Unit II Construction Practices (2)

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UNIT II CONSTRUCTION PRACTICES

Specifications, details and sequence of activities and construction co-ordination – Site Clearance – Marking – Marking – Earthwork Earthwork - masonry – masonry – stone stone masonry – masonry – Bond Bond in masonry - concrete hollow block masonry – flooring – damp proof courses – construction joints – movement and expansion joints – joints – pre cast pavements – Building foundations – basements – temporary shed – centering and shuttering – slip forms – scaffoldings – de-shuttering forms – Fabrication and erection of steel trusses – frames – braced domes – domes – laying laying brick –– brick –– weather weather and water proof – proof – roof roof finishes – finishes – acoustic acoustic and fire protection.

Sequence of activities and construction

Preparing the priority of execution of individual works of a project may be treated as the sequence of activities. The construction engineer should plan properly before starting the execution or construction. The list of activities form staring to the end of the project, called the sequence of activities, may leads to monitor the project execution. The following lists are example of sequence of activities of ordinary residential building Site clearance Marking based on the selected plan Foundation execution up to the regarding depth Laying foundation concrete Construction of foundation based on the specification Filling the sides of foundation wall using soil Basement construction Earth filling upto basement and consideration Providing DPC layer Placing the flooring concrete Construction of superstructure using brick Providing lintel/lintel cum sunshades lofts etc. Construction of brick work over lintel beams up to the roof level Providing the entering for concrete Laying reinforcement as per design UMA MAGESWARI. M

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Placing the concrete and applying water for cussing after one day Preparing doors , windows and ventilations Plastering work the ceiling Providing the electrical fitting like PVC pipes, switch boxes etc. Plastering over the wall both inner and outer ou ter after fixing the doors and windows Providing water supply and sanitary arrangements Laying floor and wall tiles White washing and colour working Earth Work In connection with excavation, transport of soil and backfilling the properties of soil must be considered. Excavation being generally paid for as measured net in the solid, it is necessary to know by what proportion it bulks, when dug out one meter measured in the ground may occupy up to 1.5 cu.m. When excavated and thrown out or thrown into containers. Earth and clays may bulk up to 50 percent sands and gravels bulk less say up to 20 percent. A given quantity of excavated material will occupy less volume when refilled than when loose the amount of ramming, the type of soil and time affecting the amount of settlement. Filling should be as uniform as possible, especially when it is required to present a constant bearing resistance to foundation loads. For this reason the soil should be spread in this layers say 6 to 12 inches deep, each of which should be rammed or rolled before the next is laid. Hand ramming is suitable for these thicknesses but a mechanical rammer is required to consolidate effectively layers upto 2 ft. thick. Methods of Excavating

The method of excavating primarily depends upon the extent of the work, the nature of soil , the depth of excavation and whether timbering and pumping are required. Manual Excavation Mechanical Excavation Removal of water

To maintain an excavation dry it is usual to one or more sumps sumps below the general level level of bottom. The water collecting in these sumps is pumped out.

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Placing the concrete and applying water for cussing after one day Preparing doors , windows and ventilations Plastering work the ceiling Providing the electrical fitting like PVC pipes, switch boxes etc. Plastering over the wall both inner and outer ou ter after fixing the doors and windows Providing water supply and sanitary arrangements Laying floor and wall tiles White washing and colour working Earth Work In connection with excavation, transport of soil and backfilling the properties of soil must be considered. Excavation being generally paid for as measured net in the solid, it is necessary to know by what proportion it bulks, when dug out one meter measured in the ground may occupy up to 1.5 cu.m. When excavated and thrown out or thrown into containers. Earth and clays may bulk up to 50 percent sands and gravels bulk less say up to 20 percent. A given quantity of excavated material will occupy less volume when refilled than when loose the amount of ramming, the type of soil and time affecting the amount of settlement. Filling should be as uniform as possible, especially when it is required to present a constant bearing resistance to foundation loads. For this reason the soil should be spread in this layers say 6 to 12 inches deep, each of which should be rammed or rolled before the next is laid. Hand ramming is suitable for these thicknesses but a mechanical rammer is required to consolidate effectively layers upto 2 ft. thick. Methods of Excavating

The method of excavating primarily depends upon the extent of the work, the nature of soil , the depth of excavation and whether timbering and pumping are required. Manual Excavation Mechanical Excavation Removal of water

To maintain an excavation dry it is usual to one or more sumps sumps below the general level level of bottom. The water collecting in these sumps is pumped out.

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Sto Stone Mas Masonry Def inition:

The ar ar t of of building building a str uctur uctur e in stone with any suitable mas masonr onr y is is called stone mas masonr onr y. y. f Stone Masonry: Types of St

masonr onr y may be br br oadly oadly class classiif ied ied into the f ollow ollowing tw two types types: Stone mas 1. Rubble Masonr onr y 2. Ashla Ashlar r M Masonr onr y

1. Rubble Masonry:

The stone mas masonr onr y in which either either undr undr ess ssed ed or r oughly oughly dr dr ess ssed ed stone ar ar e laid in a suitable mor mor tar tar is called r ubble ubble mas masonr onr y. y. In this this mas masonr onr y the joints joints ar ar e not of of unif unif or m thickness thickness.. Rubble mas masonr onr y is is f ur ther ther ssubub-divided into the f ollow ollowing thr thr ee ee types types: 

Random r ubble ubble mas masonr onr y



Squar quar ed ed r ubble ubble mas masonr onr y



Dr y r ubble ubble mas masonr onr y

1. R andom rubble masonry: The r ubble ubble mas masonr onr y in which either either undr undr ess ssed ed or hammer hammer dr ess ssed ed stones tones ar a r e us u sed is i s called r andom andom r ubble ubble mas masonr onr y. y. Fur ther ther r andom andom r ubble ubble mas masonr onr y is is als al so divided into the f ollow ollowing thr thr ee ee types types: a. Un coursed random rubble masonry: The r andom andom r ubble ubble mas masonr onr y in which stones tones ar ar e laid without f or ming ming cours coursees is know known as un cours coursed ed r andom andom r ub b ub ble le mas masonr onr y. y. This This is the r oughes ghest and cheapes cheapest type of of mas ma sonr onr y and is is of o f var va r ying ying appear appear ance. ance. The stones tones us u sed in this this mas masonr onr y ar ar e of o f diff di ff er ent ent sizes izes and shapes hapes. bef be f or e lying, all pr pr ojecting ojecting cor cor ners ners o of f stones tones ar a r e slightly knocked off off . Ver tical tical joints joints ar a r e not plumbed, plumbed, joints joints ar e f illed illed and f lus lushed. Lar Lar ge ge stones tones ar a r e us u sed at cor cor ners ners and and at jambs jambs to incr incr eas ease their their str ength. ength. Once "thr thr ough ough stone" tone" is i s us u sed f or ever eve r y squar quar e meter meter of o f the the f ace ace ar ar ea ea f or joining joining f aces aces and backing. Suitability: Used Used f or cons constr uction uction of of w walls alls of of low low height in cas case of of or or dinar dinar y buildings buildings. b. Coursed random rubble masonry: The r andom andom r ubble ubble mas masonr onr y in which stones tones ar a r e laid in layers layers of equal equal height is is called r andom andom r ubble ubble mas masonr onr y. y. In this this mas masonr onr y, y, the stones tones ar ar e laid in somew omewhat level cours coursees. Headers eaders o of f one one cours coursed ed height ar ar e placed at cer cer tain tain inter inter vals vals. The stones tones ar e hammer hammer dr d r ess ssed. ed. Used f or cons constr uction uction of of r r esidential buildings buildings, go dow downs, boundar boundar y walls alls etc. Suitability: Used UMA MAGESWARI. M

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Squared rubble masonry: The r ubble masonr y in which the f ace stones ar e squar ed on all joints and

beds by hammer dr essing or chisel dr essing bef or e their actual laying, is called squared rubble masonry.

