KTU CE 204 Construction technology notes module 6

CE 204 Construction Technology CEAA,MEA MODULE 6
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MODULE 6
Building failures – General reasons – classification – Causes of failures in RCC and Steel structures,
Failure due to Fire, Wind and Earthquakes.
Foundation failure – failures by alteration, improper maintenance, overloading.
Retrofitting of structural components - beams, columns and slabs
INTRODUCTION
The design of structures should satisfy three fundamental requirements:
1. Stability: The structure should be stable under the action of loads.
2. Strength: The structure should resist safely stresses induced by the loads.
3. Serviceability: The structure should perform satisfactorily under service loads.
GENERAL CAUSES OF BUILDING FAILURES
Some of the main causes for building collapses are
1. Bad design
2. Faulty construction
3. Foundation failure
4. Extraordinary loads: Natural disasters such as earthquakes, floods, hurricanes, cyclones and
fires
5. Unexpected failure modes
6. Combination of causes
7. Overloading
8. Failure by alteration
9. Improper maintenance
10. Bad workmanship
11. Bad material choice
1. Bad Design
Design is important thing before the building is constructed. If the design fails to fulfil the
requirement standard, it will cause the building to collapse. Bad design means
 Errors of computation
 failure to account for loads the structure will be expected to carry
 erroneous theories
 reliance on inaccurate data
 ignorance of the effects of repeated or impulsive stresses
 improper choice of materials or misunderstanding of their properties
The structural engineer is responsible for these failures, which are created at the drawing board.
Sometimes failures occur due to obvious negligence or gross human error.
2. Faulty construction
These may be departure from good practice in construction, or deficiencies in a material or product
selected.
 Use of salty sand to make concrete
 the substitution of inferior steel for that specified
 bad riveting or even improper tightening torque of nuts

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 Bad welds and other practices well known to the construction worker.
 The contractor’s failure to build in accordance with drawings and specifications can also add
to failure of structures.
 Use of inferior or sub-standard building materials is another reason buildings fail.
 Failure may occur due to consultants’ and contractors’ inadequate supervision and control of
site operations and quality control. Such errors ultimately lead to a situation, which may
involve such failures, which are related to excavation and equipment, inappropriate
sequencing, not enough temporary support; unnecessary structure weight; untimely taking
away of shoring or formwork; and non conformance to design objectives.
 Poor communication between the various design professionals involved, e.g. engineers
involved in conceptual design and those involved in the supervision of execution of works.
3. Foundation failure
Foundation is necessary to support a building and the all of its loads that are within or on it. The foundation
should be made from material that will not fail and lost its stability in the presence of ground or surface water.
Even an excellently designed and constructed structure will not stand on a bad foundation. Although the
structure will carry its loads, the earth beneath it may not. The displacements due to bad foundations may alter
the stress distribution significantly.
4. Extraordinary loads
Extraordinary loads are often natural, such as repeated heavy snowfalls, or the shaking of an earthquake,
floods, fires or the winds of a hurricane. A building that is intended to stand for some years should be able to
meet these challenges. A flimsy flexible structure may avoid destruction in an earthquake, while a solid
masonry building would be destroyed. Earthquakes may cause foundation problems when moist filled land
liquefies.
5. Unexpected failure modes
Unexpected failure modes are the most complex of the reasons for collapse. Any new type of structure is
subject to unexpected failure, until its properties are well understood. Suspension bridges seemed the answer to
bridging large gaps. Everything was supported by a strong cable in tension, a reliable and understood member.
However, sad experience showed that the bridge deck was capable of galloping and twisting without restraint
from the supporting cables. Ellet's bridge at Wheeling collapsed in the 1840's, and the Tacoma Narrows bridge
in the 1940's, from this cause.
6. Combination of causes
7. Overloading
 A building collapses when the load is beyond the strength of the building.
 Even if the foundations and the materials are strong enough for what they were originally built
for, that purpose may change.ie, if a building was designed to be a home and is then turned
into a library where boxes and boxes of books are piled up, the building may strain under the
weight.
 Another reason why the load is often heavier than the original design is because extra storeys
are added.
8. Failure by alteration
Many times alterations to a building are taken up several years after its construction. The alterations may be in
the form of providing the following.
 Openings in the walls

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 Overhead water tanks on roof
 Waterproofing course
 Additional floors
It is very important to know the structure before any alteration, what it is designed for and for what type of
loading. It is vital to know what is holding the structure together. The existing structural elements (e.g. roof,
beams columns, floor, walls etc.) should be checked thoroughly for any alterations/modifications. A number of
health and safety failures that caused collapses (with or without fatalities), because appropriate measures were
not taken into consideration.
Overloading during the life span of a building can critically weaken the structural reliability of it. Extra loads
due to unauthorised change of use or additions and alterations to the structure can intensify an under-designed
building and can contribute to its eventual failure.
Factors that need to be carefully considered during structural refurbishment are list below:
 Assessing the structural stability mechanism through a detailed structural survey and understanding the
structure as it is now;
 Designing an adequate temporary support system
 The condition of adjacent structures (if any) and their stability should be established. In particular, it is
important to explore any previous or planned underpinning and its effects on adjacent structures;
 Appointment of competent and experienced team (e.g., planning supervisor and temporary works co-
ordinator), including checking the competency and proficiency of the designer, contractor and other
key professionals involved in the project, and identifying their actual responsibilities;
 Identify clearly the load paths for each structural change;
 Method statements to include stability statements and design requirements prepared for each stage.
A structure needs to be maintained after a lapse of certain period from its construction completion.
Some structures may need a very early look into their deterioration problems, while others can sustain
themselves very well for many years depending on the quality of design and construction. Even when
structural cracks begin to appear, no actions are taken, resulting in eventual collapse.
10. Bad workmanship
 It is often the result of failure to communicate the design decisions to the persons, involved in
executing them.
 Even when workers are given the right materials to make the concrete, they mix them
incorrectly. This results in concrete which is not of the sufficient strength to hold the load.
 The developers cut costs by employing unskilled workers who are cheaper than trained
builders.
11. Improper selection of materials
 Most structural failures are associated with materials and are the consequence of human error
involving a lack of knowledge about materials or the combination of contrary materials.
 There are structural failures that can be endorsed to irregularity in materials.
 Although much reliance is given on modern structural materials, the manufacturing or
production faults may exist even in the most dependable structural materials, such as standard
structural steel. Stone frontage sheets or glass curtain walls may have hidden serious faults.
 Failure may also occur from use of defective materials. The material may have been
improperly manufactured, or may have been damaged from prior use.

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Prevention of building failure
Most of the structural failures (other than those caused by natural disasters) have occurred due to such
faults, which are controllable. Good operational planning and detailed deliberations can save the
failures of the valuable structures. The well-designed structures, coupled with the hard effort of the
experts and correct materials can ensure the structure a complete success. Some other important
points of failure prevention are:
1. The structural designs prepared by the engineer appointed by a builder must be cross-checked
by another structural engineer appointed by the municipal corporation. The municipal
corporation may hire external structural consultants for the purpose. This will prevent faulty
structural designs that may result in building failure.
2. The site execution of construction work, especially with respect to RCC work must be
supervised by an external licensed supervising engineer appointed by Municipal Corporation.
3. Soil investigation report of the site must be made mandatory and must be conducted by a
reputed institute or a laboratory. This will reduce the risk of building collapse by foundation
failure.
4. The final copies of design and drawings must be given to the owners of the building for safe
keeping which will become useful when any structural repairs are to be done in future.
5. Any structural repairs work or addition of new floors must be done only after consulting
structural engineers.
6. For buildings which are old and which are showing signs of deterioration, immediate health
check must be carried out and proper repairs must be implemented after consulting a
structural engineer.
These measures, if properly implemented by both the local authorities and the builders, will prevent
incidents of building collapses and will effectively save hundreds of lives.
TYPES OF BUILDING FAILURES
Building failure occurs when the building loses its ability to perform its intended (design) function.
Hence, building failures can be categorized into the two broad groups of physical (structural) failures
(which result in the loss of certain characteristics, e.g., strength) and performance failures (which
means a reduction in function below an established acceptable limit)
Failure may be classified as,
1. Construction failure
Construction defects usually include any deficiency in the performing or furnishing of the design,
planning, supervision, inspection, construction or observation of construction to any new home or
building, where there is a failure to construct the building in a reasonably workmanlike manner
and/or the structure fails to perform in the manner that is reasonably intended by the buyer. Some of
the most common and high-cost construction defects include: Structural integrity - concrete, masonry
& division, carpentry, unstable foundations
2. Service failure
 Resulting from errors in service-mostly caused by accidental overloading
3. Maintenance failure
 Failure due to lack of maintenance are deterioration and corrosion

