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CHAPTER 1

INTRODUCTION

1.1 General Developing countries are more vulnerable to hazards because of their increasing rate of

development and urban growth. The lack of proper disaster management leads to increase in risk

in more densely populated cities. Most of the growth in terms of civil structures and infrastructure

will concentrate in the developing countries for the next few decades. These countries are already

loaded with various urban problems like population growth, urban sprawl, building density and

lack of financial strength. The risk is continuously increasing in these countries at an alarming

rate. The sole purpose of all mitigation processes in the world is to save human lives and property

from the impact of natural disasters. It is impossible to live in a disaster free environment but it is

possible to reduce the impact of disasters by proper risk management strategies.

The pre-planned mitigation activities not only save the human lives but also reduce the

potential effect of disasters. The proper disaster management strategy at initial planning level

improves the overall functioning structure and helps us to face the ill effects of disaster.

Earthquakes can create disasters of high magnitudes when they hit metropolitan areas of large

population and infrastructure.

India having vast territory, large population and unique geo climatic conditions, and the

Indian sub continent is exposed to natural hazardous events. Even today natural hazards like

floods cyclones, droughts and earthquakes are not rare in the country. While the vulnerability

varies from region to region, a large part of the country is exposed to such natural hazards, which

often turn into disasters causing significant injury, deaths and destruction of property.

Indian subcontinent is among the world’s most earthquake prone areas. Geology

predisposes sixty percent of the country’s area vulnerable to earthquake disaster. Twelve percent

of its land is liable to severe earthquake intensity. The highest seismic risk is concentrated in the

north, near the border with Pakistan, Bangladesh, Bhutan, China and Nepal. This region of high

seismic risk is home to 610 million people, 60% of the nation’s population containing cities with

populations a over 14 million inhabitant. Seven major earthquakes have struck different parts of

India over a span of last 25 years. The approximate deaths, affected people and injured people in

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last 20 years are 32 thousand, 25 million and 200 million respectively. On 26 January 2001, a

very severe earthquake struck Bhuj and shook most parts of Gujarat, causing widespread damage

and devastation. Over 13,805 persons lost their lives, 167,000 persons were injured, over a

million homes were damaged or destroyed and there was large-scale damage to social and

physical infrastructure.

The India-Pakistan earthquake on October 8, 2005 is the most recent example of

seismicity of Himalayan region. The IMD recorded a earthquake magnitude of 7.4 on Richter

scale. The earthquake occurred in the western Himalayas in the morning at about 09.20 hrs IST

(IMD, 2005). The epicenter was 125km WNW of Srinagar near Muzaffarabad, Kashmir. The

earthquake was widely felt in Islamabad, Lahore, Punjub, Chandigarh, Delhi, Himachal Pradesh,

Uttaranchal, Rajasthan, Haryana and adjoining areas. Nearly 20,000 people are feared dead in

Pakistan and death toll in Jammu & Kashmir is reported to have crossed 600 with huge property

loss. Table 1.1 provides the details of some past earthquakes in India.

Table1.1. Past earthquakes in India

Buildings in urban areas are highly vulnerable structures in seismic events especially in

developing countries. There is a direct relationship between the damage of civil structures to the

number of casualties. Most causalities, damage and economic losses caused by earthquake result

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from ground motion acting upon buildings incapable of withstanding such motion. Damage to

buildings also causes a variety of secondary effects that can be greatly destructive. Lack of

capacity buildings leads to increase in risk of property loss in developing countries. Damage to

essential buildings substantially increases the rate of casualties. In the absence of risk analysis

tools and databases required for earthquake risk assessment, it will be very difficult to assess the

loss in post earthquake event.

1.2 Seismic Load Conditions:

Seismic design force, in each element of the damping system due to horizontal

earthquake load shall be taken as the maximum force of the following three loading conditions:

1. Stage of Maximum Displacement: Seismic design force at the stage of maximum displacement

shall be calculated Seismic forces in elements of the damping system, shall be calculated by

imposing design forces of displacement-dependent damping devices on the damping system as

pseudostatic forces. Design seismic forces of displacement-dependent damping devices shall be

applied in both positive and negative directions at peak displacement of the structure

1.3 Parametric Effects on Joint Shear Capacity:

The proposed simple and unified RC joint shear strength and deformation models

indicate that concrete Compressive strength, beam reinforcement, joint transverse reinforcement,

in-plane geometry, out-of-plane Geometry and joint eccentricity are more informative than other

parameters in determining RC joint shear Capacity. At peak response, the influence of these

parameters on RC joint shear stress vs. joint shear strain and a standard configuration is first

determined to examine the effects of These parameters on joint shear behavior. For the geometric

conditions of this standard reference point, in-plane

Geometry is an interior connection (1.0 for JP and JPRU); out-of-plane geometry has no

transverse beams (1.0 for TB); and joint eccentricity does not exist (1.0 for 1-e/bc). For the non-

geometric conditions, the median database values are simply used (34.0 MPa for concrete

compressive strength, 0.054 for joint transverse Reinforcement index (JI), and 0.32 for beam

reinforcement index (BI)). The influence of geometric parameters on peak RC joint shear stress

vs. joint shear strain behavior based on the standard configuration. An increase of values for in-

plane geometry or out-of-plane geometry results in an increase in both shear stress and shear

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strain at the peak; an increase of degree of joint Eccentricity causes a decrease in shear stress and

an increase in shear strain at the same time (i.e., decrease in joint shear stiffness). An increase of

value for in-plane geometry or out-of-plane geometry means that RC Beam-column connections

have better geometry for resisting joint shear input demand. For example, when joint Shear

demand exceeds the capacity of RC joint shear resistance mechanisms, the joint panel rapidly

expands in both the in-plane and out-of-plane directions. Thus, the existence of two transverse

beams effectively provides passive confinement to the joint panel. When the centerline of beam

member(s) does not coincide with the centerline of the column cross-section, the joint panel is

subjected to torsion due to joint eccentricity, in addition to the shear force transferred from

longitudinal beams. The weakened diagonal concrete strut and truss (joint shear resistance

mechanisms) due to the generated torsion might trigger a reduction in joint shear stiffness. The

influence of non-geometric parameters on RC joint shear stress vs. joint shear strain behavior

based on the standard configuration. An increase of concrete compressive strength or beam

reinforcement results in an increase of both shear stress and shear strain simultaneously; an

increase of joint transverse reinforcement causes an increase of joint shear stiffness. Because the

capacity of both diagonal concrete strut and truss mechanisms is dependent on concrete

compressive strength, joint shear stress vs. joint shear strain at the peak has a proportional

relation to concrete compressive strength. Beam reinforcement index represents the relative

confinement provided to the joint panel by in-plane beam reinforcement. More Confinement at

the top and bottom of the joint panel by longitudinal beam reinforcement strengthens joint shear

resistance mechanisms. Joint transverse reinforcement index represents the relative confinement

provided by joint transverse reinforcement within the joint panel. Because joint shear failure

initiates an expansion of a joint panel in the in-plane and out-of-plane directions, the improved

confinement against the joint panel’s expansion results in an increase in joint shear stiffness

1.4 Structural damage associated with system faults:

Similar failure patterns of buildings have been repeatedly observed. Investigations of past

earthquakes damage. Design requirements have been modified or added for the protection of new

constructions. However older structures designed and constructed using outdated technology, are

susceptible to the some patterns of damage during future earthquakes.

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1.4.1 Heavy Structures:

Inertial forces in horizontal and vertical directions are developed with vibration of

structure. Vertical inertial forces are developed by the vertical vibration of structure caused by

the vertical ground motion and also by the vibration of floor slabs. The dominant part of the

structural damage is caused by the horizontal inertial forces associated with lateral vibration of

the structure. The amplitude of inertial forces is proportional to the mass of the structure part in

vibration and the response acceleration developed at the point. Heavy structures such as adobe

houses and reinforced concrete construction attract larger inertial forces during earthquakes.

1.4.2 Period of Vibration:

Acceleration is an important index in engineering. Although the acceleration of an

earthquake ground motion appears to be random, the signal contains special dominant periods of

vibration, representing characteristics of surface geology at the construction site. The

acceleration amplitude of ground motion is generally is large in a period range less than 0.5 to

1.0 s, and decays with the length of periods. Therefore, the acceleration response, corresponding

to the inertia forces, is generally large for short period structures for a given duration of an

earthquake motion the short period structure is subjected to more cycles of oscillation that is the

short period structure is generally more susceptible to damage unless larger resistance is

provided.

1.4.3 Strength and deformation capacity:

A structure does not always fail immediately when the action reaches the strength

(maximum resisting capacity) of a structure. A structure collapses when deformation capacity is

reached in vertical load carrying members, such as columns and walls. The location of damage

can be controlled by selecting weak regions of a structure in design planning. A large

deformation capacity after reaching the strength, commonly known as ductility, can be built into

weak structural members so that the collapse can be delayed even after significant structural

damage is developed.

The brittle modes of failure should be prevented in vertical load carrying members. If the

brittle modes of failure cannot be corrected in construction, then higher strength must be

provided and also the mass of the construction should be reduced.

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The structural damage of a building with high lateral resistance (stiffness and strength).

Is likely to be smaller under frequent minor earthquakes than that of a building with low

resistance, regardless of the deformation capacity. Therefore, a certain minimum resistance is

necessary for the continued operation of buildings after frequent earthquakes

1.4.4 Progressive Collapse:

When a vertical member, such as structural wall, fails in a brittle mode, the shear carried

by member must be resisted by the other vertical member s in the same storey. The additional

shear often triggers brittle failure of the other members because the structural are normally

designed under the same specification, i.e., if a member fails in brittle manner, the other

members may fail in same mode. Collapse of a building in a story occurs by progressive brittle

failure of vertical members.

Failure of vertical members does not simply results in the reduction of lateral resistance,

but also results in loss of vertical load carrying capacity. The gravity load supported by the

failure member must be transferred to adjacent vertical members. The failure of gravity load

transfer causes partial collapse around the failing vertical member.

1.4.5 Concentration of Damage: The concentration of structural deformation and associated damage limited localities

should be avoided if the deformation capacity at expected damage locations is limited, especially

in reinforced concrete buildings. Collapse of a building is normally caused by the failure vertical

load carrying members of the story. In order to protect vertical members in a multi-story

construction, they should be provided with the higher strength than horizontal members so the

damage should be directed to horizontal members.

1.4.6 Vertical Irregularities:

When the stiffness and associated strength are abruptly reduced in a story along the

height, earthquake-induced deformations tend to concentrate at the flexible and/or weak story.

The concentration of damage in a story leads to large deformations in vertical members. The

excessive deformation in vertical members often leads to collapse of the story.

Soft/weak first stories are especially common in multi-story residential buildings in urban

areas, where the first story often is used for open spaces, commercial facilities or garages. For

example, structural walls that separate residential units in levels above may be discontinued in

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the first story to meet flexible usage requirements. The first story columns during strong

earthquake shaking must resist a large base shear, inevitably leading to large story drift

concentrated in the story.

1.4.7 Horizontal Irregularities: If, for example, structural walls are placed on one side of a building while the other side

has open frames, the eccentricity between the centers of mass and resistance causes torsional

vibration during an earthquake. Larger damage develops in members away from the center of

resistance. The structural wall is reducing lateral deformation and resisting large horizontal

forces, especially when they are distributed in plan.

1.5 Contribution of Nonstructural Elements: Nonstructural elements, such as masonry concrete or infill walls and stairways, are

degraded in structural analysis although they can contribute significantly to the stiffness of the

framing system. The existence of these high stiffness nonstructural elements can cause irregular

stiffness distributions in plan or along height.

Nonstructural elements are commonly neglected in modeling and analysis in design

calculations, but are placed for the purpose of building function, for example, partition wall.

When stiff and strong nonstructural elements, the interaction can lead to damage in nonstructural

and structural elements. A typical example is captive column, where deformable length is

shortened by spandrels directly attached to the column.

1.6 Pounding of Adjacent Buildings: Pounding of adjacent buildings causes structural damage. Proper distance should be

maintained between adjacent buildings. In the case of serial buildings constructed side by side in

some localities the edge buildings, the edge buildings are often pushed outward and suffer severe

damage while inner buildings are protected from excessive lateral deformation.

