earthquake resistant building forms

EARTHQUAKE RESISTING BUILDING FORMS

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AIM:

To study different types of building forms which resists damages caused by an earthquake.

HYPOTHESIS:

"EARTHQUAKE RESISTANT BUILDING FORMS HELPS TO IMPROVES THE

STABILITY OF THE BUILDING STRUCTURE AND CAUSES LESS DAMAGE AND

ENSURE BETTER LIVING"

OBJECTIVES:

To analyze what is an earthquake, the consequences and various seismic zones in

Rajasthan.

To study the various earthquake zones in rajasthan (zone-4, zone-3, zone-2) and to

formulate various design guidelines related to forms and geometrical arrangement of

building elements for a better earthquake resistant structure.

To analyze the various geometrical forms, which resists damage to buildings when an

earthquake occurs.

To analyze the need of symmetrical arrangements of building forms for better stability.

To analyze the pattern of attack of earthquake on building.

SCOPE:

To identify the best suitable geometrical forms which resist damages caused by an

earthquake.

To verify newer techniques and mediums for better living.

This study helps architects and engineers, in developing building forms which are better

in resisting earthquakes.


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NEED OF STUDY:

The main aim behind the selection of this topic is to study the various building forms/

geometrical form which resist less damage to building structure and ensure better living.

According to the BSI 2002, the earthquake is repeatedly taking place in least active zones and

hence the consequences for the same are required to be taken.

List of earthquakes in rajasthan in last 20 years:-

RAJASTHAN map showing seismic zones

Figure 1: Rajasthan Map showing earthquake zones

Source- Disaster Management and Relief Department

- Government Of Rajasthan


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METHODOLOGY :

Hypothesis

Objectives

Literature Study

Primary Study Secondary Study

To study the effects of

earthquake taken place in India.

1. Study the buildings and their

form, resting earthquake

2. Guidelines for earthquake.

Collection of Data

Cross Classification Analysis

Outcomes

Conclusion

Aim


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INTRODUCTION TO EARTHQUAKE:

Earthquakes occur due to slippage of rocks in the earth's crust or in the upper part of the mantle,

Consequent to these sudden movements strong vibrations occur on the ground in a short span of

time. The tremendous amount of energy suddenly releasing during an earthquake which

accumulates slowly due to geological process.

According to the elastic rebound theory, energy is stored in the rocks up to the elastic limit may

be for hundreds or thousands of years. Eventually the rocks snap or rupture at the weakest point,

relieving the enormous strains built up over the years. This stored up energy is released in the

form of seismic waves, which radiate outward from the point where the rocks are fractured.

Earthquakes are identified by their location (Longitude and Latitude), depth of the focus and the

energy released/size of the earthquakes. The most common measures of the size of the

earthquakes are magnitude and intensity.

SOURCE: http;/alabamaquake.com

Figure 2: FIGURE SHOWING HOW EARTHQUAKE ORIGNATES


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Definitions

Focus Point

Origin point of the earthquake lying below the earth's surface is known as Focus Point of the

earthquake, where slip starts.

Epicentre

The point just vertically above the focus on the earth surface is known as the Epicentre.

P-Waves

These waves are Primary waves which are fastest among all the waves and generally travel with

a speed between 6 to 14 km per second inside the earth. The speed of the waves remains

unaffected when passing through solid sections of the earth but slow down when passing through

liquid portions. These are longitudinal waves and create a "Push-pull" effect on rock mass like

sound waves.

S-Waves

These waves are Secondary or Shear waves and also travel inside the earth at speeds of 0.58

times that of P wave (generally 3 to 8 km per second). These waves travel easily through solid

sections but loose their identity when passing through liquid portions. These waves are

transverse waves and cause earth to move at right angles to the direction of the wave. These

wave are of most destructive nature.

SOURCE:http;/alabamaquake.com

Figure 3: EARTHQUAKE WAVE (P AND S)


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L (Surface) Waves

These waves are love waves and always travel near the surface of the earth and travel at a speed

of 0.9 times that of S wave (3 to 5 km per second). These waves in association with s-wave also

cause maximum damage.

SOURCE:http;/geo.utep.edu.com

Figure 4: L-WAVE OF EARTHQUAKE


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Magnitude

Magnitude is a measure of the amount of energy released in an earthquake. It is most commonly

determined on Richter scale devised by an American seismologist in 1935. In this method, the

magnitude is determined from the maximum amplitude (of S wave) recorded on a particular type

of seismograph.After applying a distance factor the value is extrapolated at the epicentre. It is a

fixed number and given on a logarithmic scale. An increase of one unit represents an increase in

amplitude of ground shaking by ten times and energy released thirty times. Richter scale is open-

ended, however maximum magnitude is obtained around 9.

Intensity

The intensity is the effect of earthquake on the ground and the objects in the affected area. It is

assigned on the basis of damage that depends upon the magnitude, depth of focus, distance from

the epicentre and the ground condition. It varies from place to place. It is given on grade I to XII

on Modified Mercalli (MM) or Medvedev - Sponheaer - Karnik (MSK) scale.

Tectonic plates

Tectonic plates are made of elastic but brittle rocky material. And so, elastic strain energy is

stored in them during the relative deformations that occur due to the gigantic tectonic plate

actions taking place in the Earth. But, when the rocky material along the interface of the plates in

the Earths Crust reaches its strength, it fractures and a sudden movement takes place there (the interface between the plates where the movement has taken place (called the fault) suddenly slips

and releases the large elastic strain energy stored in the rocks at the interface. For example, the

energy released during the 2001 Bhuj (India) earthquake is about 400 times (or more) that

released by the 1945 Atom Bomb dropped on Hiroshima!!

Figure 5: Movement of tectonic plates

Source: http;/geo.utep.edu.com


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Past history of earthquake in Rajasthan :

Though the state of Rajasthan has not had a major earthquake in recent years, small to

moderate earthquake have been felt in the state. Several faults have been identified in this

region out of which many show evidence of movement during the Holocene epoch. The

Cambay Graben terminates in the south-western part of the state. The Konoi Fault near

Jaiselmer trends in a north-south direction and was associated with the 1991 Jaiselmer

earthquake. Several active faults criss-cross the Aravalli range and lie parallel to each other.

