EARTHQUAKES AND EARTHQUAKE-RESISTANT DESIGN OF STRUCTURES

by

Dr. R.S. Jangid Associate Professor

Department of Civil Engineering, Indian Institute of Technology Bombay

Powai, Mumbai – 400 076 (India).

SCOPE OF PRESENTATION EARTHQUAKE AND ITS

CHARACTERIZATION EARTHQUAKE-RESISTANT DESIGN REPAIR & RETROFITTING OF

STRUCTURES EARTHQUAKE ANALYSIS OF STRUCTURES ADVANCED TECHNOLOGIES

EARTHQUAKE An earthquake may be simply described as a sudden shaking phenomenon of the earth's surface due to disturbance inside the earth.

CLASSIFICATIONS AND CAUSES OF EARTHQUAKE

Tectonic Earthquakes Non-tectonic Earthquakes

TECTONIC EARTHQUAKES

Due to disturbances or adjustments of geological formations taking place in the earth's interior. Due to slip along geological faults. Less frequent. More intensive. More destructive in nature.

ELASTIC REBOUND THEORY

NON-TECTONIC EARTHQUAKES

Due to external or surfacial causes such as: Volcanic eruptions Huge waterfalls Occurrence of sudden and major landslides Man-made explosions Impounding in dams and reservoirs Collapse of caves, tunnels etc. Very frequent, minor in intensity generally not destructive in nature.

EARTHQUAKE TERMINOLOGY

Seismograms Focus or Hypocentre Epicentre Focal Depth Hypocentral Distance Epicentral Distance Isoseismal Coseismal

EARTHQUAKE PHENOMENON

EARTHQUAKE WAVES

P Waves: Primary waves, Longitudinal waves, etc.

Speed 8 to 13 km/s

S Waves: Shear waves, Transverse waves, etc.

Speed 5 to 7 km/s

L Waves: Long waves or Surface waves, etc.

Speed 5 to 7 km/s

INTENSITY OF EARTHQUAKE Degree of destruction caused by it

Severity of the shaking of ground

MEASUREMENT OF EARTHQUAKE

Magnitude

Intensity - (MMI Scale) I to XII

M A G N I T U D E O F E A R T H Q U A K E R e l a t e d t o t h e a m o u n t o f e n e r g y r e l e a s e d b y t h e

g e o l o g i c a l r u p t u r e . M e a s u r e o f t h e a b s o l u t e s i z e o f t h e e a r t h q u a k e ,

w i t h o u t r e f e r e n c e t o d i s t a n c e f r o m t h e e p i c e n t r e . R i c h t e r ( 1 9 5 8 ) d e f i n e d m a g n i t u d e a s t h e l o g a r i t h m t o

t h e b a s e 1 0 o f t h e l a r g e s t d i s p l a c e m e n t o f a s t a n d a r d s e i s m o g r a p h s i t u a t e d 1 0 0 k m f r o m t h e f o c u s .

L a r g e s t m a g n i t u d e o f e a r t h q u a k e r e c o r d e d = 8 . 9

Log E M10 4 8 1 5 . .

( E = E n e r g y i n j o u l e s ; M = M a g n i t u d e )

Energy Magnitude Relationship

4 5 6 7 8 9 101E10

1E11

1E12

1E13

1E14

1E15

1E16

1E17

1E18

1E19

1E20

E

nerg

y R

ele

ase

d (

J)

Magnitude

Energy release increases by 32 times with increase of 1 magnitude

INTENSITY OF EARTHQUAKE

Measure of the observed damage at a particular location

Vary with distance from the epicentre and will depend on local ground conditions

Measured on the scale of intensity which is Modified Mercalli Intensity (MMI).

MMI is measured on Roman I to XII scale.

TABLE 1.1: MODIFIED MERCALLI INTENSITY SCALE (ABRIDGED).

I Not felt except by a very few under specially favourable circumstances

II Felt only by a few persons at rest, specially on upper floors of buildings; and delicately

suspended objects may swing.

III Felt quite noticeably indoors, specially on upper floors of buildings but many people do not

recognise it as an earthquake; standing motor cars may rock slightly; and vibrations may be

felt like the passing of a truck.

IV During the day felt indoors by many, outdoors by a few, at night some awakened; dishes,

windows, doors disturbed; walls make creaking sound, sensation like heavy truck striking

the building; and standing motor cars rock noticeably.

V Felt by nearly everyone; many awakened; some dishes, windows, etc, broken; a few

instances of cracked plaster; unstable objects overturned; disturbance of trees, poles and

other tall objects noticed sometimes; and pendulum clocks may stop.

VI Felt by all, many frightened and run outdoors; some heavy furniture moved; a few instances

of fallen plaster or damaged chimneys; and damage slight.

