foundation ktunotes
TRANSCRIPT
FOUNDATION
MODULE 3
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Foundation
• Sub structure or Foundation is the lower portion of the building usually located below the ground level, which transmits the load of the super structure to the sub soil
• The soil which is located below the base of the foundation is called SUBSOIL
• Lower most portion of the foundation which is in direct contact with the sub soil is called FOOTING
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GENERAL FOUNDATION DESIGN CRITERIA
For satisfactory performance, the foundation
Under maximum design load it must have an acceptable factor of safety against bearing failure in the sub soils.
Settlements during the life of the structure must not be of a magnitude that will cause structural damage, endanger piping connections or impair the operational efficiency of the facility.
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Selection of foundation type depends on:
The nature and magnitude of dead and live loads
The settlement tolerances
Type of soil
The base area of the structure
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Points to be noted during site preparation:
1. Site preparation should include the removal of the expansive soils
2. Corrosivity tests will be conducted to determine whether the site soils to be non-corrosive or corrosive for buried steel based on the chloride content and pH values.
3. Site grading may include (1) removal of existing deleterious materials (2) fill to bring the site to a final grade.
It expand when
water is added,
and shrink when they
dry out
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4. Confined temporary excavations at the site will be required during construction to remove undocumented fill or loose disturbed soils encountered during construction.
5.Hydrostatic pressures due to groundwater or temporary water loads will be considered.
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Main parts of a structure
• Foundation or substructure: The lowest artificially prepared parts of the structures which are in direct contact with the ground and which transmit the loads of the structures to the ground.
• Footing: The lowermost portion of the foundation which is in direct contact with the sub-soil.
• Superstructure: Part of the structure which is above ground level and which serves the purpose of its intended use.
• Plinth: The portion of the structure between the surface of the surrounding ground and level of the floor immediately above the ground.
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OBJECTIVE /FUNCTIONS OF FOUNDATIONS 1. Reduction of load intensity: Distribute the total load coming on the structure on a larger area
2. Even distribution of load: Distribute the non -uniform load of the superstructure evenly to the sub-soil.
3. Provision of levelled surface: Prepare a level and hard surface for concreting and masonry work
4. Lateral stability: Give enough lateral stability to the structures against various horizontal forces such as wind, rain, earthquake, etc.
5. Safety against undermining: provide structural safety against undermining or scouring due to animals, flood water etc.
6. Protection against soil movement: prevent or minimize cracks due to movement of moisture in case of weak or poor soil.
7. Support the structures
8. Transmit the super-imposed loads through side friction and end bearing in case of deep foundations
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Scouring of bridge
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ESSENTIAL REQUIREMENTS OF A GOOD FOUNDATION
Location:
Should be so located that it is able to resist any unexpected future influence which may adversely affect its performance.
Stability:
The foundation structure should be stable or safe against any possible failure.
The foundation base should be rigid enough to bring down the differential settlements to a minimum extent specially when the superimposed loads are unevenly distributed.
Settlement:
The foundation structure should not settle or deflect to such an extent so as to impair its usefulness or the stability of building or the adjoining structures
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Bearing capacity of soil It is the maximum load per unit area which the soil or material in
foundation, may be rock or soil, will support without excessive settlement or failure.
The gross pressure intensity at which the soil fails is called ultimate bearing capacity
Dimensions of the foundation should be such that it can safely transmit the load from building to the soil without any failure or significant settlement.
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Safe bearing capacity
Maximum load which the soil can carry without the risk
of shear failure
Safe bearing capacity =
Usually adopted factor of safety is 2 to 3
•
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CLASSIFICATION OF FOUNDATIONS
•Depending on depth, foundation are classified into 2 types
a)Shallow foundation
If depth of foundation is less than or equal to the width
Are relatively near to ground level
b)Deep foundation
If depth of foundation is more than its width
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SHALLOW FOUNDATIONS
i. Spread footing
ii. Combined footing
iii. Strap/Cantilever footing
iv. Continuous footing
v. Inverted arch footing
vi. Grillage foundation
vii.Raft/ Mat footing
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(i) Spread footing:• Spread the super-imposed load of wall or column over a
larger area. •Are built after opening the trenches to required depth. • Economical up to a maximum depth of 3 m. • The base of the structure is enlarged or spread to provide
individual support. • Spread foundations support either a column or wall.
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Spread foundations may be of the following types
oSingle footing for a column
oStepped footing for a column
oSloped footing for a column
oWall footing without step
oStepped footing for wallKTUNOTES.IN
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Stepped wall footing
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ii) Combined footing
A common footing constructed for 2 or more columns is known as combined footing
Provided when isolated footings of individual column overlaps or when external column is situated near boundary
Combined footing may be rectangular or trapezoidal in plan view
Trapezoidal footings are recommended in 2 situations
1. Loads acting on one of the column is very high
2. When one of the column is very close to the boundary
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iii) Cantilever/strap footing
This type of foundation is used when the 2 columns are at a reasonable distance
Used when it is impossible to place a footing directly beneath the column due to limitations of land, filled up land etc
Here columns are connected by a strap or cantilever beam.