The most prominent of them is the north-south trending Sardar Shahr Fault and the Great

Boundary Fault which runs along the Chambal River and then continues in the same

direction into Uttar Pradesh. However, it must be stated that proximity to faults does not

necessarily translate into a higher hazard as compared to areas located further away, as

damage from earthquakes depends on numerous factors such as subsurface geology as well

as adherence to the building codes.

Table showing the recent earthquakes in rajasthan Source: Disaster management and Relief department, Govt. of Rajasthan

Time period Place Density

Dec, 2012 Jaipur 3.6 magnitude

2 years ago Daosa 4.0 magnitude

4 years ago Sadri 4.6 magnitude

5 years ago Jaisalmer 5.1 magnitude

8years ago Basi 4.2 magnitude

8 years ago Govindgarh 4.0 magnitude

11 years ago Chomu 4.5 magnitude

12 years ago Nim ka thana 4.1 magnitude

16 years ago Phalodi 3.5 magnitude

18 years ago Pokaran 5.2 magnitune


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Earthquake are qualitatively classified by the destruction they cause. Generally earthquakes of

magnitude greater than 5 only cause damages while the magnitude of major earthquake is 7 or

more. A qualitative classification of earthquakes can be seen in the table below.

Magnitude (M) Classification Annual frequency of

occurrence

M8 Great Earthquake 1

M7 and


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Phases and origin

An earthquake has phases and parts. The earths plates are constantly moving away from each other, collide or slide one under the other. At shallower levels, where the rock is less elastic and

prevents movement, energy builds up until it reaches a saturation point and is suddenly released,

causing an earthquake or a tremor.

The precise point where it begins to release energy is the focus or hypocenter of the earthquake.

The point on the earths surface directly above the focus is the epicentre. Usually thats the point

with the highest damage. After a great earthquake, the rocks of the area around the outbreak

continue to move as they adjust to new positions, causing a lot of earthquakes known as

aftershocks.

The energy released by an earthquake is transmitted at high speed in all directions through the

surrounding rocks. Like another type of energy, it spreads through waves. In this case, they are

called seismic waves.

Figure 7: Origin of earthquake and seismic waves

Source : http;/geo.utep.edu.com


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Scales

There are two ways to measure the force of the earthquakes. One of the scales is called Mercalli

scale and the other is Ritcher scale.

The Mercalli Scale is a scale of 12 degrees developed to assess the intensity of earthquakes

through the effects and damage to various structures. It was named after Italian physicist

Giuseppe Mercalli. Low levels of the scale are associated with how people feel the tremor, while

higher grades are associated with structural damage observed.

The levels are:

1-Instrumental, 2-Weak, 3-Slight, 4-Moderate, 5-Rather Strong, 6-Strong, 7-Very Strong, 8-

Destructive, 9-Violent, 10-Intense, 11-Extreme, 12-Cataclysmic.

The seismic scale of Richter, also known as local magnitude scale, is an arbitrary logarithmic

scale that assigns a number to quantify the energy released in an earthquake, named in honour of

the American seismologist Charles Richter. The measurement is performed using data supplied

by seismographs, instruments to measure surface energy waves. The levels are: Less than 2.0 Micro, 2.0-3.9 Minor, 4.0-4.9 Light, 5.0-5.9 Moderate, 6.0-6.9 Strong, 7.0-7.9 Major, 8.0-9.9 Great, +10.0 Massive.

Modified Mercalli Scale:

The Mercalli scale modified by American scientists describes the effects of the earthquake as given in the table below:

Class of Earth

quakes

Description

I Not felt except by very few under especially favourable circumstances.

II Felt only by few person at rest, especially on upper floors of buildings and

delicately suspended objects may swing.

III Felt quite noticeably indoors, especially on upper floors of buildings but many

people do not recognize it as an earthquake; standing motorcars may rock

slightly. Vibration may be felt like passing of a truck.

IV During the day felt indoors by many, outdoors by a few; at night some are

awakened; dishes, windows, doors disturbed; walls make cracking sound;

sensation like heavy truck striking the building; and standing motor cars

rocked visibly.

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 and pendulum clocks may stop.


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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 construction;

considerable in poorly built or badly designed structures; some chimney

broken; noticed by persons driving motor cars.

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 structure; heavy furniture

overturned sand and mud ejected in small amounts; changes in well water and

person driving motor cars disturbed.

IX Damage considerable in specially designed; well designed framed structures

thrown out of plinth; very heavy in substantial buildings with partial collapse;

buildings 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. Shifted sand and mud; 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

slump; land slips in soft ground and rails bent greatly.

XII Total damage; waves seen on ground surface; objects thrown upward into the

air.

Source: Disaster management and Relief department, Govt. of Rajasthan

Effects :-

The effects of an earthquake can be many different, some example are explained below.

Movement and ground rupture.

They are the main effects of an earthquake on the Earths surface due to friction of tectonic plates, causing damage to buildings or structures that are rigid in the area affected by the

earthquake. Damage to buildings depends on the intensity of de movements, the distance

between the structure and the epicenter and the geological and geomorphologic conditions that

enable better wave propagation.


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Figure 8: Ground rapture

Source: - Building Materials and Technology Promotion

Council, New Delhi, India

TSUNAMI: Tsunamis are huge ocean waves that travel large amount of water moving towards the coast. In

the open sea the distance between the crest of the waves are close to 100 km. The periods range

from five minutes to an hour. According to depth of water, tsunamis can travel at speed of 600 to

800 km/h. They can travel long distances across the ocean, from one continent to another.

OTHER EFFECTS:

Land slides, Liquification, fire.

BUILDINGS AGAINST EARTHQUAKES: The behaviour of a building during earthquakes depends critically on its overall shape, size and

geometry, in addition to how the earthquake forces are carried to the ground. Hence, at the

planning stage itself, architects and structural engineers must work together to ensure that the

unfavourable features are avoided and a good building configuration is chosen. The importance

of the configuration of a building was aptly summarised by Late Henry Degenkolb, a noted

Earthquake Engineer of USA, as: If we have a poor configuration to start with, all the engineer can do is to provide a band-aid - improve a

basically poor solution as best as he can. Conversely, if

we start-off with a good configuration and reasonable

framing system, even a poor engineer cannot harm its

ultimate performance too much.

