Building has two component: –
- Foundation or Sub-structure
- Lower part of structure which transmits the load to the soil.
- The soil which is located immediately below the base of foundation = Sub-soil.
- The lower most part of the foundation which is in direct contact with the sub-soil = Footing.
- Function of foundation is to transmit loads to the soil on which building rests, in such a way that the settlement are within permissible limits & soil does not fail.
- Super Structure
Part of the structure which is above the ground level.
BEARING CAPACITY OF THE SOIL
Also known as Bearing Power or Value of the soil.
Ability of the sub-soil to support the load of the structure without yielding or displacement is called Bearing Capacity of soil.
Maximum load per unit area which soil can resist safely is called Bearing Capacity of soil.
Bearing Capacity of Hard Rock is Maximum.
Ultimate Bearing Capacity of soil
Minimum load which will cause failure of foundation is called U.B.C of the soil.
Safe Bearing Capacity of soil
Ultimate bearing capacity divided by factor of safety is called S.B.C of soil.
The maximum pressure which the soil can carry safety without any risk of shear failure is called S.B.C of soil.
Maximum Safe bearing capacity of soil is more than Allowable bearing capacity of soil.
Allowable Bearing Capacity of soil
Net loading intensity at which neither the soil fails in shear nor there is excessive settlement is called A.B.C of soil.
- TYPES OF FOUNDATION
1. Shallow Foundation
2. Deep Foundation
Foundation in which its depth is equal to or less than its width.
Those which spread the super imposed load of the structure over large area.
Spread Footing Types:
Single footing for Column
Stepped footing for Column
Sloped footing for Column
First three types of footing are made of Concrete.
When heavy structural loads from column are required to be transferred to a soil of low
bearing capacity, the most economical foundation is Grillage Foundation.
Depth of such foundation on clay is 0.9 m to 1.6 m.
Distance between the flanges of beam in steel in grillage foundation should not be less than twice the width of flange.
Constructed for two or more columns.
Shape of footing so proportioned that centre of gravity of supporting area is in the line with the centre of gravity of two column loads.
Shape of footing is rectangular or trapezoidal.
Two or more footing connected by beam called Strap.
Used where the distance between columns is so great.
Raft or Mat Foundation
Foundation consists of thick R.C. slab covering the entire area of the bottom of the structure is called Raft or Mat foundation.
Suitable when chance of Differential Settlement.
Maximum differential settlement of raft in sandy soil = 65 mm.
Maximum differential settlement of raft in clayey soil = 100 mm.
Foundation in which its depth is equal to or greater than width.
Long vertical load transferring member composed of either timber & concrete or steel & concrete.
Used when soil is compressive, water-logged and made-up type.
Most suitable for bridges.
Neoprine is suitable for used in bearing of bridges.
Hollow vertical shafts are sunk up to the hard bed and hollow portions are then filled up with inert material such as sand or lean concrete.
Suitable for heavy structure such as fly over in sandy soil.
Caisson or Well Foundation
Box of timber, metal, R.C or masonry which open both at top and bottom.
Used for building and bridge foundation.
Common type of deep foundation in India.
CLASSIFICATION OF PILE
Based on the function
Piles which do not support the load by themselves, but act as medium to transit the load from the foundation to resisting sub-stratum is called Bearing piles.
Piles which are driven in the type of soil whose strength does not increase with depth or where the rate of increase in strength with depth is very slow is called Friction piles.
Coefficient of friction between 0.30 to 0.35.
Piles which are driven in granular soil with the aim of increasing the bearing capacity of the soil are known as Compaction piles.
Piles which are driven at an inclination to resist large horizontal or inclined force are known as Batter piles.
Piles used to protect concrete deck or other water front structures from the abrasion or impact are called Fender piles.
Piles are commonly used as bulk heads or as impervious cut off to reduce seepage and uplift under hydraulic structures.
Not meant for carrying any vertical load.
Made of steel, wood or concrete.
Based on Materials and Composition
(A) Concrete Piles
Two types of concrete pile:- 1. Precast concrete pile & 2. Cast-in-situ pile.