2. Dry rubble masonry: The r ubble masonr y in which stones ar e laid without using any mor tar is called dr y r ubble masonr y or sometimes shor tly as "dr y stones". It is an or dinar y masonr y and is r ecommended f or constr ucting walls of height not mor e than 6m. In case the height is mor e, thr ee adjacent courses ar e laid in squar ed r ubble masonr y mor tar at 3m inter vals. UMA MAGESWARI. M

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This type of masonry is used in the construction of retaining walls pitching earthen dams and canal slopes in the form of random rubble masonry without any mortar. Ashlar Masonry

The stone masonr y in which f inely dr essed stones ar e laid in cement or lime mor tar is known as ashlar masonr y. In this masonr y ar e the courses ar e of unif or m height, all the joints ar e r egular , thin and have unif or m thickness. This type of masonr y is much costly as it r equir es dr essing of stones. Suitability: This masonr y is used f or heavy str uctur es, ar chitectur al buildings, high piers and

abutments of br idges. Ashlars masonr y is f ur ther sub divided into the f ollowing types: 

Ashlars f ine or coarse ashlar masonr y



Random coarse ashlars masonr y



Rough tooled ashlar masonr y



Rock or quarr y f aced ashlars masonr y



Chamf er ed ashlars masonr y



Block in coarse masonr y



Ashlar f acing

F li nt r ubble masonry

This type of masonry is used in the areas where the flint is available in plenty. The flint stones varying in thickness from 8 to 15cm and in length from 15 to 30cm are arranged in the facing in the form of coursed or uncoursed masonry as shown below.

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Brick Masonry

The art of laying bricks in mortar in a proper systematic manner gives homogeneous mass which can withstand forces without disintegration, called brick masonry. A standard metric brick has coordinating dimensions of 225 x 112.5 x 75 mm (9''×4½" ×3“) called nominal size and working dimensions (actual dimensions) of 215 x 102.5 x 65 mm (8.5“ * 4 *2.5) called architectural size.

Traditional bricks  It has not been standar dize in size  Dimensions var ies fr om place to place  Thickness var ies fr om var ies fr om cm to 7.5cm,widthvar ies fr om 10to13 cm and

length var ies fr om 20to25 cm Modular brick  Any br ick which is the same unif or m size as laid down by BIS  The nominal size of the modular br ick is 20cm x10cmx10cm  Actual size is 19x9x9 cm.

Frog 

The depression provided in the face of a brick during its manufacturing.



Depth of frog in a brick 10 to 20mm. Frog should be upward

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Bats  The portions mad by cutting standard bricks across their width are known as brick bats.  These are named according their fraction of full length of a standard brick.

Closer

The portions made by cutting across their length in such a manner that their one stretcher face remains uncut or half cut. Quoins

The external corners of walls are called quoins. The brick which form the external corner is known as quoin brick.

Classification of bonds

The bonds can be classified as follows i.

Stretcher Bond

ii.

Header Bond

iii.

English Bond

iv.

Flemish Bond

v.

Garden wall bond

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vi.

Facing Bond

vii.

Dutch Bond

viii.

Raking Bond

ix.

Zig zag Bond

x.

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English cross Bond

Stretcher bond

The length of the br ick its along with the f ace of the wall. This patter n is used only f or those wall which have thickness of half br ick. For higher thickness walls, this arrangement is not at all practicable.

Header bond

The width of the br ick s ar e thus along the dir ection of the wall. This patter n is used only when the thickness of the wall is equal to one br ick. This is also suitable for the construction of curved wall and footings for b etter load distributions.

English bond  It is the most commonly used method this bond is consider ed to be the str ongest.  This bond consists of alter nate course of str etchers and headers. It is necessary to place queen

closers after the first header in the heading cou rse for breaking the joints vertically.  Alter native courses will show either headers or str etchers in elevation

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 Ever y alter native header comes centr ally over the joint between two str etchers in cour se in

below  Since the number of ver tical joint in the header course twice the number of ver tical joints in

str etcher course, the joints in the header course ar e made thinner than the joints in the str etcher course.

Flemish bond

In this ty pe of course is compr ised of alter native headers and str etchers are laid to each course. This bond is better in appearance than the English Bond.

Facing bond

This bond is used wher e the br ick s of diff er ent thickness ar e to be used in the f acing and backing of the wall The nominal thickness of f acing br ick is 10 cm and that of backing br ick s is 9 cm the header course tis pr ovided at a ver tical inter val of 90 cm

Dutch Bond

This type of bond is a modified form of English Bond. The corners of the wall provided with Dutch bond are quite strong. The alternate courses in this type of bond are headers and stretchers. UMA MAGESWARI. M

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Raking Bond .

Inthis type of bond alternate couses are placed in different directions to get maximum strength in the wall. The raking courses are laid at certain intervals along the height of the wall in very thick walls having number of headers more than the numbers of stretchers in between facing and backing. The raking bond can be classified as two types. Herring bone bond. Diagonal bond.

Herring Bone bond . 0

In this bond, the bricks are places at an angle of 45 from the central line in both the directions. This type of bond is used in case of walls having thickness more than four b ricks or for paving, etc.

Diagonal Bond

In this type of bond bricks are laid at every fifth or seventh course along the height of the wall. Internal placing of the bricks is made in one direction only at certain angle , after the face bricks are laid.

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Zigzag Bond

This type of bond is very much similar to herring bone bond. The only difference in this type of bond is that the bricks are laid in zigzag way. This method is generally useful for paving the brick floor .

Comparison between Brick Masonry and Stone masonry  Stone masonry is cheaper at places where stone are abundantly available.  Stone masonry construction can be developed aesthetically more sound than brickwork.  Stone masonry is stronger than the brick masonry.  For public buildings and monumental structures, the stone masonry provides a solid appearance

and is found to be more useful than brick masonry.  Stone masonry is more watertight than brick masonry. It is because of fact that bricks absorb

moisture from the atmosphere and dampness can enter the building.

The brick masonry is superior to stone masonry under the following circumstances.  At places where there is a plenty of clay but stones are not easily available, brick

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masonry becomes cheaper than stone masonry.  Brick masonry construction requires less skilled labor and hence cheaper than stone

masonry.  Bricks can be lifted easily and do not require lifting devices.  Bricks offer better resistance to fire than the stones.  The action of atmospheric agents on bricks is lesser than the stones.  The construction of connections and openings in brick masonry is easier than in stone

masonry. Hollow Concrete Masonry

It is used in residential buildings, schools, churches and other public buildings. It is especially suited for low cost houses construction. These blocks can be built into various shapes and sizes depending upon their use. The face thickness of these blocks as recommended by the concrete Association of India should be less than 5 cm and neat area should be at least 55 to 60 % of the gross area. The common sizes generally adopted for building blocks are 39 cm X 19 cm X 30 cm 39 cm X 19 cm X 20 cm 39 cm X 19 cm X 10 cm Advantages  Highly Durable: The good concrete compacted by high pressure and vibration gives substantial

strength to the block.  Proper curing increase compressive strength of the blocks.  Low Maintenance, Color and brilliance of masonry withstands outdoor elements.  Load Bearing, strength can be specified as per the requirement.  Fire Resistant  Provide thermal and sound insulation: The air in hollow of the block, does not allow outside

heat or cold in the house. So it keeps house cool in summer and warm in winter.  Economical  Environment Friendly, fly ash used as one of the raw materials.  Low insurance rates.

