EQ-CLASS.pdf

AR 2079 EQ RESISTANT ARCHITECTURE

UNIT I

Fundamental of EQ

UNIT II Site planning, Performance of Ground & Building

UNIT III Seismic Design Codes and building Configuration

UNIT IV Various Types of Construction Details

UNIT V Urban planning and design

2005 NPEEE Earthquake Design Concept : Lecture 1: Impact of Earthquakes

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2005 NPEEE Earthquake Design Concept : Lecture 2: Plate Tectonics & Seismic Waves 25/23

Long time ago, a large

collection of material

masses coalesced to

form the Earth. A large

amount of heat was

generated by this

fusion, and slowly as

the Earth cooled

down, the heavier and

denser materials sank

to the center and the

lighter ones rose to

the top.

The differentiated Earth consists of the Inner Core

(radius ~1290km), the Outer Core (thickness

~2200km), the Mantle (thickness ~2900km) and the

Crust (thickness ~5 to 40km).


Convection currents

develop in the

viscous Mantle due to

prevailing high

temperatures and

pressure gradients

between the Crust

and the Core

These convection currents

result in a circulation of the

earths mass; the temperature difference

causes interlayer movement.

The hot molten lava rises and

the cold rock mass sinks into

the Earth.


The convective flow of Mantle material cause the Crust and some portion of the

Mantle, to slide on the hot molten outer core. This sliding of Earths mass takes place in pieces called Tectonic Plates.


Many such local circulations are taking place at different regions underneath the Earths surface, leading to different portions of the Earth undergoing different directions of

movements along the surface.


The Himalayas are formed due to conveyance of Indo-Australian plate

The relative movement of these plate boundaries varies across

the Earth; on average, it is of the order of a couple to tens of

centimeters per year.


after the earthquake is over, the process of strain build-up at this modified interface

between the rocks starts all over again. This is Stage AB

This is know as

Elastic Rebound

Theory

2005 NPEEE Earthquake Design Concept : Lecture 18: Vernacular Structural Systems 35/45


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Seismic Zones of India

The varying geology at different locations in the country implies that the likelihood of damaging earthquakes taking place at

different locations is different.

Thus, a seismic zone map is required so that buildings and other structures located in different regions can be designed to

withstand different level of ground shaking.

The seismic zone map of 1984 subdivided India into five zones I, II, III, IV and V.

Parts of Himalayan boundary in the north and northeast, and the Kachchh area in the west were classified as zone V.


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The seismic zone maps are revised from time to time as more

understanding is gained on the geology, the seismotectonics and

the seismic activity in the country. For instance,

Koyna earthquake of 1967 occurred in an area classified in

zone I as per map of 1966. The 1970 version of code upgraded

the area around Koyna to zone IV.

Killari (Latur) earthquake of 1993 occurred in zone I. The current

Indian seismic zone map places this area in zone III.

The zone map now has only four seismic zones II, III, IV and V. The areas falling in seismic zone I in the 1984 map were merged

with those of seismic zone II.

Chennai now comes under seismic zone III as against zone II in

1984 map.


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The national Seismic Zone Map presents a large-scale view of the seismic zones in the country.

Local variations in soil type and geology cannot be represented at that scale.

Therefore, for important projects, such as a major dam or a nuclear power plant, the seismic hazard is

evaluated specifically for that site.

Also, for the purposes of urban planning, metropolitan areas are microzoned. Seismic microzonation accounts

for local variations in geology, local soil profile, etc.


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Measuring Instruments The instrument that measures earthquake shaking, a seismograph, has three components Sensor Recorder Timer. The principle: A pen attached at the tip of an oscillating simple pendulum marks on a chart paper that is held on a drum rotating at a constant speed. A magnet around the string provides required damping to control the amplitude of oscillations. The pendulum mass, string, magnet and support together constitute the sensor; the drum, pen and chart paper constitute the recorder; and the motor that rotates the drum at constant speed forms the timer.


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One such instrument is required in each of the

two orthogonal horizontal directions. Of course,

for measuring vertical oscillations, the string

pendulum is replaced with a spring pendulum

oscillating about a fulcrum.

Some instruments do not have a timer device

(i.e., the drum holding the chart paper does not

rotate). Such instruments provide only the

maximum extent (or scope) of motion during the

earthquake; for this reason they are called

seismoscopes or scratch plate accelerometers.