Precast concrete pile
Quality of concrete used in this pile= M 150 to M 200.
Piles are usually reinforced concrete or pre-stressed concrete pile.
These piles require space for casting and storage, more time to set and cure before installations and heavy equipment before handling and driving.
Used for maximum design load about 800 KN.
Length of pile= 4.5 m to 30 m.
When pile is driven by means of water jets, water is forced through the jet of pipe under pressure of 0.7 to 1.75 N/mm2.
The thickness of concrete covering the main bars not less than 40 mm & 55 mm for pile used in sea water.
Casted in position inside the ground.
Not subjected to handling & driving stresses.
Used for maximum design load of 750 kN.
Two types of cast-in-situ pile:
1. Driven Piles:- (a) Cased cast-in-situ pile.
(b) Uncased cast-in-situ pile.
2. Bored Piles:- (a) Pressure pile.
(b) Pedestal pile. (c) Under-reamed pile.
TYPES OF CASED CAST-IN-SITU PILE
1. Raymond Pile
Used as friction pile.
Length of pile = 6 to 12 m.
Diameter at Top = 40 to 60 cm.
Diameter at Base = 20 to 30 cm.
Thickness of outer shell depends upon pile diameter and site conditions.
2. Mac-Arthur Pile
Pile of uniform diameter using corrugated steel shell which remains in place.
Casing & core driven together at required depth.
3. Sewage Pile
Used in soils where driving is very hard.
TYPES OF UNCASED CAST-IN-SITU PILE
1) Simplex Pile
Driven through soft or hard soils.
Steel tube filled with cast iron shoe is driven into ground & concrete is poured and tube is slowly withdrawn without concrete being tamped leaving behind the C.I. shoe.
2) Franki Pile
Enlarged base and a corrugated stem.
Useful in granular soil.
Diameter of pile = 500 to 600 mm.
Diameter of enlarged base = 900 mm.
Load carrying capacity = 600 to 900 kN.
3) Vibro Pile
Suited where ground is soft and offer little resistance to the flow of concrete.
4) Pedestal Pile
Used where thin bearing stratum is reached with reasonable depth.
(B) Steel Pile
Three types of Steel pile: 1. H pile, 2. Box pile & 3. Circular tube piles.
Used in hard soil by driving to desired depth by hammering.
Used in retaining walls.
H piles withstand large lateral forces, require less space for shipping.
Rectangular, square or pile consists of Octagonal in shape.
Deep beams which offer adequate frictional resistance.
Driven where H piles driven is not possible.
Circular tube piles
Made of seamless or welded pipes.
Driven either open ended or close ended depends upon soil condition at site.
(C) Timber Piles
Generally square or circular in cross-section.
Size of square and circular pile = 300 to 500 mm.
Length of pile should not be more than 20 times its top width.
To protect head of the pile from brooming, iron ring is fixed at top.
Piles can take maximum load of 200 kN.
Best spacing of timber piles from C to C = 900 mm.
Moisture content in well seasoned timber = 10 to 12%.
Timber can be more fire resistant by Sir Abel’s process.
Seasoning of timber is required to remove Sap from the timber.
(D) Composite piles
Those piles which made of two portions of two difference materials driven one above other.
(E) Screw piles
Made of hollow cast iron or steel shaft.
External diameter = 150 to 300 mm, which may terminate into helix at the base.
More efficient in soft clay or loose sand.
This pile is screwed into soil manually using capstan bars or by motive power.
(F) Disc piles
Diameter of disc = 0.6 m to 1.2 m.
More useful in sand or sandy silt.
Used in marine structure.
A temporary structure constructed in river, lack etc. for excluding water from given site to enable the building operation to be performed on dry surface is called Coffer Dam.
Different types of Coffer Dam
1. Cantilever Sheet Pile Coffer Dam: – Suitable for small height.
2. Braced Coffer Dam: – Economical for small to moderate height.
3. Embankment Protected Coffer Dam: – No height limitation.
4. Double Wall Coffer Dam: – Suitable for moderate height.
5. Cellular Coffer Dam: – Suitable for moderate to large height.
A water tight structure constructed in connection with excavation for foundation of bridges, piers etc is known as Caisson.