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Structural Advantages  In this construction system, structurally, each wall and slab behaves as a shear wall and a

diaphragm

respectively,

reducing

the

vulnerability

of

disastrous

damage

to

the

structure/building, during the natural hazards.  Due to the uniform distribution of reinforcement in both vertical and horizontal directions,

through each masonry element, increased tensile resistance and ductile behavior of elements could be achieved. Hence, this construction system can safely resist lateral or cyclic loading, when compared to other conventional masonry construction systems. This construction system has also been proved to offer better resistance under dynamic loading, when compared to other conventional systems of construction. Constructional Advantages  No additional formwork or any special construction machinery is required for reinforcing

the hollow block masonry.  Only semi-skilled labour is required for this type of construction.  It is a faster and easier construction system, when compared to the other conventional

construction systems. FLOO RS

The pur pose of f loor is to pr ovide a level surf ace capable of suppor ting the occupants of the building, f ur nitur e, equipment and some time inter ior wall The f loor must satisf y the f ollowing r equir ements  Adequate str ength and stability  Adequate f ir e r esistance  Sound pr oof  Damp r esistance  Ther mal insulations

Components of a f loor

Sub f loor , base course or f loor base Selection of f looring materials

Factor that aff ect the choice of f loor ing  Initial cost

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 A p pear ance  Cleanliness  Dur ability  Damp r esistance  Sound insulation  Ther mal insulation  Smoothness  Har dness  Maintenance

Types of f looring

1. Mud or Muram flooring 2. Brick Flooring 3. Flag stone f loor ing cement concr ete f loor ing 4. Terr azzo f loor ing 5. Mosaic f loor ing 6.

Tiled f loor ing

7. Mar ble f loor ing timber f loor ing 8. As phalt f loor ing 9. Rubber f loor ing 10. Linoleum f loor ing 11. Cor k f loor ing Muram or Mud Floors The ground floor having its topping consisting of muram o r mud is called Muram or Mud Floors

These floors are easily and cheaply repairable. Method of construction  The surface of earth filling is properly consolidated  20cm thick layer of rubble or broken bats is laid, hand packed, wet and rammed  15cm thick layer of muram or good earth is laid  2.5cm thick layer of powdery variety of muram earth is uniformly spread

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 The whole surface is well watered and rammed until the cream of muram earth rises to the

earth surface  After 12 hours the surface is again rammed for three days.  The surface is smeared with a thick paste of cow-dung and rammed for two days  Thin coat of mixture of 4 parts of cow-dung and 1 part of Portland cement is evenly applied  The surface is wiped clean by hand.  For maintaining this type of floor properly, gobri leaping is done once a week  Suitability:

These floors are generally used for unimportant building in rural areas Cement Concrete Floor:

The floor having its topping consisting of cement concrete is called Cement Concrete Floor or Conglomerate Floor Types of Cement Concrete Floor:

According to the method of finishing the topping, Cement Concrete Floor can be classified into the following two types 1- Non-monolithic or bonded floor finish concrete floor 2- Monolithic floor finish concrete floor 1- Non-monolithic or bonded floor finish concrete floor: The type of Cement Concrete Floor in which the topping is not laid monolithically with the base concrete is known as Non-monolithic or bonded floor finish concrete floor . Method of Construction:  The earth is consolidated.  10cm thick layer of clean sand is spread.  10cm thick Lime Concrete (1:4:8) or Lean Cement Concrete (1:8:16) is laid thus forming

base concrete  The topping {4cm thick Cement Concrete (1:2:4)} is laid on the third day of laying base cement concrete, thus forming Non-monolithic construction. This type of construction is mostly adopted in the field The topping is laid by two methods: I-

Topping laid in single layer:

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The topping consists of single layer of Cement Co ncrete (1:2:4), having its thickness 4cm II- Topping laid two layers: The topping consists of 1.5cm thick Cement Concrete (1:2:3), which is laid monolithically over 2.5cm thick Cement Concrete (1:3:6)

2- Monolithic Floor Finish Concrete Floor:

The Cement Concrete Floor in which the topping consisting of 2cm thick Cement Concrete (1:2:4) is laid monolithically with the Base Concrete is know as Monolithic Floor Finish Concrete Floor Method of Construction:  The surface of muram or earth filling is leveled, well watered and rammed  10cm layer of clean and dry sand is spread over  When the sub soil conditions are not favorable and monolithic construction is desired, then,

5cm to 10cm thick hard core of dry brick or rubble filling is laid.  10cm thick layer of Base Concrete consisting of Cement Concrete (1:4:8) or Lean Cement Concrete (1:8:16) is laid.  The topping {2cm thick layer of Cement Concrete(1:2:4)} is laid after 45 minutes to 4 hours of laying Base Concrete

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Brick Floors:

The floors having its topping consisting of bricks are known as brick floor Features:

These floors can easily be constructed and repaired. 

But this type of floor provides a rough surface.



These can easily absorb moisture from the surrounding areas and may cause dampness in the building.

Method of Construction :  The muram or earth filling is properly consolidated.  10cm thick layer of dry clean sand is evenly laid  10cm thick layer of Lime Concrete (1:4:8) or Lean Cement Concrete (1:8:16) is laid,

compacted and cured to form a base concrete.  Well soaked bricks are laid in Cement Mortar (1:4) in any desired bond pattern e.g.

Herring Bond, Diagonal Bond or any other suitable bond  In case the pointing is not to be done, the thickness of joints should not exceed 2mm

and the mortar in joints is struck off flush with a trowel  In case the pointing is to be done, the minimum thickness of joints is kept 6mm and the

pointing may be done as specified. Suitability: This type of floor is suitable for stores, god owns etc. Tile Floor:

The floor having its topping consisting of tiles is called tile floor. Method of Construction:  The muram or earth filling is properly consolidated.  10cm thick layer of dry clean sand is evenly laid  10cm thick layer of Lime Concrete (1:4:8) or Lean Cement Concrete (1:8:16) is

laid, compacted and cured to form a base concrete.  A thin layer of lime or cement mortar is spread with the help of screed battens.  Then the screed battens are properly leveled and fixed at the correct height.

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 When the surface mortar is harden sufficiently, 6mm thick bed of wet cement (1:5) is

laid and then over this the specified tiles are laid.  The surplus mortar which comes out of the joints is cleaned off.  After 3 days, the joints are well rubbed with a corborundum stone to chip off all the

projecting edges. 

Rubbing should not be done in case of glazed tiles



The surface is polished by rubbing with a softer variety of a corborundum or a pumice stone.



The surface is finally washed with soap.