The load from the exterior column or column resting on filled up land is partially transferred to the interior column through the strap. The strap joining the two footings need not touch the soil or rest on the ground
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iv) Continuous footing
If a single continuous RCC slab acts as a foundation of 2 or more columns then that footing is known as continuous footing
Used when there are two or more columns in one row and footings of individual columns overlap
It is safe against differential settlement and earth quake
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v) Inverted arch footing
In this type inverted arches are constructed between two walls at the base
Suitable for soil of low bearing capacity and when depth of foundation is to be kept low.
Load is transmitted to the soil through these arches and gets distributed over a wider area.
Suitable for bridges, culverts, reservoirs etc.KTUNOTES.IN
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vi) Grillage foundation
• Used to transfer heavy loads from steel columns/walls to soil having lower bearing capacity or where the depth of foundation is limited to 1 to 1.5m
• Constructed with Rolled Steel Joists
(RSJ) which are placed in two or more tier
• In double tier lower tier must be arranged perpendicular to upper tier
• All these members are embedded in concrete for protecting it from corrosion.
ROLLED STEEL JOISTS
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GRILLAGE FOUNDATION
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vii) Raft or mat foundation
Is combined footing which covers entire area beneath the structure including all columns and walls.
RCC slab of suitable thickness and with necessary reinforcement is provided
Mat foundation can face large settlement without causing any harm to the super structure, because in this case the whole structure is resting on a single foundation
If large soil water pressure, provide holes in foundation
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When to provide mat foundation?• When the allowable soil pressure is low, or the building loads are
heavy, the use of spread footings cover more than one half the area and it may prove more economical to use mat or raft foundation.
• where the soil is sufficiently erratic so that the differential settlement would be difficult to control (mat or raft tends to bridge over the erratic deposits and eliminates the differential settlements)
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• Raft foundation is also used to reduce settlement above highly compressible soils, by making the weight of structure and raft approximately equal to the weight of the soil excavated.
• In this case the loading on the soil remains practically the same after the construction of the building.
• This is known as a floating foundation
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1. Pile foundation
2. Pier foundation/Drilled caisson foundation
3. Well foundation/Caissons
DEEP FOUNDATION
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I. Pile foundationPile may be defined as a long vertical member
made up of timber, steel, concrete or RCC or a combination of any of these used to transfer the load of structure to soil.
The foundation which consists of piles is known as pile foundation
It is a deep foundation used for buildings if heavy loads are to be transferred through soil strata of low bearing capacity
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A pile is either driven into the soil or formed in situ by excavating a hole and then filling it with concrete.
used when top soil is not capable of taking the load of the structure even at 3–4 m depth.
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Pile foundations are adopted in the following situations:The load coming from the structure is very heavy and
distribution of load on soil is unevenThe subsoil water level is likely to rise or fall appreciably. The pumping of subsoil water is too costly for keeping the
foundation trench in dry condition. The construction of raft or grillage foundations is likely to
be very expensive or practically impossible. The firm bearing stratum exists at a greater depth
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TYPES OF PILES
I. Classification based on their function1) End bearing piles2) Friction piles3) Combined end bearing and friction pile4) Compaction piles5) Batter piles6) Sheet piles
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1) End bearing piles:
Their bottoms rest on a hard bed.
The ultimate bearing capacity of the pile depends entirely on the underlying material
They are act as columns or piers.
The soft ground through which the piles pass also gives some lateral support and this increases the load carrying capacity of the bearing piles. KTUNOTES.IN
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2) Friction piles (floating piles):
These piles are used where the depth of hard stratum is very high
Frictional resistance developed at the sides of the piles = the load coming on the piles.
In cohesion less soils, such as sands of medium to low density, friction piles are often used to increase the density and thus the shear strength
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The total frictional resistance can be increase in the following ways: By increasing the diameter of the pileBy driving the pile to a greater depthBy making the surface of the pile rough By placing the piles closelyBy grouping the piles
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3)Combined end bearing and friction pile
• This pile transfers the super-imposed load both through side friction as well as end bearing.• Such piles are more common, especially when the end bearing piles pass
through granular soils.
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4) Compaction piles: • When piles are driven in granular soil with the aim of increasing the
bearing capacity of soil by compact the loose soil, the piles are termed as compaction piles
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5) Batter piles
• Are inclined piles
• To resist horizontal forces
• Their stability is more against overturning
• The design of batter piles should be made by considering the fact that they will resist most of the horizontal loading.
• Batter piles used together with vertical piles assumed that part of the vertical load will be transferred to the batter piles alsoKTUNOTES.IN
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6) Sheet piles:
•Consists of vertical cut-off walls constructed by driving strips of steel/ precast concrete/aluminium/ wood into the soil
•Rarely used to furnish vertical support but are used to function as retaining wall.