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The point on the fault where slip starts is the Focus The point vertically above this on the surface of the Earth is the Epicenter

The distance from the epicenter to any point of interest is called epicentral distance

The depth of focus from the epicenter, called the Focal Depth, is an important parameter in determining the

damaging potential of an earthquake.

Most damaging earthquakes have a shallow focus with focal depths less than about 70km..

After & Before shocks More numbers


MedvedevSponheuerKarnik scale (USSR-Germany-Czechslovakia)


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.

Intensity is a qualitative measure of the actual shaking

at a location during an earthquake, and is assigned as

Roman Capital Numerals.

Two commonly used ones are the Modified Mercalli

Intensity (MMI) Scale and the MSK Scale. Both scales

are quite similar and range from I (least perceptive) to

XII (most severe).

The intensity scales are based on three features of

shaking perception by people and animals, performance of buildings, and changes to natural

surroundings


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Magnitude of an earthquake is a measure of its size. For

instance, one can measure the size of an earthquake by the

amount of strain energy released by the fault rupture. This

means that the magnitude of the earthquake is a single value for

a given earthquake.

Intensity is an indicator of the severity of shaking

generated at a given location. Clearly, the severity of shaking is

much higher near the epicenter than farther away. Thus, during

the same earthquake of a certain magnitude, different locations

experience different levels of intensity


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The peak ground acceleration (PGA), i.e.,

maximum acceleration experienced by the ground

during shaking, is one way of quantifying the

severity of the ground shaking. Approximate

empirical correlations are available between the

MM intensities and the PGA that may be

experienced.


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These waves are of two types - body waves and surface waves

Body waves consist of Primary Waves (P-waves) and Secondary Waves (S-

waves)

Surface waves consist of Love waves and Rayleigh waves.

Under P-waves, material particles undergo extensional and compressional

strains along direction of energy transmission.

Under S-waves, oscillate at right angles to it P Waves . S-waves are the

primary cause of damage to buildings.

Love waves cause surface motions similar to that by S-waves, but with no

vertical component.

Rayleigh wave makes a material particle oscillate in an elliptic path in the

vertical plane (with horizontal motion along direction of energy transmission).


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P-waves are fastest, followed in sequence by S-, Love and

Rayleigh waves.

For example,

in granites,

P- and S-waves have speeds ~4.8 km/sec and ~3.0km/sec,

respectively.

S-waves do not travel through liquids.

S-waves in association with effects of Love waves cause

maximum damage to structures by their racking motion on the

surface in both vertical and horizontal direction


Random motion in earthquake shaking occurs in all directions; therefore buildings and

structures designed to resist earthquake shaking must have strength to withstand

shaking from any direction.

2005 NPEEE Earthquake Design Concept : Lecture 3: Basic Terminology &

Consequences of EQ

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Fault

A fracture in the earth along which the opposite

sides have been relatively displaced parallel to the

plane of movement. The Earths crust breaks along surfaces known as faults which are weak areas in

the crust along which opposite sides have been

displaced relative to each other. Faults occur when

stresses within the Earth build to a point that the

elastic properties of the rock are exceeded causing

irreversible strain or fracturing of the rock. Fault

lengths may range from a few centimeters to

hundreds of kilometers.


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Elastic rebound theory

The strain along the fault exceeds the limit of the

rocks at that point to store any additional strain. The

fault then ruptures--that is, it suddenly moves a

comparatively large distance in a comparatively

short amount of time. The rocky masses which form

the two sides of the fault then "snap" back into a new

position. This snapping back into position, upon the

release of strain, is the "elastic rebound.


Consequences of EQ

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The initial rupture point of an earthquake, where strain energy is first converted to

elastic wave energy; the point within the Earth which is the center of an earthquake.

The point on the fault where slip starts is the Focus or Hypocenter


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That point on the Earth's surface vertically above the hypocenter of an earthquake is

the Epicenter


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The depth of focus from the epicenter, called as Focal Depth

earthquake depth range of 0 - 700 km is divided into three zones: shallow, intermediate, and deep.


