Transcript No Slide Title

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
MAGNITUDE OF EARTHQUAKE
Related to the amount of energy released by the
geological rupture.
Measure of the absolute size of the earthquake,
without reference to distance from the epicentre.
Richter (1958) defined magnitude as the logarithm to
the base 10 of the largest displacement of a
standard seismograph situated 100 km from the
focus.
Largest magnitude of earthquake recorded = 8.9
Log10 E  4.8  1.5M
(E = Energy in joules; M = Magnitude)
Energy Magnitude Relationship
1E20
1E19
Energy Released (J)
1E18
1E17
1E16
1E15
1E14
1E13
1E12
1E11
1E10
4
5
6
7
8
9
10
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
IX
X
XI
XII
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
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.
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.
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.
Total damage; waves seen on ground surfaces; lines of sight and
levels distorted; and objects thrown upward into the air.
Earthquake/Inertia Forces
ACCELERATION
DECELERATION
EARTHQUAKE FORCE
Force due to earthquake is
W
F  a  W ( Seismic Coefficient )
g
W = weight of structure;
g = acceleration due to gravity;
a = peak earthquake acceleration.
IS:1893-1984 provides the general principles and
design criteria for earthquake loads.
EL-CENTRO, 1940 EARTHQUAKE
0.2
0.0
-0.2
-0.4
40
Displacement (cm) Velocity (cm/sec)
Acceleration (g)
0.4
20
0
-20
-40
10
0
-10
-20
-30
0
5
10
15
Time (sec)
20
25
30
(Before Earthquake)
(After Earthquake)
House Elements Resist
Horizontal Forces
Roof Diaphragm
f1
f2
Shear Wall
fsum = f1 + f2 + f3
f3
Floor
Diaphragm
Foundation
Cripple Wall
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 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 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 EARTHQUAKE
1. 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 destruction
of 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:
POUNDING
EARTHQUAKE-RESISTANT DESIGN
OF NON-ENGINEERED BUILDING
Symmetric Plan
Less 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-resistant
Measures
Confidence
Building in
Retrofitting
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
SDOF system
m
x
xg
EQUATION OF MOTION
m (x  xg )
Free Body Diagram
m
kx
c x
Governing Equation
mx  cx  kx  mxg
m = mass of the SDOF system
c = damping constant
k = stiffness
x = displacement of the system
xg = earthquake acceleration.
MDOF System
mN
xN
kN
ki 1 ( xi  xi 1 )
ci 1 ( xi  xi 1 )
mi (xi  xg )
mi
ki ( xi  xi 1 )
m2
ci ( xi  xi 1 )
x2
(b) Free body diagram
k2
m1
x1
k1
xg
Figure 2.4
(a) MDOF system
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
Stirrups
Beam
Jacket
Strengthening of column
New stirrups
New reinforcement
Old reinforcement
Anchor bars
Drilled hole in slab
New reinforcement
New stirrups
Old reinforcement
Strengthening of column
Roughened
surface
New reinforcement
weld
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 InterStorey 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
mN
xN
Period shift
Acceleration
kN
m2
x2
m1
x1
Increasing
damping
Displacement
k2
k1
Increasing
damping
mb
Base isolator
xg
Period
Figure 3.2 Concept of base isolation.
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
110
12
30
Steel Plate
36
Rubber
6
1.5
12
Response of five-story building isolated by LRB system
1.5
Fixed base
Isolated
Top floor acceleration (g)
1.0
0.5
0.0
-0.5
-1.0
-1.5
10
xb (cm)
5
0
-5
-10
-15
0
5
10
Time (sec)
15
20
Response of a five-story isolated by FPS system
1.5
Fixed base
Isolated
Top floor acceleration (g)
1.0
0.5
0.0
-0.5
-1.0
-1.5
10
xb (cm)
5
0
-5
-10
-15
0
5
10
Time (sec)
15
20
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
Deck acceleration (g)
1.0
Non-isolated
Isolated
Non-isolated
Isolated
0.5
0.0
-0.5
Pier base shear/W
-1.0
0.4
0.2
0.0
-0.2
Bearing displacement (cm)
-0.4
W = Weight of bridge deck
10
Abutment
Pier
0
-10
0
5
10
15
Time (sec)
20
25
Figure 8.2 Time variation of bridge response in longitudinal direction to El-Centro, 1940 excitation.
30
The American River Bridge & installed friction pendulum bearing
Thjorsa Bridge with Elastomeric seismic isolation bearings
(Ice land)
Location: 1 k.m. SW of
Pelabuhan
Building : 4-Storeyed
MR RCC.
Isolator : 16 HDR
Manufacturer: MRPRA,
UK
Figure 7.1 Demonstration building in Indonesia (1994)
Location: Rancho Cucamonga
California.
Isolator :HDR
Engineers: Taylor & Gaines;
Reid & Tarics.
Year :1985
Figure 7.2 Foothill Communities Law and Justice Center,
Rancho Cucamonga,California (photo by I.D. Aiken).
Location: Los Angeles,
California.
Isolator : LRB
Engineers: KPFF
Year :1991
Figure 7.3 University of Southern California, University Hospital
(Photo by P.W. Clark).
Location: East Los Angeles
California.
Isolator :HDR
Engineers: Fluor-Daniel
Year :1990
Figure 7.4 Fire Command and Control facility, Los Angeles, California
(Naeim and Kelly 1999).
Location: Sendai,
Miyako Provience
Isolator :HDR
Year :1990
Figure 7.9 Tohoku Electric Power Company, Japan (Kelly, 1997).
SAN FRANCISCO CITY HALL
Tuned mass damper, Huis Ten Bosch tower, Nagasaki
Damper Connected Buildings
m1,n
c1,n
k1,n
m1,n-1
c1,n-1
k1,n-1
m1,i
c1,i
k1,i
m1,3
c1,3
k1,3
m1,2
c1,2
k1,2
m1,1
c1,1
k1,1
kd
cd
kd
cd
kd
cd
kd
cd
m2,m
c2,m
k2,m
m2,3
c2,3
k2,3
m2,2
c2,2
k2,2
m2,1
c2,1
k2,1
xg
Building A
Building B
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.