1) Box Caisson
Open at top and closed at bottom.
Made of Timber, R.C or Steel.
Used where bearing stratum is available at shallow depth & loads are not heavy.
2) Open Caisson
Box of timber, metal R.C or masonry which is open at both top and at the bottom.
Used for building and bridge foundation.
Also called Well foundation.
3) Pneumatic Caisson
Closed at top and open at bottom.
Compressed air is used to remove water from the working chamber at the bottom.
Useful where it is not possible to adapt open caisson.
Adopted when depth of water is more than 12 m.
Maximum depth of water up to which this caisson is used is limited from the consideration of health of the worker.
DESIGN OF SHALLOW FOUNDATION
Width of Foundation
Width of foundation for walls = Total load per m lengthAllowable B.C of the soil
Width of foundation for piers = Total load on pierAllowable B.C of the soil
The wall and piers are given footing such that the width at the base becomes equal to twice the width of wall at the plinth level.
Depth of Foundation
According to Rankine’s formula, Minimum depth of footing d = pw 1−sin∅1+sin∅ 2
Minimum depth of foundation for the load bearing wall of building is restricted to 900 mm.
Depth of excavation for foundation checked with Boning Rod.
In order to prevent entry of damp or moisture in the building, Damp Proof Course are provided at various levels of entry of damp into building.
Commonly used material in D.P.C are Hot bitumen, mastic asphalt, Bituminous asphaltic felts, metal sheets, combination of sheets and felts, stones, bricks, mortar, cement concrete and plastic sheets.
D.P.C may be Horizontal or Vertical.
At junction and corners of walls, Horizontal D.P.C should be laid continuous.
Maximum size of aggregate used in D.P.C = 10 mm.
Flexible material used for D.P.C = Bitumen Sheeting
Mastic Asphalt forms an excellent impervious layer for Damp proofing.
D.P.C should not kept exposed on the wall surface.
For D.P.C at plinth level, commonly adopted material = Cement Concrete.
Also called Hollow wall.
Consists of two separate wall called Leaves or skins with cavity or gap in between.
Used because 1. Effective method of damp prevention. 2. Constructed for giving better heat insulation to the building. 3. Also prevent the dampness to enter and act as sound insulation.
In foundation, the cavity should start near the ground level or 150 mm below the D.P.C level.
Temporary structure usually of timber having platforms raised for the workers as the building increase in height.
Consists of Standards, Ledgers, Putlogs, Transoms, Guard rail, Tee board, Braces, Bridle.
Vertical member of scaffolding.
Used to distribute the load of scaffolding to the soil.
Parallel to the wall.
Perpendicular to the standard.
Provided at 1.20 m to 1.80 m vertical distance on standards.
Perpendicular to the wall & ledgers.
Both the ends of putlog are rested on ledgers that it called transoms.
Provide diagonally to standards.
Give strength to scaffolding.
Wooden board rest on putlog for workers to stand on.
For safety purpose, Ledgers are provided around platform at 50 cm height.
TYPE OF SCAFFLODING
Single Brick Layer Scaffolding
Also known as Putlog scaffolding.
Widely used in the construction of brick work.
Double or Mason’s Scaffolding
Stronger than single scaffolding.
Used in the construction of stone work.
Also known as Independent scaffolding.
Also known as Needle scaffolding.
Used when ground is weak to support standard.
Used when construction for upper part of multi storied building is carried out. Used when ordinary scaffolding obstruct traffic on road.
Light weight scaffolding used for repair works such as painting.
Working platform suspended from roof by means of wire ropes.
Used for painting and repair work inside room, up to height of 15 m.
Easily erected and dismantled.
Strong and more durable.
Initial cost is high.
Working platform is supported on bracket which can be adjusted to any suitable height.
Construction of temporary structure required to support unsafe structure.
Racking or Inclined Shores
Inclined members called rakers are used to give temporary lateral support to unsafe wall.
Flying or Horizontal Shores
Horizontal temporary support is provided two adjacent, parallel party walls of two building where intermediate building is to be pulled down and rebuilt.
