SRI JAYACHAMARAJENDRA COLLEGE OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

MYSORE-570006

(Vishweshwaraiah Technological University)

SEMINAR REPORT ON

“CAUSES AND PREVENTION OF

CRACKS

IN BUILDING”

BY

ASHWIN P S4JC00CV007

SR No. 00147

VIIIth Semester, CIVIL

1

DEPARTMENT OF CIVIL ENGINEERING

SRI JAYACHAMRAJENDRA COLLEGE OF ENGINEERING

(AFFILIATED TO VISVESWARAIAH TECHNOLOGICAL UNIVERSITY, BELGAUM)

MYSORE - 570 006

CERTIFICATE

This is to certify that ‘CAUSES AND PREVENTION OF CRACK

IN BUILDING is a bonafied seminar report submitted by Mr ASHWIN

P S bearing USN 4JC00CV007 on partial fulfillment for the award of

degree, Bachelor of Engineering, in Civil Engineering of

Vishveshwaraiah Technological University, Belgaum during the year

2004.

Examiners Signature of the HOD

1. Dr. Syed Shakeeb-Ur-

Rahman

Professor and Head

2.

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3.

CONTENTS

I Introduction

1

Types of cracks

1

Investigation relating to crack

2

Limitations of crack width

3

II Causes for cracks

4

Structural deficiency

4

Shrinkage and temperature effect

7

Cracks due to settlement 9

Faulty workmanship and poor construction Practice 11

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III Case study

13

IV Conclusion 16 V Reference

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ACKNOWLEDGEMENT

The satisfaction that accompanies the successful completion of

any task would be incomplete without mentioning of the people who

made it possible. Many responsible for the knowledge and experience

gained during the work course.

I would like to express a deep sense of gratitude and indebt ness

to Dr K.Prakash and prof. N. M. Jagadish Civil Engineering Department,

S. J. College of Engineering, Mysore, for his constant encouragement,

guidance and inspiration, which enabled me to complete this seminar

work.

I would also like to express my gratefulness towards all the

faculty members, Department of Civil Engineering, SJCE, Mysore for

their timely suggestions.

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I am thankful to Dr. Syed Shakeeb-Ur-Rahman, Professor and

Head, Department of Civil Engineering, for bringing excellent academic

climate to finish my work successfully.

Last but not the least, I express my deepest sense of gratitude

for the inspiration, enthusiasm and help given by my parents and

friends.

ASHWIN P S

4JC00CV007

VIII semester

CAUSES AND PREVENTION OF CRACKS IN

BUILDING

I) INTRODUCTION: -

A crack is a complete or incomplete separation of concrete

into two or more parts, produced by breaking or fracturing. The crack

in concrete is an inherent feature, which cannot be completely

prevented but can only be controlled and minimized. Concrete being a

material having very low tensile strength, readily cracks when such

tensile stress beyond the tensile strength of concrete occur in

structure.

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An engineer should have a sound knowledge of all the facts

of concrete technology i.e. of the behavior of construction material,

construction techniques, and types of crack likely to occur, their

causes and respective remedial measure. In short treatment of cracks

involves detection, diagnosis and remedy. Cracks also occur due to

settlement, temperature, shrinkage effect, poor construction practice

etc. In this seminar various causes for the above mentioned cracks is

been discussed.

Types of cracks:

Cracks may be divided in two categories viz

i) Structural cracks

ii) Non structural cracks

i ) Structural cracks :

Structural cracks may arise due to various reasons

such as incorrect design, overloading of the structural components,

overloading of the soil on which the building is constructed or other

similar factors. Structural cracks endanger the stability of the building

and may be difficult to be rectified. Extensive cracks of foundations

walls, beams, columns or slabs etc, are examples of structural cracks.

ii) Non- structural cracks:

Non- structural cracks are generally due to internal

forces developed in the buildings on account of change in the size of

building components, due to moisture variation, temperature

variations, the effect of gases, liquid and solids on the building

components. The non-structural cracks can be repaired provided the

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reasons for cracks are identified and suitable remedial measures are

taken to prevent their reoccurrence.