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. Figure 1.1. Pounding can occur in adjacent buildings located very close to each other due to

earthquake-induced shaking (source: Murty 2005).

1.6.1 Separate adjacent buildings by joints:

Pounding and hammering of adjacent buildings can cause substantial damage, if not

collapse. The threat of collapse is greatest when the floor slabs of adjacent buildings are at

different levels and hit against the columns of the neighbouring building. In such cases the joints

must conform with the relevant design rules.

This implies the following:

1) the joints must have a certain minimum width (specified in the building codes)

2) the joints must be empty (no contact points) In order to enable free oscillations and avoid

impact between adjacent buildings, it is often necessary to have a substantial joint width. As long

as the structural elements do not lose their load bearing capacity at pounding.

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Figure 1.2. The pounding of two similar buildings with floors at the same levels caused

damage to the façades as well as spalling etc. to the structure (Mexico 1985).

Figure 1.3. Substantial damage resulted from the pounding of these two, very different,

buildings (Mexico 1985).

1.7 Deterioration with Age: Deterioration of structural materials with aging and aggressive environmental condition

reduces the seismic performance potential of a building, prior earthquake damage, unless

properly repaired and strengthened, has the same effect. It is important either to maintain the

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structure at regular intervals or follow rigid construction specification for durability of the

structure.

1.7.1 Foundation: The failure of foundation is caused by:

Liquefaction and loss of bearing or tension capacity

Landslides

Fault rupture

Compaction of soils

Differential settlements

It is normally difficult to design and construct a safe foundation to resist ground

movement immediately above the rupture. Although foundation failures do not pose a life threat,

the cost of damage investigation and repair work is extremely high. Therefore, it is advisable to

reduce the possibility of foundation failure.

1.7.2 Nonstructural Elements: Damage of nonstructural or architectural elements, such as partitions, windows, doors

and mechanical facilities, interrupts the use of building. The cost of repair work on a building is

often governed by the replacement of the damaged nonstructural elements, rather than the repair

work on structural elements. Damage of nonstructural elements may create a falling hazard for

people in or escaping from, the building; furthermore, fallen elements may block evacuation

routes in severely damaged buildings.

1.7.3 Damage in Structural Members: Failure type of members may be different for columns, beams, walls and beam-column

joints. It is important to consider the consequence of member failure on structural performance;

example the failure of vertical members often leads to the collapse of the building.

1.7.4 Flexural Compression Failure of Members: A reinforced concrete member subjected to axial force and bending moment normally

fails in compression of concrete after yielding of longitudinal reinforcement; the failure mode is

normally called flexural compression failure. The deformation capacity of building is influenced

by the level of axial force in the column and the amount of lateral reinforcement provided in the

region of plastic deformation. The level of axial force is limited in design to a relatively low

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level under the gravity condition. During an earthquake, however, exterior columns, especially

corner ones, are subjected to varying axial force due to overturning moment of a structure, the

axial force level in these columns may become extremely high in compression, leading to

flexural compression failure. It is often difficult to distinguish shear compression failure and

flexural compression failure, as both take place near the column ends and involves concrete

crushing. The lateral confining reinforcement can delay the crushing failure of concrete under

high compressive stresses.

1.7.5 Shear Failure in Columns: The most brittle mode failure is shear. Shear force cause tensile stress in diagonal

direction to the member axis. After the concrete cracks under tensile stress, the stress must be

transferred to the lateral reinforcement. Brittle shear occurs in the diagonal tension mode when

the maximum amount of lateral reinforcement (size, spacing and strength of shear reinforcement)

is not provided in the member.

When the minimum amount of lateral reinforcement is provided in a member, the shear

failure is developed in the form of diagonal compression failure of concrete after yielding of

lateral reinforcement. This mode failure is not brittle as the diagonal tension failure, but the

deformation capacity is limited. If an excessive amount of lateral reinforcement is provided,

diagonal compression failure takes place prior to the yielding of lateral reinforcement. Therefore,

there is an upper limit in the amount of lateral reinforcement effective for shear resistance. After

the compressive failure of concrete, the vertical load carrying capacity of the column is lost,

leading to the collapse in story.

Because the lateral reinforcement resists tensile force under shear, the ends rectilinear

lateral reinforcement should be anchored in the core concrete with 135-degree bend, or they

should be welded together. When a reinforcing bar is bent, permanent plastic deformation takes

place at the bend and the region becomes less ductile. The reinforcing steel capable of

developing high toughness and ductility before fracture must be used for lateral reinforcement.

1.7.6 Shear Failure of Flat Plate Construction: A flat plate floor without column capitals is popular in some regions because it does not

have girders below a slab level. The critical part of the flat slab system is the vertical shear

transfer between the slab and column. The shear failure at “the connection leads to the pan-cake

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collapse” of the building, leaving of space between the adjacent floors after the collapse. Serious

failure was observed in 1985 Mexico City earthquake.

1.7.7 Bond Splitting Failure:

The bond stresses acting on deformed bars cause ring tension to the surrounding concrete

high flexural bond stresses may exist in members with steep movement gradients along their

lengths. If longitudinal reinforcement of beam or column is not supported by closely spaced

stirrups or ties, splitting cracks may develop along the longitudinal reinforcement, especially

when the strength of concrete low, when large diameter longitudinal bars with high strength are

used, or when the concrete cover on the deform bars is thin. These splitting cracks result in loss

of bond stress, limiting the flexural and/or shear resistance at a small deformation.

1.7.8 Splice Failure of Longitudinal Reinforcement:

Longitudinal reinforcement is spliced in various ways, including lap splices, mechanical

splices and welded splices. Splices should be located in a region where tensile stress is low.

Splices in older buildings were located in regions of high tensile stresses because the

implications for earthquake performance were inadequately understood. Splice failure reduces

flexural resistance of the member often before yielding.

1.7.9 Anchorage Failure:

The force in longitudinal reinforcements in beams and columns must be anchored with in

beam-column connection or foundation. Connections of older building construction may be joint

transverse reinforcement; in which case the column and beam is reinforced is anchored is

essentially plain concrete. If the beam longitudinal reinforcement is not fully anchored in a

beam-column joint, the bar may pull out from the joint; example beam bottom reinforcement, in

non-seismic design, is embedded a short distance into the beam-column joint.

1.7.10 Beam-Column joint Failure:

When moment resisting frame is designed for weak-beam strong-column behavior, the

beam-column joint may be heavily stressed after beam yielding and diagonal cracking may be

formed in the connection. Wide flexural cracks may be developed at the beam end, partially

attributable the slip of beam reinforcement with in the connection. Such shear cracking may

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reduce the stiffness of a building. Failure is observed in beam-column joints with narrow

columns and also in beam-column joints without lateral reinforcement.

1.7.11 Failure of Piles:

The inertia force acting in a building must be resisted by the foundation of structure. High

bending moments combined with axial forces acting at the top of pile can cause crushing of

concrete. Such damage in the foundation structure is difficult to identify after the earthquake,

unless apparent inclination of a building is detected as a result of permanent foundation

deformation.

1.8 Quality of Workmanship and Materials:

The performance construction is affected by the quality of work during construction. For

example the material strength is specified in design documents may not be developed during

construction. The amount of reinforcement is not placed as specified design. The end lateral

reinforcement is not bent in 135 degrees as the building code specifies. Concrete cover to

reinforcement is not sufficient and the reinforcing bar is rusted with cracks in surface of the

concrete. Education of construction workers and inspection of construction work are necessary to

maintain the quality of workmanship.

The quality of materials also deteriorates with age. Proper maintenance of structure is essential.

Changes in use and occupancy often involves structural modifications without proper

investigation into the consequence in the event of an earthquake

1.9 Better understanding of effects of masonry infill walls in developing countries:

Reconnaissance after three or four of the recent earthquakes in India has shown

researchers and practitioners around the world the potentially beneficial effects of masonry infill

walls in multistory buildings. The conventional wisdom in developed countries has been to

discourage the use of masonry infill in seismic regions, but the Indian earthquake damage has

shown that masonry infill walls provide additional support in structures with rather poorly

designed and constructed reinforced concrete frames. The added support is enough to keep the

buildings from collapse. This observation has potentially huge life-saving implications in many

developing countries.

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1.10 Structure regularity:

The guiding principles governing the initial conceptual design are as follows:

a) The aspect of seismic hazard should be taken into account in the early stages of the conceptual

design of a building,

b) Structure should be simple,

c) Transmission of the seismic (inertia) forces to the ground should be direct and clear

d) Uniformity, symmetry and redundancy should be ensured,

e) Structure should be statically undetermined,

f) Bi-directional resistance and stiffness should be ensured

g) Torsion resistance and stiffness should be ensured (main structural elements should be placed

symmetrically nearby periphery of the building)

h) Structural elements should be appropriately connected with floor systems or diaphragms

(which have to have sufficient in-plane stiffness),

i) Building should have adequate foundation.

Figure1.3 (a): Examples of regular and irregular initial building designs:

a):Uniformity along the height; b): Bi-directional resistance and stiffness; c): Symmetry in plan

1.10.1 The regularity criteria in plan and in elevation:

The regularity of the structure in the plan of different floors, as well as in elevation of the

building should be ensured.

The regularity criteria in plan are: a) With respect to the lateral stiffness and mass distribution, the position of force resisting

elements should be approximately symmetrical in plan with respect to two orthogonal

axes (Figure1.4 (b)).

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Figure 1.4 (b): Regularity of a building in plan and appropriate position of force resisting

elements.

b) The plan configuration should be compact. The dimensions of recesses in one direction should

not exceed 25% of the whole dimension of floor area in this direction (compact plan

configuration which is not H, L, I, C or X – shaped). Figure 3: Regularity of initial building

design in plan according to distribution of masses and subdivision of the entire building by

seismic joints.

c) The in-plane stiffness of the floors should be sufficiently large in comparison with the lateral

stiffness of the vertical structural elements, so that the deformation of the floor has a small effect

on the distribution of the forces among the vertical structural elements.

The regularity criteria in elevation are as follows:

a) All lateral load-resisting systems, like cores, structural walls or frames should run without

interruption from the foundations to the top of the building.

b) The deflected shapes of the individual systems under horizontal loads should not be very

different. This condition may be considered satisfied in case of frame systems and wall systems.

c) Both the lateral stiffness and the mass of the individual storeys should remain constant or

reduce gradually, without abrupt changes, from the base to the top (Figure 1.5(c)).

Figure 1.5 (C): Large eccentricities and uniformity along the height and influence of

different heights of columns.

d) When set backs are present, the following additional conditions apply:

Structure is regular if set-back at any floor is not greater than 20% of the dimension of the plan

below. If the set-back does not preserve symmetry, in each face, the sum of the set-backs at all

storeys should not exceed than 30 % of the plan dimension of the first storey, and the individual

set-backs should not exceed 10% of the dimension of the plan below( Figure 1.6)

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Figure 1. .6 Regularity of set-backs.

1.10.2 Other irregularities:

Longer overhanging elements should be avoided. Columns should run directly to the

ground where this is possible. Supporting columns with beams is not recommendable. Initial

structure design should follow the above recommendations. If necessary, uniformity may be

realized by subdividing the entire building by seismic joints into dynamically independent units,

provided that these joints are designed against pounding of the individual units (Figure 3). The

construction of completely irregular structures is not explicitly forbidden, however, it is much

harder to ensure a desirable level of safety against strong earthquake for an irregular structure.

For this reason the irregular structures are in general less safe, even if the structure is capable to

withstand design forces. Non-structural elements (appendages) of buildings shall be adequately

connected to the main structure Non-structural elements (appendages) of buildings (e.g. parapets,

gables antennae, mechanical appendages and equipment, curtain walls, partitions, railings)

should be verified to resist the designed seismic action. They should be adequately connected to

the main structure. Non-structural elements (in-fills) can help to dissipate the energy, if they are

correctly arranged and connected to the structure. It is necessary to prevent negative influences

of individual non-structural elements or partial in-fills, that can damage the main R/C structure

(the effect of short column).