Suitability: This type of floor is suitable for courtyard of buildings. Glazed tiles are used in modern buildings where a high class finish is desired. Mosaic Floors:

The floors having its topping consisting of mosaic tiles or small regular cubes, square or hexagons, embedded into a cementing mixture is known as Mosaic Floors Method of Construction:  The earth is consolidated.  10cm thick layer of clean sand is spread.  10cm thick Lime Concrete (1:4:8) or Lean Cement Concrete (1:8:16) is laid thus

forming base concrete  Over this base course 5cm thick Lime Mortar or Cement Mortar or Lime and Surkhi

mortar (1:2) is laid.  The mortar is laid in small area so that the mortar may not get dried before finishing the

wearing course.  3mm thick cementing mixture is spread.  The cementing mixture consists of one part of pozzolana, one part of marble chips

and two parts of slacked lime.  After nearing 4 hours, patterns are formed on the top of the cementing material.  Now the tiles of regular shaped marble cubes are hammered in the mortar along

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 The inner spaces are then filled with colored pieces of marble.  A roller 30cm in diameter and 50cm in length is passed gently over the surface.  Water is sprinkled to work up the mortar between the marble pieces.  The surface is then rubbed with pumice stone fixed to a wooden handle about 1.5m

long.  The surface is then allowed to dry up for 2 weeks

Marble f looring  It is the super ior type of f loor ing used in bathr ooms and kitchens of r esidential building

and hos pitals, sanator ium, temples etc.  Af ter the pr epar ation of base concr ete 20 mm thick bed layer of 1:4 cement mix s pr ead

under the ar ea of each individual slabs.  Size of the slab depend upon the pattern  Thickness 20 mm to 40 mm.  Prior to laying flooring , the sub grade is cleaned, wetted and mapped properly.  Bedding mortar 1:4

ble layer is then laid over it and pr essed with wooden mallet and leveled.  The mar  The paved area is cured for a minimum period of seven days.

Timber f looring  Timber f loor ing is used f or car pentr y halls, dancing halls auditorium Etc.  These ar e not commonly used in India because its costlier .  Entire area of ground below the floor isd covered with a 15 cm layer of concrete  Sleeper walls are generally 10 cm thick  Spacing 1.8 m apart.  The sus pended type of wooden f loor is suppor ted above the gr ound.  The solid type of wooden f loor is f ully suppor ted on the gr ound.

Asphalt flooring  Dustless, elastic, durable, waterproof, acid proof and attractive in appearan ce.  Non slippery and noiseless.  Recommended for use in factories, loading platforms, swimming pools and terrace floors

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 This type of flooring is not common in India, but foreign countries it is used in

residential building as well as public building.  It is noiseless, comfortable, clean and durable.‟  This may sheet or tiles. These are fixed by glue.  The base may be of concrete. R.C.C or wood

Linoleum Flooring  Linoleum is a covering laid over wooden or concrete floors  It is a material manufactured by mixing oxidized linsed oil with powdered cork, various

types of gums and suitable coloring pigments.  Mostly sold in rolls which are 1.8 to 3.66m, thick 6 mm

Merits  It is washable, dust proof  It reduces noise effectively  It has cushioning effect which gives comfort to the users  It is economical.  Used in Residential buildings, offices, schools, hospitals, libraries ,carrages and buses

etc.. PVC flooring  PVC tiles are used to Residential l as well as Non -Residential buildings  It gives decorative floor finish, smooth and can be cleaned easily

Merits  It is a non absorbent  It is easily repairable in patches  It gives pleasant appearance  It gives more durable  It a quick laying floor  Resistant to wear

Demerits  This type of construction is very costly  Easy to fire.

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Cork Flooring  Perfectly noiseless  Used in libraries, Theatres ,Art galleries etc.  Cork obtained from oak tree  Thickness 12 mm

Glass flooring  Special type of flooring  Transmit the light from upper to lower floor  Basement to upper floors  Thick varies from 12 to 30 mm

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FOUNDATIONS

Every structure consists of two parts. (1) Foundation and (2) Super structure. The lowest artificially prepared parts of the structure which are in direct contact with the ground and which transmit the loads of the structure to the ground are known as Foundation or Substructure. The solid ground on which the foundation rest is called the “foundation bed” or foundation soil and it ultimately bears the load and interacts with the fou ndations of buildings. Requirements of a good foundation:

Following are the three basic requirements to be fulfilled by a foundation to be satisfactory 1) Location : The foundation should be located that it is able to resist any unexpected future influence which may adversely affect its performance. This aspect requires careful engineering judgment. 2) Stability: The foundation structure should be stable or safe against any possible failure 3) Settlement : The foundation structure should not settle or deflect to such an extent so as to impair its usefulness. Objects of foundations:

Foundations are provided for the following purposes 1) To distribute the total load coming on the structure on large area. 2) To support the structure 3) To give enough stability to the structures against various distributing forces such as wind, rain etc. 4) To prepare a level surface for concreting and masonry work. The general inspection of site of work serves as a good for determine the type of foundation, to be adopted for the proposed work and in addition, it helps in getting the data w.r.to the following items. i) ii) iii) iv)

Behavior of ground due to variations in depth of water table Disposal of storm water at site Nature of soil by visual examination Movement of ground due to any reason etc.

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Causes of failure of good foundation:

The different causes for foundation failure are given below 1. Non uniform settlement of sub soil and masonry 2. Horizontal movement of the soil adjacent to structure 3. Alternate swelling and shrinkage in wet and dry cycles of the season 4. Lateral pressure due to lateral movement of earth t ending to over turn the structure 5. Action of weathering agencies like sun, wind or rain 6. Lateral escape of the soil beneath the foundation of the structure Roots trees and shrubs which penetrate the foundation Types of foundations:

Depending upon their nature and depth, foundations have been categorized as follows

I.

(i)

Open foundations or shallow foundations

(ii)

Deep foundations

Open foundations or shallow foundations: This is most common type of foundation and can

be laid using open excavation by allowing natural slopes on all sides. This type of foundation is practicable for a depth of about 5m and is normally convenient above the water table. The base of the structure is enlarged or spread to provide individual support. Since the spread foundations are constructed in open excavations, therefore they are termed as open foundations. This type of foundation is provided for structure of moderate height built on sufficiently firm dry ground. The various types of spread footings are: 1. Wall footing 2. Isolated footing 3. Combined footing 4. Inverted arch footing 5. Continuous footing 6. Cantilever footing UMA MAGESWARI. M

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7. Grillage footing

Wall Footing: These footings can be either simple or stepped. The base course of these footings can

be concrete or entirely of one material simple footing are used for light structures. They have only one projection beyond the width of the wall. The base width of the concrete base course should be equal to twice the width of wall.

Isolated Footings: These are used to support individed columns. They can be of stepped type or have

projections in the concrete base. In case of heavy loaded columns steel reinforcement is provided in both directions in concrete with 15cm offsets

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3. Combined Footing: A combined footing supports two or more columns in a row A Combined footing may be rectangular or trapezoidal constructed with reinforced concrete. The location of centre of gravity of column loads and centroid of the footing should coincide. The combined footing is as shown in fig10.5.