•Sheet piles are used for : Retain soil To enclose the area required for some foundation and protect it
from the action of running water or leakageKTUNOTES.IN
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II. Classification based on materials and compositionA. Cement Concrete Piles i) Precast pile ii)Cast-in-situ pile
B. Timber pile
C. Steel pile i) H pile ii)Box pile iii) Tube pile
D. Sand piles
E. Composite pile KTUNOTES.IN
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(i) Pre-cast Piles:
• Pre-cast Piles may be defined as a reinforced concrete pile which is moulded in • circular• square• rectangular• octagonal
• The piles are cast and cured in a casting yard and then transported to the site for driving.
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•Diameter :35 cm to 65 cm ;Length : 5 m to 30 m
• Reinforcement - to resist the stresses produced on account of its handling, driving and the loading which the pile is finally expected to receive.
• The horizontal bars may be provided in the form of stirrups wound around the verticals
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(ii) Cast-in-situ Piles: •Casted in the place where they are to be used finally
• In ground at the time of concreting.
• Method is :i. Drive a hole ii. Steel reinforcement is kept in the
prepared holeiii. Filling the hole with concrete and steel.
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B. Timber piles
• Prepared from the trunks of trees
• Use of timber as pile has been recorded since the beginning of the science of civil engineering.
• The wood should be free from knots, flaws, shakes and other defects.
• Circular or square shaped
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•Diameter 300 mm to 500 mm
•Side of a square timber pile 300 mm to 500 mm.
•The length of a timber pile should not exceed 20 times its top width. Otherwise it may fail by buckling.
•At the bottom, a cast-iron shoe is provided
•At the top, a steel plate is fixed.
•The timber piles should be properly treated so as to make them durable
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C. Steel piles
Steel piles are used in the following three different forms:
a. H-Piles
b. Box Piles
c. Tube Piles KTUNOTES.IN
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a. H-Piles:•These piles are usually of wide flange section. •Piles extend above ground level and also act as columns. •Have small cross-sectional area can be easily driven in soils •Used as long piles with high bearing capacityKTUNOTES.IN
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b. Box Piles: • Rectangular or octagonal in form filled with concrete.
• Used when it is not possible to drive H-piles into hard strata.
c. Tube Piles: • In this type, tubes or pipes of steel are driven into the ground. • Concrete is filled inside the tube piles. • Because of their circular cross-section, these pipes are easy to handle and
easy to drive in
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D. Sand Piles:
•These piles are formed by making holes in the ground
•A bore of required diameter, usually 300 mm, is formed by an auger
•The hole is then filled with sand and it is well-rammed until the sand in the hole does not escape.
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•The sand to be used should be moist at the time of placing. •The top of sand pile is filled with concrete to prevent the sand to come upwards due to lateral pressure. •The sand piles are spaced at 2 m to 3 m, usually under the columns of tall structure. •The dimensions of sand pile are determined from the load coming upon it and its length is kept about 12 times its diameter.
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E. Composite Piles:• Piles of two different materials are driven one over the other, so
as to enable them to act together to perform the function of a single pile. • In such a combination advantage is taken of the good qualities of
both the materials. • Composite piles prove economical as they permit the utilization
of the great corrosion resistance property of one material with the cheapness or strength of the other.
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II. Pier foundation
•Consists of cylindrical column of large diameter to support and transfer load to firm strata below•Difference b/w pile and pier in method of construction
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Pile foundation Pier foundation
Load transfer through friction and end bearing
Load transfer through end bearing only
Used upto to any depth Used for shallow depth only
Used in almost all soils Preferred where the top strata consists of decomposed rock, overlying a strata of sound rock.
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III. Well foundation•Box like structures - circular or rectangular•Generally provided below the land or water level to desired depth•Use for foundations of bridge pier, pump house subjected to heavy load and other structures •Have larger dimension than pier foundation•Hollow inside - filled with sand - plugged at bottom•Load through perimeter wall called steining.•Not used for buildings
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MASONRY
•Masonry is defined as the construction of building units bonded together with mortar•Masonry units may be:
Stones
Bricks
Precast concrete blocks•Uses: Construction of foundation , Walls , Columns etc
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• Brick masonry is made of brick units bonded together with mortar• Components: i) Bricks ii) Mortar•Mortar Act as a cementing material and units the individual
brick units together to act as a homogeneous mass
Cement mortar
Mud mortar
Lime mortar
Lime-surkhi mortar
BRICKS MASONRY
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Bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks in a Kiln
Traditional bricks
Custom in the locality is the governing factor for deciding the size of a brick. Such bricks which are not standardized are known as the traditional bricks
Modular bricks
Made as per BIS recommendations
Size 190 mm x 90 mm x 90 mm
With mortar thickness, size of brick becomes 200mm x 100mm x 100mm—nominal size of brick
BRICKS(pg no. 167)
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Advantages of brick masonry
• All the bricks are of uniform shape and size can be laid in any definite pattern• Light weight and small size can be easily handle• Do not need any dressing• Art of brick laying can be under stood very easily• Easily available at all sites• Ornamental works can be done easily
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DEFINITIONS
1.Stretcher• Brick laid with its length parallel to the front or direction of a wall. • The course containing stretchers is called a stretcher course
2.Header• Brick laid with its breadth or width parallel to the front or direction of the wall.