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 Building collapse
 Structural cracks in slabs, walls etc
Other classification
1. Structural failure
It is the Loss of the load-carrying capacity of a component or member within a structure or of the
structure itself. Structural failure is initiated when the material in a structure is stressed to its strength
limit, thus causing fracture or excessive deformations. In practice, this corresponds to extensive
damage, partial or total collapse of the building, resulting in repair costs that are high relative to the
replacement value of the building.
Structural failure can occur from many types of problems, most of which are unique to different
industries and structural types. However, most can be traced to one of five main causes.
 The first is that the structure is not strong and tough enough to support the load, due to its size,
shape, or choice of material. If the structure or component is not strong enough, catastrophic
failure can occur when the structure is stressed beyond its critical stress level.
 The second type of failure is from fatigue or corrosion, caused by instability in the structure’s
geometry, design or material properties. These failures usually begin when cracks form at stress
points, such as squared corners or bolt holes close to the material's edge. These cracks grow as the
material is repeatedly, eventually reaching a critical length and causing the structure to suddenly
under normal loading conditions.
 The third type of failure is caused by manufacturing errors, including improper selection of
materials, incorrect sizing, improper heat treating , failing to adhere to the design, or and shoddy
workmanship. This type of failure can occur at any time and is usually unpredictable.
 The fourth type of failure is from the use of defective materials. This type of failure is also
unpredictable, since the material may have been improperly manufactured or damaged from prior
use.
 The fifth cause of failure is from lack of consideration of unexpected problems. This type of
failure can be caused by events such as vandalism, sabotage, or natural disasters. It can also occur
if those who use and maintain the construction are not properly trained and overstress the structure.
2. Aesthetic failure
A condition that renders a component unsightly, significantly detracting from its appearance, can be
termed as aesthetic failure, economic consequences often accompany aesthetic failures such as
masonry effective, although they may be subjective and difficult to quantity.
Causes of Aesthetic Failure
i) Rise of dampness
ii) Pilling of paint cause by water or void created when mixing and casting the materials (i.e.
cement, sand, coarse aggregate).
3. Functional failure
Functional failure is when a component or system does not perform the intended function expected of
it by the designer. This does not mean that this failure will pose a threat to the health and safety of the
occupants of the building. It does not directly threaten the safety and lives of the occupants, but it
does show itself to be quite the defect and deviation from its main purpose.
Functional failure in building may be caused by a lack of maintenance. Keeping up general
maintenance over time can prevent or functional failure caused by aging in general degenerating of

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material or degeneration due to overuse. Functional failure can also be caused due to lack of oversight
by engineers over the workers during construction.
Functional failure can originate from:
 Design errors
 Manufacturing errors
 Installation & commissioning errors
 Operating & maintenance errors
General functional failures
 Lighting problems due to bad orientation of building
 Thermal: Improper thermal insulation and incorrect ventilation
 Acoustics: Sound insulating system is not proper
CAUSES OF FAILURE IN RCC STRUCTURS
 Accidental loadings and overloading
 Chemical reactions
o Acid attack
o Alkali silica reaction
o Sulphate attack
 Construction errors and poor workmanship
 Corrosion of embedded metals
 Design errors
o Inadequate structural design
o Poor design details
 Erosion
 Freezing and thawing
 Settlement and movement
 Shrinkage
o Plastic
o Drying
 Temperature stresses
o Internally generated
o Externally generated
o Fire
 Weathering
 Wrong selection of materials
1. Accidental loadings
Accidental loadings may be characterized as short duration, onetime events such as the impact of a
barge against lock wall or an earth quake. Accidental loading can be defined as loads which the
building is usually not designed for and the main types are as follows:
 Explosive Loads: there are various types of explosive loads, for example, bomb detonation,
gas ignition, or transporting explosive chemical materials or gas.
 Impact Loads: Sources of this type of accidental load can be vehicles, such as collision of a
car with wall or column of a multi storey structure, and construction equipments for instance
accidental impact of crane load against a wall.

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 Other Loads: There are other loads which may be considered as accidental load. For example,
settlement of foundation, making changes to structure considerations of safety measure, earth
quake, flood etc.
Accidental loadings by their very nature cannot be prevented .Minimizing the effects of some
occurrences by proper design procedures or proper attention to detailing can be achieved.
With the vibrations in structure, concrete loose bonds with steel reinforcement and spalling of
concrete may happen from structure.
A building collapses when the load is beyond the strength of the building, ie beyond the load for
which it is designed for.
2. Chemical reactions
a. Acid attack: concrete is susceptible to acid attack because of its alkaline nature. The components
of the cement paste break down during contact with acids. example: nitric acid, hydrochloric acid,
sulphuric acid etc
b. Alkali silica reaction: it is a reaction which occurs over time in concrete between the highly
alkaline cement paste and reactive non crystalline silica which is found in many common aggregates.
The reaction causes expansion of aggregate and exerts an expansive pressure inside the material
causing spalling and loss of strength of concrete.
c. Sulphate attack: the sulphates of calcium, sodium potassium and magnesium are present in most
of soils and ground water.in hardend concrete sulphates react with the free calcium hydroxide to form
gypsum. Similarly sulphate reacts with calcium aluminium hydrate to form calcium sulphoaluminate.
the products of these reactions gypsum and calcium sulphoaluminates have a considerable grater
volume than the compounds that they replace,so that the reaction with sulphates lead to expansion
and disruption of concrete.
The general symptoms of chemical attack on concrete are disintegration and spalling of the concrete
surfaces and the opening of cracks and joints. There is also a general disruption and swelling of the
structure. The aggregate particles protrude from the matrix and there is a loss of cementation in the
cement paste.
Prevention:
 The most important requirement is to use good, sound, dense concrete. Concrete of good
quality prevents the intrusion of aggressive chemical solutions and is clearly and consistently
more resistant to chemical attack than is poor concrete.
 Concrete for use in sulphate environment should be made with sulphate resistant cement.
 In acid environments the use of limestone aggregate will somewhat inhibit attack by
neutralizing a portion of acid attacking binder.
 The cracks which do occur in concrete exposed to aggressive environment should be kept
sealed by application of bituminous sealers to prevent the penetration of chemical solutions.
 To prevent alkali aggregate reaction, specify that the maximum alkali content of cement shall
not exceed 0.6 percent.
3. Construction errors/poor workmanship
 Unstable formwork
 Misplaced reinforcement
 Improper mix design

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 Error in handling and placing concrete (segregation, bad placing, and inadequate compacting)
 curing incomplete
4. Corrosion of embedded metals
Corrosion of reinforcing steel and other embedded metal is the leading cause of deterioration in
concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel .this
expansion creates tensile tresses in concrete, which eventually cause cracking.
Corrosion of steel reinforcement causes reduction in cross sectional area of steel reinforcement in
concrete, eventually reducing the load carrying capacity.
Reinforcement steel in concrete structures gets corroded due to chemical attack or due to poor
construction practices during execution which results in less durable structure.
Corrosion of reinforcement, due to:
 Chloride ions: Chloride-induced corrosion is the single largest problem for aging concrete
highway bridges, particularly in marine environments or areas where road salts are used.
Chlorides can be cast into concrete or diffuse in from the external environment (e.g.
seawater or deicing salt). When the Cl- reach the reinforcing steel, they compete with the
OH- that form the passive oxide layer and are able to penetrate the layer and cause a defect.
A build-up of Cl-can cause the steel’s passive oxide layer to break down, which allows
corrosion to initiate.
 Carbonation: Carbonation occurs when atmospheric carbon dioxide (CO2), an acidic gas,
progressively penetrates the concrete over time and neutralizes its alkalinity. Carbonation
slowly moves through the concrete as a front, and changes the concrete’s chemistry as it
progresses. Once the depth of the carbonation front reaches the reinforcing steel, which
could take several decades, it terminates the steel’s ability to form a passive layer because
the environment is no longer alkaline. This makes the steel vulnerable to corrosion.
Preventive measures
 use of concrete with low permeability
 Adequate cover
 Use of coated reinforcement
 sealers or overlays on the concrete
 corrosion-inhibiting admixtures,
 Cathodic protection
 Strictly following codal provisions in design and construction of concrete structure for the
given region prevents such kinds of damages and defects.
 The selection of suitable painting
 use of epoxy coated steel reinforcements
Any procedure that effectively prevents access of oxygen and moisture to the steel surface or
reverses the electron flow at the anode will protect the steel. In most cases, concrete must be
allowed to breathe, that is any concrete surface treatment must allow water to evaporate from the
concrete.
5. Design errors
a. Inadequate structural design
Due to inadequate structural design the concrete will be exposed to greater stress than it can
actually handle or strain in concrete increases more than its strain capacity and fails. It includes
 Errors of computation

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 failure to account for loads the structure will be expected to carry
 erroneous theories
 reliance on inaccurate data
 ignorance of the effects of repeated or impulsive stresses
 improper choice of materials or misunderstanding of their properties
6. Poor design details
The deterioration in concrete structures occurs repeatedly in connection with certain details or that
certain effects have taken place which were not anticipated in design .some of such details are
 Re-entrant corners: causes stress concentration under the reinforcing bars
 Abrupt changes in section
 Rigid joints between precast slab units
 Leakage through joints
 Inadequate drainage
7. Erosion
Erosion of concrete, leaching or efflorescence is the result of continuous contact of concrete structure
with still or moving water, wind and continues traffic movement. It occurs when the surface of
concrete is unable to resist wear caused by rubbing and friction. As the outer paste of concrete wears
the fine and coarse aggregates are exposed and abrasion and impact will cause additional degradation
of aggregates, exposing steel reinforcement to the atmosphere. This results in corrosion of steel
reinforcement which further decreases the strength and durability of concrete. Usually seen in
hydraulic structures, such as dams, spillways etc.
8. Freezing and thawing
To some extent all concrete is porous and will absorb moisture. Having absorbed this moisture, if
exposed to sub freezing temperatures, the moisture will freeze and expand, and the resulting hydraulic
pressure will tend to cause the concrete surface to crack. Upon thawing the cracked surface will spall.
This process repeated for many cycles causes the concrete surface to disintegrate.
Prevention: minimize the porosity by using dense, sound concrete. Use air entraining admixtures it
improves resistance to weathering. Insulating the concrete against freezing is another technique.
9. Settlement and movement
When water present between soil particles is removed, the soil tends to move closer together. When
water is absorbed by soil, the soil starts to swell. This movement of soil is based on the type of soil.
Large movement is seen with clayey soils than sandy soils. These kind of movement of soil due to
change in water content affects the foundation settlement. Excessive settlement of foundation may
lead to damage to the structure. If all the soil beneath the foundation or slab swells uniformly there is
usually no problem. Problems occur when only part of the slab settles or swells. This differential
movement causes cracks or other damages.
10. Shrinkage
a. Plastic
b. Drying
Plastic shrinkage cracking-“Plastic shrinkage cracking occurs when subjected to a very rapid loss of
moisture caused by a combination of factors which include air and concrete temperatures, relative
humidity, and wind velocity at the surface of the concrete. These factors can combine to cause high