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Distance from epicenter to any point of interest is called epicentral distance


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Main shock believed to be the result of minor readjustments of stress at places in the

fault zone results in After shocks


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Dip Slip Faults

There are three primary types of fault motion (1) normal, (2) reverse, and (3)

strike slip. A normal (or gravity) fault is one in which one plate slips downward

along the plane relative to the other. The angle of dip is generally 45 to 90. A

reverse fault is one in which one plate slips upward along the plane relative to

the other. The angle of dip is generally 45 or more. Along the Himalayas,

reverse faulting is occurring.

Strike Slip Faults

A strike-slip fault is one in which the movement is predominantly horizontal

and approximately parallel to the strike of the fault. Strike-slip faults can be

classified as right lateral or left lateral depending if the fault block opposite the

viewer moved right or left, respectively. The San Andreas fault in California and

the north Anatolian fault in Turkey are examples of predominant strike-slip

faults.


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Earthquake Ground Shaking

The motion of the ground can be described in terms of displacement,

velocity or acceleration. The variation of ground acceleration with time

recorded at a point on ground during an earthquake is called an

accelerogram.

They carry distinct information regarding ground shaking; peak amplitude,

duration of strong shaking, frequency content (e.g., amplitude of shaking

associated with each frequency) and energy content (i.e., energy carried by

ground shaking at each frequency) are often used to distinguish them.

Peak Ground Acceleration, PGA) is physically intuitive. For instance, a

horizontal PGA value of 0.6g (= 0.6 times the acceleration due to gravity)

suggests that the movement of the ground can cause a maximum horizontal

force on a rigid structure equal to 60% of its weight. In a rigid structure, all

points in it move with the ground by the same amount, and hence experience

the same maximum acceleration of PGA.


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Generally, the maximum amplitudes of horizontal motions in the two orthogonal directions are about the same.

However, the maximum amplitude in the vertical direction is usually less than that in the horizontal direction.

In design codes, the vertical design acceleration is taken as a half to two-thirds of the horizontal design acceleration.

In contrast, the maximum horizontal and vertical ground accelerations in the vicinity of the fault rupture do not seem to have such a correlation.

Buildings have proved capable of withstanding vertical accelerations with the exception of horizontal cantilevers .

It is the horizontal accelerations that cause damage to buildings, and these must be designed for.


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Liquefaction

Quick sand condition in soils is a very well known

phenomenon. An upward flow of water through a sand leads to

this effect. Soil liquefaction is also known as quick-sand

condition.

If saturated cohesionless soils, like sands are subjected to

earthquake ground motions, the resultant tendency to compact

is accompanied by an increase in the pore water pressure in soil

and a resulting movement of water from the voids.

Being lighter than soil, water is caused to flow upward to the

ground surface, where it emerges and manifests in the form of

mud spouts or sand boils. The development of high pore water

pressure due to ground vibration and the resulting upward flow

of water turns the soil into a liquefied condition. Under this Fluid

conditions, heavier buildings sink, lighter buildings rise, and

unsymmetric building tilt


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Jelly on a plate


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Rupture of gas lines, overturning of

stoves and heaters, and short

circuiting of electrical wires


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Tsunamis are giant ocean waves.

The most common causes are sudden rupture or faulting of sea bed or submarine earthquakes that shift a significant area of sea

floor upwards or downwards, displacing millions of cubic tonnes of

water.

The sudden introduction of a large amount of material into the ocean by an erupting submarine volcano, or sudden slide down

slope of ocean-floor sediments, or a landslide into water from a

cliff or collapsing volcano, has a similar effect.

Tsunamis are relatively common in earthquake-prone regions around Japan and along the rim of the Pacific Plate, and the word

tsunami is Japanese for port wave or harbour wave.


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Tendency to continue to remain in the previous position is known as inertia

From Newtons First Law of Motion, even though the base of the building moves with the ground, the roof has a tendency to stay in its original position.


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Consider a building whose roof is supported on columns.

Yourself on the bus: when the bus suddenly starts, you are thrown backwards as if someone has applied a force on the upper body.

Similarly, when the ground moves, even the building is thrown backwards, and the roof experiences a force, called inertia force.

If the roof has a mass M and experiences an acceleration a, then from Newtons Second Law of Motion,

Inertia force FI = M times acceleration a,

Direction is opposite to that of the acceleration.

Clearly, more mass means higher inertia force. Therefore, lighter buildings sustain the earthquake shaking better.