Investigation relating to cracks:

A careful study of the locations of cracks (starting and finishing points)

their width and depth helps in dealing with the diagnosis of different

types of cracks.

The following information helps in diagnosing the cracks:

i) Whether the crack is old or new.

ii) Whether it appears on the opposite face of the member also.

iii) Pattern of the cracks.

iv) Soil condition, type of foundation used, and movement of ground

if any.

v) Observations on the similar structures in the same locality.

vi) Study of specification, method of construction, used and the test

result at the site if any.

vii) Climatic condition during which the structure has been

constructed.

Limitation of crack width (IS 456: 2000):

Depending on the exposure conditions limitations on crack width are

imposed as follows

1. For members in water storage units, sewage treatment plants,

structures in chemically hazardous atmosphere, etc. Cracks are

not permitted in R.C. members.

2. In severe atmosphere up to 0.1mm crack width is permitted.

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3. Moderate atmosphere up to 0.2mm crack width is permitted

4. In mild atmosphere the surface width of cracks should not, in

general exceed 0.3mm in members where cracking does not

have any serious adverse effects upon the preservation of

reinforcing steel nor upon the durability of structure.

Permissible crack width in reinforced structure as per

ACI

Exposure conditions Maximum allowable crack

width

in mm

Dry air, protective

membrane

0.41

Humidity, moist air 0.30

Sea water and seawater

spray;

Wetting and drying

0.15

Water retaining structure 0.10

Table1

II) CAUSES FOR THE OCCURANCE OF CRACKS:

The importance causes responsible for occurrence of the cracks are

1.structural deficiency resulting from design deficiency or construction

deficiency and overloading.

2. Settlement of ground

3.Temperature and Shrinkage effects.

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4. Cracks due to faulty workman ship and poor construction practice

1 .Cracks due to structural deficiency resulting from

design deficiency or construction deficiency and

overloads.

Concrete structure and individual members all

carry loads. Some carry only the weight of the materials they are made

of, while others carry loads applied to the structure. All material

change volume when subjected to stress,

Concrete is no exception. When subjected to tensile stress, concrete

stretches; when subjected to compressive stress it shortens. Concrete

possesses high compressive strength but little tensile strength, and

reinforcing steel provides the needed strength in tension. The loads

induced during construction can be far more severe than they are

experienced in service. Concrete problems, such as excessive

deflection, cracking may be caused by volume changes associated with

load effect.

Most concrete members are subjected to tensile

forces. Slabs and beams are the most common members subjected to

significant tension. Reinforcing bars are placed in the concrete to carry

tension forces. When reinforced bar are subjected to tension they

stretch. The concrete around the reinforcing bars is consequently

subjected to tension and stretches. When tension in excess of tensile

strength of concrete is reached, transverse crack may appear near

reinforcing bars.

Cracks occur due to shear, flexural and torsional steel

deficiency.

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Cracks occur due to abrupt curtailment of reinforcing bars,

construction joints etc.

Improper anchorage.

Cracks due to overloading of members

Preventive measures:

Special care need to be taken in the design and detailing of

structures in which cracking may cause a major serviceability

problem. These structures also require continuous inspection

during all phases of construction to supplement the careful

design and detailing.

Damages from unintentional construction overloads can be

prevented only if designer provide information on load limitation

for the structure and if the construction personnel heed to these

limitations.

Ensure proper anchorage to the reinforcing bars.

Follow proper design specifications.

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Flexural crack in beams Diagonal tension crack in beams Fig 1 Fig 2

Shear-flexure cracks in beams Flexural crack in cantilever beam Fig 3 Fig 4

Torsional crack in beam Fig 5 Bond cracks in beams Fig 6 Direction of concreting

Cracks due to abrupt curtailment of Bars in beams construction joint crack in beam Fig 7 Fig 8

Splitting cracks in column Flexural crack in slab

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Fig 9 Fig

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Cracks due to shrinkage and temperature effect:

Shrinkage crack :

Shrinkage cracks show up in two basic locations in

most walls; the approximate mid-point of a long section of wall, and

the narrowed section of the wall such as across a door or window head.

Shrinkage cracks are virtually uniform in width from top to bottom and

typically extend from the top of the wall to within a couple of feet of

the foundation.

