  

4. Underlying Physics Newton’s Second Law F = ma
where m = mass of building
a = acceleration of ground
ground acceleration
Question: What do the physics tell us about the magnitude of the forces that different types of buildings feel during an earthquake?

5. What is really happening?
F is known as an inertial force,
created by building's tendency to remain at rest, in its original position, although the ground beneath it is moving F
Engineering representation of earthquake force

6. Period and Frequency T = 1 / f
Frequency (f) = number of complete cycles of vibration per second
Period (T) = time needed to complete one full cycle of vibration
T = 1 / f

7. Idealized Model of Buildingk m
T = 2π
smaller k k m
increase building period k m
bigger m

8. Modes of Building Failure

9. RESONANCE

10. Typical Natural Period
Natural Period of Buildings
Each building has its own natural period (frequency)
Building Height
Typical Natural Period
Natural Frequency
2 story
0.2 seconds
5 cycles/sec
5 story
0.5 seconds ?
10 story
1.0 seconds
20 story
2.0 seconds
30 story
3.0 seconds
slower shaking

12. Example: Mexico City earthquake of September 19, 1985
RESONANCE
Resonance = frequency content of the ground motion is close to building's natural frequency
tends to increase or amplify building response
building suffers the greatest damage from ground motion at a frequency close or equal to its own natural frequency
Example: Mexico City earthquake of September 19, 1985
majority of buildings that collapsed were around 20 stories tall
natural period of around 2.0 seconds
other buildings, of different heights and different natural frequencies, were undamaged even though located right next to damaged 20 story buildings

13. SOFT FIRST STOREY
CAR PARK WEAK STOREY

14. BENDING MOMENTS IN COLUMNS AND JOINTS
LATERAL FORCE
MAXIMUM MOMENTS AT JOINT
MAXIMUM MOMENTS ON SOFT STOREY
SITUATION CRITICAL IF SOFT STOREY IS DOUBLE HEIGHT

15. Soft first story failure

16. Soft first story failure

17. Weak story failure, Kobe, 1995

18. BENDING MOMENTS IN COLUMNS AND JOINTS
BENDING FAILURE
BENDING MOMENTS IN COLUMNS AND JOINTS
LATERAL FORCE
MAXIMUM MOMENTS AT JOINT
MAXIMUM MOMENTS ON SOFT STOREY

19. DEFLECTION
LATERAL FORCE
CODE LIMITS DEFLECTION TO HEIGHT/500

20. Bending

21. Bending

22. PLINTH BEAM
LATERAL FORCE
PLINTH BEAM CUTS EFFECTIVE LENGTH OF COLUMN

23. HIGH CENTER OF MASS SWIMMING POOL OR WATER TANK AT TOP
LATERAL FORCE
MOMENTS ARE PROPORTIONAL TO DISTANCE FROM THE BOTTOM
MOMENTS ARE PROPORTIONAL TO MASS

24. High center of mass

25. Falling objects

26. Falling objects, partial wall collapse

27. Falling objects, partial wall collapse

28. FAILURES DUE TO SOIL STRATA

29. SEPTEMBER 19, 1985 MEXICO EARTHQUAKE

30. 1985 MEXICO EARTHQUAKE EPICENTER LOCATED 240 KM FROM MEXICO CITY
400 BUILDINGS COLLAPSED IN OLD LAKE BED ZONE OF MEXICO CITY
SOIL-STRUCTURE RESONANCE IN OLD LAKE BED ZONE WAS A MAJOR FACTOR

31. 1985 MEXICO EARTHQUAKE: SOIL AMPLIFICATION

32. 1985 MEXICO EARTHQUAKE: CRITICAL STRUCTURES--HOSPITALS

33. 1985 MEXICO EARTHQUAKE: ESSENTIAL STRUCTURES--SCHOOLS

34. 1985 MEXICO EARTHQUAKE: STEEL FRAME BUILDING

35. 1985 MEXICO EARTHQUAKE: POUNDING

36. 1985 MEXICO EARTHQUAKE: NUEVA LEON APARTMENT BUILDINGS

37. 1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM

40. Liquefaction, ground failure

41. Liquefaction, ground failure

42. Liquefaction, ground failure

43. GEOTECHNICAL INVESTIGATION IS A MUST FOR EVERY SITE AS SOIL IS WEAKEST MATERIAL IN THE SYSTEM AND THE FAILURE IS SUDDEN AND OFTEN LEADS TO COLLAPSE
FOOTINGS ON SANDY SOILS SHOW IMMEDIATE SETTELMENTS WHEREAS CLAYS SHOW LONG TERM SETTELMENTS
CLAYS ARE VERY STIFF WHEN DRY BUT CAN BECOME VERY SOFT WHEN SUBMERGED
RISE IN WATER TABLE CAN REDUCE THE BEARING CAPACITY SIGNIFICANTLY
CLAYS EXHIBITSWELLING PRESSURES
PLACE THE FOUNDATION ON FIRM SOIL

44. TYPE OF FOUNDATIONS AND THEIR SESMIC RESPONSE
ISOLATED FOOTINGS POOR
PROVIDE TIE BEAMS
COMBINED FOOTINGS FAIR
RAFT FOUNDATIONS BETTER
PILE FOUNDATIONS BEST

45. Column failure

46. Base Isolated Buildings
Supported by a series of bearing pads placed between the building and its foundation
Most of deformation in isolators and acceleration of the building is reduced = less damage
isolated
not isolated

47. Bay Area Base-Isolated Buildings
U.S. Court of Appeals, San Francisco Survived 1906 earthquake (seismic retrofit 1994)
San Francisco City Hall Steel frame with stone exterior (seismic retrofit 1994)

48. EARTHQUAKE PREDICTION Prediction as a means of saving human lives in earthquakes is extremely unreliable at present For saving economic losses it will be utterly useless (Seismologically weak buildings and structures remain liable to catastrophic behaviour during strong earthquakes).