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Horizontal and Vertical Shaking

Earthquakes shake the ground in all three directions along the two horizontal directions (X and Y, say), and the vertical direction (Z, say) Also, during the

earthquake, the ground shakes randomly back and forth (- and +)

All structures are primarily designed to carry the gravity loads, The downward force

Mg is called the gravity load. The vertical acceleration during ground shaking either

adds to or subtracts from the acceleration due to gravity. Since factors of safety are

used in the design of structures to resist the gravity loads, usually most structures

tend to be adequate against vertical shaking.

However, horizontal shaking along X and Y directions (both + and directions of each) can collapse buildings. Hence, it is necessary to ensure adequacy of the

structures against horizontal earthquake effects. Thus the strength of structure to

resist internal forces referred to as stiffness forces, in the vertical elements like

columns/walls, becomes critical in achieving the safety of the building.

Provided a building is provided with sufficient strength in each of the X and Y

directions it will cope with shaking in any direction. Therefore architects must

ensure that each building has a suitable structural system that can resist X and

Y direction horizontal loads.


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Flow of Inertia Forces to Foundations

Under horizontal shaking of the ground, horizontal inertia

forces are generated at level of the mass of the structure

(usually situated at the floor levels).

These lateral inertia forces are transferred by the floor slab to the walls or columns, to the foundations, and finally to the soil

system underneath.

So, each of these structural elements (floor slabs, walls, columns, and foundations) and the connections between them

must be designed to safely transfer these inertia forces through

them.


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2005 NPEEE Earthquake Design Concept : Lecture 4: Factors Affecting EQ Loads 96/23


Fundamental natural period T is an inherent property of a building. Any alterations

made to the building will change its T


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Damping is a very important dynamic characteristic of a

building. It critically controls, i.e. reduces, the response of the

structure. Damping is a property of the building material and

the way it is combined to construct the building. Hence, the

choice of the building material is a crucial indicator of damping.

Reinforced concrete structures possess more damping than

steel structures. Damping also increases with increasing

response and damage during earthquakes.

Damping reduces the build-up of earthquake inertial forces

and reduces resonance.

We experience damping in cars which are fitted with

shock-absorbers that quickly dampen out vertical vibrations caused when a car travels over a bump. The damping in

buildings has the same effect but is smaller in its intensity.

2005 NPEEE Earthquake Design Concept : Lecture 5: Earthquake Load on Simple

Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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Buildings

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2005 NPEEE Earthquake Design Concept : Lecture 6: Seismic Design Philosophy & Code

Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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Requirement

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IS 1893 (Part 1) : 2002

IS 1893 is the main code that provides the seismic zone map (Figure 3) and

specifies the seismic design force. This force depends on the mass and

seismic coefficient of the structure; the latter in turn depends on properties like

seismic zone in which structure lies, importance of the structure, its stiffness,

the soil on which it rests, and its ductility. For example, a building in Bhuj will

have 2.25 times the seismic design force of an identical building in Bombay.

Similarly, the seismic coefficient for a single-storey building may be 2.5 times

that of a 15-storey building.

The revised 2002 edition, Part 1 of IS1893, contains provisions that are

general in nature and those applicable for buildings. The other four parts of IS

1893 will cover: Liquid-Retaining Tanks, both elevated and ground supported

(Part 2); Bridges and Retaining Walls (Part 3); Industrial Structures including

Stack-Like Structures (Part 4); and Dams and Embankments (Part 5). These

four documents are under preparation. In contrast, the 1984 edition of IS1893

had provisions for all the above structures in a single document.


Requirement

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Requirement

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Requirement

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Requirement

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2005 NPEEE Earthquake Design Concept : Lecture 7:Calculation of Design EQ Loads 150/16

2005 NPEEE Earthquake Design Concept : Lecture 8: Vertical Distribution of Base Shear 165/13


Two points to note

1. 80% of the mass of a

building is in its floor

slabs, floor live loads,

and the beams,

earthquake loads are

applied at the roof and

floor levels

2. In the case of wind

loads. However, in reality

all earthquake loads act

within the building.


Effect of the Earthquake

Loads


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Strength

After calculating the earthquake loads, the structural engineer analyses

the structure, usually with the help of computer software. The shear forces,

bending moments and axial loads in each member are determined, and the

required strength is provided in them.

In the case of a RC structure, members must possess enough

longitudinal and transverse reinforcing steel to resist the shear force and

bending moments due to both gravity and earthquake loads.

