EARTHQUAKES AND EARTHQUAKE-RESISTANT DESIGN OF STRUCTURES

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-lines of equal seismic intensity Coseismal-lines designating the affected area

EARTHQUAKE PHENOMENON

Energy is released in the form of waves and radiates in all directions from its source, the focus.

What Happens During an Earthquake?

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

Body Waves Travel through Earth’s interior. Two types based on mode of travel.

Primary (P) Waves Push-pull (compress and expand – compressional waves)

motion, changing the volume of the intervening material. Therefore, can travel through solids, liquids, and gases. Generally, in any solid material, P waves travel about 1.7

times faster than S waves.

Seismic Wave Motion Animation #77

Body Waves Secondary (S) Waves

“Shake” motion at right angles to their direction of travel that changes the shape of the material transmitting them (shear waves).

Therefore, can travel only through solids. Slower velocity than P waves. Slightly greater amplitude than P waves. Lesser amplitude than L Wave.

Seismic Wave Motion Animation #77

Surface Waves Travel along outer part (surface) of the Earth. Complex motion (up-and-down motion as well as side-to-

side motion). Cause greatest destruction. Exhibit greatest amplitude and slowest velocity. Waves have the greatest periods (time interval between

crests). Often referred to as long waves, or L waves.

Seismic Wave Motion Animation #77

Seismic Wave Motion and Surface Effects Animation #78

Sensitive instruments, called seismographs, around the world record the earthquake event.

Seismographs record seismic waves.

Seismographs record the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape.

More than one type of seismograph is needed to record both vertical and horizontal ground motion.

Seismographs Animation #79

1. Three station recordings are needed to locate an epicenter.

2. Each station determines the time interval between the arrival of the first P wave and the first S wave at their location.

3. A travel-time graph is used to determine each station’s distance to the epicenter.

4. A circle with a radius equal to the distance to the epicenter is drawn around each station.

5. The point where all three circles intersect is the earthquake epicenter.

6. This method is called triangulation.

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 )

Intensity – a measure of the degree of earthquake shaking at a given locale based on the amount of damage.

The The drawback of drawback of intensity intensity scales is that scales is that destruction destruction may not be a may not be a true measure true measure of the of the earthquake’s earthquake’s actual actual severity.severity.

Magnitude – estimates the amount of energy released at the source of the earthquake.

Richter ScaleRichter Scale Based on the amplitude of the largest seismic wave recorded.Based on the amplitude of the largest seismic wave recorded. Accounts for the decrease in wave amplitude with increased distance.Accounts for the decrease in wave amplitude with increased distance. Each unit of Richter magnitude increase corresponds to a tenfold increase Each unit of Richter magnitude increase corresponds to a tenfold increase

(logarithmic scale) in wave amplitude and a 32-fold energy increase.(logarithmic scale) in wave amplitude and a 32-fold energy increase.

How Are Earthquakes Measured?How Are Earthquakes Measured?

Destruction from Seismic Vibrations 1. Ground Shaking2. Liquefaction of the Ground3. Seiches4. Tsunamis, or Seismic Sea Waves5. Landslides and Ground Subsidence 6. Fire

Amount of structural damage attributable to earthquake vibrations depends on:

Proximity to populated areas Magnitude Intensity and duration of the vibrations

Nature of the material upon which the structure rests

Design of the structure

Regions within 20 to 50 kilometers of the epicenter will experience about the same intensity of ground shaking.

Destruction varies considerably mainly due to the nature of the ground on which the structures are built.

Damage Caused by the 1964 Damage Caused by the 1964 Anchorage, Alaska QuakeAnchorage, Alaska QuakeDamage to I-5 during the Damage to I-5 during the

Northridge, CA Earthquake in 1994Northridge, CA Earthquake in 1994

Unconsolidated materials saturated with water turn into a mobile fluid.

Can cause underground structures to migrate to the surface, and buildings and other aboveground structures to settle and collapse.

Liquefaction of the Ground Dry Compaction and Liquefaction Animation #21

Result from vertical displacement along a fault located on the ocean floor.

Result from a large undersea landslide triggered by an earthquake.

Advance across oceans at great speeds ranging from ~500 to 950 km/hour (~310 to 590 miles/hour).

In the open ocean, height is usually < 1 meter. Distances between wave crests range from 100 to 700

km. In shallower coastal waters, the water piles up to

heights that occasionally exceed 30 meters (~100 feet).

As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transforms.

A tsunami travels at a speed that is related to the water depth – hence, as the water depth decreases, the tsunami slows.

The tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly constant.

Consequently, as the tsunami's speed diminishes as it travels into shallower water, its height grows.

Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast.

When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore. http://www.geophys.washington.edu/tsunami/general/physics/physics.html

As a tsunami approaches shore, it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore –

part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and turbulence.

Despite these losses, tsunamis still reach the coast with tremendous amounts of energy.

Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation.

Capable of inundating, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water associated with the inundating tsunami can crush homes and other coastal structures.

Tsunamis may reach a maximum vertical height onshore above sea level, often called a runup height, of 10, 20, and even 30 meters.

http://www.geophys.washington.edu/tsunami/general/physics/physics.html

Tsunami at Hilo, Hawaii (April 1, 1946) that originated in the Aleutian Islands near Alaska, was still powerful enough to rise 30 to 55 feet when it hit Hawaii.

Tsunami Animation #91

The rhythmic sloshing of water in lakes, reservoirs, and enclosed basins.

Waves can weaken reservoir walls and cause destruction.

Landslide caused by the 1964 Landslide caused by the 1964 Alaskan EarthquakeAlaskan Earthquake

San Francisco in flames after the 1906 EarthquakeSan Francisco in flames after the 1906 Earthquake

Short-Range Predictions Goal is to provide a warning of the location and magnitude of a large earthquake within a narrow time frame.

Research has concentrated on monitoring possible precursors – such as measuring: uplift subsidence strain in the rocks

Currently, no reliable method exists for making short-range earthquake predictions.

Long-Range Forecasts Give the probability of a certain magnitude earthquake occurring on a time scale of 30 to 100 years, or more (statistical estimates).

Based on the premise that earthquakes are repetitive or cyclical. Using historical records or paleoseismology

Are important because they provide information used to Develop the Uniform Building Code Assist in land-use planning

EARTHQUAKE FORCE

Force due to earthquake is

)( tCoefficienSeismicWag

WF

W = weight of structure; g = acceleration due to gravity; a = peak earthquake acceleration.

IS:1893-2002 provides the general principles and design criteria for earthquake loads.

ACCELERATIONACCELERATIONACCELERATIONACCELERATION

DECELERATIONDECELERATIONDECELERATIONDECELERATION

Shear WallShear Wall

Cripple WallCripple Wall

FoundationFoundationFloorDiaphragm

FloorDiaphragm

Roof DiaphragmRoof Diaphragm

f1

f2

f3

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

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(Maharashtra).

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

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 0.10

III VII 0.04 0.16

IV VIII 0.05 0.24

V IX & above 0.08 0.36

0 = Basic horizontal seismic coefficient F0 = Seismic zone factor

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

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

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. STRUCTURES

(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.