Dead or Vertical Shores
Vertical support provided to wall, roof etc when lower part of wall has to be removed for the purpose of providing an opening in wall.
Arrangement of supports provided underneath the existing structures without disturbing its stability.
Required when, Basement is provided to an existing build.
Underpinning carried out by pit or pile method.
Used to indicate the art of building the structure in stones type is called Stone Masonry.
Horizontal layer of stones.
Stone unit laid with its length perpendicular to the face of wall.
Stone unit laid with its length parallel to the face of wall.
Exterior angle or corner of wall.
Inner portion of wall between facing and backing.
Portion of brick cut in such a way that its one long face remains uncut.
Portion of brick cut in such a way that the width of its one end is half that of full brick.
Portion of brick cut in such a way that half as wide as full brick.
Portion of brick cut in such a way that half width is maintained at one end and full width is obtained at other end.
Portion of brick cut across the width.
Indentation at the top face of the brick.
Purpose is to form keyed joint between brick and mortar.
Horizontal member of stone, concrete or wood to give support for the vertical member of window.
Continuous horizontal course of masonry projecting from the face of the wall for shedding rain water off the table.
Vertical sides of finished opening for the door, window.
Exposed vertical surface left on the sides of opening after door or window frame fitted in position.
A projecting stone which is usually provided to serve as support for roof, joist, truss etc.
Horizontal moulded projection provided near the top of building.
Covering of stone, concrete, brick of terracotta placed on the exposed top of an external wall.
Course of stone masonry provided immediately above the cornice.
Course of stone provided immediately below the cornice.
Triangular shaped portion of masonry at the end of sloped roof.
Horizontal course of stone blocks provided to strengthen a wall made of irregular course of small stones.
Chips or small pieces of stones obtained as result of reducing big blocks of stone into regular stone block.
Sloping or stepped masonry projection from tall wall intended to strengthen the wall against the thrust of roof or arch.
Process of placing a stone in its position in masonry construction.
CLASSIFICATION OF STONE MASONRY
A. Rubble Masonry
Stone of irregular sizes are used.
Minimum thickness of wall in Stone masonry = 350 mm.
Coursed Rubble Masonry
Stone used are of widely different sizes from 50 mm to 20 mm.
Used in construction of public building, residential building etc.
Uncoursed Rubble Masonry
Stone are not dressed.
Used for construction compound walls, godowns, garages etc.
Random Rubble Masonry
Stone of irregular size and shape are used.
Stones arranged so to have good appearance.
Used in residential building, compound wall, godowns etc.
Dry Rubble Masonry
No mortar used in joints.
Used in compound wall, retaining wall, pitching on bridge approaches.
B. Ashlar Masonry
Square or Rectangular stone are used.
Height of stone varies from 250 mm to 300 mm.
Length of stones should not exceed 3 times the height & depth into the wall should be atleast equal to half the height.
Arrangement of laying bricks and bonding them with mortar property to form unified mass is called Brick Masonry.
Longest face of brick as seen in elevation of wall.
Shortest face of brick as seen in elevation of wall.
Edges formed by the intersection of plane surfaces of brick.
Lower surface of the brick when laid flat.
Imaginary vertical line which include the vertical joint separating two adjoining bricks.
Horizontal distance between the vertical joints of successive courses.
Brick moulded with a rounded angle.
BONDS IN BRICK WORK
All the bricks are laid as stretchers on the face of the walls.
Suitable for half brick wall only.
All the bricks are laid as headers on the face of walls.
Suitable for one brick wall only.
Bond consists of alternate course of headers and stretchers.
Most used bond for all wall thickness.
Considered as strongest bond.
Heading course should never start with queen closer.
Each course consists of alternate headers and stretchers.
Every alternate course start with header at the corner.
Two types:- 1. Double Flemish Bond & 2. Single Flemish Bond.
More pleasing appearance than English bond.
English bond is stronger than Flemish bond for walls thicker than 1½.
Bond consists of heading and stretching course so arranged that one heading course comes after several stretching courses.