4. Inverted Arch Footing : This type of construction is used on soft soils to reduce the depth of foundation loads above an opening are transmitted from supporting walls through inverted arches to the soil. In this type the end columns must be stable enough to resist the outward pressure caused by arch actions. Th e inverted arch footing is as shown in fig10.6. UMA MAGESWARI. M

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5. Continuous Footing: In this type of footing a single continuous R.C slab is produced as foundation of two or three or more columns in a row. This type of footing is suitable at locations liable to earthquake activities. This also prevents differential settlement in the structure. In order to have better stability a deeper beam is constructed in between the columns as shown in fig10.7.

Grillage footing :

This type of footing is used to transmit heavy loads from steel columns to foundation soils having low bearing power. This type of foundation avoids deep excavation and provides necessary area at the base to reduce the intensity of pressure of the foundation soil is not stiff and there is a plenty of water with spring, the sides are protected by sharing. The grillage footing is a s shown in fig 10.9.

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8. Raft Foundation: A raft or mat is a combined footing that covers the entire area beneath a structure and supports all the columns. When the allowable soil pressure is low or the structure loads are heavy the use of spread footings would cover more than one half of the area and it may be prove more economical to use raft foundation. There are also used where the soil mass contains compressible lenses so that the differential settlement would be difficult to control usually when the hard soil is not available within 1.5 to 2.5m, a raft foundation is adopted. The raft is composed of reinforced. Deep Foundations ►

Deep foundations are those founding too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths of 3 meter below finished ground level. Deep foundations can be used to transfer the load to a deeper, more competent strata at depth if unsuitable soils are present ne ar the surface.

Deep foundations are those founding too deeply below the finished ground surface for their base

bearing capacity to be affected by surface conditions, this is usually at depths >3 m below finished ground level. They include piles, piers and caissons or compensated foundations using deep

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basements and also deep pad or strip foundations. Deep foundations can be used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface. ►

Piles are relatively long, slender members that transmit foundation loads through soil strata of

low bearing capacity to deeper soil or rock strata having a high bearing capacity. They are used when for economic, constructional or soil condition considerations it is desirable to transmit loads to strata beyond the practical reach of shallow foundations. In addition to supporting structures, piles are also used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces. ►

Piers are foundations for carrying a heavy structural load which is constructed insitu in a deep

excavation. ►

Caissons are a form of deep foundation which are constructed above ground level, then sunk

to the required level by excavating or dredging material from within the ca isson. ►

Compensated foundations are deep foundations in which the relief of stress due to

excavation is approximately balanced by the applied stress due to the foundation. The net stress applied is therefore very small. A compensated foundation normally comprises a deep basement. END BEARING PILE :

These piles are used to transfer load through water or soft soil to a suitable bearing stratum. Friction pile

These piles are used to transfer loads to a depth of a friction load carrying material by means of skin friction along the length of pile. Compaction pile

These piles are used to compact loose soils, thus increasing their bearing capacity. The compaction piles themselves do not carry any load.

Hence they may be of weaker material (sand). The pile

tube, driven to compact the soil, is gradually taken out

and sand is filled in its place thus forming

a „sand pile‟. UMA MAGESWARI. M

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Under reamed pile ►

In black cotton soils and other expansive type of soils, buildings often crack due to relative ground movements. This is caused by alternate swelling and shrinking of the soil due to changes in its moisture content.

►

The under-reamed pile is used to safe guard this movement effectively. Generally this foundation is used for machine foundation, factory building, transmission line towers and other tall structures also.

Timber piles 

Timber piles are made of-tree trunks driven with small end as a point



Maximum length: 35 m; optimum length: 9 - 20m



Max load for usual conditions: 450 kN; optimum load range = 80 - 240 kN

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Disadvantages of using timber piles:

Difficult to splice, vulnerable to damage in hard driving, vulnerable to decay unless treated with preservatives (If timber is below permanent Water table it will apparently last forever), if subjected to alternate wetting & drying, the useful life will be short, partly embedded piles or piles above Water table are susceptible to damage from wood borers and other insects unless treated. Advantages:

Comparatively low initial cost, permanently submerged piles are resistant to decay, easy to handle, best suited for friction piles in granular material. Steel piles 

Maximum length practically unlimited, optimum length: 12-50m



Load for usual conditions = maximum allowable stress x cross-sectional area



The members are usually rolled HP shapes/pipe piles. Wide flange beams & I beams proportioned to withstand the hard driving stress to which the pile may be subjected. In HP pile the flange thickness = web thickness, piles are either welded or seamless steel pipes, which may be driven either open ended or closed end. Closed end piles are usually filled with concrete after driving.



Open end piles may be filled but this is not often necessary., dm

Advantages of steel piles:

Easy to splice, high capacity, small displacement, able to penetrate through light obstructions, best suited for end bearing on rock, reduce allowable capacity for corrosive locations or provide corrosion protection. Disadvantages: 

Vulnerable to corrosion.



HP section may be damaged/deflected by major obstruction

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Concrete Piles 

Concrete piles may be precast, prestressed, cast in place, or of composite construction



Precast concrete piles may be made using ordinary reinforcement or they may be prestressed.



Precast piles using ordinary reinforcement are designed to resist bending stresses during picking up & transport to the site & bending moments from lateral loads and to provide sufficient resistance to vertical loads and any tension forces developed during driving.



Prestressed piles are formed by tensioning high strength steel prestress cables, and casting the concrete about the cable. When the concrete hardens, the prestress cables are cut, with the tension force in the cables now producing compressive stress in the concrete pile. It is common to higher-strength concrete (35 to 55 MPa) in prestressed piles because of the large initial compressive stresses from prestressing. Prestressing the piles, tend to counteract any tension stresses during either handling or driving.



Max length: 10 - 15 m for precast, 20 - 30 m for prestressed



Optimum length 10 - 12 m for precast. 18 - 25m prestressed



Loads for usual conditions 900 for precast. 8500 kN for prestressed



Optimum load range: 350 - 3500 kN

Advantages:

1. High load capacities, corrosion resistance can be attained, hard driving possible 2. Cylinder piles in particular are suited for bending resistance. 3. Cast in place concrete piles are formed by drilling a hole in the ground & filling it with concrete. The hole may be drilled or formed by driving a shell or casing into the ground. Disadvantages:

1. Concrete piles are considered permanent, however certain soils (usually organic) contain materials that may form acids that can damage the concrete. 2. Salt water may also adversely react with the concrete unless special precautions are taken when the mix proportions are designed. Additionally, concrete piles used for marine structures may undergo abrasion from wave action and floating debris in the water. UMA MAGESWARI. M

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3. Difficult to handle unless prestressed, high initial cost, considerable displacement, prestressed piles are difficult to splice. 4. Alternate freezing thawing can cause concrete damage in any exposed situation.