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Figure 1.7(a). Influence of building shape: a) Buildings with simple shapes permit the

shaking induced inertia forces to flow directly to the foundation and hence perform well in

earthquakes; b) buildings with irregular shapes force the inertia forces to bend at each re-entrant

corner, which results in damage at these corners and hence poor earthquake beahvior of the

building as a whole (source: Murty 2005).

Figure 1.7(b) . Sudden changes in load path lead to poor performance of buildings in

earthquakes: a) setbacks; b) weak or flexible stories; c) sloping ground; d) hanging or floating

columns; e) discontinuous structural members (source: Murty 2005).

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1.11 Reinforced concrete:

Reinforced concrete is one of the most widely used modern building materials. Concrete

is an “artificial stone” obtained by mixing cement, sand, and aggregates with water. Fresh

concrete can be molded into almost any shape, giving it an inherent advantage over other

materials. It became very popular after the invention of Portland cement in the 19th century;

however, its limited tension resistance initially prevented its wide use in building construction.

To overcome poor tensile strength, steel bars are embedded in concrete to form a composite

material called reinforced concrete (RC).

The use of reinforced concrete construction in the modern world stems from the wide

availability of its ingredients - reinforcing steel as well as concrete. Except for the production of

steel and cement, the production of concrete does not require expensive manufacturing mills.

But, construction with concrete does require a certain level of technology, expertise and

workmanship, particularly in the field during construction. Despite this need for sophistication

and professional inputs, a large number of single-family houses or low-rise residential buildings

across the world have been and are being constructed using reinforced concrete without any

engineering assistance. Such buildings, in seismic areas, are potential death traps.

A typical reinforced concrete building (shown in Figure 1.9(a)) is generally made of a

number of plate-like horizontal elements (slabs), rib-like horizontal elements (beams) connected

to the underside of slabs, slender vertical elements (columns), and flat vertical elements (walls).

In most cases, all these elements are cast monolithically that is, beams and columns are cast at

the construction site in a single operation in order to act in unison. Fresh concrete is poured into

wood or steel forms placed around the steel reinforcement for different elements in buildings.

Such buildings are called monolithic (or cast-in-place) reinforced concrete buildings, in contrast

to precast reinforced concrete buildings, wherein each of the elements are cast separately (often

in a factory environment) and then assembled together at the building site. In monolithic

reinforced concrete buildings, the connection between the elements is achieved by providing

continuous reinforcement bars that pass from one element to another. The intersection between a

beam and a column, known as beam-column joint, plays a vital role in the capacity of these

buildings to resist lateral loads.

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Figure 1.8 (a): A typical reinforced concrete building

In reinforced concrete frames the integral action of beams, columns and slabs, provides

resistance to both gravity and lateral loads through bending in beams and columns. Reinforced

concrete frames built in earthquake-prone regions should possess ductility, or the ability to

sustain significant deformations under extreme loading conditions. Frames that are designed to

resist mainly the effects of gravity loads most often are called non-ductile (or gravity) frames.

The non-ductile reinforced concrete frame with or without infill walls is a very common building

construction technology practiced around the globe these three-dimensional reinforced concrete

frames (beam-column-slab) are made functional for habitation by building walls called infill

walls. These walls are built at desired locations throughout the building, usually in the vertical

plane defined by adjoining pairs of beams and columns. One popular material used for making

walls across the world is burnt clay brick masonry in cement mortar. Lately, the use of cement

blocks, hollow cement blocks and hollow clay tiles is on the rise across the world. In some cases,

the masonry infill walls are also reinforced with steel bars passing through them in the vertical

and horizontal directions and anchoring into the adjoining beams and columns.

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Reinforced concrete construction is extensively practiced in many parts of the world,

especially in developing countries. With the rapid growth of urban population, reinforced

concrete frame construction has been widely used for residential construction in both the

developing and industrialized countries. Design applications range from single-family dwellings

in countries like Algeria and Colombia, to high-rise apartment buildings in Chile, Canada,

Mexico, Turkey, India, and China. Examples of RC frame construction are shown figures 1.9

Figure1.9: Low-to-midrise RC frame construction: Turkey (top left; from Gulkan et

al.2002; Colombia (top right; from Mejia 2002); Taiwan (bottom left; from Yao and Sheu

2002); India (bottom right; from Jaiswal et al. 2002)

Because of the high occupancy associated with these buildings, as well as their ubiquitous

presence throughout the world, significant fatalities and property losses can be associated with

their potential poor earthquake performance. Thus, special care is required to understand the

challenges that earthquakes pose and ensure that appropriate features are incorporated in the

architectural and structural design and construction of reinforced concrete frame buildings.

depicts the construction of a modern reinforced concrete frame building.

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The estimated number of vulnerable reinforced concrete frame buildings in seismic zones

across world is staggering, including both developing and highly industrialized countries. In

industrialized countries, thousands of older RC frame buildings are considered to be at risk since

the building codes did not include requirements for special seismic detailing of reinforced

concrete structures until the 1970’s when several earthquakes demonstrated the need for more

ductile design.

FIigure1.10. Examples of RC highrises in Canada (left; from Pao and Brzev 2002) and Chile

(right; from Moroni and Gomez 2002). RC shear walls provide resistance to earthquake effects

in these buildings while columns are designed to resist gravity loads.

The role of architect and structural engineer is very vital in the planning and design of the

structure, which is seismically efficient to withstand the design earthquakes. They also should

strictly implement the code provisions, hence there is scope for the structure to with stand the

earthquakes and save lives, minimize the damage to the property. Hence the constructed

buildings lacking seismic resistance should be retrofitted and the buildings being planned for

construction should be properly planned with good collaboration of architect, structural engineer.

1.12 Future Role of Earthquake Engineering:

Safety in the event of major earthquakes is one performance objective. The importance of

ductility has been emphasized for the survival of the building; i.e., a structure should be capable

of resistance after developing plastic deformation (damage). At the same time, ductility was used

as a means to reduce the seismic forces. It is concerned that damage may develop in a structure

22

even during frequent minor earthquake motions because the structure is designed for too low

lateral load resisting relying on large ductility. It is costly to repair structural as well as non-

structural damage after minor but frequent earthquakes, and the building cannot be used during

the repair period. A structural engineer should advice a building owner about the possible cost of

repairs and losses associated with having cease to building operation during repair work if a

building is designed with low lateral resistance.

The damage level of structural and non-structural elements is known to be closely related to

story drift (inter-story deformation). Structural damage to a brittle but high resisting building is

much smaller under more frequent earthquake motions than damage to a ductile structure. A

number of damage investigations reported the effectiveness of structural walls in reducing the

damage to structural members as well as non-structural elements. The importance of limiting the

story drift during an earthquake by providing large stiffness and high lateral resistance should be

emphasized in earthquake engineering.

The non-structural elements such as windows, partitions, doors and architectural facilities, are

essential parts of a building’s function. Even if structural members suffer no or slight damage if

partitions are broken in residential building, the unit may not be occupiable until such it gets

repaired or replaced.

If the computer facilities are damaged in computer or information center of accompany, the

function of a building is lost. The cost of repair and recovery work is often governed by the

replacement of non-structural elements than the repair work on structural elements.

Falling of broken non-structural elements is dangerous for people for escaping from the building,

and falling or overturned objects may block evacuation of routes in a building. The non-

structural elements must be protected from minor frequent earthquakes to reduce the financial

burden of the building. Controlling the inter-story drift through the use of structural walls or

structural control devices and improving the method to fasten the non-structural elements to the

structure may reduce damage partitions. Stiff, weak and brittle brick walls; filled in a flexible

moment-resisting frame, fail at an early stage even during medium-intensity earthquakes; such

damage may reduced by providing some gap between the brick wall and columns.

23

The response (acceleration or velocity) of a structure must be controlled to prevent heavy

furniture and equipment from falling of shelves; otherwise the contents of the building should be

properly fastened to the structure.

Earthquake resistant design technology has progressed significantly in the last few

decades. Damage investigations have demonstrated the poor performance of older buildings

designed using out-dated technology. The retrofitting is of deficient buildings is an urgent task

for owners, who are responsible for the maintaining performance of their building to the existing

code level. An efficient and reliable seismic assessment procedure should be employed for to

identify probably deficient buildings. New structural wall may be added to enhance the lateral

resistance of weak buildings as long as the foundation has sufficient capacity to support the

additional weight caused by the walls. Steel bracings can be installed if the foundation is

defective. The ductility of columns can be improved by steel plate jacketing or carbon fiber

plastic sheet wrapping.

The behavior of a structure under lateral loading with irregularities in its plan and torsion

can be avoided by provision of seismic joint or separation joint. The joint provided divides the

structure into parts by which the each part behaves individually and the column shears and

moments are reduced. Hence the pounding effect under earthquake loading can be avoided.

1.12.2 Lessons Learned From Earthquakes:

Earth quake engineering is not a pure science but has been done through the observation

of failure of structures during earthquakes. The sole aim of the engineering has been not repeat

the same mistakes in the event of future earthq This section reveals the observation of damage of

man made construction, with emphasis on damage to reinforced concrete buildings. Those

defects found in existing constructions should be identified for vulnerability assessment and

retrofitted for safety in the event of future earthquakes.

1.13 The regularity criteria in plan and in elevation:

The regularity of the structure in the plan of different floors, as well as in elevation of the

building should be ensured. The regularity criteria in plan are: With respect to the lateral stiffness

and mass distribution, the position of force resisting elements should be approximately

symmetrical in plan with respect to two orthogonal axes.

24

Figure 1.11: Regularity of a building in plan and appropriate position of force resisting elements.

The plan configuration should be compact. The dimensions of recesses in one direction should

not exceed 25% of the whole dimension of floor area in this direction (compact plan

configuration which is not H, L, I, C or X – shaped).

Figure 1.12: Regularity of initial building design in plan according to distribution of masses and

subdivision of the entire building by seismic joints.

1.14 Global plastic mechanisms shall be ensured:

Columns and beams of the frame system have to be constructed in a such way that the

damage occurs mainly at the ends of the beams and at the bottoms of the columns in the ground

floor. Such mechanism is called global plastic mechanism. Local plastic mechanisms have to be

avoided by adequate planning and reinforcing of beams and columns of the frame. In general,

this can be achieved if the columns are designed to be

stronger than beams (the principle of “weak beams and strong columns”).

1.15 Eccentricity in irregular multistory buildings:

The position of the center of rigidity at a floor level as defined as the "load center" or

"centroid of loads" on that floor. The suggestion to compare torques and torsional shears when

these quantities are computed by static (using the real eccentricities) versus dynamic modal

analysis in the three examples is well taken. This comparison is useful to demonstrate the

difference between the static and dynamic estimates of the torsional effect on the example

buildings is the torsional moment comparison for the three example buildings. In the dynamic

analysis, for simplicity only the fundamental mode contribution is taken into account. The higher

modal contributions are in fact insignificant for these three buildings. To make the comparison

25

meaningful, the dynamic results are normalized such that the base shears are the same for both

the static and the dynamic calculation. It can be seen that while the shapes of the torsional

moment envelopes are similar, the dynamic torsional moment envelopes are considerably larger

than the envelopes calculated by statics using the actual structural eccentricity values. The total

(lateral and torsional) shear envelope comparison between static and dynamic calculation for a

critical lateral load-resisting element. For buildings A and B, the shears on element 4 are taken

for comparison. For building C, element 1 is more susceptible to torsional effects and the

comparison is based on the shears in this element. Again, the dynamic shear exceeds the static

shear envelope in all three buildings, although this difference between the shear envelopes is less

than the difference between the torsional moment envelopes. Since most lateral loadings on

buildings are dynamic in nature, a comparison of the given three examples based on static and

dynamic methods of analysis shows that some modification on the static eccentricity is necessary

if the static approach is to be used to obtain a realistic estimate of the torsional effect due to wind

and or earthquake loading. For example, in NBCC 85’s torsional provision for earthquake

effects, an amplification factor of 1.5 is applied to the structural eccentricity value in calculations

of torsional moment.

