Earthquake and earthquake resistant design
Click here to load reader
-
Upload
khushi-jangra -
Category
Engineering
-
view
131 -
download
43
Transcript of Earthquake and earthquake resistant design
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.