Common cause for shrinkage cracks in concrete

walls would be excessive water content within the concrete. In general

terms, higher water content within a concrete mix will result in a

greater amount of shrinkage. This is quite evident in some concrete

walls where there are an excessive number of cracks.

Shrinkage crack in wall Shrinkage crack in cantilever slab masonry Fig 11 Fig 12

On exposure to atmosphere, concrete loses some of its original

water and shrink. Drying shrinkage, if unrestrained, results in

shortening of the member without a build-up of shrinkage stress. If the

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member is restrained from moving, stress build-up may exceed the

tensile strength of the concrete. This over-stressing results in dry

shrinkage cracking.

Temperature effect:

The effect of temperature on concrete structure

and member is one of volume change. The volume relationship to

temperature is expressed by the coefficient of thermal

expansion/contraction. Volume changes create stress when the

concrete is restrained. The resulting stress can be of any type: tension,

compression, shear, and etc. the stressed conditions may result in

undesirable behavior such as cracking, spalling and excessive

deflection.

A typical case of occurrence of cracks due to

temperature variation is that of roof slab being exposed to the heat of

sun, which is subjected to alternate expansion and contraction. This

movement of slab may result in pushing out top course of masonry and

develop horizontal cracks in the supporting walls.

Thermal crack in masonry

Fig 13

Preventive Measures:

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Adequate insulating or terracing treatment over roof slab and

by introducing joint between the slab and the supporting wall.

Painting top of roof with reflective finish such as white wash

can also minimize cracks.

Chances of cracking due to temperature variation can be

minimized by introducing expansion, contraction joints at

appropriate locations.

Cracks due to settlement:

Uneven (differential) settlement can be a major

structural problem in small residential buildings, although serious

settlement problems are relatively uncommon. Many signs of masonry

distress are incorrectly diagnosed as settlement-related when in fact

they are due to moisture and thermal movements.

Fig 14

Indications of differential settlement are vertical distortion

or cracking of masonry walls, warped interior and exterior openings,

sloped floors, and sticking doors and windows. Settlement most often

occurs early in the life of a building or when there is a dramatic change

in underground conditions. Often such settlement is associated with

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improper foundation design, particularly inadequate footers and

foundation walls.

Soil consolidation under the footings

Soil shrinkage due to the loss of moisture to nearby trees or

large plants

Soil swelling due to inadequate or blocked surface or house

drainage

Soil heaving due to frost or excessive root growth

Gradual downward drift of clay soils on slopes

Changes in water table level

Soil erosion from poor surface drainage, faulty drains, leaking

water mains or other underground water movements

(occasionally, underground water may scour away earth along

only one side of a footer, causing its rotation and the subsequent

buckling or displacement of the foundation wall above)

Soil compaction or movement due to vibration from heavy

equipment, vehicular traffic, or blasting, or from ground tremors

(earthquakes).

Gradual differential settlement over a long period of time may produce no

masonry cracking at all, particularly in walls with older and softer bricks and high lime

mortars; the wall will elastically deform instead. More rapid settlements, however,

produce cracks that taper, being largest at one end and diminishing to a hairline at the

other, depending on the direction and location of settlement below the wall.

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Differential settlement caused by variable soil types

Fig 15

Cracking is most likely to occur at corners and adjacent to

openings, and usually follows a rough diagonal along mortar joints

(although individual masonry units may be split). Settlement cracks (as

opposed to the similar-appearing shrinkage cracks that are especially

prevalent in concrete block) may extend through contiguous building

elements such as floor slabs, masonry walls above the foundation, and

interior plaster work. Tapering cracks, or cracks that are nearly vertical

and whose edges do not line up, may occur at the joints of projecting

bay windows, porches, and additions. These cracks indicate differential

settlement due to inadequate foundations or piers under the projecting

element.

Often settlement slows a short time after construction

and a point of equilibrium is reached in which movement no longer

occurs. Minor settlement cracking is structurally harmful only if long-

term moisture leakage through the cracks adversely affects building

elements. Large differential settlements, particularly between

foundation walls and interior columns or piers, are more serious

because they will cause movements in contiguous structural elements

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such as beams, joists, floors, and roofs that must be evaluated for loss

of bearing and, occasionally, fracture.