Figure 1.13. Seismic Performance Assessment of Reinforced Concrete Structures with Masonry Infilled Panels:The Case of Block # 22 of the Santa Maria Hospital in Lisbon

26

1.16 Initial Linear Model:

The building block # 22 is located in the north wing of the Hospital, as shown in Figure

2. The structure consists of nine storeys, with six N-S, reinforced concrete plane frames with a

spacing of approximately 5.75 m. The building plan is rectangular, 28.91×12.65 m for the first 5

floors, with a setback of 4.31 m in the direction of the frames for the top storey. The storey

height varies between 3.0 and 4.0 m. The cross-sectional dimensions of members vary along the

height, particularly the columns whose cross-sectional area at the top floor is less than 25% of

that of the lowest storey. All the slabs are one-way, spanning between the frames. The building

was modelled using a 3D finite element model, with frame elements representing beams and

columns. Considering that the analysis was performed in the N-S direction (direction of the

expansion joints), no interaction with building blocks # 21 and # 23 was accounted for. The

external and internal masonry infill panels were also modelled using a pair of diagonal frame

elements for each panel, the details of which are discussed later in this section. The storey slabs

were represented by equivalent beams and modelled as rigid diaphragms. The nonlinear static

analysis requires the consideration of the actual force-deformation relationships for all sections

which, in this case, were based on the longitudinal reinforcements of the beams and columns,

taken from the original project drawings. The numerical analyses (dynamic elastic and static

inelastic) were carried out with the SAP2000 Nonlinear, Version 7.42 Program (CSI, 2001). As

expected, the preliminary bare RC frame numerical model led to fundamental period values

much higher than the experimental ones, thus leading to the inclusion of the masonry stiffening

effect in the final numerical model.

1.17 Reinforced Concrete Frame Buildings with Masonry Infill Walls:

To improve the understanding of the poor seismic performance of reinforced concrete

frame buildings with masonry infill walls, and 2) to offer viable alternative construction

technologies that can provide a higher level of seismic safety. Causes for the unsatisfactory

seismic performance of these RC frame buildings lie in (a) the poor choice of a building site, (b)

the inappropriate choice of building architectural forms that offer poor seismic performance, (c)

the absence of structural design for expected earthquake behavior, (d) the lack of special seismic

detailing of key structural elements, (e) inadequately skilled construction labor, (f) poor quality

building materials, and (g) the absence of construction supervision. The problem is aggravated

27

further by the use of unreinforced masonry infill walls, usually made of clay bricks or hollow

clay tiles. The effect of infills is usually not accounted for in the design, however these walls

may significantly affect the way in which the building responds to earthquake ground shaking

and may even cause the building to collapse (as reported often after several major earthquakes

worldwide). In general, achieving satisfactory seismic performance of RC frame buildings

subjected to several cycles of earthquake ground shaking is considered to be a challenge even in

highly industrialized countries with advanced construction technology. Keeping these challenges

in mind, this document proposes two alternative building technologies characterized by a higher

level of seismic safety at a comparable cost and construction complexity to RC frame

construction; these technologies are confined masonry construction and RC frame construction

with RC shear walls .Considering the enormous number of existing RC frame buildings with

infills in regions of moderate to high seismic risk across the world, this document also discusses

some generic seismic retrofit strategies for these structures that may reduce associated risks. It is

important that all those involved in the construction process understand how these buildings

perform during earthquakes, what the key challenges are related to their earthquake safety, and

what construction technology alternatives might be more appropriate. Authors of this document

believe that better understanding of these critical issues will result in improved construction and

retrofit practices for buildings of this type, reducing life and property losses in future

earthquakes.

1.17.1 Out-of-plane seismic resistance of masonry infills:

The difficulty in isolating masonry infill walls from RC frames is that such walls become

susceptible to collapse in the out-of-plane direction, that is, in the direction perpendicular to the

wall surface. This is particularly pronounced when the story height is large or when the column

spacing is large. Once masonry walls crack, continued shaking can easily cause collapse in the

heavy infill blocks and pose a serious life safety threat to building inhabitants. frame buildings

that have columns of different heights within one story suffered more damage in the shorter

columns than in the taller columns located in the same story. Short columns are stiffer, and

require a larger force to deform by the same amount than taller columns that are more flexible.

This increased force generally incurs extensive damage on the short columns, as illustrated by

earthquake damage photos.

28

a) b) c) Figure 1.14. Out-of-plane seismic resistance of masonry infills

Infill walls influence the behavior of a RC frame: Figure (a) a bare frame; Figure (b) infill walls

must be uniformly distributed in the building; and Figure (c) if the inflls are absent at the ground

floor level this modifies the load paths, which is detrimental to earthquake performance

1.18 Statement

‘T’ shaped unsymmetrical structures 10,20,30 and 40 was considered. In this analysis the

input parameters were change in number of stories, joint width and earthquake loading in X and

Z directions.compared continuous building with gap building and

For the analysis, the structure considered varied in number of stories, the dimensions of

the structure are explained below

Earthquake analysis has been carried out for ‘T’ shape irregularity varying different

parameters, which are listed and explained below.

Floor height is considered to be 3.2m.

Column to column spacing is maintained as 5m.

Foundation depth is taken as 3.2m

Column dimensions are 600×600mm&300×600mm

Beam dimensions are 300×450mm

Walls are modeled as Infill brick walls with diagonal strut compression members and

thickness of wall is assumed as 230mm.

Slabs are modeled as master slave

29

1.19 Objective:

“T” shape irregularity is considered with 10, 20, 30 and 40 stories, for the seismic

analysis. earthquake loading in X and Z directions. To make the configuration simpler, the ‘T’

can be divided into two simple rectangles. Three cases are considered in the present analysis

namely 1) Without any joint 2) Disjointed structure with gap between the rectangular shapes and

3) With seismic joint providing Elastomer material.For above three cases study Maximum joint

displacement, Axial force in columns, Bending moment(My and Mz) in columns and

eccentricity.

30

CHAPTER 2

LITERATURE REVIEW Building configuration play very important role in seismic response of structures normal

irregular structure like L-shape and T-shape buildings are converted in to simple regular

configuration by providing seismic joints. Brief Literature on the topic is presented in this

chapter.

Proença, Carlos S. Oliveira and J.P. Almeida[1] Performance-Based Design, Seismic

Assessment, Masonry Infilled Structures Early, pre-code, reinforced concrete structures present

undetermined resistance to earthquakes. This situation is particularly unacceptable in the case of

essential facilities, such as healthcare structures. Amongst these, the Santa Maria Hospital –

finished in 1953 with a total area of 120,000 m2 – in Lisbon, was designed without explicit

consideration for earthquake loading. Given the crucial importance of this healthcare facility in

the case of a strong earthquake in the greater Lisbon metropolitan area, the Portuguese Health

Ministry requested a seismic vulnerability assessment of the Hospital structure, as well as of the

major non-structural components, medical equipment and basic infrastructure lifelines. The

structural seismic vulnerability assessment stages comprised the development of linear dynamic

and nonlinear static numerical models for some of the more representative building blocks.

Nonlinear static analyses were conducted on one of the Hospital’s most representative buildings

according to displacement-based seismic design methodologies, A first nonlinear model was

significantly modified through the introduction of diagonal struts, representing the stiffening

effect of infill masonry walls, to match the experimentally determined fundamental frequencies.

The analysis was carried out by means of two distinct nonlinear models, in terms of the load

patterns. The first model (as described above) was used until all struts at a given intermediate

storey collapsed, leading to a substantial change in the deformation and load pattern. The

subsequent second model differed from the first model by the removal of the struts that had

collapsed. A sensitivity analysis was carried out by changing the strength parameters of the

diagonal struts. The final capacity curve was computed combining the former two capacity

curves, and the

31

performance point was subsequently estimated through the Capacity Spectrum Method (CSM).

The results show that the structure does not collapse but the high damage concentration in the

intermediate storey renders the building partially inoperative.

Murthy [2] You must know this earthquakes take place at locations where there are mountains.

If you want to know the exact locations, take the relief globe from your drawing room and run

your finger along the mountain line. You now have the complete data on where most earthquakes

have been occurring in the world. Now, that is not the end of it. Earthquakes can and have been

occurring at other locations too, particularly where there are not necessarily any major mountain

ranges; the 1993 earthquake in Deccan plateau of Marathwada in central India is a recent

example of this from our country. This means that in India, virtually over 60% of the area is

under the threat of moderate to strong earthquake shaking. Earthquake prediction is possible or

not, one has to learn to live with them if one insists on living in areas with earthquake hazard. So,

most effort of scientists and engineers is focused on earthquake preparedness, from both

engineering and sociological points of view. An earthquake imposes displacement on the

structure, while winds and waves apply force on it. The displacement imposed at the base of the

structure during earthquake causes inertia forces to be generated in it, which are responsible for

damage in the structure. As a consequence of this, the mass of the structure being designed

assumes importance; the more the mass, the higher is the inertia force.

Slak and Kilar[3] The article briefly summarizes code requirements that are important, and

should be considered already during initial conceptual building design. It is important to stress

that the buildings with extremely unfavourable/unregular floor plan cannot be transformed into a

safe design simply with the help of good static calculation. Any safety verified in such a way is

only imaginary and can be easily disproved by a first stronger earthquake impact. The author

hope’s that engineers-architects will find the synopsis helpful when designing/planning

earthquake resistant reinforced concrete structures with irregularities.

32

Emilla Juhasova [4] The general use of new European Standard from packages of structural

Euro codes will appear in near future .The construction of new structure strengthening and repair

of existing ones are based on the decision regarding the target life or remaining the indicative

design service live in EN 1990:2002 are lower in comparison with national standards STN

730031:1989 (Table 1). The structure shall be designed such that even if its performances

deteriorate over it design service life the performance of the structure does not fall below the

intended level. However, the environmental effects can influence the structural safety both in

view of action changes and the deterioration of material properties as well possible source of

frequent or permanent vibrations that should be considered include walking, synchronized

movements of people machinery ground born vibration form traffic and wind action. Accidental

vibrations are those from blast earthquakes, impact subsidence and explosions. The largest

vibrations occur on the surface. The waves amplitude decreases with depth surface ray light

waves cause vertical and horizontal motions of practical in vertical plan oriented in the direction

of waves propagation their velocity VR is usually less than 92% of shear. Shear wave velocity

Vs but it may have higher value depending on poison ratio. Surface low waves or similar to shear

axes, but locking vertical displacement their velocity Vt.

Hemanth B. Kaushik Et Al. [5] Reinforced concrete (RC) frame buildings are the most

common type of constructions in urban India, which are subjected to several types of forces

during their lifetime, such as static forces due to dead and live loads and dynamic forces due to

wind and earthquakes. Unlike static forces, amplitude, direction and location of dynamic forces,

especially due to earthquakes, vary significantly with time, causing considerable inertia effects

on buildings. Behaviour of buildings under dynamic forces depends upon the dynamic

characteristics of buildings, which are controlled by both their mass and stiffness properties,

whereas the static behaviour is solely dependent upon the stiffness characteristics. Performance

of buildings largely depends on the strength and deformability of constituent members, which is

further linked to the internal design forces for the members. The internal design forces in turn

depend upon the accuracy of the method employed in their analytical determination. Analysing

and designing buildings for static forces is a routine affair these days because of availability of

affordable computers and specialized programs which can be used for the analysis. On the other

33

hand, dynamic analysis is a time-consuming process and requires additional input related to mass

of structure, and an understanding of structural dynamics for interpretation of analytical results.

Somayya Ammanagi S.Venkatesha and C.S.Manahor[6] Methods for experimentally

establishing dynamic characteristic linear vibrating structures, such as, matrix of impulse

response functions. Complex frequency response function or modal characteristic, namely,

national frequencies, modal damping and mode shapes are currently well established these

characteristic depend upon the physical properties of the structures such as elastic constants,

mass density, boundary conditions and geometric characteristic. Any such modification is treated

in the present study as a “structural damage “. The methods of vibration based structural

inspection are based on the premises that (a) these changes are observable and (b) via the

application of inverse procedures, these changes can be related to the causative modifications to

the physical parameters of the scope of their inspection includes the detecting locating and

quantifying the structural damages. A combine experimentally and analytical program of

research aimed at developing methods for structural damage detection using vibration dotes

under ambient loads and Bayesian methods for FE model. Updating is currently under way at the

Indian Institution of Science .Damage in linear system which are based on frequency and modal

domain descriptions. These procedures are applied on synthetically and experimentally dotes

.Experimental studies are conducted on cantilever beams and on three – storied building frame

model and this has involved measurement of a set of frequency response function using impulse

hammer tests on the structures in its original state and in a modified and subsequent extraction of

model parameters using curve fitting methods. The analytical methods of damage identification,

when applied to experimental, are shown to be successful in characterizing structural

modification with reasonable accuracy.