Even when a building designed and constructed to meet all the requirements required by the

rules of earthquake resistant design and construction, there is always the possibility of an

earthquake even stronger than they have been provided and must be resisted by building without

damage occurring.


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In tall buildings with large height-to-base size ratio, the horizontal movement of the floors during

ground shaking is large. In short but very long buildings, the damaging effects during earthquake

shaking are many. And, in buildings with large plan area like warehouses, the horizontal seismic

forces can be excessive to be carried by columns and walls.

Figure 9: Oversizes buildings do not perform well during earthquake

Source: - Building Materials and Technology Promotion


Figure 10: Basic Geometric Shapes that resists earthquake

Source: IITK, Kanpur

Buildings with one of their overall sizes much larger or much

smaller than the other two, do not perform well during earthquakes.

In general, buildings with simple geometry in plan have

performed well during strong earthquakes. Buildings with re-

entrant corners, like those U, V, H and + shaped in, have

sustained significant damage. Many times, the bad effects of these

interior corners in the plan of buildings are avoided by making the

buildings in two parts. For example, an L-shaped plan can be

broken up into two rectangular plan shapes using a separation

joint at the junction. Often, the plan is simple, but the

columns/walls are not equally distributed in plan. Buildings with

such features tend to twist during earthquake shaking.


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Basics principles of building Regular shape: The geometry of the building must be simple in plan and elevation. Complex

shapes, irregular or asymmetrical cause bad behaviour when the building is rocked by an

earthquake. Irregular geometry bring on the structure undergoes torsion or attempt to turn in a

disorderly manner. The lack of uniformity makes it easier in some corners are presented intense

concentrations of power that can be hard to resist.

SOURCE :- CRITERIA FOR EARTHQUAKE RESISTANT

DESIGN OF STRUCTURES BIS 2002

A. Building on slopy ground B.Buildings with walls on two/one sides (in plan)

.

Building Materials and Technology Promotion


Figure 11: Buildings have unequal vertical members; they cause the building to twist about a vertical axis


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Damages in buildings, infrastructures and people The main cause of damage caused by earthquakes is shaking itself. This shock causes the

collapse of numerous objects and the collapse of the buildings. The collapse of building cause in

its habitants trapped in the rubble, often perish by being crushed. Also falling objects can cause

numerous injuries; even death if it is very heavy objects (furniture, heavy lamps, suspended

ceiling, etc) or cutting (pieces of glass windows).

Most accidents can be caused by earthquakes are due mainly to the following types of effects:

- Effects on buildings and infrastructure:

resistant features. Destruction and partial collapse of buildings (falling from ceilings, walls,

partitions,balconies, exterior walls, cracks in walls, etc). Fires caused by a short, exhaust gas and

flammable materials. Flooding from broken dams, water pipes, etc.

,

tiles, pots, etc. Fall of broken glass and ceramic tiling, especially dangerous when they fall from

upper floors. Fall of furniture, hanging objects, etc.

and installations. Partial damage to the roads (roads, bridges, tunnels, railways, etc) due to

settlements landslides and mudslides. Fall of utility poles and power lines.

Pounding can occur between adjoining buildings due to horizontal vibrations of the two

buildings.


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LITERATURE STUDY :-

PRIMARY STUDY

EARTHQUAKE ZONES IN RAJASTHAN:

As per the BMPTC Atlas the State of Rajasthan State falls under earthquake zones II, III and IV.

Some area of Districts of Jalore, Sirohi, Barmer and Alwar districts fall in zone IV where as

many parts of Bikaner, Jaisalmer, Barmer, Jodhpur, Pali, Sirohi, Dungarpur, Alwar, Banswara,

fall in zone III. A table showing zones and likelihood of earthquakes of different intensity and

magnitude is shown below.

S.

No.

Seismic Zone Intensity

MSK

Magnitude District

1 IV [High Damage

Risk Zone]

VII-VIII 6.0 - 6.9 Some area of Barmer [Chohtan Block],

Jalore [Sanchore Block] Alwar [Tijara

Block] and Bharatpur [Block Nagar,

Pahari]

2 III [Moderate

Damage Risk Zone]

VI-VII 5.0 - 5.9 Parts of Udaipur, Dungarpur, Sirohi,

Barmer, Jaisalmer, Bikaner, Jhunjhunu,

Parts of Sikar, Jaipur, Dausa,

Bharatpur.

3 II [Low damage

Risk Zone]

IV-VI 4.0 - 4.0 Ganganagar, Hanumangarh, Churu,

Jodhpur, Pali, Rajasamand, Chittorgarh,

Jhalawar, Baran, Kota, Bundi,

Sawaimadhopur, Karauli, Dholpur,

Banswara, some area of Bikaner,

Udaipur, Jhunjhunu, Sikar, Jaipur.

Source: Disaster management and Relief department, Govt. of Rajasthan

The earthquake of Kutch in 2001 was felt in many parts of Rajasthan as well. Its effect was felt

more severely in the Western District namely Jalore, Barmer and Jaisalmer. Many buildings in

these districts like schools, rest houses and privately owned buildings had developed huge cracks

and had been rendered unsafe. Many other buildings developed cracks making them unsafe for

further use without proper retrofitting. Many of the public buildings mainly schools are still lying

in dilapidated conditions.


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Case Study 1 : Gujarat Earthquake

1. 2001 Bhuj Earthquake

The Bhuj earthquake in Gujarat, India occurred on the 26 January 2001 and caused massive

destruction to property and loss of life. This earthquake had a moment magnitude Mw = 7.9

USGS and struck the Kutch region of India at 8.46am local time, with the shaking lasting for a

few minutes. Kutch has a population of about 1.3 million people. Other major cities in Gujarat eg

Ahmedabad and Jamnagar, which are hundreds of kilometres away, were also effected by the

earthquake.

In Kutch, major towns such as Bhuj (pop 150,000), Anjar (pop 50,000), Bhachau (pop 40,000),

and Rapar (pop 25,000) were almost totally destroyed and many villages surrounding these

towns were badly damaged. To date over 20,000 persons are reported dead and over 167,000

injured, predominantly from the Kutch region. The reported deaths will increase as towns are

cleared, an operation which will take many years.

