EARTHQUAKE EFFECTS ON TALL BUILDINGS Dr Ravindra Nagar

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

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

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 5

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

Idealized Model of Building m T = 2π rk lle ma s k m k increase building period m bigge rm k 7

Modes of Building Failure 8

RESONANCE 9

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 10

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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 12

SOFT FIRST STOREY CAR PARK WEAK STOREY 13

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 14

Soft first story failure 15

Soft first story failure 16

Weak story failure, Kobe, 1995 17

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

DEFLECTION LATERAL FORCE CODE LIMITS DEFLECTION TO HEIGHT/500 19

Bending 20

Bending 21

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

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 23

High center of mass 24

Falling objects 25

Falling objects, partial wall collapse 26

Falling objects, partial wall collapse 27

FAILURES DUE TO SOIL STRATA 28

SEPTEMBER 19, 1985 MEXICO EARTHQUAKE 29

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 30 MAJOR FACTOR

1985 MEXICO EARTHQUAKE: SOIL AMPLIFICATION 31

1985 MEXICO EARTHQUAKE: CRITICAL STRUCTURES-HOSPITALS 32

1985 MEXICO EARTHQUAKE: ESSENTIAL STRUCTURES-SCHOOLS 33

1985 MEXICO EARTHQUAKE: STEEL FRAME BUILDING 34

1985 MEXICO EARTHQUAKE: POUNDING 35

1985 MEXICO EARTHQUAKE: NUEVA LEON APARTMENT BUILDINGS 36

1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM 37

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Liquefaction, ground failure 40

Liquefaction, ground failure 41

Liquefaction, ground failure 42

q. 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 q. FOOTINGS ON SANDY SOILS SHOW IMMEDIATE SETTELMENTS WHEREAS CLAYS SHOW LONG TERM SETTELMENTS q. CLAYS ARE VERY STIFF WHEN DRY BUT CAN BECOME VERY SOFT WHEN SUBMERGED q. RISE IN WATER TABLE CAN REDUCE THE BEARING CAPACITY SIGNIFICANTLY q. CLAYS EXHIBITSWELLING PRESSURES q. PLACE THE FOUNDATION ON FIRM SOIL 43

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

Column failure 45

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 not isolated 46

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) 47

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). 48

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% 49

BUILDING TYPES IN INDIA 50

SEISMIC VULNERABILITY OF BUILDINGS 51

VULNERABILITY FUNCTIONS If Reconstruction cost = 100% Loss Ratio Damage Grade > 75% Collapse G 5 45 - 60% Destruction incl. Partial G 4 Collapse 30– 45% Moderate Damage G 3 < 30% Low Damage G 2 Reinforcing of masonry buildings lowers loss ratio by 12 -15%, hence to Damage of G 3 or lower. 52

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. 53

BUILDING CODES FOR ENGINEERED CONSTRUCTION 1. 2. 3. 4. 5. IS: 1893 -2002 "Criteria for Earthquake Resistant Design of Structures, Part I (Fifth Revision)" July 2002. IS: 13920 -1993 "Ductile Detailing of Reinforced Concrete Structures subjected to Seismic forces - Code of Practice" November 1993. IS: 4326 -1993 "Earthquake Resistant Design and Construction of Buildings - Code of Practice (Second Revision)" October 1993. Many Good Books Large Nos. of Conference Proceedings 54

GUIDELINES FOR NON-ENGINEERED CONSTRUCTION 1. 2. 3. 4. 5. 6. 7. IS: 4326 -1993 : Earthquake Resistant Design and Construction of Buildings – Code of Practice (Second Revision)” October 1993. IS: 13828 -1993 "Improving Earthquake Resistance of Low Strength Masonry Building - Guidelines" August 1993. IS: 13827 -1993 "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). 55

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) 56

BENEFIT/COST OF SEISMIC RESISTANCE • Extra cost in providing Seismic Resistance Building Masonry RCC framed Buildings in in Cement Mortar 4 -8 storeyed Zone III 1. 5 – 2 % 2. 6 – 3. 2 % Zone IV 3 – 4 % 3. 2 – 4. 0 % Zone V 5 – 6 % 5. 0 – 6. 0 % • 57

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. 58

THANKS 59