V. Jaya, G.R. Dodagoudar and Boominathan[7] Seismic response of a structure founded on

soil deposit is quite different from the structure founded on rock. Seismic excitation experienced

by the structure in general is a function of the earthquake source, travel path effects, local site

effects and soil-structure interaction effects. The result of the first three of these factors is a free-

field ground motion. Structural response to free-field motion is influenced by soil-structure

interaction. In particular, acceleration within structure are effected by flexibility of the

34

foundation and free-field motions. Consequently, an accurate assessment of inertial forces and

displacement in the structures requires a rational treatment of soil-structure interaction effects.

The foundation flexibility has a significant effect on the seismic response of tall slender

structures and the soil nonlinearity could increase or decrease the displacement response

depending on the characteristics of the ground motion and the structure. Have The foundation

embedment and stain dependent dynamic properties of soil media surrounding the foundation

have a significant effect on the seismic response of deeply embedded structures due to the effects

of soils structure interaction. Soil foundation structures should consider the variation of soil

characteristics with depth and nonlinear behavior of the soil existing at the site of interest. The

characteristics of the seismic motions will be modified by the presence of a rigid foundation,

particularly for embedded foundations. The stack structure is modeled using conventional finite

elements such as brick and shell elements. The characteristics of the soils such as shear wave

velocity. Response spectra of acceleration and displacement at different levels of ventilation

stack or obtained from the SFSI analysis. Two cases involving stack with and without

embedment are considered for the interaction analysis a parametric sensitivity analysis is also

carried out to understand the various factors affecting the SFSI and the overall seismic response

of the ventilation stack.

Sanjaya Kumar Patro and Ravi Sinha [8] Energy dissipation systems with sliding friction

based devices are being increasingly used for a seismic design of structures. In recent years a

number of these devices have been installed in structures throughout the world. Houser et al.

surveyed various technologies of structural control, including supplemental energy dissipation

devices. The friction device usually consists of a semi rigid friction joing formed by two sliding

surfaces and an intermediate layer of inexpensive friction material that are joined and fastened by

controllable high strength bolts. These devices have proved to be very efficient in dissipating

larger amount of energy that any other method that involves yielding of steel plates, viscoelastic

materials and viscous materials. The use of friction devices typically requires fewer damping

devices in a building to provide the required amount of energy dissipation. Typically these

devices have very good performance characteristics and load amplitude, excitation frequency, or

the number of applied load cycles does not significantly affect their behavior. They can be

designed not to slip during low or moderate earthquake and wind excitations.

35

The sliding friction between metals droops from a higher static to a lower kinetic value,

usually abruptly and is termed as stiction or stic slip effect. Stick slip motion is observed in cases

where the coefficient of friction has its maximum velocity. In such cases, the slope of the curve

between friction coefficient and sliding velocity in negative. This decrease friction coefficient

with increase in sliding velocity is defined as stribec effect. The stribeck velocity (us) governs

the rate of change of friction coefficient and its value depends on response memory (history of

response) material properties and surface finish. The stribeck velocity (us) can be regarded as the

decay rate of the sliding friction coefficient.

S. R. Balsubramanin K .Balaji Rao [9] Loss estimation due to an earthquake is one of the areas

wherein, a lot of effort has been devoted during the recent past, because, it is of importance to

those: who directly own/ maintain facilities like building/infrastructures; who indirectly maintain

such facilities (say, insurance companies); who manage relief operations/emergency situation;

who are responsible for setting up the regulations for such facilities. ‘Risk analysis’ is a well

accepted methodology for making such informed decisions in social economic, socio technical

sectors. Earlier the authors developed a methodology for estimating the expected number of

unreinforced brick masonry buildings that would be damaged, when exposed to earthquakes, in

faridkot district of Punjab. In this paper a methodology has been presented for carrying out the

regional risk analysis of brick masonary buildings and the same has been carried out for different

districts of four states of india (viz uttar Pradesh, uttarakhand, Punjab and Tamilnadu) Fixing the

focal depth of earthquakes; since this information is not available in the earthquake catalogue,

the same is generated using STAI. The STAI divides the country into 43 blocks (each having its

own range of latitude and longitude). Details of earthquakes that have occurred, focal mechanism

solutions for most of these events, tectonic information have been provided in the STAI. The

average focal depth of different earthquakes in each block, covering the entire country, has been

evaluated. In addition approximately 25 blocks around the border (into the other countries such

as Pakistan, Nepal, Banglades, Bhutan, Myanmar and China) of the country have been

considered for the analysis. Since the information of focal depth of earthquakes in these blocks is

not readily available, it has been taken as the shallowest among those adjacent blocks for which

the average focal depth is available in STAI. Thus the updated version of the earthquake

catalogue containing the information of focal depth has been prepared.

36

Sudhir Kumar Jain [10] It is important in seismically active areas to provide safe and

economical protection for life and limb by making adequate provisions for earthquake resistance

in buildings. For most ordinary buildings, it is sufficient to provide earthquake resistance in the

building by means of a suitable building code. This usually involves static analysis of the

building for the prescribed lateral forces, which take into account in an approximate manner the

effects of building characteristics, soil characteristics, seismic risk in the area, importance of the

building, etc. however, there are buildings that have some special characteristics, which make it

difficult to model their dynamic behavior satisfactorily by a code type static analysis. Such

buildings warrant detailed dynamic analysis for satisfactory answers to questions concerning the

behavior during earthquakes. Included in the category are high-rise buildings, buildings with

extreme plan dimensions (e.g.; long and narrow buildings), building with eccentric center of

mass or stiffness, (this leads to coupled torsional and transitional moments), buildings with

vertical setbacks, soft first-story buildings or buildings with other unusual characteristics.

Ugur Ersoy [11] Every year more than 300 000 earthquakes occur on the earth. Many of these

are of small intensity and do not cause any damage to our structures. However, earthquakes of

larger intensity in the vicinity of populated areas cause considerable damage and loss of life. It is

estimated that on average 15000 people have been killed each year throughout the world because

of earthquakes.

The main objective of this paper is to lay down some basic principles for producing

earthquake resistant reinforced concrete structures. These are simple principles and easy to

apply. They have been developed in the light of analytical and experimental research done and

on observations made from past earthquakes.

Seismic resistance should be initiated at the architectural design stage. If the general

configuration chosen by the architect is wrong, it is very difficult and expensive for the structural

engineer to make the building seismic resistant. As a general principle the floor plan should be as

symmetrical as possible. The length of wings (T, L, cross shaped buildings) causing re-entrant

corners should not be large. If the length of the wings is not short, then a seismic Joint should

separate these from the main building.

37

CHAPTER 3

IRREGULARITIES IN STRUCTURES

3.1 General

The experiences from the past strong earthquakes prove that the initial conceptual design

of a building is extremely important for the behavior of the building during an earthquake. It was

shown repeatedly that no static analysis could assure a good dissipation of energy and favourable

distribution of damage in irregular buildings, such as, for example, structures with large

asymmetry or distinctively soft storeys.

Figure 3.1. A building with very irregular shape suffered extensive damage in Bhuj (2001)

The responsibility for a “good” initial conceptual design lies with the architect, as well as

with the structural engineer providing numerical proof of the structure’s safety. The guidelines

for a “good” conceptual design are included in building codes, however, the codes are much

more suited to the needs of structural engineers as to the needs of architects. where many

requirements related to initial design include formulae with parameters that could be obtained

only by preliminary static analysis. On the other hand, same requirements are formulated only as

recommendations and their fulfillment depends on experience and judgment of the designer.

From this point of view the cooperation between architect and structural engineer would be

therefore necessary also during the initial phase of the design of the building. In practice it is

38

difficult to perform static analysis if, for example, the floor plan is still under discussion, so this

cooperation is not working properly in many cases (especially for less complex buildings). It is

evident that architects should be familiar with the basic rules of earthquake resistant design, so

that they can be incorporated in their building solution already from the first sketch.

3.2 Architect, constructor and initial building design:

The initial building design is usually proposed by an architect who should harmonize the

needs of investor with his own ideas and concepts, as well as with all static and other technologic

requirements. It is also necessary to adapt the functionality of the building, to define the major

dimensions of the building and to propose the arrangement of the rooms in the way that

correspond best to the given location, as well as to the needs of the investor and/or user. Of

course the architect also tends to design a recognizable structure and strives to fulfill the

architectural, urban and artistic criteria. On this basis the outline scheme of the building is

usually selected. Many times at that point the structure is already well defined and often also

confirmed by the investor. The structural analysis, that follows, might reveal some mistakes and

in this case it is necessary to correct the project. This phase causes many contradictions between

architectural and structural field. Conflicts start in most cases between the architect, who does

not have enough knowledge about construction, and civil engineer who do not have the

understanding of complexity of the architect’s work and his artistic mission when designing a

building and site. In the usual practice nowadays it seems that the choice of the structure layout

is left to the architect and the proof of its safety is left exclusively to the structural engineer. This

approach is ineffective and should be treated as old-fashioned. More and more complex and

pretentious architectural creations that we are witnessing today demand a dynamic cooperation

among architects and engineers from all fields. We hope the presented synopsis will – at least to

some extend – help to overcome the extensive problem of so needed mutual cooperation.

39

3.3 The philosophy of the structural design on seismic areas:

The destroying power of the energy brought in a structure by an earthquake is enormous.

Due to economic reasons most of the structures cannot be made strong enough accommodate all

of that energy without any plastic deformations (i.e. damage). Depending on the structure and its

life cycle, a certain damage of the structure therefore must be tolerated. For this reason the actual

(elastic) seismic forces are reduced to design forces by behavior factor q. The adopted reduction

factors are valid for the structures with reasonable regularity in plan and elevation. We should be

aware that during a real earthquake, the forces could be much larger than the design forces (up to

6 times) so all numerical proofs based on reduced forces and elastic analysis cannot warranty the

favourable behaviour during a strong earthquake. A structural designer can choose between three

ductility classes. Ductility class defines balance between allowed reduction of seismic load and

the complexity of structural design and realization of details. These ductility classes are low

(DC/Low), medium (DC/Medium) and high (DC/High). Low ductility class prescribes larger

calculated seismic forces in combination with less complicated realization of details, whereas the

high ductility class prescribes reduced earthquake forces in combination with high-quality

realization of details and the use of more accurate calculating methods.

3.4 Factors affecting buildings vulnerability:

The earthquake engineering community believes that there are four virtues on which the

vulnerability of building depends.

1. Good Structural Configurations

2. Lateral Strength

3. Adequate Stiffness

4. Good Ductility

3.4.1 Structural Configuration:

A building is a typical composition of structural and non-structural elements. The

structural elements include vertical components (such as columns and walls) and horizontal

components (such as floors, roofs, beams and girders). The performance of any building in an

earthquake mainly depends upon these structural elements. Structural elements are those

elements of the building that help to support the horizontal and vertical forces acting on it. There

are basically two types structural framing possible to withstand gravity and seismic load, viz.

40

load bearing wall construction and framed construction. The framed constructions can be used

for a greater number of storeys compared to a bearing wall construction. The strength and

ductility can be better controlled in framed constructions through design. The strength of the

framed construction is not affected by the size and number of openings. Non-structural elements

are those elements of buildings that are connected to a structural system but without a load

carrying system. The non-structural elements include varieties of different architectural,

mechanical, electrical components and other house contents. According to the response to the

earthquake motion and in order to assess their damage, these elements are classified into two

classes; acceleration sensitive nonstructural elements and drift sensitive non-structural elements.

The components comes under acceleration sensitive are cantilever, parapets, racks, cabinets,

piping system, HVAC system, lighting fixtures etc. They are called acceleration sensitive

because their cause of damage floor acceleration. The components comes under drift sensitive

are nonbearing walls, partitions, exterior wall panels, veneer, finishes and penthouses. They are

called drift sensitive because their cause of damage is an inter story drift.

