elastic rebound theory earthquake phenomenon
TRANSCRIPT
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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).
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SCOPE OF PRESENTATION EARTHQUAKE AND ITS
CHARACTERIZATION EARTHQUAKE-RESISTANT DESIGN REPAIR & RETROFITTING OF
STRUCTURES EARTHQUAKE ANALYSIS OF STRUCTURES ADVANCED TECHNOLOGIES
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EARTHQUAKE An earthquake may be simply described as a sudden shaking phenomenon of the earth's surface due to disturbance inside the earth.
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CLASSIFICATIONS AND CAUSES OF EARTHQUAKE
Tectonic Earthquakes Non-tectonic Earthquakes
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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.
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ELASTIC REBOUND THEORY
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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.
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EARTHQUAKE TERMINOLOGY
Seismograms Focus or Hypocentre Epicentre Focal Depth Hypocentral Distance Epicentral Distance Isoseismal Coseismal
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EARTHQUAKE PHENOMENON
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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
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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
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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 )
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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
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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.
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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.
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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.
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Earthquake/Inertia Forces
ACCELERATIONACCELERATIONACCELERATIONACCELERATION
DECELERATIONDECELERATIONDECELERATIONDECELERATION
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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 .
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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)
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(Before Earthquake)
(After Earthquake)
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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
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Damage Resulting from Base Shear
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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.
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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.
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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.
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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.
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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
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An aerial view of the destructionof houses in Bhachau and Anjar towns during the Gujarat, 2001 earthquak
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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.
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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.
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Post Office Building, Killari
Damaged but not collapsed
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Public Building in Sastoor
Damaged but not collapsed
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MEERP Programme
Before MEERP
After MEERP
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1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM
1985 MEXICO EARTHQUAKE: RAILROAD SYSTEM
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1985 MEXICO EARTHQUAKE: POUNDING
1985 MEXICO EARTHQUAKE: POUNDING
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EARTHQUAKE-RESISTANT DESIGN OF NON-ENGINEERED BUILDING
Symmetric PlanLess Opening
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Interlocking of Stones
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Interlocking by Through Stones (Haider)
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Through Stones in Existing Walls
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Seismic Bands (Very Important)
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Construction Practice (Marathwada Region)
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Construction Practice (Satara, Kolhapur Region)
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Strengthening of Existing Houses
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Confidence in Earthquake-resistantMeasures
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Confidence Building inRetrofitting
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EARTHQUAKE-RESISTANT DESIGN OF ENGINEERED BUILDINGS
Collapse of open ground story RC frame residential building in Bhuj.
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2001 Gujarat Earthquake
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2001 Gujarat
Earthquake
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Buildings with First-Soft Story
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Buildings with Heavy Water Tanks
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EARTHQUAKE ANALYSIS
xm
gx
SDOF system
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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.
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(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
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DESIGN CRITERIA FOR EARTHQUAKE LOADS (IS-1893-1984)
Country is divided into five zones for the purpose of design of structures for earthquake loads
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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
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Distribution of earthquake forces in multi-story building
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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
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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
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New stirrups
New reinforcement
Old reinforcement
Roughened surface
Drilled hole in slab
Roughened surface
Slab
StirrupsBeam
Jacket
Strengthening of column
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New stirrups
New reinforcement
Old reinforcement
Anchor bars
Drilled hole in slab
New reinforcement
Old reinforcement
New stirrups
Strengthening of column
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weld
Roughened surface
New reinforcement
Beam Strengthening
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Strengthening of bare frame
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Strengthening of masonry
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FRP strengthening
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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
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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
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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
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Fixed base building Base-isolated building
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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
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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
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Elastomeric bearings
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Sliding bearings
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36
110
61.5
30Steel Plate
Rubber
12
12
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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)
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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)
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DAMAGE OF BRIDGES DURING EARTHQUAKES
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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
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SEISMIC ISOLATION OF BRIDGES
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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
)
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The American River Bridge & installed friction pendulum bearing
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Thjorsa Bridge with Elastomeric seismic isolation bearings
(Ice land)
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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
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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
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Figure 7.3 University of Southern California, University Hospital(Photo by P.W. Clark).
Location: Los Angeles, California.
Isolator : LRBEngineers: KPFFYear :1991
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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
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Figure 7.9 Tohoku Electric Power Company, Japan (Kelly, 1997).
Location: Sendai, Miyako Provience
Isolator :HDRYear :1990
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SAN FRANCISCO CITY HALL
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Tuned mass damper, Huis Ten Bosch tower, Nagasaki
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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
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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.