VII Everybody runs outdoors, damage negligible in buildings of good design and construction;

slight to moderate in well built ordinary structures; and some chimneys broken, noticed by

persons driving motor cars.

VIII Damage slight in specially designed structures; considerable in ordinary but substantial buildings with partial collapse; very heavy in poorly built structures; panel walls thrown out of framed structures; falling of a chimney, factory stacks, columns, monuments, and walls; heavy furniture overturned, sand and mud eject in small amounts; changes in well water; and disturbs persons driving motor cars

IX Damage considerable in specially designed structures; well designed framed structures thrown out of plumb; very heavy in substantial buildings with partial collapse; building shifted off foundations; ground cracked conspicuously; and underground pipes broken.

X Some well built wooden structures destroyed; most masonry and framed structures with foundations destroyed; ground badly cracked; rails bent; landslides considerable from river banks and steep slopes; shifted sand and mud; and water splashed over banks.

XI Few, if any, masonry structures remain standing; bridges destroyed; broad fissures in ground, underground pipelines completely out of service; earth slumps and landslips in soft ground; and rails bent greatly.

XII Total damage; waves seen on ground surfaces; lines of sight and levels distorted; and objects thrown upward into the air.

Earthquake/Inertia Forces

ACCELERATIONACCELERATIONACCELERATIONACCELERATION

DECELERATIONDECELERATIONDECELERATIONDECELERATION

E A R T H Q U A K E F O R C E

F o r c e d u e t o e a r t h q u a k e i s

)( tCoefficienSeismicWag

WF

W = w e i g h t o f s t r u c t u r e ; g = a c c e l e r a t i o n d u e t o g r a v i t y ; a = p e a k e a r t h q u a k e a c c e l e r a t i o n .

I S : 1 8 9 3 - 1 9 8 4 p r o v i d e s t h e g e n e r a l p r i n c i p l e s a n d d e s i g n c r i t e r i a f o r e a r t h q u a k e l o a d s .

EL-CENTRO, 1940 EARTHQUAKE

0 5 10 15 20 25 30-30

-20

-10

0

10

Dis

pla

ce

me

nt (cm

)

Time (sec)

-40

-20

0

20

40

Ve

locity (

cm

/se

c)

-0.4

-0.2

0.0

0.2

0.4

Acce

lera

tio

n (

g)

(Before Earthquake)

(After Earthquake)

Shear WallShear Wall

Cripple WallCripple Wall

FoundationFoundationFloorDiaphragm

FloorDiaphragm

Roof DiaphragmRoof Diaphragm

House Elements Resist Horizontal Forces

f1

f2

f3

fsum = f1 + f2 + f3fsum = f1 + f2 + f3

Damage Resulting from Base Shear

PREDICTION OF EARTHQUAKES Cannot be predicted so far. Short time warning after arrival of

P-waves. Fore Shocks (minor tremors

before major quake) Peculiar behaviour of Snakes,

Rats etc.

BEFORE AN EARTHQUAKEBEFORE AN EARTHQUAKE

1. Store heavy objects near ground or floor.

2. Secure tall objects, like bookcases to the wall.

3. Secure gas appliances to prevent broken gas lines

and fires.

4. Learn where your exits, evacuation route, and

meeting places are. Know the safe spot in each

room.

5. Keep emergency items , such as a flashlight, first

aid kit and spare clothes, food in your car or office.

DURING AN EARTHQUAKEDURING AN EARTHQUAKE

1. If indoors, stay in the building.

2. Take shelter under solid furniture, i.e. tables or desks,

until the shaking stops.

3. Keep away from overhead fixtures, windows, cabinets

and bookcases or other heavy objects that could fall.

Watch for falling plaster or ceiling tiles.

4. If driving- STOP, but stay in the vehicle. Do not stop

on bridge, under trees, light posts, electrical power

lines or signals.

5. If outside, stay outside. Move to an open area away

from buildings, trees, power lines and roadways.

AFTER AN EARTHQUAKEAFTER AN EARTHQUAKE1. Check for injuries. Give first aid as

necessary.2. Check for safety hazards: fire, electrical,

gas leaks, etc. and take appropriate actions.3. Do not use telephones and roadways unless

necessary so that these are open for emergency uses.

4. Be prepared for aftershocks, plan for cover when they occur.

5. Turn on your radio/TV for an emergency message. Evacuate to shelters as instructed.

6. Remain calm, try to reassure others. Avoid injury from broken glasses etc.

2001 GUJARAT EARTHQUAKE Houses Collapsed = 2, 33, 660

Partially Collapsed=9, 71, 538

Damage to R.C.C. Structures in Ahmedabad (700 Killed).