Load distribution is not uniform in this bond.
Bonding bricks are laid at any angle other than zero or 90°.
Bricks are laid diagonally.
Bricks are laid at angle of 45° from the centre in both directions.
Commonly used for Brick Paving.
Bricks are laid in Zig-zag manner.
Modified form of English Bond.
Corners of wall are strengthened.
RETAINING WALL A wall of increasing thickness, built to resist pressure of earth filling.
Required in construction of hill road masonry dam and wing walls.
Section of wall should be so proportioned that it will not overturn by lateral pressure.
Weep holes is provided to drain off the water from the filling behind.
Total horizontal pressure p = wh2 1−sin∅1+sin∅ act at h3 from base.
Built to protect natural sloping ground from cutting action of weathering.
A thin internal wall constructed to divide space within the building into rooms or areas.
Partition wall may be folding, collapsible and fixed.
Thickness of partition wall = 10 cm.
Also known as Load bearing wall.
Plain brick partition
Half brick thick constructed by laying bricks as stretchers in cement mortar.
Reinforced brick partition
Stronger than plain.
Used when wall carry other super imposed load.
Precast concrete partition
Precast concrete slab may be quite thin like 25 mm to 40 mm.
Concrete mixer adopted is M 150.
Brick nogging partition
Brick work built within a frame work of wooden member.
The vertical wooden members are called Studs.
Nogging is intermediate horizontal wooden member.
Nogging pieces are housed in the studs at vertical distance of about 600 to 900 mm.
TYPE OF FLOORING
Especially suited for godowns, stores, warehouses etc.
Bricks are laid at any good looking pattern.
Cement concrete flooring
Used for residential, commercial and industrial buildings.
When hard wearing surface is required, this flooring is used.
Decorative and good wearing property.
Used in residential building, hospitals, offices, schools and other public building.
Flooring made with broken tiles of china glazed.
Used in residential, offices, schools, hospitals etc.
Used where extra ordinary cleanliness is required like hospital, bathroom, kitchens etc.
Recommended for swimming pools, because it is non slippers.
Not recommended for bathrooms, kitchens etc.
Widely used for all residential and non-residential buildings.
Sequence of steps provided to afford the means of ascent and descent between the floors is called Stair.
Opening or space occupied by stair is called stairway.
Size of step commonly for Residential building = 250 mm x 160 mm & for Hospital = 300 mm x 100 mm(T x R).
Width of stair depends upon Its location in building & Type of building.
Number of steps in ordinary flight not more than 12 & not less than 3.
Stair Width for Residential building = 900 mm & for Public building = 1.5 m to 1.8 m.
Width of Landing > Width of Stair.
Pitch of stair never exceeds 40°.
Sum of Tread + Rise = 40-45 cm.
In designing stair, Going in cm + 2 x Rise in cm = 60 Approx. & Going in cm x Rise in cm = 400.
Distance between tread and soffit of the flight immediately above it should not be less than 2 m.
Thickness of tread in wooden stair = 38 mm.
Half turn stair change their directions through 180°.
Horizontal upper part of a step on which foot is placed in ascending or descending a stairway.
Vertical portion of step providing a support to the tread.
Straight step having a parallel width of tread.
Unbroken series of steps between two landing.
Horizontal platform at the top or bottom of flight between the floors.
Angular steps used for changing direction of stairs.
Vertical distance between two successive tread faces.
Horizontal distance between two successive riser faces.
Projecting part of the tread beyond the faces of riser.
Moulding provided under the nosing to beautify the elevation of step & provide strength to nosing.
Under surface of stair.
Pitch or Slope
Angle which the line of nosing of the stair makes with horizontal.
String or Stringers
Sloping member which support the steps in stair.
Vertical member of wood or metal to support the hand rails.
Combined frame work of handrail and balusters.
Horizontal or inclined support provided at convenient height.
Vertical member placed at the ends of flights to connecting the ends of string and hand rails.
Structure constructed to span across an opening.
Inner curve of an arch.
Inner surface of an arch.
Outer curve of an arch.
Wedge shaped units of masonry forming an arch.