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rates of surface evaporation in either hot or cold weather.” When moisture evaporates from the
surface of freshly placed concrete faster than it is replaced by bleed water, the surface concrete
shrinks. Since plastic shrinkage cracking is due to a differential volume change in the plastic
concrete, successful control measures require a reduction in the relative volume change between the
surface and other portions of the concrete. These measures include the use of fog nozzles to saturate
the air above the surface and the use of plastic sheeting to cover the surface between finishing
operations.
Drying shrinkage-A common cause of cracking in concrete is restrained drying shrinkage. After
hardening concrete begins to shrink as water not consumed by cement hydration leaves the system.
Water above that required to hydrate cement is required for proper workability and finish. The higher
the water content, the greater is the amount of drying shrinkage. If the shrinkage of concrete could
take place without restraint, the concrete would not crack. Drying shrinkage can be reduced by
increasing the amount of aggregate and reducing the water content.
11. Temperature stresses
a. Internally generated – heat of hydration
b. Externally generated – variations in climatic conditions
c. Fire
The thermal effect is the result of continuous drying and wetting of concrete or where the temperature
is high. In this case, the steel and concrete in concrete structure expands and contracts at a different
rates and bond is lost with concrete. This also results in crack in concrete members and thus spalling
of concrete may happen.
Temperature differences within a concrete structure may be caused by portions of the structure losing
heat of hydration at different rates or by the weather conditions cooling or heating one portion of the
structure to a different degree or at a different rate than another portion of the structure. These
temperature differences result in differential volume changes. When the tensile stresses due to the
differential volume changes exceed the tensile stress capacity, concrete will crack. Cracking in mass
concrete can result from a greater temperature on the interior than on the exterior.
Procedures to help reduce thermally-induced cracking include reducing the maximum internal
temperature, use as low cement content as possible, use a low heat cement, provide contraction and
expansion joints. Delaying the onset of cooling, controlling the rate at which the concrete cools, and
increasing the tensile strength of the concrete.
12. Weathering
The weathering processes that can cause cracking include freezing and thawing, wetting, drying,
heating and cooling. Cracking of concrete due to natural weathering is usually conspicuous, and it
may give the impression that the concrete is on the verge of disintegration, even though the
deterioration may not have progressed much below the surface. Damage from freezing and thawing is
the most common weather-related physical deterioration. Concrete is best protected against freezing
and thawing through the use of the lowest practical water cement ratio and total water content,
durable aggregate and adequate air entrainment. Adequate curing prior to exposure to freezing
conditions is also important. Allowing the structure to dry after curing will enhance its freezing and
thawing durability. Other weathering processes that may cause cracking in concrete are alternate
wetting and drying, and heating and cooling. Both processes produce volume changes that may cause
cracking. If the volume changes are excessive, cracks may occur.

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12. Wrong selection of materials
 Unsuitable materials
 Unsound aggregate
 Reactive aggregate
 Contaminated aggregate
 Using the wrong type of cement
 Cement manufacturer error
 Wrong type of admixture
 Substandard admixture
 Contaminated admixture
 Organically contaminated water
 Chemically contaminated water
FAILURE IN STEEL STRUCTURES
TYPES OF FAILURE IN STEEL STRUCTURES
1. Failure of a connection (shear failure)
This is one of the most critical and most frequent failures in the steel structure. Connections typically
have high shearing forces that an engineer must consider when designing the connection. We can
design any steel member quite beautifully with exact precision, but to design a joint, it becomes
tedious. You need to consider the load envelope and then design the joint for the maximum possible
force. But generally the connection fails first in case there is an unpredicted force. Any steel member
can take the secondary loads because the material is uniform and casted
2. Failure of Beams (flexural failure)
Flexural failure occurs when the beam fails in bending. Or you can say when the lateral loads on the
beam increase beyond its limit then this kind of failure takes place.
But there is one more important failure of beams which is Failure due to lateral torsional buckling.
3. Failure in compression
Applied load on a structural member causes compressive stress. Similar to beams, column members
subjected to high compressive stresses may experience buckling. A consideration to take into account
when designing a column is its slenderness ratio; a member with a high slenderness ratio is more
susceptible to buckling than one with a lower ratio. Members with low slenderness ratios may still
fail when the compressive stresses exceed the material’s ultimate capacity.
4. Failure in Tension
This failure occurs when you stretch a material bit too far. The possibility of this is very rare if the
structure is designed properly. In this kind of failure the member is yielded first, then the necking
phase comes into the picture and then it fails at the reduced cross section. This leads to a very high
strain energy and it takes a large amount of load to fail the member in tension.
5. Local failure
Suppose if your member is very strong and it cannot fail at global level like tension or compression or
bending or anything. But then if the forces exceeds from a certain limit, then it can lead to some local
failure. One of the most common local failure is local buckling of I sections.

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When the stresses exceed but not enough to fail the member completely then there occurs a local
failure called local buckling of beams. In this failure there are high local stresses developed at
imperfect locations of the member. This local members cause the beam to show some unorthodox
behaviour and fails in certain region. This causes a reduction in the stiffness of the member but it can
still carry load. This kind of failure is a very good failure as it gives an indication that the structure
should either be repaired or it should be demolished.
CAUSES OF FAILURE IN STEEL STRUCTURES
 Corrosion of steel – symptoms are pitted, oxidized surface, usually showing loose flakes or
scales of oxide and typically reddish brown rust colored appearance.
 Abrasion – symptoms are worn, smooth appearance of abraded surface.
 Loosening of connection - Rivets and ordinary bolts in connections for steel structure
subject to shock or impact loading tend to work to loose with time. Loosening of the
connections induces slip in the joints causes distortion of the structure. Creates areas of
extreme stress concentration and increases vulnerability of the structure to fatigue failure.
 Fatigue - It may be defined as the fracture of a structural member. Due to repetitive,
fluctuating load occurring at stresses at or below usual allowable design values. The
symptoms are small fractures, oriented perpendicular to the line of stress, and are serious
sources of danger, largely because the resulting fractures may be extremely difficult to
detect.
 Impact - Exposed steel sections are sensitive to damage from the impact of moving objects,
much more so than are sections of concrete or heavy timber. lmpact damage is
characterized by local distortion of the affected members, usually in form of a crimp or a
bow of short wave length.
 Under design in which the dead and live load are not included,
 wind forces combination not included which causes steel structure frame failure
 Weak steel connection that did not calculate moment forces acting on the members
 Did not consider earthquake/seismic factors
 Did not include dynamic movements in structure which would have convert into lateral
forces
 Poor workmanship such as flawed welding or improperly torqued bolts.
 Poor execution can be inferior materials substituted to increase the profit margin for the
builder.
 Improper design of joints
 Lack of adequate bracing
 Overloading
 Foundation movements
 Other chemical impurities like Sulphur and Phosphorous (Brittleness is caused and the
weldability decreases due to Sulphur and phosphorous)
 Fire: The strength of hot rolled structural steel decreases with temperature.
PREVENTIVE MEASURES
1. Keeping the structure clean
Corrosion will be much accelerated if dirt or debris is allowed to accumulate in contact with the
member. The reason is that the dirt or debris retains rain or wash water and maintains this moisture in
contact with the steel surface.

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2. Protective Coatings
Painting - The application of a paint coating is a cost-effective way of preventing corrosion. Paint
coatings act as a barrier to prevent the transfer of electrochemical charge from the corrosive solution
to the metal underneath. The paint prevents oxygen from reaching the surface of the steel and once
the seal is not perfectly air tight it no longer prevents the oxidization as well as when the seal was air
tight.
Bituminous Paints
Powder coating - Another possibility is applying a powder coating. In this process, a dry powder is
applied to the clean metal surface. The metal is then heated which fuses the powder into a smooth
unbroken film. A number of different powder compositions can be used, including acrylic, polyester,
epoxy, nylon, and urethane
3. Encasement
Permanent or semi permanent protection may be provided by encasing the entire member with
concrete or plastics by sheathing it with nonferrous metals or other no corroding materials.
a.Concrete
b.Reinforced bituminous coatings{wrapping): these provide excellent protection against
corrosion and are widely used for the encasement of buried members in highly corrosive soils
c. Other materials
4. Corrosion resistant alloys
For a given environment the rate of corrosion of a steel structure may be decreased by the use of
corrosion resistant alloy of ordinary carbon steel.
5. Sacrificial Coatings
Sacrificial coating involves coating the metal with an additional metal type that is more likely to
oxidize; hence the term “sacrificial coating.”There are two main techniques for achieving sacrificial
coating: cathodic protection and anodic protection.
Cathodic Protection
The most common example of cathodic protection is the coating of iron alloy steel with zinc, a
process known as galvanizing. Zinc is a more active metal than steel, and when it starts to corrode it
oxides which inhibits the corrosion of the steel. This method is known as cathodic protection because
it works by making the steel the cathode of an electrochemical cell. Cathodic protection is used for
steel pipelines carrying water or fuel, water heater tanks, ship hulls, and offshore oil platforms.
Anodic Protection
Anodic protection involves coating the iron alloy steel with a less active metal, such as tin. Tin will
not corrode, so the steel will be protected as long as the tin coating is in place. This method is known
as anodic protection because it makes the steel the anode of an electrochemical cell. Anodic
protection is often applied to carbon steel storage tanks used to store sulfuric acid and 50% caustic
soda. In these environments cathodic protection is not suitable due to extremely high current
requirements.
6. Armoring
It is used as a means for protecting the structure against damage due to abrasion
7. Influence of design details