Total Casualties = 13,811

Injuries = 1,66,836 (20,217 seriously).

Magnitude = 6.9~7.9

An aerial view of the destructionof houses in Bhachau and Anjar towns during the Gujarat, 2001 earthquak

 

Devastated village - Jawaharnagar which was relocated at this site after the Anjar earthquake of 1856. The same has collapsed as no aseismic design interventions were made during the rehabilitation and reconstruction of this village.

1993 LATUR EARTHQUAKE

The earthquake struck at 3.56 Hrs. on 30-9-1993 with epicentre at Killari Dist. Latur.

The intensity of earthquake was 6.4 on the Richter Scale.

3,670 people died in Latur District.

446 were seriously injured making them handicapped.

37 Villages were totally collapsed.

728 villages suffered damages of varying degree.

Nearly 1,27,000 familites were affected.

Post Office Building, Killari

Damaged but not collapsed

Public Building in Sastoor

Damaged but not collapsed

MEERP Programme

Before MEERP

After MEERP

1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM

1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM

1985 MEXICO EARTHQUAKE: POUNDING

1985 MEXICO EARTHQUAKE: POUNDING

EARTHQUAKE-RESISTANT DESIGN OF NON-ENGINEERED BUILDING

Symmetric PlanLess Opening

Interlocking of Stones

Interlocking by Through Stones (Haider)

Through Stones in Existing Walls

Seismic Bands (Very Important)

Construction Practice (Marathwada Region)

Construction Practice (Satara, Kolhapur Region)

Strengthening of Existing Houses

Confidence in Earthquake-resistantMeasures

Confidence Building inRetrofitting

EARTHQUAKE-RESISTANT DESIGN OF ENGINEERED BUILDINGS

Collapse of open ground story RC frame residential building in Bhuj.

2001 Gujarat Earthquake

2001 Gujarat

Earthquake

Buildings with First-Soft Story

Buildings with Heavy Water Tanks

EARTHQUAKE ANALYSIS

xm

gx

SDOF system

EQUATION OF MOTION

m

)( gxxm

kxxc

Free Body Diagram

Governing Equation

gxmkxxcxm m = mass of the SDOF systemc = damping constantk = stiffnessx = displacement of the systemgx= earthquake acceleration.

(a) MDOF system

m1

m2

mN

k1

kN

k2

2x

1x

gx

Nx

(b) Free body diagram

mi

)( 11 iii xxk

)( 11 iii xxc

)( 1 iii xxk

)( 1 iii xxc

)( gii xxm

MDOF System

Figure 2.4

DESIGN CRITERIA FOR EARTHQUAKE LOADS (IS-1893-1984)

Country is divided into five zones for the purpose of design of structures for earthquake loads

SEISMIC ZONING

SEISMIC ZONE MMI 0 F0

I V 0.01 0.05

II VI 0.02 0.1

III VII 0.04 0.2

IV VIII 0.05 0.25

V IX & above 0.08 0.40

0 = Basic horizontal seismic coefficient F0 = Seismic zone factor

Distribution of earthquake forces in multi-story building

DUCTILE DETAILING OF R.C.C. STRUCTURRES (IS:13920-1993)

• To Add Ductility and Toughness (Special confining reinforcement)

• Should be applied for all R.C.C. Structures Seismic Zone IV and V Seismic Zone III but I >1 Seismic Zone III (Industrial Buildings) Seismic zone III (> 5 Storey)

• Flexural Memberes Stress > 0.1 fck

b/D > 0.3 b > 200 mm D > Clear Span/4

Condition assessment

• Tapping by hammer• Rebound Hammer• Indentation method• Ultrasonic Pulse Velocity Transmission Test• Covermeter / Pachometer• Radiography• Chloride Content• Testing for Depth of Carbonation• Tests on Concrete Cores

New stirrups

New reinforcement

Old reinforcement

Roughened surface

Drilled hole in slab

Roughened surface

Slab

StirrupsBeam

Jacket

Strengthening of column

New stirrups

New reinforcement

Old reinforcement

Anchor bars

Drilled hole in slab

New reinforcement

Old reinforcement

New stirrups

Strengthening of column

weld

Roughened surface

New reinforcement

Beam Strengthening

Strengthening of bare frame

Strengthening of masonry

FRP strengthening

CONVENTIONAL SESIMIC DESIGN Sufficient Strength to Sustain

Moderate Earthquake Sufficient Ductility under Strong

Earthquake

Disadvantages Inelastic Deformation Require Large Inter-

Storey Drift Localised Damages to Structural Elements

and Secondary Systems Strengthening Attracts more Earthquake

Loads

BASE ISOLATION Aseismic Design Philosophy Decouple the Superstructure from

Ground with or without Flexible Mounting

Period of the total System is Elongated

A Damper Energy Dissipating Device provided at the Base Mountings.