Buildings constructed on expansive soil are liable to cracks due to

volumetric changes in the sub-soil conditions due to changes in moisture contents.

Expansive soil is a kind of clayey soil, which exhibits swelling and shrinkage properties

due to variation in seasonal moisture content. The structures built on such soils are

subjected to severe stress due to alternate swelling and shrinkage and undergo distress.

Light structures suffer more.

Preventive Measures:

In case of shrinkable soils, adopt under reamed pile foundation.

The structural design of the foundation should be carried out in

such a manner as to achieve uniform distribution of pressure on

the ground to avoid differential settlement.

The foundation should be so proportioned that the safe bearing

capacity of soil is not exceeded.

The soil should be well compacted

Cracks due to faulty workman ship and poor

construction practice:

Methods used to construct concrete structures are different

from methods used in other type of construction. Concrete is one of

the few materials in which raw ingredients are brought together at, or

near, the construction site, where they are mixed, placed and molded

into a final product. Every building process includes a sequence of

necessary step-by-step operation-from conceptual plan to finished

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structure. There are so many variables affecting the production of

concrete that there is always a potential for something to go wrong.

Causes :

Improper reinforcing steel placement

Improper bar detailing

Premature removal of forms

Improper column form placement

Cold joints

Segregation

Plastic shrinkage cracking

Preventive measures:

By providing proper water cement ratio.

Proper curing.

Proper support for forms.

Following proper design codes and recommendations.

III) Case study:

The case study described in this paper is an

example of a report on P.W.D office building Yelandur. The building

was inspected on 21st May 1988 and the following observations where

made.

The soil below the foundation and around the

building is black cotton soil. Construction of the building is reported to

be completed during 1981. It was learnt that that rainfall in the area

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where the building was situated was scanty. It was also learnt that no

precautionary measures where taken during construction.

A team of experts from Karnataka Engineering

Research station,

Krishnarajasagar visited the spot and after investigation gave advise to

implement certain remedies such as replacing the soil around the

building by good gravelly soil for a depth of about 1foot, removing the

vegetation and trees around the building, filling the pits around the

building with gravelly soil, providing drainage facilities etc. But they

where partially implemented, i.e., soil around the building was

replaced by gravelly soil. It was observed that cracking continued

further.

Possible causes of distress:

When a building is founded on an expansive soil with normal

footing, the swelling and shrinkage of the soil below the

foundation due to variation in water content gives rise to

moments. As the moisture content variation under the entire

building will be uneven, this normally results in cracks in the

buildings.

Improper drainage around the building may lead to variation in

water content of the formation soil.

Unequal settlement of the structure may occur due to its

construction on filled up soil.

Growth of trees with dominant surface roots or fast growing

trees, closely to the building may be the cause of distress.

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Due to increasing number of bore wells and drought situation,

the water table may considerably go down. Due to this the water

content of the soil may reduce causing considerable shrinkage.

This may result in unequal settlement and finally leads to

distress of the buildings.

Remedial measures:

Where the expansive soil is shallow, say about 2m, the most

economical method will be to remove the soil & fill it with firm

good soil and use sand or murram for the fill.

Use under-reamed pile foundation.

Damage due to uplift of expanding clay can be prevented by

applying heavy super-imposed loads.

The building may be supported on footing at a depth below the

surface and near enough to the water table, so that; the water

content of the clay is not affected by climatic changes.

Growth of trees near the foundation should be avoided.

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IV) CONCLUSION

The individual cracks in members are unique by

themselves.

They are versatile diagnostic devices, clearly indicating

the specific problems in the concerned members. In

addition, they also indicate the degree of seriousness of

the problem.

The cracks throw light on the discipline in the associated

structural designs and construction quality.

The corrective measures to be implemented are clearly indicated

by these cracks.V) REFERENCES: Peter H.

Emmons-“concrete repair and maintenance”

1. P.C.Varghese-“Limit State Design Of Reinforced concrete

2. H.P. Rossmanith-“Fracture and damage of concrete”

3. M.S. Shetty-“ concrete technology”

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DIRECTION OF CONCRETING

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