Most people were killed or badly injured because of:

a) poorly constructed buildings either totally or partially collapsing

b) walls collapsing within narrow streets, burying people escaping into them

c) untied roofs and cantilevers falling onto people

d) free standing high boundary walls, parapets and balconies falling due to the severe shaking

e) gable walls falling over

f) the failure of modern reinforced structures with large open spaces at ground to first floor level,

for example garage or shop spaces, collapsing and burying occupants (soft storey collapses)

g) inhabitants not knowing how to respond to the shaking and collapse of walls around them.

Figure 12: Earthquake waves showing the area affected

Source: Earthquake Engineering Research Institute, EERI Web site at www.eeri.org.


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Generally, commercial buildings were worst affected by the earthquake because of poor

workmanship, use of materials and inadequate attention to detailing.

Low-rise rubble masonry buildings were totally destroyed near to the epicentre, but some

survived (though badly damaged) when further away. These were also older forms of

construction. Cutstone masonry and more modern reinforced concrete framed buildings faired

much better, although damaged to varying extents. These later building types are largely built by

owner-occupiers and hence better care was taken in the materials used and their workmanship.

Many lessons can be learnt from those non-engineered low rise buildings which survived.

Large earthquakes can still cause damage to buildings even if designed to the relevant Indian

codes and this Guide. However, the seismic measures taken are intended to absorb damage in a

controllable way and save lives. They are not intended to ensure that a building always survives

intact. If seismic measures had been taken into account in the design of buildings the loss to life

would have been significantly reduced as many buildings would have not collapsed.

Damage to buildings were caused by a combination of affects:

Old decaying buildings predating modern construction practices

New Buildings not being designed to Indian earthquake codes

Lack of knowledge, understanding or training in the use of these codes by local engineers

Unawareness that Gujarat is a highly seismic region

Buildings erected without owners seeking proper engineering advice

Improper detailing of masonry and reinforced structures

Poor materials, construction and workmanship used, particularly in commercial buildings

Buildings having poor quality foundations or foundations built on poor soils

A majority of building structures in Gujarat can be divided into the following two broad

categories: (i) load bearing masonry and (ii) reinforced concrete frames with unreinforced

masonry infill walls.

Load bearing masonry:

A majority of buildings in the Kachchh region are built in unreinforced load bearing masonry. A

large number of such buildings also exist in areas outside Kachchh, including inurban centers

such as Ahmedabad. The types of masonry units used include (i) random rubble stones, (ii)

rough dressed stones, (iii) clay bricks, and (iv) solid or hollow concrete blocks. The units are

assembled with mud mortar, lime mortar, or cement mortar. The stone blocks used in load

bearing masonry are generally quite large, the commonly used dimensions being 400 mm by 600

mm by 225 mm thick. The roof structure consists of either Manglore clay tiles laid on timber

planks supported by purlins and rafters made from wooden logs or a reinforced concrete slab.

When the building has more than one storey, the floors and roofs are generally reinforced

concrete slabs.


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Figure 13: A village house in Kachchh; stone masonry with manglore roof


Many buildings in Kutch of up to 2 storeys in height are made of random rubble masonry

construction. The 26 January 2001 earthquake caused massive damage to these buildings. A

great many partially or completely collapsed, especially close to the epicentre in Bhuj, Anjar,

Bachau and Sukhpur, where the destruction was almost total. Towns and villages that are further

from the epicentre of the earthquake were less affected but only in the sense that total collapse

was not as widespread. For example, near the villages of Kera or Naranpur buildings of this

nature were still standing with sometimes only partial collapse.

Figure 14: Destruction of heavy stone masonry walls that had no reinforcement and were not tied to each other



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Figure 15: Partial collapse of gable wall for a single storey random masonry wall in kera


During the earthquake, many buildings easily separated at corners and T-junctions resulting in

walls overturning and roofs collapsing, which killed thousands of people. This was because the

random rubble walls were made of uneven stone and the stones were laid on either weak soil or

mortar bedding. Under the heavy seismic shaking, the tensile strength of the mortar (and rubble) was easily exceeded, and walls bulged or totally collapsed.

Figure 16: Heavily damaged single storey rubble masonry wall with concrete roof in Manukawa & Sukhpur. Note: Walls survived due to diaphragm action from roof. Cantilever beams embedded in walls also helped this.

Note: window openings are also not close to corners. Source: Beneficial effects of masonry infill walls on seismic performance of RC frame buildings. 12th World

Conference on Earthquake Engineering, Auckland, New Zealand, Paper No.1790.


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NON-ENGINEERED CUT-STONE MASONARY WALL BUILDINGS:

Generally, cut-stone and concrete blockwork buildings are built with more care and attention

than rubble masonry structures but again were not seismically designed. Older buildings had

timber floors and roof, while newer construction have concrete floors with a flat concrete roof or

a clay tiled timber roof. Many were damaged but did not collapse. Damage varied from slight to

heavy damage.

The masonry buildings which performed the best, have the following features in common:

Cut-stones were bedded in cement mortar

Roofs were properly fixed to the top of the walls.

Window openings were sensibly sized in relation to the total wall length;

Buildings were symmetrical with no concentrated masses;

Many had cross walls at sensible spacing, although it was unclear whether they were

adequately tied at T and L junctions;

Foundations were typically founded at 0.5 to 1.0m depth, probably on firm to medium dense soils or rock.

Figure 17: Cut-stone building in Bhuj


An old government building (predating 1900s) made with solid cut stone masonry walls is

shown in Figure 17. This building received slight to moderate damage although it is in the centre

of Bhuj and all around, rubble buildings have totally collapsed.


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Figure 18 shows a two-storey modern cut-stone wall building near Bhuj, in town called

Mirzapur.

The building has cut-stone walls about 0.225 to 0.3m thick and has a 1st level concrete floor and

a pitched timber roof. The window openings are not close to the edge and are also sensibly

spaced. This is probably one of the main reasons why it survived with so little damage. Even so

some vertical bending cracking has happened near to the corners, again due to out of plane shear

forces.