Rigid under Wind or Minor Earthquake

Advantages of Base Isolation Reduced floor Acceleration and Inter-storey Drift Less (or no) Damage to Structural Members Better Protection of Secondary Systems Prediction of Response is more Reliable and Economical.

Non-isolated Base-isolated

Fixed base building Base-isolated building

SEISMIC BASE ISOLATION

gx

1x

2x

Nx

m 1

m 2

mN

k1

kN

k2

m b

Base isolator

16

Figure 3.2 Concept of base isolation.

Period

Dis

plac

emen

t Increasing damping

Increasing damping

Period shift

Acc

eler

atio

n

BASE ISOLATION SYSTEMS LRB System NZ System P-F System R-FBI System EDF System S-RF System Friction Pendulum System (FPS) High Damping Rubber Bearing

Elastomeric bearings

Sliding bearings

36

110

61.5

30Steel Plate

Rubber

12

12

Response of five-story building isolated by LRB system

0 5 10 15 20-15

-10

-5

0

5

10

x b (c

m)

Time (sec)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Fixed base Isolated

Top flo

or

acc

ele

ratio

n (

g)

Response of a five-story isolated by FPS system

0 5 10 15 20-15

-10

-5

0

5

10

x b (c

m)

Time (sec)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Fixed base Isolated

Top flo

or

acc

ele

ratio

n (

g)

DAMAGE OF BRIDGES DURING EARTHQUAKES

DUCTILE DETAILING OF R.C.C. STRUCTURRES

(IS:13920-1993)• To Add Ductility and Toughness

• Should be applied for all R.C.C. Structures Seismic Zone IV and V Seismic Zone III but I >1 Seismic Zone III (Industrial Buildings) Seismic zone III (> 5 Storey)

• Flexural Memberes Stress > 0.1 fck

b/D > 0.3 b > 200 mm D > Clear Span/4

SEISMIC ISOLATION OF BRIDGES

0 5 10 15 20 25 30

-10

0

10 Abutment Pier

Bea

ring

dis

plac

emen

t (c

m)

Time (sec)

-0.4

-0.2

0.0

0.2

0.4

W = Weight of bridge deck

Non-isolated Isolated

Pie

r ba

se s

hear

/W

-1.0

-0.5

0.0

0.5

1.0

Figure 8.2 Time variation of bridge response in longitudinal direction to El-Centro, 1940 excitation.

Non-isolated Isolated

Dec

k ac

cele

ratio

n (g

)

The American River Bridge & installed friction pendulum bearing

Thjorsa Bridge with Elastomeric seismic isolation bearings

(Ice land)

Figure 7.1 Demonstration building in Indonesia (1994)

Location: 1 k.m. SW of Pelabuhan

Building : 4-Storeyed MR RCC.

Isolator : 16 HDRManufacturer: MRPRA, UK

Figure 7.2 Foothill Communities Law and Justice Center,Rancho Cucamonga,California (photo by I.D. Aiken).

Location: Rancho Cucamonga California.

Isolator :HDREngineers: Taylor & Gaines;

Reid & Tarics.Year :1985

Figure 7.3 University of Southern California, University Hospital(Photo by P.W. Clark).

Location: Los Angeles, California.

Isolator : LRBEngineers: KPFFYear :1991

Figure 7.4 Fire Command and Control facility, Los Angeles, California(Naeim and Kelly 1999).

Location: East Los Angeles California.

Isolator :HDREngineers: Fluor-Daniel Year :1990

Figure 7.9 Tohoku Electric Power Company, Japan (Kelly, 1997).

Location: Sendai, Miyako Provience

Isolator :HDRYear :1990

SAN FRANCISCO CITY HALL

Tuned mass damper, Huis Ten Bosch tower, Nagasaki

m1,n

kd

cd

kd

cd

kd

cd

kd

cd

c1,1

c1,2

c1,3

c2,1

c2,2

c2,3

c2,mc1,i

c1,n-1

c1,n

k1,1

k1,2

k1,3

k1,i

k1,n-1

k1,n

m1,1

m1,2

m1,3

m1,i

m1,n-1

k2,1

k2,2

k2,3

k2,m

m2,1

m2,2

m2,3

m2,m

Building BBuilding Agx

Damper Connected Buildings

CONCLUDING REMARKS Earthquakes are not predictable Construct Earthquake-Resistant

Structures It is possible to evaluate the earthquake

forces acting on the structure. Design the structure to resist the above

loads for safety against Earthquakes. Base isolation can also be used for

retrofitting of structure.