Earthquake Resistant designs with exp... all the things u need to know
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Transcript of Earthquake Resistant designs with exp... all the things u need to know
EARTHQUAKE
RESISTANT DESIGNS
Submitted by-
PRATEEK SRIVASTAVA
Guided by – AR. Madhura YadavRoll no - 27
S.Y. B.ARCH
SEMINAR PROJECT
Contents
What is earthquake?
Why is it deadly?
India’s profile
Need for earthquake resistant design.
Important considerations for design
Sesmic vibration control
What is Earthquake
An earthquake (also known as
a quake, tremor or temblor) is the result of a
sudden release of energy in the Earth’s crust that
creates seismic waves.
In its most general sense, the word earthquake is
used to describe any seismic event — whether
natural or caused by humans — that generates
seismic waves
The most recent large earthquake of magnitude
9.0 or larger was a 9.0 magnitude earthquake in
Japan in 2011 (as of March 2011), and it was the
largest Japanese earthquake since records began.
CONTINENTL DRIFT
Source: from internet
Fault
A fault is nothing but a crack or weak zone inside the Earth. When two blocks of rock
or two plates rub against each other along a fault, they don’t just slide smoothly.
As the tectonic forces continue to prevail, the plate margins exhibit deformation as
seen in terms of bending, compression, tension and friction. The rocks eventually
break giving rise to an earthquake, because of building of stresses beyond the
limiting elastic strength of the rock.
Effects of earthquakes
Types-
Shaking and
ground rupture
Landslides and
avalanches
Fires
Soil liquefaction
Tsunami
Floods
M > 8 Great Very great
7 - 7.9 Major Great
6 - 6.9 Strong Moderate
5 - 5.9 Moderate Moderate
4 - 4.9 Light Slight
3 - 3.9 Minor Slight
M < 3 Micro
earthquake
EARTHQUAKE MAGNITUDE CLASS
USGS IMD
Magnitude Annual Average No.
M > 8 2
7 - 7.9 20
6 - 6.9 100
5 - 5.9 3000
4 - 4.9 15,000
3 - 3.9 >100,000
GLOBAL EARTHQUAKE OCCURRENCE
Records of Worlds Largest
Earthquakes
Earthquake as the deadliest
Natural Disaster
The Vulnerability Profile - India
59% of land mass prone to earthquakes
40 million hectares (8%) of landmass prone to floods
8000 Km long coastline with two cyclone seasons
Hilly regions vulnerable to avalanches/landslides/Hailstorms/cloudburst
68% of the total area susceptible to drought
Different types of manmade Hazards
Tsunami threat
1 million houses damaged annually + human, economic, social and
other losses
More than 60 % area is earthquake prone.
Zone V 12 %
Zone IV 18 %
Zone III 26 %
Zone II 44 %
Fig. courtesy: nicee
Casualties during past events
1004 768
8000
38 63
14000
0
2000
4000
6000
8000
10000
12000
14000N
um
be
r o
f d
ea
ths
Bh
uj
Ch
am
oli
Ja
ba
lpu
r
Killa
ri
Utt
ark
as
hi
Bih
ar
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Earthquake Do Not Kill people
Improperly Designed
Structures Do!
Earthquake Design Philosophy
Need for Earthquake Resistant
Design Earthquake Resistant Design is the scientific field
concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels.
Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading, thus considered as a subset of both structural and geotechnical engineering.
However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering and from the social sciences, especially sociology, political sciences, economics and finance.
Earthquake Resistant Design
The main objectives of earthquake engineering
are:
Foresee the potential consequences of
strong earthquakes on urban areas and civil
infrastructure.
Design, construct and maintain structures
to perform at earthquake exposure up to the
expectations and in compliance with building
codes.
A properly engineered structure does not
necessarily have to be extremely strong or
expensive. It has to be properly designed to
withstand the seismic effects while sustaining an
acceptable level of damage.