Figure 18: Modern cut-stone masonry building in Mirzapur


Many buildings which did not collapse suffered from severe diagonal cracking at their corners,

some with partial collapse at corners, primarily because of window openings being too close to

the corner and because of lack of toothing between returns.


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NON-ENGINEERED REINFORCED CONCRETE BUILDINGS:

In the last 10 to 15 years reinforced concrete frame structures have become a common

construction feature of domestic buildings in Kutch. These are usually frames of concrete

column and slab construction with either a flat concrete roof or a pitched timber roof to keep the

interior of the building cool in the summer. They are usually up to 2 to 3 storeys in height. These

buildings were designed to support the vertical weight of the structure. The majority were

damaged in the earthquake because they were not designed to resist horizontal forces caused by

seismic loading.

Figure 19: The inset shows large deformations were concentrated at

column heads, which caused many soft storey failures, as per picture. Buildings if designed with uniform deflections as per left diagram

of insert would have survived without collapse. Source : Gujarat Relief Engineering Advice Team (GREAT)

Figure 19 shows a building, which collapsed because part of the floor area was converted to an

opening for car parking. The building was subjected to torsion about its centre of rigidity and

failed because of soft storey behaviour with large deformations and rotations concentrated at the

top of the columns.


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Figure 20 : Soft storey second floor collapse in Sukhpur

Source : Gujarat Relief Engineering Advice Team (GREAT)

Figure 20 shows a building where the owner had a middle floor supported on columns with large

internal open spaces, and hardly any masonry infill walls. Under seismic loading, large

deformations occurred at the top and bottom of the columns and a soft storey collapse occurred,

the upper floor storey falling onto the first storey. This shows that soft storey collapses do not

always occur at ground floor.

Often, the owner retained an local architect and sometimes a local structural engineers practice

to design the building. Even so, no buildings were designed for seismic shaking. If it were not for

buildings having non-structural infill wall panels many more buildings might have experienced total collapse.

Seismic shear force and deformations would have been

concentrated at the column heads, causing soft storey

failures as occurred in many multi-storey structures with large

openings at ground level.


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Example of a 3-Storey reinforced concrete frame structure, which is severely

damaged in Kundanpur (near Kera) Kutch:

An example of a recently completed reinforced concrete frame building with block work

masonry infill walls which was severely damage, caused by a catalogue of poor design practices

is described below. The owner of this property had retained the service of a local engineer to

design his building.

a) Poor building configuration (resulting in torsion during earthquakes). The ground

floor plan was asymmetrical (L-shaped internally) relative to the floors above. As a result,

the whole building at ground floor level has twisted clockwise under the heavy mass from

the floors above. Severe damage has occurred to the walls and columns at ground floor

level. The reason for the L shape plan at ground level was because the owner wanted a large

open plan living room area.

b) Discontinuous columns. Figure 21 shows that the external columns along the wall are

not continuous with the columns at first floor level and above. Only the corner columns are

continuous through all the floors. This was a building where the owner decided during

construction that the engineer had not allowed enough columns and he decided to place a

few more between the walls. Unfortunately, they were placed randomly along the walls as

shown.

c) Large window openings. Figure 21 also shows that the window openings between

columns are large, exceeding the limit of 33% of total wall length as advised by the Indian

codes for a three storey plus roof structure.

d) Short column failures. Short column failure (diagonal cracking) can be seen to have

occurred over the mid height of all the external concrete columns (these were 225mm

square) and through the masonry columns. This is because when infill walls with wide

openings are attached to columns, the portion of column that will deform under lateral

seismic loading becomes very short compared to its normal height. Such short columns

become much stiffer and attract much larger shear forces resulting in severe diagonal

tension and cracking failure in the columns.

Under the action of the seismic shear and torsional effects, the damage to this building was

largely concentrated at ground floor level with upper floors remaining intact and undamaged.

The first floor concrete slab and beams were undamaged by the earthquake.

The foundation plans show walls were on concrete strip foundations, 0.75m wide, founded at a

depth of 0.9m below ground. The external canopy columns were on 1.2m square pad foundations

located at the same depth. The building was founded on a mixture of weak weathered sandstone

rock at one end and medium dense to dense sand at the other end. The owner stated that the

foundations had not failed. Photos and videos examined by the authors confirmed this was

correct. There was no evidence of the structure experiencing significant total and differential

settlement.


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Figure 21: Floor plans


Figure 22: Building under construction one year prior to earthquake



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Figure 23: Damage to completed building after earthquake

Figure 24: Large window openings close to corners and short

column failures

Figure 24 a : Diagonal cracking at corner column caused by twisting

of frame and short column failure.



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Performance of reinforced concrete frame buildings

A large number of reinforced concrete frame buildings located in Ahmedabad suffered serious

damage or collapsed. As stated earlier, Ahmedabad is about 300 km from the epicenter. At such

a distance the intensity of ground motion would not be expected to be large. The fact that a

number of buildings in Ahmedabad suffered damage could be attributed to several factors. Many

buildings were founded on deep sediments deposited by the Sabarmati river. This may have

amplified the ground motion experienced by such buildings.

Another important factor contributing to the damage was the use of open first storey combined

with poor detailing and indifferent quality of construction. Almost all buildings with open first

storey suffered some damage. In some cases the buildings collapsed, while in some others the

damage was so severe that the buildings had to be written off. At the time of our visit, which is

about 7 weeks after the earthquake, the rubble from the collapsed building had been cleared but

the severely damaged buildings had not been pulled down.

Figure 25: A block of damaged reinforced concrete frame buildings in Ahmadabad


A typical example of a framed building with open first storey is shown in Fig. 25, which shows

what was once a complex of four identical five-storey blocks. Each block had a reinforced

concrete frame construction with an open first storey and brick infill walls in upper storeys. Two

of the four blocks, which were located in the foreground of the picture, completely collapsed

killing several residents. The other two blocks that are seen standing in the picture suffered

severe damage. The owners have decided to pull them down. Temporary supports have been

provided to the buildings in their lowest storey so that the useful contents of the buildings could

be salvaged.