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o Either parts of the structure should be accessible for maintenance or if not accessible the
members should be encased or provided with some form of permanent protection
o Select structural shapes which will have a minimum of exposed surface
o Avoid shapes or details which will catch dirt or debris. lf economically feasible, use rounded
sections
o Eliminate pockets, low spots and crevices which will trap water
o Column bases should be protected with concrete encasement or pedestal projecting above the
ground line or floor level
o avoid details which include narrow crevices which cannot be sealed or painted
o for riveted or bolted joints or for sections placed back to back inhibit water penetration b/w
adjacent place or shapes by assuring that all adjacent metal surfaces are drawn up tight
o pipe or tubular column should be concrete filled or sealed, air tight
FORMWORK FAILURE
Causes of Formwork Failure
The main causes of formwork failure are:
 Improper stripping and shore removal
 Inadequate bracing
 Vibration
 Unstable soil under mudsills
 shoring not plumb
 Inadequate control of concrete placement
 Lack of attention to formwork details.
Remedies:
 Provide adequate horizontal bracings to support formwork
 Soil should be compacted well before erecting formwork
 Remove formwork only after the concrete attained sufficient strength
 Bracings should be nailed properly to formwork
FAILURE DUE TO WIND
Wind direction, speed and frequency will influence the building design including bracing
requirements, roof and wall cladding selection, weather tightness detailing, building entry locations,
window size and placement and provision of shelter for outdoor spaces. The higher the building, the
more exposed it will be to higher winds, particularly where the building is taller than adjacent
buildings or vegetation.
The prevailing wind direction must be considered in relation to the design of a building, in particular,
for locations of doors and opening windows, and provision of shelter for outdoor areas. Other aspects
of wind to consider include:
 The direction of the strongest wind
 The direction of the coldest wind
 Humid/dry winds
 Wind that comes off the sea (salt spray issues)
 The wind direction that brings most of the rain.

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Various phenomena occur to buildings and their surroundings during strong winds, sometimes
leading to failure. Table summarizes wind-induced phenomena/damage and their onset wind speeds.
It should be noted that the damage depends not only on wind speed but also on the strength or quality
of structures, and the phenomena/damage in the table can be different.
Correct lateral design is essential to wind-resistant construction. Wind can act on the structure from
any direction, so the design must withstand lateral forces in two directions at right angles to each
other.
Wind-resistant structures are designed to handle lateral forces acting along both the length and the
width of the structure, as well as an uplift vertical force, in addition to the obvious downward vertical
load path. The forces, acting in all directions, act on every element, and every connection between
elements, of the structure
FACTORS EFFECTING WIND DAMAGE
1. Exposure: The characteristics of the terrain (i.e., ground roughness and surface irregularities in the
vicinity of a building) influence the wind loading. Smoother the terrain, the greater the wind
pressure will be.
2. Topography: Abrupt changes in topography, such as isolated hills, ridges, cause wind to speed up.
Therefore, a building located near a ridge would receive higher wind pressures than a building
located on relatively flat land.
3. Building height: Wind speed increases with height above the ground. Taller buildings are exposed
to higher wind speeds and greater wind pressures
4. Internal pressure (building pressurization/depressurization): Openings through the building
envelope, in combination with wind interacting with a building, can cause either an increase in the
pressure within the building (i.e., positive internal pressure), or it can cause a decrease in the
pressure (i.e., negative internal pressure).
5. Building shape: The highest uplift pressures occur at roof corners because of building
aerodynamics (i.e., the interaction between the wind and the building). The roof perimeter has a
somewhat lower load compared to the corners, and the field of the roof has still lower loads.
Exterior walls typically have lower loads than the roof. The ends (edges) of walls have higher
suction loads than the portion of wall between the ends. However, when the wall is loaded with
positive pressure, the entire wall is uniformly loaded.
Building shape affects the value of pressure coefficients and, therefore, the loads applied to the
various building surfaces. For example, the uplift loads on a low-slope roof are larger than the
loads on a gable or hip roof. The steeper the slope, the lower the uplift load.
Building irregularities, such as re-entrant corners, bay window projections, a stair tower projecting
out from the main wall, dormers, and chimneys can cause localized turbulence. Turbulence causes
wind speed-up, which increases the wind loads in the vicinity of the building irregularity.
VARIOUS FEATURES OF DAMAGE TO BUILDING ELEMENTS DUE TO WIND
Wind-induced disaster can be classified into three types.
 Strength failure of frames - Collapse of the whole structure and members (Local failure).
 Instability phenomenon - occurs for example aero elastic instability.
 Deformation - control of structure serviceability design.
There are other types of failure such as fatigue of structural member, cladding materials strength
failure, roof tiles blew away and membrane broken by strong wind

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1. Total roof lift-off - can also be triggered by damage to openings such as glass windows, allowing
wind into the room and increasing the underneath pressure.
2. Partial lift-off of clay tiles
3. Damage to steel plate roofs -Most damage to these roofs is induced by local suction at the eaves
and periphery, insufficient strength of connections between the tight frame and its supporting
beam or between the supporting beam and the lower structure.
4. Canopies - Even if canopies are horizontal, they take a large upward or downward fluctuating
load, depending on the size and shape of the building, the locations of the canopies, objects placed
underneath them, and so on. The tips vibrate a lot, thus causing repeated deformation and fatigue
conditions there. Furthermore, if they project from the wall, there is a high possibility of wind-
borne debris hitting them
5. Protrusions on roofs - If a roof has protruding parts like short chimneys, skylight roof windows,
the flow over the roof surface is locally disturbed, sometimes producing local high suction and
turbulence. Special attention to wind resistant design is therefore necessary around these
protrusions.
6. Rain gutters, gables, verges and copings - There is often insufficient consideration of the wind
resistance of rain gutters, spoutings, verges and copings in roof peripheral areas, where local wind
pressures become large. Damage to these lightweight members may trigger large-scale damage to
roof cladding, leading to total roof destruction. It is therefore necessary to design the plate
thickness and the connection spacing.
7. Lift-off of waterproofing material with heat insulation
8. Windowpanes are often damaged by wind pressure or wind-borne debris. Breakage of windows
not only damages property inside the building, but also induces total roof lift-off. Wind resistant
performance of glass is improved by increasing the rigidity of the supporting members such as
sashes, and decreasing sealing and gasket deformation.
9. Warehouses, factories, garages, and so on suffer a lot of damage to their steel shutters. Damage
starts with dislocation of slats and central guide columns. Damaged shutters can lead to total
building destruction due to increased internal pressure. Thus, shutters can never be neglected just
because they are light. It is important to ensure sufficient plate thickness, rigidity and strength of
slats, and depth of rail grooves.
10. In some cases, steel frames of buildings under construction collapse during strong winds.
Especially in the case of steel-encased reinforced concrete buildings, the cross sectional area of
steel frames themselves is relatively small. Thus, they are very vulnerable to wind during
erection, and it is therefore necessary to thoroughly plan for construction and safety.
11. Structural damage to external cladding
12. Wall collapse: Collapse of non-load-bearing exterior walls is common during hurricanes and
tornadoes, but is less common during other storms
13. Structural system: Structural damage (e.g., roof deck blow-off, blow off or collapse of the roof
structure, collapse of exterior bearing walls, or collapse of the entire building or major portions
thereof) is the principal type of damage that occurs during strong and violent tornadoes
TECHNIQUES FOR WIND RESISTANCE
 Good wind performance depends on good design (including details and specifications),
materials, installation, maintenance, and repair.
 Large openings: Use windows and doors that are rated for high wind and impact damage.
Picture windows, sliding glass doors, garage doors, and other large openings are extremely