Highest point of the extrados.
Inclined or splayed surface on the abutment on which the arch rests.
Part of the wall on which the arch rests.
Wedge shaped unit at the crown of arch.
Voussoir next to skew back.
Imaginary line joining the lowest parts of Springer.
Bottom portion of an arch between the skew back and crown.
Clear horizontal distance between the supports.
Intermediate support of an arch.
Clear vertical distance between the springing line and highest point on the intrados.
Depth or Height
Perpendicular distance between the intrados and extrados.
Thickness or Breadth of soffit
Horizontal distance measured perpendicular to the front and back faces of an arch.
CLASSIFICATION OF ARCH
According to Shape
(a) Flat Arch
Skewback is made to rest in an inclined position so as to make an angle of 60° with springing line, thus forming an equilateral triangle with intrados as the base.
Intrados given a camber of about 10 mm to 15 mm per metre.
Extrados kept horizontal and flat.
(b) Segmental Arch
Centre of arch lies below the springing line.
(c) Semi-Circular Arch
Centre of arch lies on the springing line and shape of arch is semicircle.
(d) Semi-Elliptical Arch
Shape of semi-ellipse and have either three or five centre.
(e) Pointed or Gothic Arch
Arch consists of two curves which meet at the apex of the triangle.
Triangle formed may be equilateral or isosceles.
The latter type is known as Lancet Arch.
According to Workmanship
(a) Rough Arch
Bricks used are rectangular in shape.
Joints at the extrados are wider than those at intrados.
(b) Axed Arch
Made from bricks which are cut to wedge shape by means of an axe.
Joints of arch are of uniform thickness varying from 3 mm to 6 mm.
(c) Gauged Arch
Made from bricks which are cut to exact size and shape by means of wire saw.
Joints formed in gauged arch are fine, thin (0.75 mm to 1.50 mm) and truly radial.
According to Material
(a) Stone Arch
Made in rubble masonry.
Rubble masonry is weak and used for inferior type of work.
Span limited to about one metre or so.
Used as over wooden lintels, Relieving arches.
(b) Brick Arch
Made from ordinary bricks.
(c) Concrete Arch
Made from pre-cast cement concrete block or monolithic concrete.
DOORS & WINDOWS
Open able barrier secured in opening left in a wall for the purpose of providing access to the users of the structure.
Opening made in a wall for the purpose of providing day light, vision and ventilation.
Frame: – Consists of group of horizontal and vertical members which form a support for door or window.
Head: – Top most horizontal part of frame.
Sill: – Bottom most horizontal part of window frame.
Horn: – Horizontal projection of head or sill beyond the face of frame.
Style: – Vertical outside member of the shutter of door or window.
Louvers: – Timber or glass pieces fixed in inclined position in a frame of ventilator.
Jamb: – Vertical member which support the frame of the door and window.
Reveal: – External jamb of door or window opening at night angles to the wall face.
Rebate: – Depression or recess made inside the door frame to receive the door shutter.
Mullion: – Vertical member of frame which is employed to sub-divide or window or door opening vertically.
Transom: – Horizontal member of frame which is employed too sub-divide window opening horizontally.
TYPES OF WINDOW
Provided at corner of room.
It has two faces in two perpendicular direction so that light and air enters from two direction.
Improve elevation of building.
Vertical window provided in the gable end of roof.
Vertical window provided on the sloping roof with the object of providing light and air to the enclosed space below the roof.
Window projects outward from the walls of room to provide an increased area of opening for admitting greater light and ventilation.
Window is usually provided near the main roof of room and open above the adjoining verandah.
Common type of window provided in building.
Shutters of this type of window open like door.
Sash or Glazed Window
Type of casement window in which the panels are fully glazed.
Upper most part of building which provides a structural covering to give protection to the building against rain, sun, wind etc.
Important terms: –
Horizontal distance between the internal faces of walls or supports.
Vertical distance between the wall plate and top of the ridge.
Inclination of the sides of roof to the horizontal plane.
Apex line of sloping roof.
Ridge formed by intersection of two sloped surface having an exterior angle less than 180°.