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Any number of examples can be cited of the damage suffered by the open first storeys in

multistory reinforced concrete buildings in Ahmedabad. A particularly tragic case was of a ten-

storey building known as Shikhara. The building was in the shape of an H. It had been completed

only recently and was not fully occupied. One of the open arms of the H collapsed during the

earthquake causing the death of 89 persons. Details of the building are shown in Figs. 26 and 27.

The collapse was evidently caused by the failure of the columns in the open first storey. The

first-storey columns in parts of the building that remain standing are severely damaged. Attempts

have been made to repair these columns, as shown in Fig. 26, but the residents are unwilling to

return to the building.

The technique used for repairs to the columns of the first storey can be observed from Fig. 27.

The columns are being prepared for concrete jacketing. In the present case they have been

encased in four vertical angle sections, one at each corner. The angles are tied together by

welding horizontal steel bars. Forms will be erected around this assembly and concrete will be

poured from an open space at the top of the forms to complete the concrete jacket.

Figure 26: One wing of the Shikhara building detached itself from the building and collapsed.



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Figure 27: Repairs to damaged columns in the first storey of the shikhra building


Another large reinforced concrete frame building whose failure attracted much publicity was the

Mansi building located in downtown Ahmedabad. The building is 12 stories tall and consists of

two identical but separate blocks. A part of one of the two blocks completely collapsed killing

22 people. The open first-storey columns of the parts that remain standing are heavily damaged.

The building has been abandoned and its fate remains to be decided. Figures 28 and 29 show

some details of the damaged building. An observation of the remaining parts of this building

indicates that the most likely cause of the collapse was the soft first storey. The masonry infills in

the upper stories of the building make the building stiff, attracting significantly higher

earthquake forces. The high shears imposed on the first-storey columns have caused damage to

the visible hinge regions at the top of the columns, as well as shear failure in some of the

columns, as seen in Figure 29.


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Figure 28: The portion of the Mansi building that collapsed detached itself from the block seen in the

foreground; the other block in the background is still standing, but its first-storey columns are heavily damaged.

Figure 29: Shear failure of a first-storey column in the Mansi building.



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Concrete frame buildings with open first storeys and masonry infill walls in the upper levels

located in the epicentral region of Bhuj, Anjar, and Gandhidham suffered a worst fate. First, the

ground motion was more intense in these areas; second, the infills were in most cases made with

heavier stone blocks rather than in clay bricks. Some examples of damaged or collapsed

buildings are shown in Figs. 3032. Figure 30 shows the collapsed open first storey of a four

storey concrete frame building in Bhuj in which the upper storeys have come down as a rigid

body. Figure 31 shows a similar building also in Bhuj. In this case the columns on one side of the

building failed and the building came down to rest on its side. Figure 32 shows some columns in

the first storey of a building in Anjar. The loss of concrete cover and the lack of sufficient hoop

reinforcement have caused the columns in the open storey to be severely damaged in the hinge

region.

Figure 30: The open first storey of this building in Bhuj was crushed bringing the upper three storeys down.

Figure 31: The columns on one edge of the open first storey of this building in Bhuj collapsed bringing the

building down on its side.



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Figure 32: Failure of column through plastic hinging and buckling of longitudinal reinforcement due to loss of

concrete cover and insufficient hoop reinforcement.



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Summary and conclusions from the case study:

The moment magnitude Mw 7.7 earthquake that struck the Kachchh region of the province of

Gujarat in India at 8:46 a.m. on 26 January 2001 caused tremendous loss of life and property.

The epicenter of the earthquake was located at 50 km northeast of the town of Bhuj. The

earthquake was felt over a large part of India, and while the greatest damage due to the

earthquake occurred in the region of Kachchh, many other parts of Gujarat, including the major

urban center of Ahmedabad, were quite severely affected. The official estimate of casualties is

20 000. The number of injured is reported to be 166 000. The earthquake caused extensive

ground movement, cracking, liquefaction, and lateral spreading in the region of Kachchh. About

370 000 houses and huts were completely destroyed, while another 931 000 were partially

destroyed. The total financial loss is estimated at $7.1 billion (around 379,850,000,000 Indian

rupees).

Important conclusions that can be drawn from the present survey can be summarized as follows:

1. There is a need for a study of the type of earthquakeresistant construction that would be

suitable for the rural areas and smaller urban centers of developing countries. Most of the

destruction caused by earthquake has taken place in such countries, and in the present age of

global interaction and global economy it is incumbent upon developed countries such as Canada

to undertake such a study.

2. The beneficial effect of masonry infill walls in reinforced concrete frames in resisting

earthquake forces was evident in the performance of various buildings during the Gujarat

earthquake. The infills prevented the collapse of many buildings even though such infills were

neither reinforced nor positively tied to the boundary elements. A comprehensive study is

required to assess the effectiveness of infill panels in providing resistance to earthquake forces.

3. Experience during the Gujarat earthquake has shown that building codes and standards should

form the basis of regulations governing building design, so that they have a legal standing.

Although India has a comprehensive set of codes and standards governing earthquakeresistant

design, they do not have a legal standing and are thus only advisory in nature. A consequence of

this was that the designers in Gujarat had little incentive to conform to the codes and standards,

and even the engineered buildings did not conform to the recommendations of the relevant codes

and standards.

4. The Gujarat earthquake reestablished the need for designing the lifeline structures and

essential facilities to ensure their survival during such events, so that the services necessary for

rescue and recovery are not adversely affected. Widespread failure of power in the district of

Kachchh was caused because a large number of control room buildings in the electric substations

collapsed, damaging the control equipment and batteries. A number of hospital buildings,

telephone exchange buildings, civil administration buildings, and water service buildings were

damaged or destroyed, seriously hampering the rescue and relief operations.


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SECONDARY STUDY:-

China Country of many earthquakes.

China locates between the two largest seismic belts, i.e. the circum-Pacific seismic belt

and the circum-Indian seismic belt. Squeezed by the Pacific plate, the Indian plate and the

Philippine plate, the seismic fracture zones are well developed in this area. Ever since we entered

the 20th century, more than 800 earthquakes of more than magnitude 6 have happened in China.

Earthquakes have happened in almost all the provinces, municipalities and autonomous regions

except in Guizhou, Zhejiang and Hong Kong.