5. Pier f oundation

A pier f oundation consist of a cylindr ical column of lar ge diameter to suppor t tr ansf er lar ge super imposed loads to the f ir m str ata below Gener ally pier f oundation is shallower in depth than the pile f oundation It has two types o Masonr y o concr ete pier Drilled caissons

Well f oundation or caissons ar e box lik e str uctur es – cir cular or r ectangular which ar e sunk fr om the surf ace of either land or water to the desir ed depth Caisson f oundations ar e used f or major f oundation wor k such as Br idge pier and abutments in r iver Whar ves and quay walls dock s Lar ge water fr ont str uctur es such as pump houses, subjected to heavy ver tical and hor izontal loads Well f oundations ar e caissons ar e hollow fr om inside, which may f illed withstand and ar e plugged at the bottom, the load is tr ansf err ed to the per imeter wall called as steining UMA MAGESWARI. M

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Well foundation is a box of timber, metal, reinforced concrete or masonry which open both at the top and bottom, and is used for building for building and bridge foundations. Types of well shapes: ►

Circular

►

Rectangular

►

Double – D

Twin circular etc

Pier f oundation  A pier f oundation consist of a cylindr ical column of lar ge diameter to suppor t tr ansf er lar ge

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super imposed loads to the f ir m str ata below  Gener ally pier f oundation is shallower in depth than the pile f oundation  It has two types

o Masonr y o concr ete pier Drilled caissons  Well f oundation or caissons ar e box lik e str uctur es – cir cular or r ectangular which ar e sunk

fr om the surf ace of either land or water to the desir ed depth  Br idge pier and abutments in r iver  Whar ves and quay walls dock s  Lar ge water fr ont str uctur es such as pump houses, subjected to heavy ver tical and hor izontal

loads

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Joints Expansion Joints

The joints provided to accommodate the expansion of adjacent parts in a building are

•

known as expansion joints. •

These joints essentially consist of a space between the adjacent parts of a structure and may sometimes be provided with the load transmitting devices between the parts.

•

They are generally filled with expansion joint filler of approved quality.

•

The function of these joints is to accommodate the expansion of adjacent parts of a building and relieve the compressive stresses that may otherwise develop.

•

These joints are provided in long masonry walls, roofs and floors, roof or floor to wall joints, framed structures etc. For spacing of these joints in different locations.

•

The design and location of joints usually depend upon the type of structure, the method of construction and the jointing materials available.

•

The provisions of joints should be adequate to accommodate all the dimensional changes caused by expansion and contraction of materials used in the structure.

•

In case of masonry walls, the vertical control joints (expansion joints) should be provided from top of the wall to the top of the concrete foundations and not through the foundation concrete. The reinforcement should not pass through such joints.

•

In case of masonry walls resting on pile foundation, the vertical control joints should be taken up to the top of grade beam i.e. concrete cap over the piles without making use of any reinforcement passing through the joints.

•

In case of reinforced framed structures, the vertical control joint between any two columns should extend from top of the column to the top of the pedestal provided over the RCC footing. S.NO

Item and description

spacing

1

Walls:

30 m intervals.

Load bearing walls with cross walls at intervals. Traditional type UMA MAGESWARI. M

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of one-brick thick or more Walls warehouse type construction Expansion joints in walls at 30 m (without cross-walls)

maximum intervals. (If the walls are panel walls between columns at not more than 9 m centers, no joints are necessary). Control joints over centre of openings may be provided at half the spacing of expansion joints

2

Chajjas, balconies and parapets.

3

Roofs :

(a) Ordinary

roof

slabs

6 to 12 m intervals.

of 20 to 30 m intervals and at changes in

RCC protected by layers of direction as in L, T, H and V shaped mud

phuska

or

other structures.

insulating media in framed construction. Thin unprotected slabs 4

15 m intervals

Frames :

Joints in structure through slabs,

Corners of L, T, H and V shaped

beams, columns etc, dividing the structures at 30 m intervals in long building

into

two

independent uniform structures

structural units.

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Contraction Joints or Control Joints

Control Joints (often confused with expansion joints) are cuts or grooves made in concrete or asphalt at regular intervals. These joints are made at locations where there are chances of cracks or where the concentration of stresses are expected, so that when a concrete does crack, the location will be known to you. In such a way a concrete will not crack randomly but in a straight line (i.e. control joint). In other words Contraction or Control Joints are Pre-Planned Cracks. The cracks may be due to temperature variations or drying shrinkage or other reasons. Joints depth should be 25% of the depth of the slab. For instance a 4" thick slab should have 1" deep cut. Joints Interval (taken in feet) should not be more than 2 - 3 times the slab thickness (in inches). Let say a 6" slab should have joints 2 x 6=12 to 3 x 6 = 18 feet apart. For fresh concrete grooving tools are used while saw is used for hardened concrete. The joints introduced in concrete structures to localize shrinkage movements are known as contraction joints. The contraction joints are in the form of separations or planes of weakness.

The function of these joints is to localize shrinkage movements which would otherwise lead unsightly cracks.

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Construction Joints •

The joints provided at locations where construction stops for any reason and when their location does not coincide with that of expansion or contraction joints are called construction joints.

•

These joints are constructed in a similar manner as contraction joints but these joints are not intended to accommodate movement due to contraction.

•

Every effort should be made to prevent movement occurring at such joints. However, extra care may be taken to obtain a good bond between abutting sections of concrete

•

Since, cracks frequently develop at these joints as a result of stresses arising from variations in temperature, moisture content or loading, therefore, it is most desirable that construction joints should coincide with expansion or contraction joints wherever possible.

•

The function of these joints is to simplify the construction of a structure.

•

Construction joints in floor should be located in the middle of spans of slabs, beams or girders unless a beam intersects the girder at this point in which case the joints in the girders are provided at a distance equal to twice the width of beam.

• •

Adequate provision should be made for shear by use of inclined reinforcement. Joints in column should be made at the underside of the floor.

Unintentional provision may occur due to 

Unexpected shortage of material



Equipment Failure



Bad weather.

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Slip form

Slip form is similar in nature and application to jump form, but the formwork is raised vertically in a continuous process. It is a method of vertically extruding a reinforced concrete section and is suitable for construction of core walls in high-rise structures – lift lift shafts, stair shafts, towers, etc. It is a self-contained formwork system and can require little crane time during construction. This is a formwork system which can be used to form any regular shape or core. The formwork rises continuously, at a rate of about 300mm per hour, supporting itself on the core and not relying on support or access from other parts of th e building or permanent works. Commonly, the formwork has three platforms. The upper platform acts as a storage and distribution area while the middle platform, which is the main working platform, is at the top of the poured concrete level. The lower platform provides access for concrete finishing. Benefits  Careful planning of construction process can achieve high production rates

mo ve upwards, minimising crane use.  Slip form does not require the crane to move  Since the formwork operates independently, formation of the core in advance of the

rest of the structure takes it off the critical path – path – enhancing enhancing main structure stability.

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 Availability of the different working platforms in the formwork system allows the

exposed concrete at the bottom of the rising formwork to be finished, making it an integral part of the construction process.  Certain formwork systems permit construction of tapered cores and towers.  Slip form systems require a small but highly skilled workforce on site.

Safety  Working platforms, guard rails, ladders and wind shields are normally built into the

completed system.  Less congested construction site due to minimal scaffolding and temporary works.  Completed formwork assembly is robust.  Strength of concrete in the wall below must be closely controlled to achieve stability

during operation.  Site operatives can quickly become familiar with health and safety aspects of their job  High levels of planning and control mean that health and safety are normally addressed

from the beginning of the work. Other considerations 

This formwork is more economical for buildings more than seven storeys high.



Little flexibility for change once continuous concreting has begun therefore extensive planning and special detailing are needed.



Setting rate of the concrete had to be constantly monitored to ensure that it is matched with the speed at which the forms are raised.



The structure being slip formed should have significant dimensions in both major axes to ensure stability of the system.



Standby plant and equipment should be available though cold jointing may occasionally be necessary.