3.4.2 Shape of the building:

An important feature is the general planning and design consideration of proposed

buildings. The general planning includes symmetry and regularity in the overall shape of a

building. The building should be kept symmetrically about both the axes. Asymmetry leads to

torsion during earthquakes and is not very stable. Simple rectangular shapes behave better in an

earthquake than shapes with many projections. Torsion effects of ground motion are pronounced

in long narrow rectangular blocks.

3.4.3 Height and Number of storeys: Height is perhaps one of the most important elements in a building’s configuration.

When the height of the building is bigger, then the displacement of the buildings is greater. In

tall buildings with large height-to-base size ratios, the horizontal movement of the floors in an

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

during shaking are many. And, in buildings with large plans area like warehouses, the horizontal

seismic forces can be excessive to be carried by columns and walls. Buildings that have fewer

columns or walls in a particular storey or with unusually tall storeys tend to damage or collapse,

which is initiated in that storey. Many buildings with an open ground storey intended for parking

are more prone to collapse or were severely damaged. Among those multi-storey buildings that

41

collapsed in Gujarat during the 2001 Bhuj earthquake, a majority of them had the ground storey

left open for parking convenience without any walls built between the columns.

3.4.4 Building Proximity:

The separation distance between buildings is an important factor for preventing it from

hammering or pounding damage in case of a seismic event. A physical separation of 3 to 4 cm

between two blocks throughout the height above the plinth level will be adequate for up to 3

storied buildings. The separation section can be treated just like expansion joints or it may be

filled or covered with a weak material, which would easily crush and crumble during earthquake

shaking. Such separation may be considered in larger buildings since it may not be convenient in

small buildings. Every multistoried building can swing according to its own natural frequency

during an earthquake. The probable displacement of a building can be found out from a structural

analysis. The minimum separation distance between two buildings must be 4 % of the height of

the buildings - this is basically with the assumption that most structures will not drift more than 2

% during the occurrence of an earthquake.

3.4.5 Lateral Strength:

The lateral strength of any building is the maximum lateral force that it can resist, such

that the damage induced in it does not result in collapse. The lateral force largely depends upon

the total weight of the superstructure and stiffness of the building. Larger the stiffness for given

mass, shorter the fundamental period of vibration of the structure. The inertia forces are

proportional to the mass of the building and only that part of the loading action that possesses

mass will give rise to seismic force on the building. The lighter the material, the smaller will be

the seismic force.

3.4.6 Building Stiffness:

The height of a building is related to another important structural characteristic: the

building flexibility. Taller buildings tend to be more flexible than short buildings. Consider a thin

metal rod. It is very difficult to bend a short metal rod by hand of same diameter than a rod of

somewhat longer in length. A building behaves similarly. We say that a short building is stiff,

while a taller building is flexible. Obviously, flexibility and stiffness are really just the two sides

of the same coin. If something is stiff, it isn't flexible and vice-versa.

42

3.4.7 Ductility:

Ductility is the ability to undergo distortion or deformation bending under severe

earthquake shaking even after yielding. Different individual buildings shaken by the same

earthquake respond differently. It is far more desirable for a building to sustain a limited amount

of deformation than for it to suffer a complete breakage failure. The ductility of a structure is in

fact one of the most important factors affecting its earthquake performance. The building should

possess enough ductility to withstand the size and types of earthquakes it is likely to experience

during its lifetime.

3.5 Foundation: Buildings, which are structurally strong to withstand earthquakes sometimes, fail due to

an inadequate foundation design. Tilting, cracking and failure of superstructures may result from

soil liquefaction and differential settlement of footing. Certain types of foundations are more

susceptible to damage than others. For example, isolated footings of columns are likely to be

subjected to differential settlement particularly where the supporting ground consists of different

or soft types of soil. Mixed type of foundations within the same building may also lead to

damage due to differential settlement. Very shallow foundations deteriorate because of

weathering, particularly when exposed to freezing and thawing in the regions of cold climate.

Buildings can be constructed on firm and soft soils but it will be dangerous to build them on

weak soils. Hence appropriate soil investigations should be carried out to establish the allowable

bearing capacity and nature of soil. Weak soils must be avoided or compacted to improve them

so as to qualify as firm or soft.

3.6 Building Material and Construction Technique:

Construction material and technique affect the seismic performance of a building. The

construction technique is largely depending upon the building material used for building

construction. Two types of construction techniques generally used in Indian context. These are

load-bearing construction and RC framed construction. The building materials used in

construction of load bearing structure and RC framed structures are given in the table below. A

building constructed of bricks in cement mortar will behave much better than constructed of

bricks in mud mortar, provided all other parameters remain the same. To resists the internal

forces caused by earthquakes it is helpful if the materials perform well both in compression and

43

in tension. Materials, which perform well only in compression, are often reinforced by other

materials with good tensile strength qualities.

3.7 Damage limitation requirement:

This criteria demands that the structure withstand an earthquake without the occurrence of

damage and the associated limitations of use, the costs of which would be disproportionately

high in comparison with the costs of the structure itself.

3.8 Global stability requirement:

The stability of the entire structure against collapse and slide also has to be examined. It also

has to be examined whether the foundations and ground have the capacity of withstanding the

shocks of an earthquake without suffering major permanent deformations.

3.9 Evolution of Building Separation Requirements: This provision requires buildings to be separated to reduce pounding damage during

earthquakes in the 1994 UBC. As early as 1952, the UBC included a nonspecific requirement to

provide building separation. From the 1961 to 1985 editions, structures were required to provide

separation “to avoid contact under deflection from seismic action.” A professional guideline

recommended that a separation of 3/K times the calculated deflection be provided, where K was

a horizontal force factor used in calculating design base shear. The 1988 UBC integrated this

guideline by requiring the separation to be to 3(Rw / 8), here Rw was a structural response

modification factor approximately equal to 8/K. In effect, the requirement specified the

separation to be three times the design deformation.

Pounding and hammering of adjacent buildings can cause substantial damage, if not collapse.

The threat of collapse is greatest when the floor slabs of adjacent buildings are at different levels

and hit against the columns of the neighboring building. In such cases the joints must conform

with the relevant design rules. This implies the following: 1) the joints must have a certain

minimum width (specified in the building codes) 2) the joints must be empty (no contact points)

In order to enable free oscillations and avoid impact between adjacent buildings, it is often

necessary to have a substantial joint width. As long as the structural elements do not lose their

load bearing capacity at pounding, other solutions are also possible. When designing a building,

it is important to visualize the dynamic behavior of the structure as realistically as possible. In

44

this T-shaped building, the stiffnesses of the two wings, respective to each principal direction,

are very different. The two wings will tend to oscillate very differently but will also hinder each

other. This leads to large additional stresses, particularly at the corners of the floor slabs and at

the end of each wing, and may necessitate heavy structural measures. The problem can be

avoided by separating the two wings by a joint respecting relevant seismic design rules. The

result is two compact rectangular buildings that are «dynamically independent»

3.10 Rapid Screening and Evaluation of Damaged Buildings:

Moderate or large earthquakes in urban areas may place heavy demands on the design and

construction professions. Damaged buildings must be identified and screened to guide decisions

on the safety of continued occupancy and the need to post some structures as unsafe. The

demand for rapid screening and the urgent need for shelter may require help from a broad

segment of the design and construction professions. Previous earthquake experience, good

advance training, or both, are essential for proficiency in post-earthquake screening and

evaluation. Currently the engineering community participates in such a training program with the

Office of Emergency Services (OES), through the Structural Engineers Association of California

(SEAOC) and the American Society of Civil Engineers (ASCE). In 1991 CCAIA became a

participant in OES volunteer damage assessment programs, training courses for architects have

been held, and architects are now included in the OES plan for post-earthquake evaluations. This

participation is highly commendable, and should continue as rapidly as possible. Thus architects

can also acquire the skills needed for effective post-earthquake screening and evaluation. With

adequate training, they can make significant contributions to earthquake disaster response.

Participation in training and post-earthquake site visits are excellent ways to increase architects’

seismic knowledge, which will also assist them in their regular practice

45

Figure 3.2. This facade cladding was insufficiently anchored and could not follow the

deformations the reinforced concrete frame structure (Northridge, California 1994).

Figure 3.3. In these houses also, the slabs consisted only of precast elements, which were

insufficiently connected between each other and with the walls (Armenia 1988)

46

CHAPTER 4

EARTHQUAKE ANALYSIS OF REINFORCED CONCRETE BUILDINGS

4.1 General:

Most recent earthquakes have shown that the irregularities in plan, elevation, distribution

of mass, stiffness and strengths may cause serious damage in structural systems. However an

accurate evaluation of the seismic behavior of irregular buildings is quite difficult and a

complicated problem. Due to the variety of parameters and the choice of possible models for

torsionally unbalanced systems, there is as yet neither common agreement nor any accurate

procedure advised by researchers on common practice in order to evaluate the torsional effects.

Performance of reinforced concrete structures largely depends on the strength and

deformability of constituent members, which is further, linked to the internal design forces for

the members. The internal design forces in turn depend upon the accuracy of the method

employed in their analytical determination. Analysing and designing buildings for static forces is

a routine affair these days because of availability of affordable computers and specialized

programs which can be used for the analysis. On the other hand, dynamic analysis is has a vital

role in lateral loading and requires additional input related to mass of structure, and an

understanding of structural dynamics for interpretation of analytical results.

To perform well in earthquake, a building should possess four main attributes, namely simple

and regular configuration, and adequate lateral strength, stiffness, and ductility. Buildings having

simple and regular geometry and uniformly distributed mass and stiffness suffer much less

damage.

On the other hand buildings with irregular configurations suffer seviour damage, which is

incomparable. When such irregularrities are unavoidable, these structures should be treated

specially and designed with the provision seismic joint or separation joint. These seismic joints

should be placed at appropriate place, the place of a joint should be in such away that the effects

of irregularities are avoided or at least minimized.

In the present thesis work ‘T’ irregularity is chosen by varying different parameters such

as number of stories, direction of lateral loading and width of the joint. Dynamic analysis is

adopted, for the chosen structure to study the behaviour with joint, continuous and with gap in

the structure.

47

4.2 Dynamic analysis:

Dynamic analysis represents the response of the structure to dynamic effects. Dynamic

analysis is defined as time varying response. The loads and response vary with time, so it is

evident that the dynamic problem does not have single solution as static problem dose. Thus the

internal moment and shear must equilibrate not only the externally applied force but also inertia

forces resulting from the acceleration of the structure. Inertia forces, which resist acceleration of

the structure, represent the most important distinguishing characteristic of the structural

dynamic problem s, in general if the inertial forces represent significant portion of the total

loads equilibrated by the internal elastic forces of the structure then the dynamic characteristic

of the problem must be account for this solution. In other words if the motion are very slow that

the inertia forces are negligibly small, the analysis for any desired instance of time may be made

by static structural analysis procedure even though the load response may be time varying.

There are two methods of analysis as prescribed by the code [IS: 1893-(1984 and 2002).

Bureau of Indian Standard] the two methods are listed below.

Seismic coefficient method.

Response spectrum method.

4.3 Seismic coefficient method:

In the seismic co-efficient method, the design lateral force shall first be computed for the

whole building as a whole. This design lateral force shall then be distributed to the various floor

levels. The overall design seismic force is then obtained at each floor level, shall then be

distributed to individual lateral load resisting elements depending upon the floor diaphragm

action. Seismic co-efficient that could generally be adopted in different zones of the country

though, of course a rigorous analysis considering all the factors involved has to be made in the

case of all important projects in order to arrive at a suitable seismic co-efficient for design.

48

4.4 Response spectrum method:

Response spectrum analysis is procedure to compute the peak response of a structure

during an earthquake directly from earthquake response or design spectrum without the need of

the response history analysis of the structure, by this analysis we can obtain peak response,

which is sufficiently accurate for the structural analysis of the structure.

In this method natural frequencies and mode shapes are obtained by a free vibration

analysis. For each significant natural mode, the response acceleration co-efficient (sa/g) is

obtained the code (IS: 1893-2002).

For the present thesis work response spectrum method is adopted for the dynamic analysis of the structure. 4.5 Problem description:

Building taken for seismic analysis: ‘T’ shaped unsymmetrical structure was considered. In this analysis the input parameters

were change in number of stories, joint width and earthquake loading in X and Z directions.