Earthquakes occurring in China were characterized by their high frequencies, seismic intensity,

shallow epicenter and wide distributions. China, as a matter of fact, is a country with many

earthquakes. Ever since 1900, over 550,000 people died in earthquakes in China, which takes up

53% of the total casualties in earthquakes around the world. Ever since 1949, more than 100

destructive earthquakes have happened in the provinces, municipalities and autonomous regions

of China, among which 14 of them are provinces in East China. These earthquakes caused the

death of more than 270,000 people, which took up 54% of the total death toll caused by natural

disasters in China. The earthquake stricken districts cover an area of 300,000 square kilometers

and more than 7 million rooms were destroyed by earthquakes. The earthquakes and other

natural calamities are becoming the main threats to China in peaceful time.


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1.Taipei 101, Taiwan, China

Taipei 101 formerly known as the Taipei World Financial center, is a landmark skyscraper

located in Taipei, Taiwan. The building ranked officially as the worlds tallest from 2004 until

the opening of the burj khalifa in dubai 2010.

In july 2011, the building was awarded LEED platinum certification, the highest award in the

Leadership in Energy and Environmental design (LEED).

Taipei 101 is designed to withstand the typoon winds and earthquake tremors common in its

area of the Asia-Pacific. Planner aimed for a structure that could withstand gale winds of

60m/sec (197 ft/s, 216 km/hr) and the strongest earthquake likely to occur in a 2,500 year

cycle.

Figure 33: Typical Floor Plan

The form of the building is simple geometric shape and symmetrical itself.


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2.Sky city, Hunan, China

Sky City, an 838-meter (2,750-ft) building to be built by Chinese construction company Broad

Sustainable Building (BSB), of Broad Group, will not just be the tallest skyscraper on the planet,

but also it will be most sustainable building on the planet and most earthquake proof structure.

According to Gizmag: If the target is met, the 838-meter (2,750-ft) Sky City One will take

only a twentieth of the time that the Burj Khalifa, the worlds current tallest building, took to

construct, and will stand 10 meters (33 feet) taller still upon completion.

Sky City One advertises itself as an earthquake-resistant, carless city which will accommodate

approximately 100,000 people and provide retail and leisure facilities.

The structural engineers of the sky city confidents about the buildings stability and assured that

the building can bear earthquake of 9.0 m at a time.

Figure 34: Sky city, Hunan


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The National Disaster Management Authority, in its recently released guidelines have made it

mandatory for all new constructions in Delhi and Mumbai to have earthquake-resistant

structures. Delhi falls in seismic zone IV, which makes it highly vulnerable to earthquakes.

While rajasthan comes under zone II and zone III.

India's increasing population and extensive unscientific constructions mushrooming all over,

including multistoried luxury apartments, huge factory buildings, gigantic malls, supermarkets as

well as warehouses and masonry buildings keep - India at high risk. During the last 15 years, the

country has experienced 10 major earthquakes that have resulted in over 20,000 deaths. As per

the current seismic zone map of the country (IS 1893: 2002), over 59 per cent of Indias land area is under threat of moderate to severe seismic hazard.

The North-Eastern part of the country continues to experience moderate to large earthquakes at

frequent intervals including the two great earthquakes. Since 1950, the region has experienced

several moderate earthquakes. On an average, the region experiences an earthquake with a

magnitude greater than 6.0 every year.

Source The National Disaster Management Authority of India

The Bureau of Indian Standards (BIS), updated the seismic hazard map of India in 2006. Apart

from the merging of Zones I and II, there are no major changes in the new hazard map with

respect to the state of Rajasthan, as compared with the previous 1984 BIS map.

Western parts of the districts of Barmer and Sirohi as well as northern sections of Alwar district

lie in Zone IV, where the maximum intensity could reach 8.0M. The remaining areas of Barmer

and Sirohi districts, as well as the districts of Bikaner, Jaiselmer and Sirohi lie in Zone III. The

north-eastern districts of Jhunjhunu, Sikar, Bharatpur and the rest of Alwar also lie in Zone III.

The maximum intensity expected in these areas would be around 7.0 M. The rest of the state,

including the capital, Jaipur, lie in Zone II, where the maximum intensity expected would be

around 6.0M .It must be noted that BIS estimates the hazard, based in part, on previous known

earthquakes. Since the earthquake database in India is still incomplete, especially with regards to

earthquakes prior to the historical period (before 1800 A.D.), these zones offer a rough guide of

the earthquake hazard in any particular region.

Source http://asc-india.org/seismi/seis-rajasthan.htm


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According to the Indian Standard CRITERIA FOR EARTHQUAKE RESISTANT

DESIGN OF STRUCTURES, The building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity so that the centres of mass and rigidity of the building coincide with each other in which case no separation sections other than expansion joints are necessary. If symmetry of the structure is not possible in plan, elevation or mass, provision shall be made for torsional and other effects due to earthquake forces in the structural design or the parts of different rigidities may be separated through crumple sections. The length of such building between separation sections shall not preferably exceed three times the width. Buildings having plans with shapes like, L, T, E and Y shall preferably be separated into rectangular parts by providing separation sections at appropriate places.

Figure 35: TYPICAL SHAPES OF BUILDING WITH SEPARATION SECTIONS

Source: Indian Standard CRITERIA FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURES


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Separation of adjoining structures or parts of the same structure is required for structures having different total heights or storey heights and different dynamic characteristics. This is to avoid collision during an earthquake.


Figure 36: An irregular shape faces more torsion on the vertical section.


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Figure 37: Plan with vertical irregularities



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Inferences

In the previous chapters we have seen that how earthquake attacks the buildings/structure

and also, we had studied about the buildings that resists these earthquake not completely but

partially.

Now we will study about the building forms, affects of earthquake forces and various properties

of building forms based on the earthquake building codes.

With the above study, it is concluded that earthquake behaves with some forces i.e.,

1. Elastic behavior, and 2. Non-elastic behavior

On buildings.