• Course containing headers is called a header course
3.Arrises
• Edges formed by the intersection of plane surfaces of brick
4.Bed
• Lower surface of the brick when laid flat
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5.Bed joint
• Horizontal layer of mortar upon which the bricks are
laid
6.Perpends
• Vertical joints separating bricks in either length or cross directions
• For good bond, perpends in alternate courses should be vertically one above the other
7.Lap
• Horizontal distance between the vertical joints in successive courses• For good bond, lap should not be less than one-fourth of a brick
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8.Closer• Piece of brick with the cut made longitudinally used to close
up the bond at the end of brick courses•Helps in preventing the joints of successive courses to come
in a vertical line•Generally closer is not specially moulded but it is
prepared by the mason with the edge of the trowel
9.Queen closer•Obtained by cutting the brick longitudinally
in 2 equal parts
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10.King closer
• Obtained by cutting a triangular portion of the brick such that half a header and half a stretcher are obtained on adjoining cut faces• Used near door and window openings
11.Bevelled closer
• Obtained by cutting a triangular portion of half the width but of full length• Used for splayed brickwork
12.Mitred closer
• Obtained by cutting a triangular portion of the brick through its width and making an angle of 45-60 degree with the length of brick• Used at corners, junctions etc
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13.Bat
• It is portion of brick cut across the width
14.Bullnose
• Brick moulded with a rounded angle
• Used for a rounded quoin
external angle on the face side of wall
15.Cownose
• Brick moulded with a double bullnose on end
16.Frog
• Is a mark of depth about 10-20mm which is placed on the face of a
brick to form a key for holding the mortar
Bullnose
cownose
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BONDS IN BRICK MASONRY
• Method of arranging the bricks in courses• Individual units are tied together and the vertical joints of the successive
courses do not lie in same vertical line• Bond types are distinguished by their elevation• Bond types:
i. Stretcher bond v. English cross bond
ii. Header bond vi. Dutch bond
iii. English bond vii. Brick on edge bond
iv. Flemish bond viii. Raking bond
ix. Garden wall bond
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1. Stretcher bond• All bricks are laid with their lengths in the longitudinal direction of the
wall; Thickness = half brick• Only stretcher is visible in elevation• Use: partition wall, sleeper walls
2. Header bond• All bricks are laid as headers towards the face of the wall.• Suitable for one brick thick walls and also for
construction of curved walls
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3. English bond• Alternate courses of stretchers and headers are laid• A queen closer is placed after the first header in
the header course to stagger the vertical joints
of successive courses.
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4. Flemish bond• Stretchers and headers are laid in the same course• Header in any course is centrally supported over a stretcher below it. • Queen closers are placed next to the quoin header in alternate courses
for staggering vertical joints.
Header at the corner
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Flemish bonds may be further classified as
(a) Double Flemish Bond : Both faces of the wall have Flemish look, i.e. each course consist of alternate header and stretcher.
(b) Single Flemish Bond: Outer faces of walls have Flemish look whereas inner faces have look of English bond.
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Flemish bond or English bond good????• Construction of Flemish bond needs greater skill. It gives
more pleasing appearance. But it is not as strong as English bond.
• If only pointing is to be used for finished wall, Flemish bond may be used to get good aesthetic view. If plastering is going to be used, it is better to use English bond.
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5. English cross bond (St. Andrews cross bond)• Modified form of the English bond • It is used to add beauty in the appearance of the wall. • Alternate courses of headers and stretchers are provided as in English
bond queen closers are placed next to quoin header header is introduced next to quoin stretcher in stretcher course in every alternative stretcher
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6. Dutch bond:• This is a modified form of the English bond and by this bond, the
corner of the wall is strengthened.
• The alternate courses are of headers and stretchers.
• Every quoin stretcher is ¾ brick bat• A header is introduced next to the ¾ brick bat in every stretcher course
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7. Brick on-edge bond ( silverlock's bond )• Stretcher bricks are laid on edge instead of bed. • The bricks are laid as headers and stretchers in
alternate courses in such a way that the headers are
laid on bed and the stretchers are laid on edge continuous cavity formed. • This bond is economical as it consumes less number of bricks and less
quantity of mortar.• It is however not strong and hence it is used for the construction of garden
walls, compound walls, partition walls, etc.
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8. Raking bond
•Used in thick walls
•Bricks are arranged in inclined direction, in the space between the external stretchers of the wall
•Walls is done by headers only weak in the longitudinal direction
•Wall is done by English bond Longitudinal stability increases
•Not provided in successive courses;4-8 course interval provided in the height of the wall• The three types of raking bonds are :
i. Diagonal bond
ii. Herring-bone bond
iii. zig-zag bond
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i.Diagonal bond
• The bricks are laid at 45° angle and extreme corner of
the series remain contact with external line of stretcher
• The triangular pieces of bricks required near the sides are cut to shape.
• This bond is useful for walls having thickness of 2 to 4 bricks.