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vulnerable to damage in high wind events. Not only are they easy targets for wind-borne
debris, but their large surface area is acted upon with a large force during wind events.
 Clay tile roofs - Nailing the sheathing roof boards over the entire roof area including the
central part, filling gaps with lime plaster, and so on. It is desirable to carry out inspections
every 5 - 6 years and replacement every 20 - 30 years.
 Damage to steel plate roofs - This can be controlled by increasing the thickness of the folded
plate in the peripheral areas, selecting individual assembling members that can maintain
sufficient wind resistant performance, and ensuring tight fixing to the lower structure.
 Reinforce vulnerabilities: When storms are imminent, reinforce or protect large openings and
weak areas.
 Use hip roofs: Hip roofs perform better than gable roof styles during high-wind events. This is
because hip roofs are more aerodynamic and do a better job of supporting the top of the
exterior walls as compared to gable roofs.
 Include safe shelter: Consider adding a safe room or a basement for sheltering building
occupants from dangers associated with hurricanes and tornados
 Avoid staples because they offer less resistance to blow-off than nails.
 Use deformed shank nails to improve the resistance of sheathing to negative pressure.
 For roof framing to wall connection, use a light-gauge metal uplift connector attached on the
exterior of the exterior walls.
 The most effective way to provide lateral and, in some cases, uplift load continuity is to attach
adjacent wall sheathing panels to one another over common framing.
 Extend wood structural panel sheathing at the bottom of the wall to lap the sill plate. The
connection of the wall sheathing to the sill plate is important because this is where the uplift
forces are transferred into the sill plate and into the foundation through the anchor bolts.
 Other factors to consider include building size and shape, exposure category, roof slope,
openings in the building envelope, and design wind speed
 A lot of damage during strong winds has been due to wind-borne debris. An extraordinary
amount and variety of materials are blown off in strong winds, not only cladding materials
such as clay tiles and steel plate roofs, but also other materials such as gravel and square
timbers. Therefore, it is important to adopt countermeasures to avoid collision of wind-borne
debris with windows and walls.
 For tall buildings, there is also a high possibility of wind-borne debris hitting the lower levels.
It is therefore desirable to protect them with metal shutters. Furthermore, measures such as the
use of glass with an internal plastic film are effective in preventing escalation of damage if the
window is hit by wind-borne debris
FAILURE IN BUILDINGS DUE TO EARTHQUAKE
An Earthquake is the result of a sudden release of energy in the earth’s crust that creates seismic
waves. The seismic activity of an area refers to the frequency, type and size of earthquakes
experienced over a period of time.
Earthquake causes ground motions in random fashion, both horizontally and vertically, in all
directions radiating from the epicenter. Consequently, structures founded in ground vibrate, inducing
inertial forces on them. It is therefore essential to ensure stability, strength and serviceability at
acceptable levels of safety by way of suitable designing and detailing.
The Characteristics (intensity and duration) of seismic ground vibrations expected at any location
depends upon

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 Magnitude of the earthquake
 Its depth of focus
 Distance from epicenter
 Characteristics of the path through which seismic waves travel
 The soil strata on which the structure stands.
The ground motions can be resolved in three mutually perpendicular directions. The prominent
direction of ground vibration is usually horizontal.
Intensity is an indicator of the severity of shaking generated at a given location. Severity of shaking is
much higher near the epicenter than farther away.
CAUSES
Earthquakes are natural ways of releasing energy by earth. An earthquake occurs in certain pockets of
the earth which has geological faults. Such areas have already been identified.
EFFECTS
Structural damage: Earthquakes may cause physical damage to the buildings, roads, dams and
monuments. High rise buildings or building built on weak foundations are especially susceptible to
earthquake damage. Household articles including electronic goods and furniture get damaged. Human
and livestock deaths or serious injuries from collapsing of building are common followed by outbreak
of epidemics like cholera, diarrhoea, and infectious diseases. Utilities such as water supply, sewerage,
communication lines, power-lines, transportation network, and railways get damaged.
WHAT ARE THE SEISMIC EFFECTS ON STRUCTURES?
Inertia Forces in Structures
Earthquake causes shaking of the ground. So a building resting on it will experience motion at its
base. From Newton’s First Law of Motion, even though the
base of the building moves with the ground, the roof has a
tendency to stay in its original position. This tendency to
continue to remain in the previous position is known as
inertia. But since the walls and columns are connected to it,
they drag the roof along with them.
If the roof has a mass M and experiences an acceleration a,
then from Newton’s Second Law of Motion, the inertia force
FI is mass M times acceleration a, and its direction is
opposite to that of the acceleration. Clearly, more mass means higher inertia force. Therefore, lighter
buildings sustain the earthquake shaking better.
Effect of Deformations in Structures
The inertia force experienced by the roof is transferred to the
ground via the columns, causing forces in columns. During
earthquake shaking, the columns undergo relative movement
between their ends. But, given a free option, columns would
like to come back to the straight vertical position, i.e.,
columns resist deformations.
In the straight vertical position, the columns carry no
horizontal earthquake force through them. But, when forced

19
to bend, they develop internal forces. The larger is the relative horizontal displacement between the
top and bottom of the column, the larger this internal force in columns. Also, the stiffer the columns
are (i.e., bigger is the column size), larger is this force. For this reason, these internal forces in the
columns are called stiffness forces. In fact, the stiffness force in a column is the column stiffness
times the relative displacement between its ends.
Horizontal and Vertical Shaking
Earthquake causes shaking of the ground in all three directions, along the two horizontal directions
(X and Y, say), and the vertical direction (Z, say). Also, during the earthquake, the ground shakes
randomly back and forth (- and +) along each of these X, Y and Z directions.
All structures are primarily designed to carry the gravity loads, i.e., they are designed for a force
equal to the mass M (this includes mass due to own weight and imposed loads) times the acceleration
due to gravity g acting in the vertical downward direction (-Z). The downward force Mg is called the
gravity load. The vertical acceleration during ground shaking either adds to or subtracts from the
acceleration due to gravity. Since factors of safety are used in the design of structures to resist the
gravity loads, usually most structures tend to be adequate against vertical shaking
However, horizontal shaking along X and Y directions (both + and – directions of each) remains a
concern. Structures designed for gravity loads, in general, may not be able to safely sustain the effects
of horizontal earthquake shaking. Hence, it is necessary to ensure adequacy of the structures against
horizontal earthquake effects.
Flow of Inertia Forces to Foundations
Under horizontal shaking of the ground, horizontal inertia forces are generated at level of the mass of
the structure (usually situated at the floor levels). These lateral inertia forces are transferred by the
floor slab to the walls or columns, to the foundations, and finally to the soil system underneath. So,
each of these structural elements (floor slabs, walls, columns, and foundations) and the connections
between them must be designed to safely transfer these inertia forces through them.
Walls or columns are the most critical elements in transferring the inertia forces. But, in traditional
construction, floor slabs and beams receive more care and attention during design and construction,
than walls and columns. Walls are relatively thin and often made of brittle material like masonry.
They are poor in carrying horizontal earthquake inertia forces along the direction of their thickness.
Similarly, poorly designed and constructed reinforced concrete columns can be disastrous.
FACTORS AFFECTING DAMAGE DUE TO EARTHQUAKE
1. Building configuration
An important feature is regularity and symmetry in the overall shape of a building. A Building shaped
like a box, as rectangular both in plan and elevation, is inherently stronger than one that is L-shaped
or U shaped, such as a building with wings. An irregularly shaped building will twist as it shakes,
increasing the damage.
Architectural Features:
A desire to create an aesthetic and functionally efficient structure drives architects to conceive
wonderful and imaginative structures. Sometimes the shape of the building catches the eye of the
visitor, sometimes the structural system appeals, and in other occasions both shape and structural
system work together to make the structure a marvel. However, each of these choices of shapes and
structure has significant bearing on the performance of the building during strong earthquakes.

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Size of Buildings:
In tall buildings with large height-to-base size ratio, the horizontal
movement of the floors during ground shaking is large. In short
but very long buildings, the damaging effects during earthquake
shaking are many. And, in buildings with large plan area like
warehouses, the horizontal seismic forces can be excessive to be
carried by columns and walls.
Horizontal Layout of Buildings:
In general, buildings with simple geometry in plan have performed
well during strong earthquakes. Buildings with re-entrant corners,
like those U, V, H and + shaped in plan, have sustained significant
damage. Many times, the bad effects of these interior corners in the
plan of buildings are avoided by making the buildings in two parts.
For example, an L-shaped plan can be broken up into two
rectangular plan shapes using a separation joint at the junction
Often, the plan is simple, but the columns/walls are not equally
distributed in plan. Buildings with such
features tend to twist during
earthquake shaking.
Vertical Layout of Buildings:
The earthquake forces developed at different floor levels in a building
need to be brought down along the height to the ground by the shortest
path; any deviation or discontinuity in this load transfer path results in
poor performance of the building.
Buildings with vertical setbacks (like the hotel buildings with a few
storeys wider than the rest) cause a sudden jump in earthquake forces at
the level of discontinuity.
Buildings that have fewer columns or walls in a particular storey or with
unusually tall storey tend to damage or collapse which is initiated in that
storey.
Buildings on sloppy ground have unequal height columns along the
slope, which causes ill effects like twisting and damage in shorter
columns. Buildings with columns that hang or float on beams at an
intermediate storey and, do not go all the way to the foundation, have
discontinuities in the load transfer path . Some buildings have reinforced
concrete walls to carry the earthquake loads to the foundation. Buildings,
in which these walls do not go all the way to the ground but stop at an
upper level, are liable to get severely damaged during earthquakes.
2. Adjacency of Buildings:
When two buildings are too close to each other, they may pound on
each other during strong shaking. With increase in building height, this
collision can be a greater problem. When building heights do not
match, the roof of the shorter building may pound at the mid-height of
the column of the taller one; this can be very dangerous.