Ridge formed by intersection of two sloped surfaces having exterior angle less than 180°.
Lower edges of roof which are resting upon or projecting beyond the supporting wall.
Horizontal wooden or steel members used to support the common rafters of sloping roof when span is large.
Triangular upper part of a wall formed at the end of pitched roof.
Edge to gable, running between the eaves and ridge.
Small blocks of wood which are fixed on the rafters or ceiling.
Square or Rectangular block of stone or concrete provided under the end of the beam or truss to spread the load from the roof over a large area of bearing.
Inclined wooden member laid from the ridge to the eaves.
Sloping rafter which forms the hip of sloped roof.
These are shorter in length than common rafter and are laid from hip or valley to the eaves.
These are sloping rafters and are laid diagonally from the ridge to eaves for supporting valley gutters.
Frame work usually of triangle designed to support the roof covering or ceiling over rooms.
Triangular portion between two adjacent arches and the tangent to their crown.
THREE TYPES OF ROOF
Pitched or Sloping Roofs
Have sloping top surface and useful where rainfall is heavy.
Useful at places where rainfall is moderate.
Top surface curved in the form of shells and domes.
Suitable where architectural view needed like theatres, libraries etc.
TYPES OF PITCHED ROOF
Roof consists of only common rafters to each slope without any intermediate support.
Known as verandah, shed, pent and aisle roof.
Rafters slope to one side only.
Suitable to maximum span of 2.4 m.
2. Couple Roof
Formed by couple of common rafters which slope to both the sides.
Suitable for spans up to 3.5 m.
3. Couple close Roof
Similar to couple roof except legs of the common rafters are connected by tie beam.
Economically suitable for span up to 5 m.
4. Collar beam Roof
Similar to upper one except a tie beam is raised and placed at higher level.
Tie beam is than known as Collar beam.
Suitable for span up to 5 m.
Double or Purlin Roofs
Span exceeds about 2.4 m, size for rafters becomes uneconomical.
To reduce size of rafters, intermediate support called purlin is provided.
Span of roof exceeds 5 m, then the framed structures known as trusses are used.
Forms of truss:-
1. King post truss
Central vertical post known as king post forms a support for tie beam.
Inclined member known as struts prevent the bending from principal rafter.
Suitable for span from 5 to 8 m.
2. Queen post truss
Having 2 vertical posts known as queen posts.
Suitable for spans varying from 8 to 12 m.
3. Mansard truss
Combo of king post and queen post.
Two-storey truss with upper portion king post & lower portion queen post.
4. Truncated truss
Similar to mansard except that top is formed falt with gentle slope to one side.
Used when it is required to provide a room in the roof.
5. Bel-fast roof truss
Known as latticed roof or bow string truss.
Truss is in the form of bow.
Used for long span about 30 m.
6. Steel truss
More economical for larger span greater than 12 m.
Resist effectively both tension and compression.
Substance which reduce surface tension.
Addition of this, increase the strength and density of concrete and decrease w/c ratio.
Flush Pointing: – Type of pointing in which the mortar is first pressed into the raked joints and then finished off flush with the EDGE of bricks or stones.
Tuck Pointing: – Type of pointing in which the mortar is first pressed into the raked joints and then finished off flush with the FACE of bricks or stones.
Process of filling up all nail holes, cracks with putty is called Stopping.
Putty is made up of powered chalk and raw linseed oil.
For lowering of water table by about 10 m, Well point method is used.
Vacuum method of well points is used for draining fine sands and silty sands.
Surkhi is added to lime mortar to import hydraulicity.
P.V.C is thermo plastic material.
Optimum number of revolutions over which concrete is required to be mixed in mixer machine = 20.
Gauged mortar is obtained by adding sand and lime to cement.
Role of super plasticizer in cement paste is to disperse the particles, remove air bubbles and to retard setting.
In machine foundation, the material used for preventing transmission of vibration = Felt.
Expansion joint provided in wall lengths more than 40 m.
Thickness of expansion joint more than 20 mm.
Blistering: – Development of one or more local swellings on the finished plastered surface is called Blistering.