• Direction is reversed in every alternate courseKTUNOTES.IN
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ii.Herring-bone bond
• The bricks are laid at an angle of 45° from the centre in both the directions. • This bond is useful for walls having thickness of more than
four bricks.• It is also used to give ornamental finish to the face work and
for making ornamental panels in the flooring of bricksKTUNOTES.IN
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iii.Zig-zag bond• Bricks are laid in a zig-zag fashion. • It is commonly used for making ornamental panels in the flooring of
bricks
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9. Garden-wall bond:
• The wall is one brick thick wall and the height does not exceed 2 metres.
• Used for the construction of boundary walls, compound walls, garden walls etc.
• The wall may be constructed either in the English bond or the Flemish bond.
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• In the English garden-wall bond, one header course is provided to three or five stretcher courses.
• The quoin headers are placed in alternate courses and a quoin closer is placed next to the quoin header in a header course to develop the necessary lap
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• In the Flemish garden-wall bond (Scotch bond )each course contains one header after three to five stretchers through out the length• A ¾ brick bat is placed next to quoin header in every alternate course
to develop the necessary lap. • A header is placed centrally over each middle stretcher.
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STONE WORK BRICK WORK
Not easily available and costly Easily available and cheaper
More strong, durable and weather resisting, and less in fire resistance
Less Strength and durability ,fire resistance is more
Create a solid appearance hence, for public buildings and monumental structures is found to be more useful
Does not create that much solid appearance
More watertight and not easily affected by water Less watertight , hence absorb moisture from the atmosphere and may affect the life and appearances
Complicated lifting devices are necessary No complicated lifting devices are necessary to carry
Can be done by skilled masons only Easy to build and unskilled mason can also do the work
Needed to be dressed every time. Hence labour and time requirement is more.
Not needed to be dressed. While buying, they are in standard size. Hence, labour and time requirement is less.
plastering is not mandatory. Plastering is mandatory.
COMPARISON OF STONE WORK AND BRICK WORK
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Some important terms used in stone masonry(pg no.143,208)
Corbel:
•Projecting stone provided to serve as support for roof truss, beam, weather shed, etc.
•The corbels are generally moulded and given ornamental treatment.
•The corbels should extend at least two-third of their length into the wall.
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Cornice:
•Projecting ornamental course moulded near the top of the wall/junction of the wall and ceiling
•It is weathered and throated to dispose off rain water.
• To prevent the overturning of the cornice extra weight at the top in the form of a parapet wall should be provided.
Coping:
•A coping is a covering of stone, concrete, brick which is laid at the top wall so as to protect the wall from rain water.
• This course is generally provided at the top of a compound
wall or a parapet wall and it is suitably weathered and throated
The upper surface of stones is dressed in a sloping way so that the water may flow off easily
A groove is provided on the underside of the sill, cornice and coping so that the rain water can be discharged clear of the wall surface
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COMPOSITE WALL (pg.no.215)
•Masonry is constructed by 2 or more types of building material
Types:
1. Stone composite masonry
2. Brick stone composite masonry
3. Cement concrete masonry
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1. Stone composite masonry
• Combination of ashlar masonry and rubble masonry
Good appearance facing Irregular backing
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2. Brick stone composite masonry
• Bricks and stones are simultaneously used
i. Brick – backed; ashlar- facing
•. Cement mortar used
•. Bricks laid in proper bond
•. Alternate course of ashlar may be header
ii. Brick – backed ; stone slab- facing
•. Marble stones are used commonly
•. Fine dressed stone slabs used in big panels
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iii. Rubble – backed; brick facing
•. Used where rubble stone is available in large
•. Each alternative brick course consists quoin header
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3. Cement concrete masonry
•Use cement concrete blocks with stone facing
i . Solid concrete block with stone facing :•Manufactured from dense aggregate•Used in load bearing walls
ii. Hollow concrete block with stone facing :•Manufactured from light weight aggregate• > 25% of gross area is void area•Used both for load bearing and non load bearing walls
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The measures adopted to prevent such unequal settlement are as follows:
• By using large number of through stones for stone composite masonry.
• By providing metal cramps, dowels, lead plugs, etc. between facing and backing of the wall.
• By constructing the backing or facing portion in rich cement mortar.
• By carrying up the facing and backing portions of the wall simultaneously.
stone set with its longest dimension perpendicular to the face of a wall
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Advantages of composite masonry(1)Cost:
Available materials can be used to achieve optimum economy total cost of the structure is reduced.
(2) Appearance:
The appearance can be improved by suitable selection of materials for construction
(3) Durability:
Materials of better quality and good workmanship in the facing work minimize the effects of atmospheric agents More durable structure
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CAVITY WALL•A cavity wall or a hollow wall consists of
two separate walls (leaves or skins), with a cavity in between them. • 2 leaves of the cavity wall may be of equal
or unequal thickness. • The former arrangement is adopted for non-
load bearing wall • In the latter arrangement, the internal leaf
may be made thicker than the external leaf to meet with the structural requirements
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CONSTRUCTION DETAILS OF CAVITY WALL
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Width
• The width of cavity varies from 50 mm to 100 mm and it stands vertically.