21
3. Opening size
In general, openings in walls of a building tend to weaken the walls, and fewer the openings less the
damage it will suffer during an earthquake. If it is necessary to have large openings through a
building, or if an open first floor is desired, then special provisions should be made to ensure
structural integrity.
4. Rigidity distribution
The rigidity of a building along the vertical direction should be distributed uniformly. Therefore,
changes in the structural system of a building from one floor to the next will increase the potential for
damage, and should be avoided. Columns or shear walls should run continuously from foundation to
the roof, without interruptions or changes in material.
5. Ductility
By ductility is meant the ability of the building to bend, sway, and deform by large amounts without
collapse. The opposite condition in a building is called brittleness arising both from the use of
materials that are inherently brittle and from the wrong design of structures using otherwise ductile
materials.
Brittle materials crack under load; some examples are adobe, brick and concrete blocks. It is not
surprising that most of the damage during the past earthquakes was to unreinforced masonry
structures constructed of brittle materials, poorly tied together.
The addition of steel reinforcements can add ductility to brittle materials. Reinforced concrete, for
example, can be made ductile by proper use of reinforcing steel and closely spaced steel ties.
6. Foundation
Buildings, which are structurally strong to withstand earthquakes sometimes fail due to 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 types 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.
7. Construction quality
In many instances the failure of buildings in an earthquake has been attributed to poor quality of
construction, substandard materials, poor workmanship, e. g., inadequate skill in bonding, absence of
“through stones” or bonding units, and improper and inadequate construction.
REASONS FOR FAILURE OF BUILDINGS IN AN EARTHQUAKE
Reason 1: The Soil Fails
Earthquakes move the ground, side to side and up and down simultaneously. The force behind this
movement is powerful enough to turn soft soil instantly into quicksand, eliminating its ability to bear
weight. It’s enough to quickly transform sloped sites into landslides or mudslides. Buildings
constructed on either soft soil or on steeply sloped sites in a seismic zone, therefore, are at special
risk. Taller buildings or those built of rigid concrete may stay intact but topple over in the unstable
soil.

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The design lesson here is a simple one: Avoid building on sites with precarious slopes in earthquake
zones. Sand boils, bogs, or bad soils are to be avoided, as well.
If soft soils are unavoidable, a building’s piers should be set as deeply as possible all the way to the
bedrock where feasible and the building’s foundation should be designed to be as rigid as possible,
without being brittle. Since deep, dense soils and bedrock will move less than the less dense soils
above, anchoring a building deep in the ground will make it better able to withstand.
Reason 2: The Foundation Fails
One of several factors that determine a foundation’s ability to withstand the forces of an earthquake is
the building’s mass. All buildings can carry their own weight; even poorly constructed ones can resist
some additional lateral loads, such as those from a normal wind. But buildings are not necessarily
designed or constructed to resist the irregular, multidirectional, and intense side-to-side loads that
occur during an earthquake, particularly when earthquakes hit in a series of waves.
Such is the case during a foundation connection failure, when a building literally slides off its
foundation. This kind of failure is an indication that as the foundation was moved by shock waves, it
was not strong enough to pull the structure above along with it.
A building’s height also impacts its ability to withstand the forces of an earthquake. The higher the
building, the greater its potential to break apart especially near the foundation as it shifts back and
forth, often out of sync with the foundations below.
Reason 3: A “Soft Floor” Fails
Medical office buildings, hospitals, or other structures constructed on top of a parking garage or an
expansive ground-floor lobby. These lower-level floors are known as “soft floors,” i.e., floors with
minimal interior shear walls, additional floor-to-floor height, or large open spaces with concentrations
of building mass above. The upper levels of a building often remain intact while the lower floors
crumble. This is because the concentration of forces is at the ground floor, where most soft floors are
located.
Wherever they are, however, soft floors represent a break in a building’s structural continuity. With
fewer walls and little infill, soft floors are typically less rigid than the building constructed on top of
them, making soft floors and the columns that support them susceptible to failure in an earthquake.
One solution, of course, is to avoid soft floors altogether. A more practical alternative, however, is to
“harden” these spaces with additional engineered shear support. The spans between columns should
be as small as possible, and column connections at ground level should be designed to resist and
distribute lateral forces.
Reason 4: A Building Joint Fails
The problem, at least with many older buildings, is that newer additions were rigidly connected with
the old buildings even if they were of different heights and construction materials. In older masonry
buildings, in fact, it’s not uncommon to find building expansions that share a common wall with the
original structure.
If these connections don’t accommodate the natural inclination of the different structures to move
independently of each other, or if there is insufficient clearance between the different structures, the
results can be disastrous in an earthquake.
Structural engineers and architects now understand that buildings need room to move in an
earthquake. This is why expansion joints are now added between significant changes in building
mass, and why adequate room must be provided for beams and columns to slip over one another
without either failing.

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In designing new facilities, the key is to take irregular shapes and break them into regular shapes.
An L-shaped building, for example, might in reality be designed as three separate square structures,
each separated by expansion joints.
Reason -5: The Building Fails
A building’s ability to withstand an earthquake also depends on the materials it is made of
lightweight wooden structures that bend and deform without breaking.
Not all building failures result in total collapse. Building failures are also at play when large portions
of a roof or façade fall from a building during or after an earthquake.
These failures can occur because several diverse building elements have been treated like a single
system when, in fact, they should be tied separately back to the structure, with space between them to
allow for the differential movements of the dissimilar elements. Consider, for example, a parapet at
the top of an older brick building.
When unbraced at the top, the roof will channel all lateral forces into the base of the parapet, causing
it to fail at the roof line and come crashing to the street below.
If the parapet is braced to the roof membrane, however, lateral stresses are distributed across a wider
area, minimizing the risk of collapse.
EARTHQUAKE-RESISTANT DESIGN
Three important aspects to be considered in the design of earthquake resistant structures are given
below:
1. Ductility: The structure should be ductile, like the use of steel in concrete buildings. For these
ductile materials to have an effect, they should be placed where they undergo tension and thus
are able to yield.
2. Deformability of structures is also essential. Deformability refers to the ability of a structure to
dispel or deform to a significant degree without collapsing. For this to happen, the structure
should be well- proportioned, regular and tied together in such a way that there are no area of
excessive stress concentration and forces can be transmitted from one section to another despite
large deformations. For this to happen, components must be linked to resisting elements
3. Damageability is another aspect to be taken into consideration. This means the ability of a
structure to withstand substantial damage without collapsing. To achieve this objective
“minimum area which shall be damaged in case a member of the structure is collapsed” is to be
kept in view while planning. Columns shall be stronger than beams for that purpose and it is
known as strong column and weak beam concept.
TIPS FOR EARTHQUAKE-RESISTANT DESIGN:
 Generally building design is approved by the concerned municipal authorities according to
build by laws and safety requirements. Training of the builders, architects, contractors,
designers, house owners and government officials is important
Planning stage
 The building plan should be in a regular and symmetrical shape such as square or rectangular.
 Avoid weak storey and provide strong diaphragm
 Don’t add appendages which will create difference in Centre of mass and centre of rigidity

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 Conduct soil test to avoid soil liquefaction
 The structure of the building should be dynamically simple and definite
 The height of each storey should be kept below 3.2m.
 The formation should generally be based on hard and uniform ground
 Building materials - Based on experience the performance of precast concrete has been fairly
satisfactory
 The configuration of the building (Plan and elevation) should be as simple as possible.
Design stage
 Avoid weak column and strong beam design.
 Provide thick slab which will help as a rigid diaphragm. Avoid thin slab and flat slab
construction.
 Provide cross walls which will stiffen the structures in a symmetric manner.
 Provide shear walls in a symmetrical fashion. It should be in outer boundary to have large
lever arm to resist the EQ forces.
 The members resisting horizontal forces should be arranged so that torsional deformation is
not produced.
 The frame of the building structure should have adequate ductility in addition to required
strength.
 Deformations produced in a building should be held to values, which will not provide
obstacles to safety use of building.
 Increase in the transverse (Shear) reinforcement.
 Horizontal lintel ,plinth and roof bands should be provided
 Reinforcing bars should be provided at the corners and the junctions of the walls.
 The thickness of load bearing wall should be at least 200mm
 The clear width between a door and nearest window should not be less than 600mm
Construction stage
 Compact the concrete by means of needle vibrator.
 Cure the concrete for at least a minimum period.
 Experienced supervisor should be employed to have good quality control at site
EARTHQUAKE RESISTANT CONSTRUCTION TECHNIQUES
• Shear walls
• Bracing
• Dampers
• Base Isolation
• Bands
• Reinforcements
Shear Wall
 Building Reinforced concrete buildings often have vertical plate-like RC walls called Shear Walls
in addition to slabs, beams and columns. These walls generally start at foundation level and are
continuous throughout the building height.
 Their thickness can be as low as 150mm, or as high as 400mm in high rise buildings.

25
 Shear walls are usually provided along both length and width of
buildings. Shear walls are like vertically-oriented wide beams that
carry earthquake loads downwards to the foundation.
 It provides large strength and stiffness to buildings.
 It should be symmetrical in plan along both the axis.
 The openings provided in shear wall should be symmetrical.
 Effective when located in the exterior perimeter of the building.
Advantages
 Efficient in terms of cost, effectiveness, construction
 Helps in minimising the effect on non structural elements eg glass ,windows
Bracing
Cross bracing is a system utilized to reinforce building structures in which diagonal supports
intersect. Cross bracing can increase a building’s capability to withstand seismic activity. Bracing is
important earthquake resistant building because it helps keep a structure standing. Cross bracing is
usually seen with two diagonal supports placed in an X shaped manner; these support compression
and tension forces. Depending on the forces, one brace may be in tension while the other is slack. It
helps make buildings sturdier and more likely to withstand lateral forces.
Seismic Dampers
Another approach for controlling seismic damage in buildings and improving their seismic
performance is by installing seismic dampers in place of structural elements, such as diagonal braces.
These dampers act like the hydraulic shock absorbers in cars – much of the sudden jerks are absorbed
in the hydraulic fluids and only little is transmitted above to the chassis of the car.
When seismic energy is transmitted through them, dampers absorb part of it, and thus damp the
motion of the building. Commonly used types of seismic dampers include viscous dampers (energy is
absorbed by silicone-based fluid passing between piston-cylinder arrangement), friction dampers
(energy is absorbed by surfaces with friction between them rubbing against each other), and yielding
dampers (energy is absorbed by metallic components that yield) .
Base Isolation
The concept of base isolation is explained through an example building resting on frictionless rollers.
When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force
is transferred to the building due to shaking of the ground; simply, the building does not experience
the earthquake. Now, if the same building is rested on flexible pads that offer resistance against
lateral movements, then some effect of the ground shaking will be transferred to the building above.
If the flexible pads are properly chosen, the
forces induced by ground shaking can be a
few times smaller than that experienced by
the building built directly on ground,
namely a fixed base building. The flexible
pads are called base-isolators, whereas the
structures protected by means of these
devices are called base-isolated buildings.
The main feature of the base isolation
technology is that it introduces flexibility in