The strength of the building will be developed at a given amount of

sideways deflection or drift. After reaching its maximum strength members of

a ductile building will begin to yield in a ductile manner and the building will

drift with no significant gain or loss of strength.

The maximum building strength is greater than the Design strength. This

is because reinforcing steel and (hopefully) the concrete is stronger than that

specified.


Columns had no ductile detailing.


Poorly designed buildings may not collapse, but may be irreparably damaged

2005 NPEEE Earthquake Design Concept : Lecture 9: Overview of EQ resistant Structural

Systems

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Systems

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Systems

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Systems

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Consider a well configured building comprising flat slab construction and shear walls.

Gravity loads are resisted by the slabs and columns, while horizontal loads in both the

X and Y direction, are resisted by shear walls. The flat slab-column system will not

resist any significant horizontal forces because it is much more flexible than the stiff

shear walls


Systems

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Systems

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frames to perform well during strong shaking columns must be stronger than

beams. As a rule-of-thumb, columns must be at least as deep as the beams.


Systems

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Systems

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Systems

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Systems

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Systems

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The first requirement is that the wall must be continuous from foundation to roof.

Secondly, a strong foundation system is required to resist overturning moments


Systems

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Systems

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Systems

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Systems

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Systems

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Systems

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Y

X

Y

X Plan

Plan

Frame in

X and Y-directions

Shear walls in

Y-direction

Frame in

X-direction

Figure 19

Examples of Structural System per Direction


Systems

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Systems

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2005 NPEEE Earthquake Design Concept : Lecture 10: Earthen & Stone Wall Building 199/29

Classification of Earthen

Constructions

2005 NPEEE Earthquake Design Concept : Lecture 11: Load Bearing Masonry Buildings 228/35

2005 NPEEE Earthquake Design Concept : Lecture 13: MRF buildings 263/33


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Components of Moment-Resisting Frames

It is good practice to make the column cross-section rectangular and deeper

so that it can possess enough bending and shear strength. Note that the frame

is effective in the direction of the plane of the frame only. The frame will not

resist any loads at right angles to its length as its columns are too weak and

there are no beams framing into the columns in that direction.

RC moment-resisting frames require special reinforcement detailing, their

members should not be too small. The minimum size of columns should be 230

mm wide by 400 deep and such small members might even be too small for a

building over two storeys high depending on the seismic zone etc.

Since small structural member sizes are not recommended, the spans of

moment-resisting frames to resist seismic loads as well as gravity loads from

floor slabs, the distance between column centre-lines should typically be in the

range from 5m to 8m. Once the span exceeds 8m the beams become quite

deep and might not allow enough clear inter-storey height.


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The Indian Standard IS:1893 (Part 1) 2002 defines two types of earthquake

load moment-resisting frames.

1. Ordinary RC moment-resisting frames for which a Response Reduction Factor R=3.0 is specified. Then there are Special RC moment-resisting frames, or ductile frames with a R=5.0. Special frames require a Capacity Design Approach and special detailing to achieve the required amount of

ductility. Ordinary frames are not provided with such ductile features but

are designed stronger, in fact by 67%. In spite of their extra strength their

lack of ductility has lead to the Standard allowing their use in Seismic Zone

2 only.

2. Although in theory Special RC moment-resisting frames are ductile, in

practice it is very difficult to achieve the intentions and the requirements of the

Standard both in the design office and on the construction site. For a ductile

frame to have a high level of reliability very high design and construction quality

is necessary. If there is doubt about such quality assurance it is better to

consider using RC shear walls instead to resist seismic loads.

2005 NPEEE Earthquake Design Concept : Lecture 14: Ductility of MRFs 294/37


An unreinforced masonry structure in a high seismic hazard zone


All occupants in this strong-beam weak-column building were killed in the collapse

2005 NPEEE Earthquake Design Concept : Lecture 15: Cross-Braced Frames 327/22


Especially for one or two-bay

frames, tension piles may

become necessary to prevent a

braced frame from overturning

2005 NPEEE Earthquake Design Concept : Lecture 16: Floor & Roof Diaphragm 345/23

2005 NPEEE Earthquake Design Concept : Lecture 17: Load Paths 368/16

2005 NPEEE Earthquake Design Concept : Lecture 19: Plan Configuration 420/26

2005 NPEEE Earthquake Design Concept : Lecture 17: Vertical Configuration 446/30


This is one of the most common

configuration deficiencies. It leads to

many buildings collapsing in

damaging earthquakes. Such

buildings are commonly known as

Soft-Storey Buildings.