Thickness
• The outer wall is generally of 1/2 brick thickness and the inner wall may be of 1/2 or 1 brick thickness.
Metal ties/wall ties
• The two portions of the wall are connected by means of metal ties or specially prepared bonded bricks.
• The metal ties are generally of wrought iron or mild steel and they are coated with tar or galvanised so as to have protection against rust.
• Where corrosion is heavy, the metal ties of copper or bronze may be adopted.
• The maximum horizontal spacing of wall ties is 900mm and maximum vertical spacing is 450mm
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Construction of Cavity Wall• cavity wall doesn’t require any footings under it, just a strong concrete
base is provided on which cavity wall is constructed centrally.• Two leaves are constructed like normal masonry, but minimum cavity
must be provided in between them.• The cavity may be filled with lean concrete with some slope at top up
to few centimeters above ground level
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• Weep holes are provided for outer leaf at bottom with an interval of 1 m.
• Normal bricks are used for inner leaf and facing bricks are used for outer leaf.
• Different masonry is also used for cavity wall leaves. The leaves are connected by metal ties or wall ties, which are generally made of steel and are rust proof.
• The wall ties are provided in such a way that they do not carry any moisture from outer leaf to inner leaf.
Weep holes
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• For half brick thickness leaves, stretcher bond is provided. And for one brick thickness or more thickness, English bond or Flemish bonds type constructions are provided.
• While laying bricks, care should be taken without filling the cavity with cement mortar.
• To prevent mortar dropping in cavity, wooden battens are provided in the cavity with suitable dimensions.
• These battens are supported on wall ties and whenever the height of next wall tie location is reached, then the battens are removed using wires or ropes and wall ties are provided.
• two leaves should be constructed simultaneously. Spacing should be uniform and it is attained by predetermining the location of wall ties.
• Damp proof course is provided for two leaves separately.
• In case of doors and windows, weep holes are provided above the damp proof course.
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FEATURES OF CAVITY WALL
1) Ventilation
2) Shape and slope of ties
3) Construction at openings
4) Base
5) Construction at the top
6) Dropping of mortar, bats, etc.
7) Design
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(1) Ventilation: • Provide enough ventilation to the hollow space of the cavity wall. • Openings should be provided at top and bottom of the wall so that a
free current of air is established. • The openings are to be fitted with gratings to prevent entry of rats and
other vermins. • Sometimes, the air bricks, are used for this purpose.
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(2) Shape and slope of ties: • The metal ties which are used to connect the outer and inner portions • It should be so shaped and placed that water from outer portion does
not pass along the inner portion. • They should thus be sloped away from the inner portion.
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(3) Construction at openings:
•The cavity is discontinued at the openings such as doors, windows, etc.
•The jambs of openings for doors and windows are constructed solid either in brickwork or with layers of slates or tiles.
•Specially prepared metal frames can be used, if metal windows are to be used.
•An inclined flexible D.P.C. is provided to act as a bridge over the cavity.
•The D.P.C. should extend lengthwise beyond the frame for a distance of about 150mm trim on either side.
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(4) Base:
• The cavity may be started from the top of foundation concrete and the hollow space, upto a level of about 100 mm to 300 mm below the damp-proofing course at plinth level, may be filled with plain cement concrete of proportion 1: 2 : 4. • But, as the cavity below damp-proof course does not serve
any purpose, the brickwork upto a level of 100 mm to 300 mm below the damp-proofing course at plinth level may be constructed solid. • The increased thickness of wall will also be helpful in
supporting the load to be carried by the wall.
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(5) Construction at the top: • It is necessary to take adequate steps at top to prevent the entry
of dampness to the inside portion of the wall. It can be done in two ways.
i. The cavity may be constructed upto the coping of the parapet wall
ii. It may be closed at the bottom of parapet wall by a damp-proofing course. • In case of a pitched roof, the tops of two portions are connected
by solid brickwork to support the roof truss and damp-proofing course is inserted immediately below this solid portion.
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(6) Dropping of mortar, bats, etc.:
• During construction of a cavity wall, necessary care should be taken so that mortar, bats, etc., do not fall in the hollow space. • The presence of such materials in the hollow space seriously affects
the working of a cavity wall.
• Some bricks at the bottom are left out and bats, etc. falling in the cavity are removed from these holes.
• It should also be seen that the vermins or mosquitoes do not find access in the cavity.
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(7) Design: • The outside portion of a cavity wall is not a load bearing wall but it is
treated only as a protecting skin. • The inside portion should have sufficient thickness to carry safely the
loads coming on it.
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NECESSITY TO PROVIDE A CAVITY OR A HOLLOW SPACE IN A WALL
(1) Prevention of dampness:
The penetration of dampness from outside to inside of the building can be reduced to a large extend.
(2) Heat insulation:
The air in the cavity, which is a bad conductor of heat prevent heat transfer and hence the uniform temperature is maintained inside the building.
(3) Sound Insulation:
External noise is not allowed to enter the inside of a building by adopting cavity wall construction.
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(4) Load on foundation:
Solid thickness of wall is less and so the loads on foundation are considerably reduced.