1. ELASTIC BEHAVIOUR:

Elastic earthquake behavior of buildings is primarily controlled by configuration and

Stiffness, out of the four virtues of configuration, stiffness, strength and ductility. All buildings

discussed in this Chapter are designed for full gravity load and lateral load equal to 10% of the

total building weight to illustrate various concepts of elastic behavior of buildings; the actual

design lateral force of similar buildings will depend on many factors, like seismic zone, and type

of framing system, as specified by the design codes. The total lateral force is distributed over the

building height and plan using provisions given in the Indian Seismic Code IS:1893 (Part 1) 2007.

Buildings oscillate during earthquake shaking and inertia forces are mobilized in them.

Then, these forces travel along different paths, called load paths, through different structural

elements, until they are finally transferred to the soil through the foundation. The generation of

forces based on basic oscillatory motion and final transfer of force through the foundation are

Significantly influenced by overall geometry of the building, which includes:

(a) plan shape, and

(b) Plan Aspect ratio.

Plan Shape: The influence of plan geometry of the building on its seismic performance is best

understood from the basic geometries of convex- and concave-type lenses (Figure 38). Buildings

with former plan shape have direct load paths for transferring seismic inertia forces to its base,

while those with latter plan shape necessitate indirect load paths that result in stress

concentrations at points where load paths bend. Buildings with convex and simple plan

geometries are preferred, because they demonstrate superior seismic performance than those with

concave and complex plan geometries.


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Figure 38: convex- and concave-type building plans

To illustrate the above concept, five-storey moment frame buildings with seven plan shapes

are considered; six of them have complex plan geometries and one has the simple rectangular

Geometry (Figure 3.1). Each building has a basic frame grid with columns spaced at 4m, i.e.,

each unit is of 16m2 area. The rectangular having plan dimensions of 12m16m, with 3 and 4

bays in the two perpendicular plan directions (Figure 3.2).


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Figure 39: Plan shapes of buildings

Buildings with (a) simple shapes undergo simple acceptable structural seismic behaviour, while

(b) those with complex shapes undergo complex unacceptable structural seismic behavior.

Figure 40: Rectangular building plan

Each building with complex shape is composed of the basic 3 bay by 4 bay rectangular modules with column spacing of 4m in each plan direction.


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Rectangular (or square) columns are good in resisting shear and bending moment about

axes parallel to their sides. Thus, it is important to have buildings oscillating primarily along

their sides translation along diagonals or torsional motions are NOT good for seismic performance of columns, and hence, of buildings (Figure 3.3). Further, in regular buildings, the

overall motion is controlled by the first few modes of oscillation; the fundamental mode

(corresponding to largest natural period) usually contributes maximum, followed by the 2nd

mode, 3rd mode, etc. Thus, it is desirable to have pure translation modes as the lower modes of

oscillation and push torsional and diagonal translational modes to the higher ranks. Primarily,

these undesirable (diagonal translation and torsional) modes arise when there is lack of

symmetry in the plan shape of buildings along the sides. It is important to have regular plan

shape of buildings.

Figure 41: Diagonal translational and torsional oscillatory motions


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Six buildings, without any irregularity in mass or stiffness, but with complex shapes are

chosen to compare the effect of plan shape on elastic behavior of buildings 42. These

buildings have approximately the same plan area of about 2496m2.

Figure 42: Buildings of different plan shapes

Buildings with complex shapes, particularly with projections or re-entrant corners, exhibit

special modes of oscillation, in addition to translatory (pure or diagonal) or torsional modes.

These include an opening-closing mode, and the unique local-high-frequency oscillatory mode

like, that of the wagging of a dogs tail. Dog tail wagging mode of oscillation is interesting

because in this mode, only a slender or long projection oscillates and the remaining part of the

building almost remains still, just like the dogs body remains still when its tail wags. The effect of these special modes of oscillation is to induce high stress concentration at the re-entrant

corners that may cause minimum structural damage.

Another common discontinuity in load path in moment frames arises with set-back columns,

i.e., when a column coming from top of the building is moved away from its original line, again

usually at the ground storey. In such cases, loads from the over hanging portions take detour and

cause severe stress concentration at the re-entrant corners while traveling to the nearest set-back

column. In addition, the set-back divides the span of beams into smaller segments, and thereby,

pushes these beams into shear action (as against flexural action; Figure 3.36). These beams then

draw large amount of shear force, and can fail in brittle shear mode. As a consequence, set-back

columns subjected to large axial force, become vulnerable to combined axial-moment-shear

failure.


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Figure 43: Building with lack of grid planning

Non-uniform distribution of forces can cause localized failures in members thereby affecting the

structural integrity of the building.

(A)


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(B)

(C)

(D)

Figure 44: Buildings with lack of grid, showing BM distribution

Source: Earthquake behavior of buildings, Govt. of Gujarat


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2. INELASTIC BEHAVIOUR

Some structural damage is allowed during strong earthquake shaking in normal buildings,

even though no collapse must be ensured. This implies that nonlinearity will arise in the overall

response of buildings, which originates from the material response being nonlinear. This

nonlinearity arising from the material stress-strain curve is called material nonlinearity. But,

sometimes, the stress-strain curve may be nonlinear and also elastic, whereby on unloading, the

material retraces the loading path. Structural steel has definite yield behavior and does not

retrace its loading path when unloaded after yielding. Such a response is more commonly

referred to as inelastic response. When an inelastic material is subjected to reversed cyclic

loading (of displacement type) which takes the material beyond yield, hysteresis takes place, i.e.,

the material under the applied loading absorbs/dissipates energy. Reinforced concrete and

structural steel are candidate materials for inelastic behavior. Under strong earthquake shaking,

normal reinforced concrete and steel buildings experience inelastic behavior.

Hence, with the help of above data and analysis it is noted that to design an earthquake resistant

structure, both the building form and structural details are to be considered in designing.

The four important properties of earthquake are to be considered:

1. Stiffness

2. Strength 3. deformation 4. energy based

Of the four methods of design, the deformation-based design method is the most advanced, and

is expected to give best earthquake performance. It requires more engineering experience and

judgment, but the results build more confidence in designers to arrive at a building that is more

likely to perform as intended. Therefore, this method is best suited for special buildings, where

earthquake performance of the building should be guaranteed, e.g., critical and lifeline buildings

that are required to remain functional after the earthquake.


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earthquake resistant building forms

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