The Indian seismic code (IS:1893 (Part1) - 2002) mentions another approach. It states

that the frame should be 2.5 times stronger than usual, or provide a RC shear wall

whose strength is 1.5 times the forces appearing on the ground storey elements


Poor behaviour of short columns is due to the fact that in an earthquake, a tall

column and a short column of same cross-section move horizontally by same

amount .

However, the short column is stiffer as compared to the tall column, and it

attracts larger earthquake force. Stiffness of a column means resistance to

deformation the larger is the stiffness, larger is the force required to deform it.

If a short column is not adequately designed for such a large force, it can suffer

significant damage during an earthquake. This behaviour is called Short

Column Effect. The damage in these short columns is often in the form of X-

shaped cracking as a result of brittle shear failure


This question is often asked by architects!

The answer goes like this:

you may have slender columns, but only if you provide another structural

system, such as RC shear walls somewhere else in plan, that will resist all

earthquake loads. This technique then frees up the slender columns to carry

gravity load only in which case they can be slender.


In plaza type buildings, the usual solution is to separate the podium from the tower.

2005 NPEEE Earthquake Design Concept : Lecture 21: Masonry Infill Walls 476/32

Infill walls can be a valuable means of bracing for

low-rise buildings (no more than four storeys high,

provided they are continuous up the building, there

a plenty of infills in each principal direction and they

are reasonably symmetrically placed. However, so

often infills cause structural problems that lead to

building collapse.

2005 NPEEE Earthquake Design Concept : Lecture 22: Non-structural Elements 508/30


The architect should obtain the inter-storey drifts from the structural engineer and then

ensure the glazing is separated from its frames by sufficient clearances. If the

clearances required are quite large, special seismic mullions which provide considerable clearance can be used.

2005 NPEEE Earthquake Design Concept : Lecture 19: Pounding & Seismic Joints 538/14


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At the level of roof of the lower building, maximum drift = 0.02x15,000

= 300mm

Total gap required = 2x300mm

= 600mm.

This can be reduced by 50% if floor levels are aligned, and further if the structure

is less flexible than specified by the standard.

2005 NPEEE Earthquake Design Concept : Lecture 24: Cantilever, Foundation 553/9


Although the design of building foundations is the

responsibility of the structural engineer, who may consult a

geotechnical engineer when designing large buildings and

where difficult soil conditions exist, architects need to

understand the process and arrange sufficient funding from

the client.

2005 NPEEE Earthquake Design Concept : Lecture 25: Retroffiting & Base-Isolation 562/25

Retrofitting is the process of structural

upgrading of an existing building to meet

seismic design standards close to or

equivalent to standards expected of new

buildings.


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Seismic isolation is a relatively recent and evolving technology. It has been in

increased use since the 1980s, and has been well evaluated and reviewed

internationally.

Base isolation has now been used in numerous buildings in countries like Italy,

Japan, New Zealand, and USA. Base isolation is also useful for retrofitting

important buildings (like hospitals and historic buildings). By now, over 1000

buildings across the world have been equipped with seismic base isolation.

In India, base isolation technique was first demonstrated after the 1993 Killari

(Maharashtra) Earthquake [EERI, 1999].

Two single storey buildings (one school building and another shopping complex

building) in newly relocated Killari town were built with rubber base isolators

resting on hard ground.

Both were brick masonry buildings with concrete roof. After the 2001 Bhuj

(Gujarat) earthquake, the four-storey Bhuj Hospital building was built with the

base isolation technique.

2005 NPEEE Earthquake Design Concept : Lecture 27: Urban Planning and Professional

Communication

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Communication

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Communication

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Communication

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Communication

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This building was pushed upwards by about 7cm during the 2001 Bhuj earthquake


Communication

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Communication

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Steeper slopes have greater tendency to

undergo sliding failure under strong earthquake

shaking, particularly if the soil is saturated.

Steep slopes are prone to sliding in

earthquakes


Communication

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Communication

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Communication

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Communication

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Communication

EQ-CLASS.pdf

Documents

impact of earthquakes

seismic design codes

mantle thickness

plate tectonics seismic

crust thickness

outer core thickness

fundamental of eq unit

viscous mantle