(5) Efflorescence:
The construction of a cavity wall results in the reduction of efflorescence to a great extent.
(6) Economical:
The cost for construction of a cavity wall is about 20% less than the construction cost of a corresponding solid wall.
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PARTITION WALLS(pg no.261)
•A partition wall may be defined as a wall or division made up of bricks, glass or other such material. • The purpose of providing partitions walls are dividing one
room or portion of a room from another, providing privacy from consideration of sight or sound or both. • Partition walls are provided on the ground floor or on upper
floor. • Light weight partitions can also be constructed on the floor
slabs directly.
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• The partition walls are designed to take up their own weight only and therefore they should be cheap, light in weight, thin and easy in construction.
• They are generally carried either for the full
height or just above the eye-level at 2 to 2.5 metres
above the floor level.
• Generally the partition walls are non-load bearing
• They can be of folding, collapsible or fixed type
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CHARACTERISTICS OF GOOD PARTITION WALLS
• It should act as a sound barrier especially when it divides a room into two units.
• It should be strong enough to carry its own dead weight.
• It should be light, thin, cheap, fire-resistant and easy to construct.
• It should possess enough strength to support some wall fixtures, sinks, wash basins.
• It should have the capacity to support suitable decorative surface.
• It should be capable of resisting impact developed due to the use of the building
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TYPES OF PARTITION WALLS
1. Brick Partition
2. Glass Partition
3. Plaster Slab Partition
4. Clay Block Partition
5. Metal Lath Partition
6. Wood-Wool Slab Partition
7. Concrete Partition
8. Asbestos Cement Sheet Partition
9. Timber Partitions
10. Strawboard Partitions
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1. Brick Partition:
• The half-brick partitions are very common and they may be plain, reinforced and brick nogging
• The plain brick partitions of half-brick thickness cannot take heavy load and their height is restricted to about 2 metres
• The reinforced brick partitions of half-brick thickness are more durable and possess more strength
Brick work build up within the wooden member
Reinforced brick partition
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2. Glass Partition:
• Glass partition may be in the form of glass sheets or glass bricks.
a) Glass sheet
•) Glass sheets are fixed within wooden frame work
•) Wooden frame work consists of number of horizontal (nogging) and vertical posts(stud), suitably spaced to divide the area into panels
•) Light weight , sound proof, damp proof etc
b) Glass block/glass brick
•) Translucent units of glass are of different shapes and sizes and provide 10cm thickness normally
•) Usually laid in cement – lime mortar using fine sand
•) Up to 15 cm block height, strip reinforcement is provided in every 3-4 course
•) Another type of glass brick are in the form of glass brick with joggles
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3. Plaster Slab Partition:
• A number of plaster boards are available in the market under different trade names.
• They are generally made of burnt gypsum or plaster of paris and in order to reduce their weight some fibrous material such as saw dust, wood wool, asbestos etc. is mixed.
• The plaster boards are 1 to 2m long, and 30 cm high and the thickness of the boards varies from 50 mm to 100 mm.
• The thicker slabs are cast hollow so as to make them more heat and sound insulating and to reduce their weight
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4. Clay Block Partition:
• Prepared from clay or terra-cotta, and they are either be solid or hollow.
• For light partitions, hollow clay blocks are commonly used.
• They are good insulators for heat and sound and also fire resistant
• The hollow clay blocks are usually 30 cm long, 20 cm high and 5 to 15 cm wide.
• The blocks are provided with grooves on top, bottom and sides.
• Grooves provide rigid joints, and serves as key to plaster. The blocks are laid in cement mortar.
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5. Metal Lath Partition:
• Placing 2 cm or 2.5 cm channels vertically (studs) and fixing metal lath to it on one side.
• Plaster is then applied to both the sides.
• The channels are spaced 15 to 30 cm apart.
• Metal lath is tied to channels by galvanized iron wire.
• The channels are fixed to the floor and roof by driving holes.
• The thickness of such partition may vary between 5 and 75 cm.
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6. Wood-Wool Slab Partition:
• These slabs are prepared from a mixture of Portland cement and wood wool.
• A small quantity of gypsum is sometimes added.
• The partitions of these slabs have sufficient heat and sound insulating properties.
• The slabs are available in the market under different trade names and are extremely light weight
Wood wool
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7. Concrete Partition:• Plain or reinforced partition walls constructed in concrete, plain or reinforced,
may be cast-in-situ or built from panels or blocks precast well in advance of the commencement of work. • Generally for cast-in-situ walls, 10 cm thick and below, the reinforcement
consisting of mild steel bars is placed in the centre of the wall thickness. • The wall is cast monolithically with the intermediate columns so as to be rigid
and stable, both along its length and height• Pre cast slab units quit thin(25-40mm) and concrete mix usually adopted in the
work is M 15 (1 : 2 : 4).
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8. Asbestos Sheet or G.I. Sheet Partitions: • Made of asbestos cement sheet and fixed into the timber framework. • These sheets are placed in position and joined by cement mortar. • The asbestos cement sheets are made of 1 cm thick comprising of two
sheets with an inner corrugated sheet of 5 mm in thickness. • They are light in weight, impervious, durable, water tight and fire-proof.