26
the structure. As a result, a robust medium-rise masonry or reinforced concrete building becomes
extremely flexible. The isolators are often designed to absorb energy and thus add damping to the
system. This helps in further reducing the seismic response of the building. Base isolation is not
suitable for all buildings. Most suitable candidates for base-isolation are low to medium-rise
buildings rested on hard soil underneath; high-rise buildings or buildings rested on soft soil are not
suitable for base isolation.
Reinforcements in Masonry Building
The walls, if constructed with plain masonry would be incapable of resisting the magnitude of
horizontal shear and bending forces imposed on them during earthquakes. For this reason, in the
modern reinforced masonry systems, reinforcing steel is incorporated to resist the shear and tensile
stresses, so developed. When these walls are subjected to lateral forces acting on them, they behave
as flexural members spanning vertically between floors and horizontally between pilasters/ lateral
walls. Therefore reinforcement in both vertical and horizontal directions is required to be provided to
develop resistance against torsion.
When the ground shakes, the inertia force causes the small-sized masonry wall piers to disconnect
from the masonry above and below. These masonry sub-units rock back and forth, developing contact
only at the opposite diagonals. Embedding vertical reinforcement bars in the edges of the wall piers
and anchoring them in the foundation at the bottom and in the roof band at the top, forces the slender
masonry piers to undergo bending instead of rocking
The most common damage, observed after an earthquake, is diagonal X-cracking of wall piers, and
also inclined cracks at the corners of door and window opening. When a wall with an opening
deforms distorts and becomes more like a rhombus. Steel bars provided in the wall masonry all
around the openings restrict these cracks at the corners. In summary, lintel and sill bands above and
below openings and vertical edges, provide protection against this type of damage.
Horizontal Bands
 Horizontal bands are provided to hold a masonry building as a single unit by tying all the walls
together. There are four types in a typical masonry building named after their locations in the
building. They are:
o Plinth band: This should be provided in those cases where the soil is soft or uneven in their
properties, as it usually happens in hilly areas. This band is not too critical.
o Lintel band: This is the most important band and covers all door and window lintel.
o Roof band: In buildings with flat reinforced concrete or reinforced brick roofs, the roof band is
not required because the roof slab itself plays the role of a band. However, in buildings with flat
timber or CGI sheet roof, a roof band needs to be provided. In buildings with pitched or sloped
roof, the roof band is very important.
o Gable band: It is employed only in buildings with pitched or sloped roofs.
EFFECT OF AN EARTHQUAKE ON THE REINFORCED CONCRETE STRUCTURES:
An RC structure is made up of horizontal parameters like beams and slabs; along with the horizontal
parameters, it also includes the vertical parameters like the columns and walls. The foundation supports
the RC structure and the RC frame is nothing but the RC columns with the joining beams, it takes part in
the opposing the forces of the earthquake. The forces generated during the earthquake moves in a
downward direction like from the slabs to the beams, from the beams to the columns and also to the walls
and finally to the foundation, from the foundation they are scattered or spread along the ground. The
major elements of the reinforced concrete structure are as follows:

27
 Floor slabs
 Masonry walls
BEHAVIOR OF BRICK MASONRY WALL UNDER EARTHQUAKE
Masonry buildings are brittle structures and one of the most vulnerable of the entire building stock
under strong earthquake shaking. Thus, it is very important to improve the seismic behavior of
masonry buildings.
Ground vibrations during earthquakes causes inertia forces at locations of mass in the building. These
forces travel through the roof and walls to the foundation. The main emphasis is on ensuring that
these forces reach the ground without causing major damage or collapse. Of the three components of
a masonry building (roof, wall and foundation, the walls are most vulnerable to damage caused by
horizontal forces due to earthquake. A wall topples down easily if pushed horizontally at the top in
the direction perpendicular to the plane (termed weak direction), but offers much greater resistance if
pushed along its length (termed strong direction).
Horizontal inertia forces developed at the roof transfers to the wall acting either in the weak or in the
strong direction. If all the walls are not tied together like a box, the walls loaded in their weak
direction tend to topple.
To ensure good seismic performance, all walls must be joined properly to the adjacent walls. In this
way, walls loaded in the weak direction can take advantage of the good lateral resistance offered by
walls loaded in strong direction. Further, walls also need to be tied to the roof and foundation to
preserve their overall integrity.
Causes of earthquake damage in masonry structures
The main deficiencies in the conventional non- engineered/ un-reinforced masonry construction and
other reasons for the extensive damage in such buildings are:
1. Heavy dead weight and very stiff buildings, attracting large seismic inertia forces.
2. Very low tensile strength, particularly with poor mortars.
3. Low shear strength, particularly with poor mortars.
4. Brittle behaviour in tension as well as compression.
5. Weak connection between wall and wall.
6. Weak connection between roof and wall.
7. Stress concentration at corners of doors and windows.
8. Overall asymmetry in plan and elevation of the building
9. Asymmetry due to imbalance in the sizes and positions of openings in the wall.
10. Defects in construction, such as use of sub standard materials, unfilled joints between bricks.
FOUNDATION FAILURE
TYPES OF FOUNDATION FAILURE UNDER LOADS
Types of foundation failure depend on the load it is subjected to. A foundation can fail in three
different ways under loads and they are:
 Punching shear failure of foundation
 One-way shear failure of foundation
 Flexure failure of foundation.

28
The above three modes of foundation failure should be checked during design stage of concrete
foundation for the given load.
1.Punching shear failure of foundation:
Punching shear failure is also known as diagonal tension failure of
foundation. In this mode of failure, foundation fails due to formation of
inclined cracks around the perimeter of the column.
The critical section for punching shear failure is taken at d/2 from the face
of the column, where d is the effective depth of footing.
To avoid punching shear failure, the ultimate upward shear force at this
section in the foundation should be less than the shear resistance of
concrete for the given percentage of concrete. Additional reinforcement
should be provided to resist punching shear in case of shear resistance of
concrete with reinforcement provided is not sufficient.
The failure of foundation in this mode appears as
truncated cone or pyramid around the column, stanchion or pier as shown in figure.
3. One Way shear failure of foundation:
Foundations in one-way shear failure fails in inclined cracks across full width of the
footing that intercept the bottom of the footing slab at a distance d from the face of
the column (called critical section), where d is the effective depth of footing slab. To
avoid one-way shear failure of foundations, the shear stress at the critical section of
footing should be less than the shear strength of concrete with given percentage of
reinforcement used. One way shear failure of footing is shown in figure.
4. Flexure failure of foundations:
During design of footing, Mu/bd2 is calculated to get the percentage of
reinforcement for the moment the foundation is exposed to. Mu is the ultimate
or factored moment; b is the width of footing. The critical section for flexure is
considered at distance d from the face of footing. The standard codes take care
of flexure failure during design by providing percentage of reinforcement
required to resist the bending moment. But in case, when bending moment
increases in footings, then footing fails as shown in figure on right side.
CAUSES OF FOUNDATION FAILURE
 Unequal settlement of sub soil
 Unequal settlement of masonry:
 Sub-soil moisture movement:
 Lateral pressure on the walls:
 Lateral Movement of sub-soil.
 Weathering of sub-soil due to trees and shrubs.
 Atmospheric action.
 Improper maintenance
 Load transfer failure
 Drag down and heave
 Earthquake

29
 Vibration effect
 Inadequate geotechnical investigation and design error
 Foundation failure due to landslide/slope instability
 Foundation failure due to uplift
1.Unequal settlement of sub soil
Footing resting on different type of soil, different bearing capacity and unequal load distribution will
result in the unequal settlement or what we call it a differential settlement .Differential settlement can
cause tilting of the structure. Unequal settlement of the sub-soil may lead to cracks in the structural
components and rotation thereof. Unequal settlement of sub-soil may be due to (i) non-uniform nature
of sub-soil throughout the foundation, (ii) unequal load distribution of the soil strata,
and (iii) eccentric loading. The failures of foundation due to unequal settlement can be checked by
: (i) resting the foundation on rigid strata, such as rock or hard moorum, (ii) proper design of the base
of footing, so that it can resist cracking, (iii) limiting the pressure in the soil, and (iv)avoiding
eccentric loading.
2. Unequal settlement of masonry: This portion of masonry, situated between the ground level and
concrete footing (base) has mortar joints which may either shrink or compress, leading to unequal
settlement of masoray. Due to this, the superstructure will also have cracks. This could be checked
by (i) using mortar of proper strength, (ii) using thin mortar joints, (iii) restricting the height of
masonry to 1 m per day if lime mortar is used and 1.5 m per day if cement mortar is used, and (iv)
properly watering the masonry.
2.Sub-soil moisture movement: This is one of the major causes of failures of footings on cohesive
soil, where the sub-soil water level fluctuates. When water table drops down, shrinkage of sub-soil
takes place. Due to this, there is lack of sub-soil support to the footings which crack, resulting in the
cracks in the building. During upward movement of moisture, the soil (specially if it is expansive)
swells resulting in high swelling pressure. If the foundation and superstructure is unable to resist the
swelling pressure, cracks are induced.
4. Lateral pressure on the walls: The walls transmitting the load to the foundation may be subjected
to lateral pressure or thrust from a pitched roof or an arch or wind action. Due to this, the foundation
will be subjected to a moment (or resultant eccentric load). If the foundation has not been designed
for such a situation, it may fail by either overturning or by generation of tensile stresses on one side
and high compressive stresses on the other side of the footing.
5. Lateral Movement of sub-soil This is applicable to very soft soil which are liable to move out or
squeeze out laterally under vertical loads, specially at locations where the ground is sloping. Such a
situation may also arise in granular soils where a big pit is excavated in the near vicinity of the
foundation. Due to such movement, excessive settlements take place, or the structure may even
collapse. If such a situation exists, sheet piles should be driven to prevent the lateral movement or
escape of the soil. Lateral movement in soil is also possible when there is removal of existing side
support adjacent to a building or there is excessive overburden on backfill or lateral thrust on the
backside of a retaining wall. Lateral movement is also observed during earthquake when structure
fails due to lateral movement of soil beneath the foundation following liquefaction.
6. Weathering of sub-soil due to trees and shrubs. Sometimes, small trees, shrubs or hedge is grown
very near to the wall. The roots of these shrubs absorb moisture from the foundation soil, resulting in