Slipform construction is a method for building large towers or bridges bridges from concrete concrete.. The name refers to the moving form the concrete is poured into, which moves along the project as the previously poured concrete hardens behind it. The technique has also been applied to road construction. The technique was in use by the early 20th century for building silos and grain elevators. Vertical slip form relies on the quick-setting properties p roperties of concrete requiring a UMA MAGESWARI. M

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balance between early strength gain and workability. Concrete needs to be workable enough to be placed to the formwork and strong enough to develop early strength so that the form can slip upwards without any disturbance to the freshly placed concrete.

A notable use of the method was the Skylon Tower in Niagara Falls, Ontario, which was completed in 1965. The technique was soon utilized to build the Inco Super stack in Sudbury, Ontario and the CN Tower in Toronto. It is the most common method for construction of tall buildings in Australia.

From foundation to rooftop of even the very tallest projects, with the system‟s hydraulic jacks, installing steel reinforcement and pouring concrete become much easier and faster, plus can be more efficiently controlled to assure the highest quality finished cement structure. SLIPFORM technology virtually eliminates unnecessary waste and hazards, making this construction system even more efficient and economical.



SLIPFORM saves investment



SLIPFORM saves time



SLIPFORM saves labor



SLIPFORM is safety

DAMP PROOF COURSE

Damp prevention and fire protection are the chief requirements to ensure the safety of UMA MAGESWARI. M

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buildings against dampness and fire respectively. The sources, effects, techniques and methods of damp prevention, materials used for damp-proofing (D.P.C) damp-proofing treatments in buildings, treatment of dampness are discussed under damp proof chapter. 14.1

Sources of dampness(causes)

Dampness in building in generally due to one or more of the following causes (i)

Faulty design of structure

(ii)

Faulty construction or poor workmanship

(iii)

Use of poor materials in construction These cause give rise to an easy access to moisture to enter the building from different points, such as rising of moisture from ground, rain penetration through walls, roofs and floors etc. The moisture entering the building from foundation and roofs, travels in different directions further under the effects of capillary action and gravity respectively. The entry of water and its movements, in different parts of the building are positively due to the one or more of the causes listed above.

Effects of dampness:

The various effects caused due to dampness in buildings mainly results in poor functional performance, ugly appearance and structural weakness of the buildings. 1. A damp building creates unhealthy living and working conditions for the occupants 2. Presence of damp condition causes efflorescence on building surfaces which ultimately results in the disintegration of bricks stones, tiles etc and hence red uction of strength 3. It may result in softening and crumbling of plaster 4. It may cause bleaching and flaking of the paint which results in the formation of coloured patches on the wall surfaces and ceilings 5. It may result in the corrosion of metals used in the construction of buildings 6. The materials used as floor coverings such as tiles are damaged because they lose adhesion with the floor bases UMA MAGESWARI. M

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7. Timber when in contact with damp condition, gets deteriorated due to the effect of warping, buckling and rolling of timber 8. All the electrical fittings gets deteriorated, causing leakage of electric current with the potential danger of a short circuit 9. Dampness promotes the growth of termites and hence creates unhygienic conditions in buildings Damp Proof

10. Dampness when accompanied by the warmth and darkness, breeds the germs of tuberculosis, neuralgia, aute and chronis neumatism etc which some times result in fatal diseases 14.3

Techniques and methods of damp prevention:

The following are the precautions to be taken to prevent dampness in buildings, before applying the various techniques. 1. The site should be located on high ground and well drained soil to safe guard against foundation dampness 2. All the exposed walls should be of sufficient thickness to safeguard against rain protection (minimum 30cm) 3. Bricks of superior quality free from defects should be used 4. Good quality cement mortar (1:3) should be used to produce definite pattern and perfect bond in the building 5. Cornices and string courses should be provided to through rain water away from the walls 6. All the exposed surfaces like top of walls, compound walls etc should be covered with water proofing cement plaster 7. Cavity walls are more reliable than solid walls in preventin g the dampness

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Techniques:

1. Use of damp proof courses 2. Water proof or damp proof treatments 3. Cavity walls or hallow walls 4. Guniting or shot concrete or shotcrete 5. Pressure grouting or cementation 1. Use of damp-proof courses (D.P.C.)

These are layers or membranes of water repellent materials such as bituminuous felts, mastic asphalt, plastic sheets, cement concrete, mortar, metal sheets, stone s etc which are interposed in the building structure at all locations wherever water entry is anticipated or suspected. The best location or position of D.P.C. in the case of building without basement lies at plinth level or structures without any plinth level, it should be laid at least 15cm above ground level. The damp proof course provided horizontally and vertically in floors, walls etc. In the case of basements, laying of D.P.C. is known as taking Fig 14.1 shows the D.P.C. treatment above ground level.

2. Water proof surface treatments: The surface treatment consists in filing up the pores of the material exposed to moisture by UMA MAGESWARI. M

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providing a thin film of water repellent material over the surface (internal / external ) . External treatment is effective in preventing dampness Many surface treatments, like pointing, plastering, painting, distempering etc are given to the exposed surfaces and also to the internal surface . The most commonly used treatment to protect the walls against dampness is lime cement plaster (1:6) (1-cement, 6-lime) mix proportion. Generally employed as water proofing agent in surface treatments are sodium or potassium silicate. Aluminium or zinc sulphate, Barium Hydroxide and magnesium sulphate in alternate applications. Soft soap and alum also in alternate applications, unie and unseed oil; coal tar, bitumen, waxes and fats; resins and gums Waxes and fats are not suitable in tropics as they melt with rise in temperatures 3. Integral damp-proofing treatments :

The integral treatment consists of adding certain compounds to the concrete or mortar during the process of mixing, which when used in construction acts as barriers to moisture penetration under different principles i)

Compounds like chalk , talc, fallers earth etc have mechanical action principle (i.e.,)

they fill the pores present in the concrete or mortar and make them dense and water proof

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Compounds like denser and water proof sulphates, calcium chlorides etc

work on chemical action principle (i.e.) they react chemically and fill the pores to act as water-resistant iii)

The compounds like soaps , petroleum, oils fatty acids compounds such as

sterates of calcium, sodium ammonium etc work on the repulsion principle i.e., they are used as admixture in concrete to react with it and become water repellent 4. Cavity walls or hallow walls: A cavity wall consists of two parallel walls or leaves or skins of masonary separated by a continuous air space or cavity. The provision of continuous cavity in the wall per effectively prevent the transmission or percolation of dampness from outer walls or leaf to inner wall or leaf. The following are the advantages of cavity wall. (i)

As there is no contact between outer and inner walls of cavity wall, possibility of moisture penetration is reduced to a minimum.

(ii)

A cavity wall prevents the transmission of heat through wall.

(iii) A cavity wall offer good insulation against sound. (iv)

The cavity wall tends to reduce the nuisance of efflorescence.

(v)

The cavity wall also provides benefits such as economy, better comfort and hygienic conditions in buildings

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The cavity wall construction and D.P.C. details for flat roofs is as shown in fig no 14.2

Fig 14.2 Cavity wall construction and D.P.C. details for flat roofs

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Guniting: (or shot concrete) : The technique of guniting consists in forming an

imperious layer of rich cement mortar (1:3) or fine aggregate mix for water proofing over the exposed concrete surface or over the pipes, cisterns etc for resisting the water pressure. By this technique, an impervious layer of high 2

compressive strength (600 to 700 kg/cm ) is obtained and hence this is also very useful for reconditioning or repairing old concrete works 6.Pressure grouting or (cementation). The mixture of cement, sand and water under pressure into the cracks, voids or fissures present in the structural component or the ground. In general, the foundations are given this treatment to avoid the moisture penetration. This technique also used for repairing structures, consolidating ground to improve bearing capacity, forming water cut-offs to prevent seepage etc.