For the analysis, the structure considered varied in number of stories, the dimensions of

the structure are explained below with plan and isometric view figures.

Earthquake analysis has been carried out for ‘T’ shape irregularity varying different

parameters, which are listed and explained below.

49

Figure 4.1. Plan of continuous building

50

Figure 4.2. Plan of gap building

Figure 4.3. Plan of joint (Elastomer) building

51

Figure 4.4.One side selected critical columns are highlighted

Figure 4.5 .One side selected critical columns are highlighted

52

Figure 4.6. Plane view of the ten storeyed building

Figure 4.7 .Plane view of the twenty storeyed building

53

Figure 4.8. Plane view of the thirty storeyed building

54

Figure 4.9 .Plane view of the forty storeyed building

55

4.6 Dimensions of structural members :

Floor height is considered to be 3.2m.

Column to column spacing is maintained as 5m.

Foundation depth is taken as 3.2m

Column dimensions are 600×600mm&300×600mm

Beam dimensions are 300×450mm

Walls are modeled as Infill brick walls (compression members) and thickness of wall

is assumed as 230mm.

Slabs are modeled as master slave

The master/slave option provided in STAAD allows the user to model specialized

linkages (displacement tying, rigid links) in the system. For example, SLAVE FY … connects

the two joints such that the Y displacement at the slave will be the sum of Y displacement at the

master plus the rigid rotation. The master-slave option enables us to specify rigid links or

specialized linkages in the structure. This facility can be used to model special structural

elements such as ties or a floor diaphragm which makes the floor rigid for in plane movements

4.7 Load calculations:

Self-weight is assigned which covers the dead load of beams, columns, slabs and walls.

Floor finish is assigned as 1.5kN/m2.

Live load is considered as 4 kN/m2.

Using IS 1893-2002 seismic load definition for response spectrum following

parameters are assigned

Zone III

Zone factor (Z) 0.16

Importance factor (I) as1

Response reduction factor (R) as 3

SS1

All the dead loads assigned with factor one where as live loads are assigned with factor of

0.25 in the response spectrum definition.

56

Lateral load coefficient is calculated as 0.026 (Z/2×I/R)

Combination method SRSS

Spectrum type acceleration

Interpolation type linear

Damping ratio 5 %( 0.05)

Scale 1

Sub soil class Medium soil

Torsion is assigned.

4.8 The Input Parameters:

Number of stories 10, 20,30 and 40

Direction of lateral loading X and Z

1. Joint width is varied depending upon the structure

Ten storeyed

1. Continuous

2. 13mm joint width in dir.-X

3. 18mm joint width in dir.-Z

4. Gap of 18mm & 13mm

Twenty storeyed

1. Continuous

2. 30mm joint width in dir.-X

3. 42mm joint width in dir.-Z

4. Gap of 42mm & 30mm

Thirty storeyed

1. Continuous

2. 50mm joint width in dir.-X

3. 72mm joint width in dir.-Z

4. Gap of 50mm & 72mm

Forty storeyed

1. Continuous

2. 76mm joint width in dir.-X

57

3. 110mm joint width in dir.-Z

4. Gap of 76mm & 110mm

For the above given input parameters the above shown models are analysed. The

resultant moments, axial force, and eccentricities are compared for different variant input

parameters.

Ten storeyed building:

Maximum story drift = 11.807mm

Joint width = R/2 × maximum story drift

= 3/2 ×11.807mm

= 17.71mm (approx 18mm)

Twenty storeyed building:

Maximum story drift = 27.801mm

Joint width = R/2 × maximum story drift

= 3/2 ×27.801

= 41.70mm (approx 42mm)

Thirty storeyed building:

Maximum story drift = 47.795mm

Joint width = R/2 × maximum story drift

= 3/2 ×47.795

= 71.69mm (approx 72mm)

Forty storied building:

Maximum story drift = 73.272mm

Joint width = R/2 × maximum story drift

= 3/2 ×73.272

= 109.908mm (approx 110mm)

58

CHAPTER 5

RESULTS AND DISCUSSIONS 5.1 Results Column Moments and Axial Force Results (One Side Critical Columns): Table 5.1 Comparison of axial load in columns varying in joint width for a ten storeyed building

with earthquake loading in ‘Z’ direction

Axial force in kN 10 storeyed dir-Z

Column nos.

Continuous Gap (18mm)

Joint (18mm)

103 15265 15899 15930

104 14657 15317 15348

124 10909 10625 10646

130 3827 10857 10911

131 3169 10356 10394

134 12389 13490 13515

149 13231 14012 14038

150 10925 13563 13589

59

Table 5.2 Comparison of axial load in columns varying in joint width for a ten storeyed building

with earthquake loading in ‘Z’ direction

Moment (My) in (kN-m) 10 storeyed dir-Z

Column Continuous Gap(18mm)

Joint(18mm)

nos.

103

2770 2669 2638

104

2764 2662 2668

124

2898 2791 2798

130

522 419 447

131

522 443 444

134

2762 2661 2667

149

2769 2668 2674

150

2763 2661 2667

60

Table 5.3 Comparison of moments in columns varying in joint width for a ten storeyed building

with earthquake loading in ‘Z’ direction

Moment (Mz) in (kN-m) 10 storeyed dir-Z

Column nos.

Continuous Gap

(18mm)

Joint

(18mm)

103 2283 2207 2213

104 2179 2107 2089

124 2221 2142 2148

130 1257 1213 1216

131 1269 1217 1221

134 2231 2149 2155

149 2412 2312 2319

150 2300 2205 2213

61

Table 5.4 Comparison of axial load in columns varying in joint width for a twenty

storeyed building with earthquake loading in ‘Z’ direction

Axial force in (kN) 20 storeyed dir-Z

Column nos. Continuous

Gap (42mm)

Joint (42mm)

103 48673 58180 58283

104 47720 57659 57761

124 36772 35573 35650

130 5654 38089 38161

131 7038 36582 36638

134 39728 42799 55628

149 48386 56938 57040

150 48083 56646 56749

62

Table 5.5 Comparison of moments in columns varying in joint width for a ten storeyed building

with earthquake loading in ‘Z’ direction

Moment (My) in (kN-m) 20 storeyed dir-Z

Column nos. Continuous

Gap (42mm)

Joint (42mm)

103 5637 5841 5855

104 5630 5834 5848

124 5920 6134 6149

130 1074 961 963

131 1070 956 958

134 5627 5831 5844

149 5635 5839 5852

150 5628 5832 5845

63

Table 5.6 Comparison of moments in columns varying in joint width for a twenty storeyed

building with earthquake loading in ‘Z’ direction

Moment (Mz) in (kN-m) dir-Z

Column nos.

Continuous

Gap (42mm)

Joint (42mm)

103 4608 4459 4470

104 4384 4243 4254

124 4472 4319 4331

130 2552 2468 2476

131 2571 2478 2486

134 4507 4348 4360

149 4908 4715 4732

150 4667 4484 4500

64

Table 5.7 Comparison of axial load in columns varying in joint width for a thirty storeyed

building with earthquake loading in ‘Z’ direction

Axial force in (kN) 30 storeyed dir-Z

Column nos. Continuous Gap Joint

72(mm) 72(mm)

103 95644 123000 123000

104 94098 123000 123000

124 76910 74304 74507

130 8446 79018 78974

131 76410 76364 1623

134 73242 68117 68282

149 106000 129000 130000

150 106000 129000 129000

65

Table 5.8 Comparison of moments in columns varying in joint width for a thirty storeyed

building with earthquake loading in ‘Z’ direction

Moment (My) in (kN-m) 30 storeyed dir-Z

Column Continuous Gap Joint

72(mm) 72(mm)

103 8535 8958 8981

104 8528 8952 8975

124 8971 9410 9434

130 1631 1461 1465

131 1623 1453 1457

134 8522 8942 8965

149 8530 8951 8974

150 8524 8944 8967

66

Table 5.9 Comparison of moments in columns varying in joint width for a thirty storeyed

building with earthquake loading in ‘Z’ direction

Moment (Mz) in (kN-m) 30 storeyed dir-Z

Column Continuous Gap Joint

72(mm) 72(mm)

103 6948 6726 6746

104 6604 6395 6413

124 6744 6518 6539

130 3859.4 3739 3752

131 3886 3754 3767

134 6805 6570 6592

149 7435 7154 7183

150 7064 6798 6825

67

Table 5.10 Comparison of axial load in columns varying in joint width for a forty storeyed

building with earthquake loading in ‘Z’ direction

Axial force in (kN) 40 storeyed dir-Z

Column Continuous Gap Joint

(110mm) (110mm)

103 125000 176000 181000

104 139000 143000 144000

124 131000 127000 128000

130 10852 114000 117000

131 17663 127000 130000

134 81111 188000 192000

149 186000 230000 232000

150 186000 230000 232000

68

Table 5.11 Comparison of moments in columns varying in joint width for a forty storeyed

building with earthquake loading in ‘Z’ direction

Moment (My) in (kN-m) 40 storeyed dir-Z

Column Continuous Gap Joint

(110mm) (110mm)

103 11463 11333 12221

104 11456 11327 12215

124 12050 11893 12830

130 2192 1832 1979

131 2180 1823 1969

134 11446 11307 12195

149 11454 11318 12205

150 11447 11311 12198

69

Table 5.12 Comparison of moments in columns varying in joint width for a forty storeyed

building with earthquake loading in ‘Z’ direction

Moment (Mz) in (kN-m) 40 storeyed dir-Z

Column Continuous Gap Joint

(110mm) (110mm)

103 9309 9014 9043

104 8845 8567 8595

124 9037 8737 8772

130 5177 5021 5043

131 5213 5040 5063

134 9123 8812 8851

149 9983 9609 9665

150 9482 9129 9182

70

Table 5.13 Comparison of axial load in columns varying in joint width for a ten storeyed

building with earthquake loading in ‘X’ direction

Axial force in (kN) 10 storeyed dir-X

Column nos.

Continuous Gap (13mm)

Joint (13mm)

103 13453 13971 14001

104 12848 13389 13418

124 3761 11945 11965

130 3169 9577 9630

131 11274 9134 9172

134 11227 11869 11894

149 11738 12387 12413

150 12373 12210 12234

71

Table 5.14 Comparison of moments in columns varying in joint width for a ten storeyed building

with earthquake loading in ‘X’ direction

Moment (My) in (kN-m) 10 storeyed dir-X

Column nos. Continuous Gap (13mm)

Joint (13mm)

103 2328 2237 2243

104 2298 2207 2213

124 438 2337 2343

130 439 375 376

131 2327 373 374

134 2320 2229 2235

149 2327 2236 2242

150 2320 2230 2236

72

Table 5.15 Comparison of moments in columns varying in joint width for a ten storeyed

Building with earthquake loading in ‘X’ direction

Moment (Mz) in (kN-m) 10 storeyed dir-X

Column nos. Continuous Gap

(13mm)

Joint

(13mm)

103 2719 2635 2640

104 2593 2513 2518

124 1498 2555 2561

130 1510 1449 1452

131 2788 1454 1458

134 2657 2566 2572

149 2877 2766 2773

150 2741 2636 2643

73

Table 5.16 Comparison of axial load in columns varying in joint width for a twenty storeyed

building with earthquake loading in ‘X’ direction

Axial force in (kN) 20 storeyed dir-X

Column nos.

Continuous

Gap (30mm)

Joint (30mm)

103 41954 49799 49900

104 45401 49262 49363

124 6043 41171 41243

130 7505 32566 32647

131 33575 31285 31350

134 40006 47542 47625

149 41693 48768 48868

150 41360 48444 48544

74

Table 5.17 Comparison of moments in columns varying in joint width for a twenty storeyed

building with earthquake loading in ‘X’ direction

Moment (My) in (kN-m) 20 storeyed dir-X

Column nos.

Continuous

Gap (30mm)

Joint (30mm)

103 4700 4857 4870

104 4693 4851 4863

124 895 5098 5111

130 892 801 803

131 4697 796 798

134 4690 4847 4860

149 4698 4855 4868

150 4691 4848 4861

75

Table 5.18 Comparison of moments in columns varying in joint width for a twenty storeyed

building with earthquake loading in ‘X’ direction

Moment (Mz) in (kN-m) 20 storeyed dir-X

Column nos.