IMPORTANT CONSIDERATIONS TO MAKE A
BUILDING EARTHQUAKE RESISTANT
1. Configuration
2. Ductility
3. Quality control
4. Base Isolation
5. Passive Energy Dissipating Devices
6. Active Control Systems
A terminally ill patient , however
effective the medication, may
eventually die.
Similarly, a badly configured building Cannot be engineered for an improved performance beyond a certain limit.
1. Configuration
Regular Configuration
Regular configuration is seismically ideal. These configurations have low heights to base ratio, symmetrical plane, uniform section and elevation and thus have balanced resistance.
These configurations would
have maximum torsional
resistance due to location
of shear walls and
bracings. Uniform floor
heights, short spans and
direct load path play a
significant role in seismic
resistance of the building.
Irregular Configuration
Buildings with irregular configuration
Buildings with abrupt changes in lateral
resistance
Buildings with abrupt changes in
lateral stiffness
Re-entrant corner
Discontinuity in diaphragm Stiffness
Discontinuity in Diaphragm Stiffness
FLEXIBLE
DIAPHRAGM
R I G I D
D I A P H R A G MO P E N
Vertical Components of Seismic Resisting System
Out of plane Offsets
Shear Wall
Out-of-Plane Offset
in Shear Wall
Shear
walls
Non-parallel
system
ELEVATION IRREGULARITIES
1) Soft-Storey/Pan-caked 2) Set-backs 3) Connections
Pancaking
Soft storey
ELEVATION IRREGULARITIES
4) Pounding 5) Breaks in
Columns
or Beams
6) Staggered
Levels
7) In-fills
Open ground storey building (soft storey)
Right or Wrong…?
Short column effect
Ductility
Let us first understand how different materials behave.
Consider white chalk used to write on blackboards and steel pins with solid
heads used to hold sheets of paper together. Yes… a chalk breaks easily!!
On the contrary, a steel pin allows it to be bent back-and-forth. Engineers define
the property that allows steel pins to bend back-and-forth by large amounts, as
ductility; chalk is a brittle material.
The currently adopted performance criteria in the earthquake codes are
the following:
i. The structure should resist moderate intensity of earthquake shaking
without structural damage.
ii. The structure should be able to resist exceptionally large intensity of
earthquake shaking without collapse.
The strength of brittle construction materials, like masonry and concrete, is highly sensitive to the
1. quality of construction materials
2. workmanship
3. supervision
4. construction methods
Quality control
special care is needed in construction to ensure that the elements meant to be ductile are indeed provided with features that give adequate ductility.
Thus, strict adherence to prescribed standards of construction materials and construction processes is essential in assuring an earthquake-resistant building.
Elements of good quality control.
1.Regular testing of construction materials at qualified laboratories (at site or away)
2. Periodic training of workmen at professional training houses, and
3. On-site evaluation of the technical work
Prepared by CT.Lakshmanan
Seismic vibration control
After the seismic waves enter a superstructure, there are a number of ways to control them in order to soothe their damaging effect and improve the building's seismic performance, for instance:
to dissipate the wave energy inside a superstructure with properly engineered dampers.
to disperse the wave energy between a wider range of frequencies
to absorb the resonant portions of the whole wave frequencies band with the help of so called mass dampers
Oldest Technique
However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation.
For this, some pads are inserted into or under all major load-carrying elements in the base of the building which should substantially decouple a superstructure from its substructure resting on a shaking ground.
The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, a city in ancient Persia, now Iran: it goes back to 6th century BCE. Below, there are some samples of seismic vibration control technologies of today.
Mausoleum of Cyrus,
the oldest
base isolated
structure in the world
Dry –stone walls control
Dry-stone walls of Machu Picchu Temple of the
Sun, Peru
Dry-stone walls control
People of Inca civilization were masters of the polished 'dry-stone walls', called ashlar, where blocks of stone were cut to fit together tightly without any mortar. The Incas were among the best stonemasons the world has ever seen, and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.