Fire protection:

It is defined as the protection of the occupants of the building, contents and structure of the building and adjacent buildings from the risks of fire and spread of fire. The objective is achieved by using fire-resistive materials in the construction. By suitable planning of the building internally and in relation to adjacent building internally and in relation to adjacent building and by providing suitable means of quick escape for the occupants. These measures are essential to minimize the spread of fire and limit the total damage to a minimum

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Important considerations in fire protection:

1. It should be the objective of every engineer and architect while planning and designing the building that the structure offer sufficient resistance against fire so as to afford protection to the occupants, use of fire-resisting materials and construction techniques and providing quick and safe means of escape in the building. 2. All the structural elements such as floors, walls, columns, beams etc should be made of fire resisting materials 3. The construction of structural elements such as walls, floors, columns, lintels, arches etc should be made in such a way that they should continue to function atleast for the time, which may be sufficient for occupants to escape safely in times of fire. 4. The building should be so planned or oriented that the elements of construction or building components can with stand fire for a given time depending upon the size and use of building, to isolate various compartments so as to minimize the spread of fire suitable separation is necessary to prevent fire, gases, and smoke from spreading rapidly through corridors, staircases left shafts etc. 5. Adequate means of escape are provided for occupants to leave the building quickly and safely in terms of outbreak of fire. 6. In multi-storeyed office buildings suitable equipment for detecting, extinguishing and warning of fire should be installed in the niches.

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Fire-resistant construction:

National building code classifies the construction into four classes, namely type 1, type 2, type 3 and type 4 on the basis of fire-resistance offered by building components for 4hours, 3-hours, 2-hours and 1-hour respectively. To achieve the objective of fireresistance, due considerations should be made in design and construction of the structural members and use of combustible material should be avoided as far as possible in the construction a) Walls and columns b) Floor and roofs c) Wall openings d) Building fire escape elements (i.e.,) stair, staircase, corridors, entrances etc. a) Walls and columns: The load-bearing non-load bearing walls should be plastered with fire resistive mortar to improve fire resistance. Normally 20cm thick common wall is sufficient from fire resistance point of view. Bricks should be preferred to stones if the construction is solid bearing wall. If it happens to be a framed structure then R.C.C. frames are preferred to those of steel frame. Partition walls, should also be fire resistant materials. In case of wooden partitions are employed, they should be covered with metal lath and plaster. Sufficient cover to R.C.C. members like beams or columns should be to enable them to function satisfactorily, under the fire maximum time. It has been recommended that a cover of atleast 5cm inside the main reinforcement of structural members, like columns, girders, trusses etc, 38mm for ordinary beam, long span slabs, arches etc, 25mm for

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partition walls, short spans should be provided. The fire proofing treatments, w hich can possibly to concrete and steel column construction are as shown in the fig 14.3.

Fig 14.3 Fire proofing treatments to concrete and steel columns

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b) Floors and roofs: The floors and roofs should be made of fire-resisting material as they act as horizontal barriers to spread of heat and fire in vertical direction. For fire-resistant construction, the floor such as concrete jack arch floor with steel joists embedded in concrete or hallow tiled ribbed floor, R.C.C. floor etc should be used as shown in fig. 14.4.

Fig 14.4 Fire-resisting in floors

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Wall openings: From fire resistance point of view, firstly the openings in the walls

should be restricted to a minimum and secondly they should be protected by suitable arrangements in case of fire. These days, wire-glass panels are preferred for windows, where as steel rolling shutters are becoming popular for door ways and window openings in garages, godowns, shops etc due to their ability in preventing the spread of fire d) Building fire escape element: Staircases, corridors, Lobbies, entrances etc are the fire escape elements should be constructed out of fire-resistant materials and be well separated from the rest of the building. Doors to the staircase, corridors and lefts should be made of fire-proofing materials. Staircase should be created next to the outerwalls and should be accessible from any floor in the direction of flow towards the exits from the building. 14.5

General measures of fire safety in building :

In important buildings, in addition to the fire-resisting materials and adopting fire resistant construction, the following general measures of fire-safety have been recommended (i) Alaram system (ii) Fire extinguishing arrangements (iii) Escape routes for public buildings Scaffolding  These are temporary erections constructed (when working height exceeds 1.5 m) to

support a number of platform at different heights raised for the conven ience of workers  This temporary framework or scaffold is useful in building construction,

demolition, maintenance and repair works  The scaffolding may be done on one side or both sides of the wall.

Component parts of a scaffolding Standards -These are central members of scaffolding. UMA MAGESWARI. M

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Ledgers- These are horizontal members at right angles to the standards. Braces- These members are fixed diagonally on the standards Planks or Boarding : They form the horizontal platforms for supporting men, materials and

appliances. Putlogs : these members are placed on horizontal members at right angles to the walls, one end

of which is held in wall. Guard boards: These members are provided at working level to guard against materials. Toe Boards : These members are placed parallel to the ledgers and used for protection at the level

of working platform. Types of scaffolding

Single scaff olding or br ick layer scaff olding Dou ble scaff oldings or masons scaff oldings Cantilever

or

needle

scaff oldings

Sus pended scaff oldings Tr estle scaff olding Steel scaff olding Patented scaff oldings

Single Scaffolding

This being cheap, is most commonly used in the construction of brickwork. In this type of scaffolding, most of the members except platforms are usually made of bamboos and poles. It consists of a single row of standards which are driven into the ground at a distance of about 1.5 to 2.0 m apart and about 1.2 m away from the wall to be constructed where it is found difficult to fix the standards into the ground. The standards are then connected to each other by ledgers placed at right angles and spaced at a vertical distance of about 1.20 to 1.50 m such that one end is supported on the ledgers and the other end is held in the holes provided in the wall. As the work proceeds, the platform is raised to higher levels by extending the standards by adding extra pieces, if necessary. After removing the putlogs the holes must be filled solid immediately. UMA MAGESWARI. M

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Double scaffolding

This type of scaffolding is stronger than the single scaffolding and is sued in the construction of stone work. The formwork is similar to the single scaffolding except two rows of standards are used, one row close to the wall within 15 cm of the wall face and the other at 1.2 to 1.5 m away from the face of the wall. This type of scaffolding is completely independent of the wall and no holes are made in the wall to support putlogs.

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Ladder scaffolding or patented scaffolding

This is a modification over a double scaffolding and can be easily assembled. Now a days ,several patent ladder scaffolding are available in the market. In this type , the working platforms are supported on brackets which can be adjusted to any desired height. Such patented scaffoldings are very suitable for light works such as exterior walls ,paintings and decorations.

Cantilever scaffolding or Needle Scaffolding

The use of this type of scaffolding becomes necessary under the following circumstances Where it is not possible to fix the standards into the ground in the usual manner. Where the scaffolding is to be provided on the side of a busy street without obstructing the traffic on road. Where the scaffolding is required for construction operations of upper storeys of a tall building.

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Unit II Construction Practices (2)

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