Continuous

Gap (30mm)

Joint (30mm)

103 5528 5362 5372

104 5256 5099 5109

124 3063 5194 5205

130 3085 2971 2978

131 5693 2982 2990

134 5408 5231 5243

149 5897 5684 5699

150 5605 5403 5417

76

Table 5.19 Comparison of axial load in columns varying in joint width for a thrity storeyed

building with earthquake loading in ‘X’ direction

Axial force in (kN) 30 storeyed dir-X

Column nos.

Continuous

Gap (50mm)

Joint (50mm)

103

81609

104000

104000

104 96185 104000 104000

124

89973

87068

87247

130

8446

7836

7893

131

10921

64631

64658

134

65150

59307

59438

149

20722

21613

21660

150 89938 109000 109000

77

Table 5.20 Comparison of moments in columns varying in joint width for a thrity storeyed

building with earthquake loading in ‘X’ direction

Moment (My) IN (kN-m) 30 storeyed dir-X

Column nos.

Continuous

Gap (50mm)

Joint (50mm)

103

7059

7393 7414

104

7090

7423

7444

124

7456

7801

7823

130

1356

1213

1217

131

1342

1181

1184

134

7085

7415

7436

149

7093

7423

7444

150

7086

4179

7437

78

Table 5.21 Comparison of moments in columns varying in joint width for a thrity storeyed

building with earthquake loading in ‘X’ direction

Moment (Mz) in (kN-m) 30 storeyed dir-X

Column nos.

Continuous

Gap

(50mm)

Joint

(50mm)

103

8355

8107

8124

104 7938 7704

7721

124

8110

7858

7877

130

4644

4512

4523

131

4675

4529

4541

134

8186

7925

7945

149

8955

8645

8670

150 8506 8213

8237

79

Table 5.22 Comparison of axial load in columns varying in joint width for a forty storeyed

building with earthquake loading in ‘X’ direction

Axial force in (kN) 40 storeyed dir-X

Column nos.

Continuous

Gap (76mm)

Joint (76mm)

103

132000

173000

178000

104 164000 173000 177000

124

155000

139000

140000

130

10852

110000

112000

131

25092

107000

109000

134

148000

156000

157000

149

157000

193000

195000

150 157000 193000 195000

80

Table 5.23 Comparison of moments in columns varying in joint width for a forty storeyed

building with earthquake loading in ‘X’ direction

Moment (My) in (kN-m) 40 storeyed dir.-X

Column nos.

Continuous

Gap (76mm)

Joint (76mm)

103

9519

9387

10125

104

9512

9381

10118

124

10003

9847

10626

130

1819 1519

1641

131

1810

1511

1633

134

9504

9364

10102

149

9511

9374

10111

150

9504

9367

10104

81

Table 5.24 Comparison of moments in columns varying in joint width for a forty storeyed building with

earthquake loading in ‘X’ direction

Moment (Mz) in (kN-m) 40 Storeyed dir-X

Column nos.

Continuous

Gap (76mm)

Joint (76mm)

103

11206

8862

8856

104 10645 8420 8415

124

10881

8771

8792

130

6237

5093

5112

131

6279

5115

5135

134

10989

8938

8971

149

12039

10128

10219

150 11433 9623 9710

82

Table 5.25 Joint displacements when earth quake loading in ‘X’ and ‘Z’ directions for 10,20,30

and 40 storeyed structures

Joint displacements when earth quake loading in ‘X’ and ‘Z’ directions

Directions Of

Loading

Storeyed

Continuous

Gap

Joint

X

10 10 10 10

20 23 22 23

30 39 39 40

40 60 57 60

Z

10 14 14 15

20 36 38 38

30 67 79 78

40 108 140 139

83

Figure 5.1 Comparison of column joint displacement continuous structure with gap and joint

structures 10,20,30&40 storeyed buildings with earthquake loading in ‘X’ direction

Figure 5.2 Comparison of column joint displacement continuous structure with gap and joint

structures for 10,20,30&40 storeyed buildings with earthquake loading in ‘Z’ direction.

0.5%

2.5%

0.5%

5%

3.5%

3.5%

2%

1%

0

10

20

30

40

50

60

70

Join

t disp

lace

men

t in

(mm

)

10storeyed 20storeyed 30storeyed 40storeyed In 'X' Direction

CONTINUOUS

GAP

JOINT

2%

6.5%

18%

29%

10%

5.5%

17.5%

29%

0

20

40

60

80

100

120

140

160

Join

t disp

lace

men

t in

(mm

)

10storeyed 20storeyed 30storeyed 40storeyed In 'Z' Direction

CONTINUOUS

GAP

JOINT

84

Figure 5.3 Comparison of column axial force continuous with gap and joint structures for

10,20,30&40 storeyed buildings with earthquake loading in ‘X’ direction.

Figure 5.4 Comparison of column axial force continuous structure with gap and joint for

10,20,30&40 storeyed buildings with earthquake loading in ‘Z’ direction.

4%

8.5%

8%

5.5%

4.5%

9%

8%

8%

020000400006000080000

100000120000140000160000180000200000

Axi

al fo

rce

in (k

N)

10storeyed 20storeyed 30storeyed 40storeyedColumn 104 in 'X' direction

CONTINUOUS

GAP

JOINT

4.5%

21%

29.5%1.5%

5%

21%

33%3%

0

20000

40000

60000

80000

100000

120000

Axi

al fo

rce

in (k

N)

10storeyed 20storeyed 30storeyed 40storeyedColumn 104 in 'Z' direction

CONTINUOUS

GAP

JOINT

85

Figure 5.5 Comparison of column moment continuous structure with gap and joint structures for

10,20,30&40 storeyed buildings with earthquake loading in ‘X’ direction.

Figure 5.6 Comparison of column moment continuous structure with gap and joint structures

10,20,30&40 storeyed buildings with earthquake loading in ‘Z’ direction.

3%

3%

3% 21%

3%

3%

3% 21%

0

2000

4000

6000

8000

10000

12000M

omen

t in

(kN

-m)

10storeyed 20storeyed 30storeyed 40storeyedColumn 104 in 'X' direction

CONTINUOUS

GAP

JOINT

3%

3%

3%

3%

4%

3%

3%

3%

0100020003000400050006000700080009000

10000

Mom

ent i

n (k

N-m

)

10storeyed 20storeyed 30storeyed 40storeyedColumn 104 in 'Z' direction

CONTINUOUS

GAP

JOINT

86

Figure 5.7 Comparison of column axial force continuous structure with gap and joint structures

for 10,20,30&40 storeyed buildings with earthquake loading in ‘X’ direction.

Figure 5.8 Comparison of column axial force continuous structure with gap and joint structures

10,20,30&40 storeyed buildings with earthquake loading in ‘Z’ direction

1.3%

17%

21%

23%

1.3%

17%

21%

25%

0

50000

100000

150000

200000

250000

Axi

al fo

rce

in (k

N-m

)

10storeyed 20storeyed 30storeyed 40storeyedColumn 150 in'x' direction

CONTINUOUS

GAP

JOINT

24%

18%

22%

24%

24.5%

18%

22%

25%

0

50000

100000

150000

200000

250000

Axi

al fo

rce

IN (k

N-m

)

10storeyed 20storeyed 30storeyed 40storeyedColumn 150 in 'Z' direction

CONTINUOUS

GAP

JOINT

87

Figure 5.9 Comparison of column moment continuous structure with gap and joint structures for

10,20,30&40 storeyed buildings with earthquake loading in ‘X’ direction

Figure 5.10 Comparison of column moment continuous structure with gap and joint structures

for 10,20,30&40 storeyed buildings with earthquake loading in ‘Z’ direction

4%

3.5%

3.5%16%

3.5%

3.5%

3%15%

0

2000

4000

6000

8000

10000

12000

14000

Mom

ent i

n (k

N-m

)

10storeyed 20storeyed 30storeyed 40storeyedColumn 150 in 'X' direction

CONTINUOUS

GAP

JOINT

4%

4%

4%

4%

4%

3.5%

3.5%

3%

0100020003000400050006000700080009000

10000

Mom

ent i

n (k

N-m

)

10storeyed 20storeyed 30storeyed 40storeyedColumn 150 'Z' direction

CONTINUOUS

GAP

JOINT

88

Table 5.26 Eccentricity results: T-shape 10, 20, 30&40 storeyed earthquake loading in both X &Z directions:

Serial number

Type of structure Eccentricity in X - direction

Eccentricity in Z -direction

1

Continuous 25 10

2

Joint 25 10

3 Gap (no plastic material)

25 10

5.2 Discussions 5.2.1 Column Moments for Gap and Joint Structure:

For corner column 104 When loading in ‘X’-direction the decrement in Moments Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 3%-

3%, 3%-3%, 3%-3% and 21%-21% respectively.

For corner column 104 When loading in ‘Z’-direction the decrement Moment in Gap and

Joint structures when compare to continuous structure 10,20,30 and 40 storeyed are 3%-4%, 3%-

3%, 3%-3% and 3%-3% respectively

5.2.2 Axial Force for Gap and Joint Structure:

For corner column 104 When loading in ‘X’-direction the increment in Axial force Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 4%-

4.5%, 8.5%-9%, 8%-8% and 5.5%-8% respectively.

For corner column 104 When loading in ‘Z’-direction the increment in Axial force Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 4.5%-

5%, 21%-21%, 29.5%-33% and 1.5%-3% respectively.

89

5.2.3 Column moments for gap and joint structure:

For corner column 150 When loading in ‘X’-direction the decrement in Moments Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 4%-

3.5%, 3.5%-3.5%, 3.5%-3% and 16%-15% respectively.

For corner column150 When loading in ‘Z’-direction the decrement in Moments Gap and

Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 4%-4%,

4%-3.5%, 4%-3.5% and 4%-3% respectively.

5.2.4 Axial force for gap and joint structure:

For corner column 150 When loading in ‘X’-direction the increment in Axial force Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 1.3%-

1.3%, 17%-17%, 21%-21% and 23%-25% respectively.

For corner column 150 When loading in ‘Z’-direction the increment in Axial force Gap

and Joint structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 24%-

24.5%, 18%-18%, 22%-22% and 24%-25% respectively

5.2.5 Joint displacement for ‘X’ and ‘Z’-directions:

When loading in ‘X’-direction the increment in Joint displacement Gap and Joint

structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 0.5%-3.5%,

2.5%-3.5%, 0.5%-2% and 5%-1% respectively.

When loading in ‘Z’-direction the increment in Joint displacement Gap and Joint

structures when compare to continuous structure 10, 20, 30 and 40 storeyed are 2%-10%, 6.5%-

5.5%, 18%-17.5% and 29%-29% respectively

90

5.2.6 Eccentricity:

The eccentricity in ‘X’ direction is 25, and `Z’ direction is 10, in T-shaped three types of

structures (continuous, gap, & joint) the eccentricity is same.

91

5.3 Conclusions In the present work ’T’ shape plan irregular building is considered for the analysis

(a) Continuous buildings

(b) Gap buildings

(c) Joint with Elastomer buildings

Based on the work carried out, the following conclusions are drawn.

For taller buildings (40storeyed):

a) Provision of seismic joints with elastomers would reduce the column moments (Mz) by

about 25% and (My) increasing 7% when compared to a continuous structure. But the

axial forces are increasing by about 25%

b) Provision of seismic joints with elastomers would increase maximum joint displacement by 29%

when compared to a continuous building

For shorter buildings (10storeyed):

a) Provision of seismic joints with elastomers would reduce the column moments (Mz)

and(My) by about 4% when compared to a continuous structure. But the axial forces are

increasing by about 5%

b) Provision of seismic joints with elastomers would increase maximum joint displacement

by 10% when compared to a continuous building

92

SCOPE OF FUTURE STUDY

1 Other irregularities such as ‘H’, ’X’, ’C’ vertical and mass irregularities may be

studied

2. Effect of seismic joints on irregular buildings with soft storey.

3. Irregular buildings may be analysed and compared the results of seismic coefficient

method and response spectrum method.

93

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