49. EARTHQUAKE HAZARD ZONES 2002
Zone V MM IX or more
“ IV MM VIII
“ III MM VII
Zone II MM VI
“ I MM V or less
together now make
Zone II MM VI or less
Area under the zones
V 12%
IV 18%
III ~27%
Table damageable
~ 57%

50. BUILDING TYPES IN INDIA

51. SEISMIC VULNERABILITY OF BUILDINGS

52. VULNERABILITY FUNCTIONS
If Reconstruction cost = 100%
Loss Ratio Damage Grade
> 75% Collapse G5
% Destruction
incl. Partial G4
Collapse
30– 45% Moderate Damage G3
< 30% Low Damage G2
Reinforcing of masonry buildings
lowers loss ratio by 12-15%,
hence to Damage of G3 or lower.

53. ASSESSMENT OF LOSSES
Direct Damage- Damages to fixed assets, and inventories of finished and
semifinished goods, raw materials, and spare parts.
Indirect Damage-Indirect losses are measured in montetary, non- physical,
terms and may include, among others, the following:
- Increased operational expenditure due to the destruction of physical
infrastructure
-Additional costs incurred in transportation (alternate routes longer than normal
routes).
- Increased costs for providing services
-  Loss of corporate income as a result of the inability to provide services, such
as utilities,
-   Loss of personal income due to total or partial loss of means of livelihood. 
-   Unexpected expenditures related to health and hygien.
-   Loss of production of industry destroyed, and to suppliers and purchasers.
The indirect losses mostly occur resulting from Direct damages.
Prevention or minimization of direct physical damage will certainly reduce the
indirect losses also in a big way, hence the critical importance of engineering
intervention.

54. BUILDING CODES FOR ENGINEERED CONSTRUCTION
IS: "Criteria for Earthquake Resistant Design of Structures, Part I (Fifth Revision)" July 2002.
IS: "Ductile Detailing of Reinforced Concrete Structures subjected to Seismic forces - Code of Practice" November 1993.
IS: "Earthquake Resistant Design and Construction of Buildings - Code of Practice (Second Revision)" October 1993.
Many Good Books
Large Nos. of Conference Proceedings

55. GUIDELINES FOR NON-ENGINEERED CONSTRUCTION
IS: :Earthquake Resistant Design and Construction of Buildings – Code of Practice (Second Revision)” October 1993.
IS: "Improving Earthquake Resistance of Low Strength Masonry Building - Guidelines" August 1993.
IS: "Improving Earthquake Resistance of Earthen Buildings- Guidelines" October 1993.
Arya A.S. et al, Earthquake Resistant Non-Engineered Construction, Monograph Pub. by International Association for Earthquake Engineering, 1980, Revised 1986 (translated into Spanish for use in various Spanish countries).
Arya A.S., Protection of Educational Buildings in Seismic Areas, Digest 13, Pub. by UNESCO,Bangkok, 1987 (translated into Persian for use in Iran).
Guidelines–Pub. by BMTPC, Ministry of Urban Affairs & Employment, Government of India after Jabalpur and Chamoli Earthquakes.
Guidelines-Pub. By Gujarat State Disaster Management Authority, (GSDMA) Ghandinagar after Kachchh earthquake in Gujarat (authored by Dr. A.S. Arya).

56. RETROFITTING STRATEGY FOR EXISTING CONSTRUCTIONS
Priority - I. Area under Seismic Zones V and IV, 
(a)   Buildings: The following and others to be identified:
(i) Instructional, laboratory and library buildings of educational institutions
(schools, colleges, institutes and Universities).
(ii) Hospitals including wards, dispensaries, clinics, etc.
(iii) Congregation halls, temples, churches, cinemas, theatres etc.
(iv)Residences of VIP's and top administrative officers in the districts (Collector,
SP, CMO and the like needed for immediate Response
(b)   Service Structures & Infrastructure: The following among others:
(i)  Water tanks and towers
(ii) Telephone exchanges, fire stations, water supply pump houses
(iii) Bridges and culverts
(iv) Electric power houses and substations
(v) Monuments, Heritage Buildings, Museums
(vi) Critical and Hazardous industries
(vii) Railway stations, Airport buildings and towers
Priority – II – Area under Seismic Zone III (As above)

57. BENEFIT/COST OF SEISMIC RESISTANCE
Extra cost in providing Seismic Resistance
Building Masonry RCC framed Buildings
in in Cement Mortar storeyed  
Zone III – 2 % – 3.2 %
Zone IV – 4 % – 4.0 %
Zone V – 6 % – 6.0 %

58. CONCLUSION
Carry out the engineering, architecture and planning measures
- Land use zoning.
- Planning of habitat,
- Implementation of building codes in all new constructions, and
- seismic retrofitting of existing buildings and infrastructure.
Create the supportive structure of
- public awareness,
- education and training
- research and development about the safety from earthquake hazard.
Appropriate policy, financial and institutional support at national and state levels
need to be provided for putting this strategy into a workable action plan.

59. THANKS