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9. Timer Partitions: • This type of partition consists of a wooden framework either
supported on the floor or by side walls. • The framework consists of a rigid arrangement of timber members
which may be plastered or covered with boarding etc. from both the sides. • Such partitions are not fire resistant and the timber for the partition is
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10. Strawboard partitions
• The slabs are prepared from compressed straw and covered with thick paper or hardboard are used.
• These slabs possess good heat and sound insulation and the partitions of these slabs can be easily constructed.
• The partitions of strawboard are useful at places where frequent removal of partitions is anticipated.KTUNOTES.IN
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SCAFFOLDING(pg no.416)
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•When the height of wall or column or other structural member of a building exceeds about 1.5m, temporary structures are needed to support the platform over which the workmen can sit and carry on the constructions.
• These temporary structures, constructed very close to the wall, is in the form of timber or steel framework, commonly called scaffolding.
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COMPONENT PARTS OF A SCAFFOLDING
• Standards: These are the vertical members of the framework and they are either supported on the ground or drums or embedded into the ground.
• Ledgers: These are the horizontal members parallel to the wall.
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• Putlogs: These are the transverse pieces which are placed on the ledgers and which are supported on the wall at one end. They are at right angles to the wall.• Transoms: These are putlogs, but their
both ends are supported on the ledgers.• Braces: These are the diagonal or cross
pieces fixed on the standards.
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•Guard rail: This is a rail provided like a ledger at the working level.
• Toe board: This is a board placed parallel to the ledgers and supported between the putlogs. It is provided to work as a protective measure on the working platform.
•Raker: This is an inclined support. KTUNOTES.IN
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TYPES OF SCAFFOLDING
1. Single scaffolding or bricklayer's scaffolding
2. Double scaffolding or mason's scaffolding
3. Cantilever or needle scaffolding
4. Suspended scaffolding
5. Trestle scaffolding
6. Steel scaffolding
7. Patented scaffolding
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1. Single scaffolding or bricklayer's scaffolding
•.This is the most common type of scaffolding and is widely used in the construction of brickwork•.It consists of a single row of standards placed at a distance of about
1.20 m from the wall•.The distance between the successive standards is about 2 m to 2.50 m•.The ledgers are then fixed to the standards at a vertical distance of
about 1.20 m to 1.80 m
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• Putlogs are placed with one end at wall and other end at ledgers• Commonly used for bricklaying•Also known as putlog scaffolding
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2. Double scaffolding or mason's scaffolding: •Used in stone masonry as it is difficult to provide holes in
stone masonry
• The framework is similar to the single scaffolding except that two rows of standards are provided.
• The distance between the face of the wall and the first row of standard is about 200 mm to 300 mm and next row is placed 1m from the first one.
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•Putlogs are then supported on both the frames.
• The rakers may be provided to make the scaffolding more strong.
•This type is also sometimes known as independent scaffolding.
•This scaffolding is stronger than the single scaffoldingKTUNOTES.IN
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3. Cantilever or needle scaffolding:
• This type of scaffolding is useful under the following circumstances: The proper hard ground is not available for the standards to
rest. It is required to keep the ground near wall, free for traffic
etcThe construction work is to be carried out for upper parts of
a multi-storeyed building
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• Can be of putlog scaffolding(single type) or independent scaffolding(double type)
• In single type, standards are supported on series of needles taken out through opening or through holes in wall
• In double type, needles or projecting beams are strutted inside the floors through the openings.
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4. Suspended scaffolding:
•Very light type of scaffolding
•Used only for the maintenance works such as painting, pointing, whitewashing, distempering, etc.
• The working platform is suspended from the roofs by means of ropes, wires or chains and arrangements are made such that the platform can be raised or lowered.
•Does not create any obstruction on the ground
• It is the most effective as it always provides the optimum level for working.
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5. Trestle scaffolding: •Working platform is supported on movable contrivances such
as ladders, tripods, etc., mounted on wheels.
•Useful for minor repairs or painting work inside the rooms
•Maximum height can be adopted is about 5 m from the supporting surface.
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6. Steel scaffolding: • In place of timber, the steel tubes
can be effectively used for the scaffolding work. •Wooden members are replaced by
steel tubes and rope lashings are replaced by steel couplets or fittings.• The diameter of the tubes is about
40 mm to 50 mm and the thickness is about 5 mm.
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The advantages of steel scaffolding are:
• The scaffolding can be used upto any height
• It is strong and more durable
• It can be easily erected and dismantled
• It possesses high scrap value • It is resistant to fire KTUNOTES.IN
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The disadvantages of steel scaffolding are:
• The initial cost is high
• It requires skilled labour
• It also requires periodical paintingKTUNOTES.IN
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7. Patented scaffolding: •Now a days, the various patented scaffoldings made
of steel, with special types of couplings and frames, are available. •Usually the working platform is supported on a
bracket which can be adjusted to any suitable height.•Are equipped with special couplings, frames etc.
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