Peru is a highly seismic land, and for centuries the mortar-free construction proved to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications.
Base isolators
Prepared by CT.Lakshmanan
Basic example
Lead rubber bearing
Lead Rubber Bearing or LRB is a type of base isolation employing a heavy damping. It was invented by Bill Robinson, a New Zealander.[24]
Heavy damping mechanism incorporated in vibration control technologies and, particularly, in base isolation devices, is often considered a valuable source of suppressing vibrations thus enhancing a building's seismic performance.
However, for the rather pliant systems such as base isolated structures, with a relatively low bearing stiffness but with a high damping, the so-called "damping force" may turn out the main pushing force at a strong earthquake.
The bearing is made of rubber with a lead core.
Many buildings and bridges, both in New Zealand and elsewhere, are protected with lead dampers and lead and rubber bearings.
Te Papa Tongarewa, the national museum of New Zealand
New Zealand Parliament Buildings
Both have been fitted with the bearings.
Both are in Wellington, which sits on an active earthquake fault.
Te Papa Tongarewa,
the national
museum of New
Zealand
New Zealand
Parliament
Buildings
Simple roller bearing
Simple roller bearing is a base isolation device which is intended for protection of various building and non-building structures against potentially damaging lateral impacts of strong earthquakes.
This metallic bearing support may be adapted, with certain precautions, as a seismic isolator to skyscrapers and buildings on soft ground. Recently, it has been employed under the name of Metallic Roller Bearing for a housing complex (17 stories) in Tokyo, Japan
Tuned mass damper
Typically, the tuned mass dampers are huge concrete blocks mounted in skyscrapers or other structures and moved in opposition to the resonance frequency oscillations of the structures by means of some sort of spring mechanism.
Taipei 101 skyscraper needs to withstand typhoon winds and earthquake tremors common in its area of the Asia-Pacific. For this purpose, a steel pendulumweighing 660 metric tons that serves as a tuned mass damper was designed and installed atop the structure. Suspended from the 92nd to the 88th floor, the pendulums sways to decrease resonant amplifications of lateral displacements in the building caused by earthquakes and strong gusts.
Tuned
Mass
Dampers
Taipei101
Building
Elevation
Control
Transamerica
Pyramid
Building,
San Francisco,
USA
Building elevation control Building elevation control is a valuable source of vibration
control of seismic loading. Pyramid-shaped skyscrapers continue to attract attention of architects and engineers because such structures promise a better stability against earthquakes and winds. The elevation configuration can prevent buildings' resonant amplifications because a properly configured building disperses the shear wave energy between a wide range of frequencies.
Earthquake or wind quieting ability of the elevation configuration is provided by a specific pattern of multiple reflections and transmissions of vertically propagating shear waves, which are generated by breakdowns into homogeneity of story layers, and a taper. Any abrupt changes of the propagating waves velocity result in a considerable dispersion of the wave energy between a wide ranges of frequencies thus preventing the resonant displacement amplifications in the building.
A tapered profile of a building is not a compulsory feature of this method of structural control. A similar resonance preventing effect can be also obtained by a proper tapering of other characteristics of a building structure, namely, its mass and stiffness. As a result, the building elevation configuration techniques permit an architectural design that
Building during
Earthquake
CROSS-BRACING
The vertical structural system of a building consists of columns, beams and bracing, and functions to transfer seismic forces to the ground. Engineers have several options when building the vertical structure. They often build walls using braced frames, which rely on trusses to resist sideways motion. Cross-bracing, which uses two diagonal members in an X-shape, is a popular way to build wall trusses. Instead of braced frames or in addition to them, engineers may use shear walls --vertical walls that stiffen the structural frame of a building and help resist rocking forces. Engineers often place them on walls with no openings, such as those around elevator shafts or stairwells.
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