30
reduction of their voids and even weathering. Due to this the ground near the wall depresses down. If
the roots penetrate below the level of footing, settlements may increase, resulting in foundation
cracks.
7. Atmospheric action. The behaviour of foundation may be adversely affected due to atmospheric
agents such as sun, wind, and rains. If the depth of foundaion is shallow, moisture movements due to
rains or drought may cause trouble. If the building lies in a low lying area, foundation may even be
scoured. If the water remains stagnant near the foundation, it will remain constantly damp, resulting
in the decrease in the strength of footing or foundation wall. Hence it is always recommended to
provide suitable plinth protection along the external walls by (i) filling back the foundation trenches
with good soil and compacting it, (ii) providing gentle ground slope away from the wall and (iii)
providing a narrow, sloping strip of impervious material (such as of lime or lean cement concrete)
along the exterior walls.
Proper care of your foundation is very important in preserving the integrity of the structure. Soils
have the ability to expand (when wet) at alarming rates. This requires that an even and relatively
constant level of moisture be maintained in the soil supporting the foundation. Defects in foundations
occur when the supporting soil is too wet or too dry or when one area around the foundation is overly
wet, while other areas remain dry. Improper foundation maintenance can result in severe movement
in just a few days. Non-uniform moisture content can be caused by any of the following:
 Improper drainage: Poor drainage conditions around your foundation can cause the over-
saturation of the soil which causes instability around the foundation.
 Excess watering near the foundation
 Plumbing leaks: Water from leaky plumbing is often a major contributor to foundation problems.
When excess water is present due to plumbing leaks, the soil supporting your foundation can
erode. When a plumbing leak occurs under the foundation, the moisture content becomes
distorted. When moisture is added to the soil because of a plumbing leak, the soil and foundation
will move, causing foundation settlement. The degree of movement depends on the soil type, soil
density, soil moisture content prior to the leak and the length of time over which the leak has
occurred.
 An improper watering program
 Neglect
 Runoff water not properly diverted away from the foundation
 Trees and large bushes growing too close to the foundation
9. Load transfer failure
The objective of foundation is to transfer the load on superstructure to the foundation soil on a wider
area. It works as an interface between superstructure (over the ground) and substructure (under the
ground). The size of the footing is decided in such a way that it distributes the pressure on the subsoil
and it is expected that the applied pressure never exceeds the permissible limit of the subsoil. A factor
of safety in geotechnical design is adopted to take care of different sources of uncertainty involved in
geotechnical design and practice.
Hence, load bearing capacity of soil is always predicted with some uncertainty and there is a
possibility that foundation is inadequate to take the load from superstructure and failure may occur.
Under such circumstances, the most commonly adopted remedial measure to rectify the problem is
underpinning .Underpinning is the process of strengthening and stabilizing the foundation of an
existing building or other structure.Underpinning is accomplished by extending the foundation in

31
depth or width so that it either rests on a more supportive soil stratum or distributes its load across a
greater area.
10.Drag down and heave
When footing is located on a compressible soil, there is a chance of foundation failure by drag down
and heave. In plastic soils, new settlements (drag down) are often accompanied by upward
movements and heave some distance away.
When foundation failure occurs, it is usually the result of differential settlement or heaving of the soil
that supports the foundation.
In swelling and shrinking soils, hot dry wind and intense heat will often cause the soil to shrink
beneath the foundation. This settlement may cause cracks to appear throughout the structure. Uneven
saturation of the soil around foundation (located in expansive soils) can cause the soil to heave as it
expands and contracts after drying.
Heaving is a leading cause of foundation failure. As a preventive measure, rain gutters provided to
collect water from roof play a vital role in protecting foundation by controlling moisture or rain water
entering the foundation soil. Also, Soil stabilization is the most widely used technique to deal with
expansive soils. Stabilization with lime, lime-fly ash, Portland cement, and bituminous materials is
very popular.
11.Earthquake
Violent shaking of an earthquake is capable of damaging homes, buildings, bridges or any other
manmade structures. The most noticeable damage appears in the walls or roofs of buildings, but
building foundations are also drastically affected by the Earth’s sudden movement.
During an earthquake the foundation of the building moves with the ground and the superstructure
and its contents shake and vibrate in an irregular manner due to the inertia of their masses (weight).
If the foundation of a building is a mat foundation, it can easily crack into pieces. Damage to
foundations & structures may result from different seismic effects: (i) Ground failures (or instabilities
due to ground failures), (ii) Vibrations transmitted from the ground to the structure, (iii) Ground
cracking, (iv) Liquefaction, (v) Ground lurching, (vi) Differential settlement, (vii) Lateral spreading,
and (viii) Landslides.
12.Vibration effect
Construction activities such as blasting, pile driving, dynamic compaction of loose soil, and operation
of heavy construction equipment induce ground and structure vibrations.
Monitoring and control of ground and structure vibrations provide the rationale to select measures for
prevention or mitigation of vibration problems, and settlement/damage hazards.
13.Inadequate geotechnical investigation and design error
Proper subsurface investigation is essential to safe guard the building, and for proper design of
foundation as well as efficient super-structure system. In most of the codes, it is recommended that
soil investigation up to the depth of 1.5 –2.0B, where B is the least lateral dimension of the building
should be carried out. Occurrence of foundation failure due to improper geotechnical investigation
and design error should be avoided.
The extent of site investigation depends heavily on the project but should provide the information:
 To determine the type of foundation required (Shallow or Deep)
 Sufficient data/laboratory tests to estimate the allowable load capacity of the foundation and
to make settlement predictions.
 Location of GWT and its fluctuation over a period of time.

32
 Identification and solution of potential construction as well as environmental problems.
Often, a deficiency in engineering ethics is found to be one of the root causes of an engineering
failure.
14.Foundation failure due to landslide/slope instability
Foundation failure due to rapid movement of landmass over a slope results when a natural or man-
made slope on which structure exists becomes unstable. The major causes of slope instability/
landslide can be identified as, (i) Steep slope,(ii) Groundwater Table Changes / heavy rainfall,
(iii)Earthquakes and other vibrations, and, (iv) removal of the toe of a slope or loading the head of a
slope, both of which may be the result of man-made and geological factors.
The resistance to a landslide or slope instability is offered by the type of soil and the geometry of the
slope. Preventive and remedial measures include modifying the geometry of the slope, controlling the
groundwater; constructing tie backs, spreading rock nets, providing proper drainage system, provision
of retaining walls, etc.
15.Foundation failure due to uplift
Generally the foundation is subjected to three types of loads, i.e., the downward force (compression),
the uplift (tension) and the horizontal shear. One of the major causes of foundation failure due to
uplift is presence of expansive soil beneath the foundation. Expansive soils pose a significant hazard
to foundations for light buildings. Swelling clays derived from residual soils can exert uplift
pressures, which can do considerable damage to lightly-loaded wood-frame structures.
In case of pile foundations that are used to resist the uplift forces due to wind loads, such as, in
transmission line towers, high rise buildings, chimney, etc., the available uplift resistance of the soil
becomes the one of the most decisive factor in defining the stability of foundation.
Remedies for foundation failure due to soil movement:
1. Use of pile foundations where the soil is shrinkable, so that forces are transferred to the hard strata
or rock.
2. Taking the foundation levels down to avoid foundation on shrinkable soils.
3. The vegetation is removed from the construction site and its roots are removed. Any cavity due to
roots of vegetation shall be compacted and filled with concrete.
4. Presence of any mining areas needs to be inspected and professional help shall be taken while
construction new buildings in such areas.
FAILURE DUE TO FIRE
Fires are events of burning something. They are often destructive taking up toll of life and property. It
is observed that more people die in a fire than in a cyclone, earthquake, floods and other natural
disasters combined. Fires are a great threat to forests and wild life because they spread speedily and
cause tremendous damage in a short time. In cities fires break out in home,buildings specially
godowns and factories. Fire can spread to a large area. Many people may die of burns and
asphyxiation. It may also cause contamination of air, water and soil, which may affect the crops,
plants and animals, and soil fertility.
CAUSES
During summer months such fires results in casualties and enormous economic losses. There are
numerous causes of fires. Some important ones are given here

KTU CE 204 Construction technology notes module 6

KTU CE 204 Construction technology notes module 6

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