UNIT 2
Construction
Components of building & its functions
1. FOUNDATION
A foundation is necessary to evenly distribute the entire building load on the soil in such a manner that no damaging settlements take place. Hence, the foundations need to be constructed on good/solid ground.
2. PLINTH
A plinth is normally constructed just above the ground level and immediately after the foundation. It raises the floor above the ground level and herewith prevents surface water from entering the building.
3. DAMP PROOF COURSE (DPC)
- Damp proof course is a layer of water proofing material such as asphalt or waterproof cement. Walls are constructed above the damp proof course.
- Damp proof course prevents surface water from rising into the walls.
- Dampness reduces the strength of the walls and creates unhealthy living conditions. Also it affects the paint and plaster and increasing the cost of maintenance.
- Damp proofing layer is not required where a plinth beam is constructed, because the plinth beam already performs like a DPC.
4. PLINTH BEAM
A plinth beam is constructed depending upon the type of the structure of the building and nature of the soil. It provides additional stability in regard to settlements of the building and earthquake damages.
5. FLOOR
- This is the surface on which we do most of our activities. Floorings is laid over the filling of the plinth and on subsequent floors.
- Flooring can be done with different materials, but care must be given that the ground below the floor is well compacted. Flooring is done to prevent dampness from rising to the top and to have a firm platform that can be kept hygienic and clean.
6. WALLS
- Walls are the vertical elements on which the roof finally rests. They can be made of different materials like bricks, stones, mud, concrete blocks, lateritic blocks etc. If the walls are very long, columns can be provided to carry the roof.
- Walls provide privacy and enclosure. Walls also provide security and protection against natural elements such as wind, rain and sunshine.
- Openings are to be provided in wall for access and ventilation.
7. OPENINGS
- Openings are normally provided in the walls as door, windows and ventilators.
- Doors provide access; windows and ventilators provide light and ventilation.
- Lintels are constructed just above the openings. It is normally a stone slab or a concrete slab.
- Sill is the part of the wall that is just below the window.
- Lintels are constructed to hold up the walls above the openings. In earthquake prone areas a continuous lintel beam is provided all over the walls.
8. STAIRS
- A stair is a sequence of steps and it is provided to afford the means of ascent and descent between the floors and landings.
- The apartment or room of a building in which stair is located is called staircase. The space or opening occupied by the stair is called a stairway.
- There are different kind of stairs are used in buildings, like RCC stair, wooden stair, metal stair, brick stair etc.
9. ROOF
The roof provides protection for the building and the people living in it. The roof rests on the walls and requires proper anchoring so that wind and other mechanical impact cannot destroy it. A roof can have different shapes but it is always either flat or sloping.
Roof is typically made of RCC, stone slab, tiles etc.
10. SURFACES / FINISHES
External finishes are the outer most layer of protection, which protect the structure from weathering. Internal finishes are the layers given on internal faces. They give durability and pleasing appearance to the inside.
Types of foundations
SHALLOW FOUNDATIONS
Shallow foundations are also called spread footings or open footings. The 'open' refers to the fact that the foundations are made by first excavating all the earth till the bottom of the footing, and then constructing the footing. During the early stages of work, the entire footing is visible to the eye, and is therefore called an open foundation. The idea is that each footing takes the concentrated load of the column and spreads it out over a large area, so that the actual weight on the soil does not exceed the safe bearing capacity of the soil.
There are several kinds of shallow footings: individual footings, strip footings and raft foundations.
The various types of spread footings are:
1. Wall footings
2. Isolated footings
3. Combined footings
4. Inverted arch footings
5. Continuous footings
6. Cantilever footing
7. Grillage footing
1. Wall Footings:
These footings can either be simple or stepped. The base course of these footings can be concrete or of entirely one material. They have only one projection beyond the width of the wall on either side. The width of the concrete base should be at least equal to twice the width of the wall. The depth of the concrete bed is at least equal to the projection. Generally the projection provided in the footing is 15cm, on either side and the concrete mix comprises of cement, sand and aggregate in proportion of 1:3:6 or 1:4:8.
2. Isolated or Column Footings:
They are used to support individual columns. In case of heavy loaded columns, steel reinforcements is provided. Generally, 15cm offset is provided on all sides of concrete bed. The footing of concrete columns may be slab, stepped or sloped type.
3. Combined Footings:
A combined footing supports two or more columns in a row. The combined footing can be rectangular in shape if both the columns carry equal loads or can be trapezoidal if both the loads are unequal. Generally they are constructed of reinforced concrete. The location of the center of the gravity of the column loads and centroid of the footing should coincide.
4. Inverted arch footing:
This type of footing is used on soft soils to reduce the depth of the foundation. Loads above an opening are transmitted from supporting walls through inverted arches to the soil. In this type of footings the end columns must be stable enough to resist the outward pressure caused by the arch action.
5. Continuous footings:
In this type of footing a single continuous R.C. Slab is provided 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 settlements in structures.
6. Strap or cantilever footings:
Strap footing consists of two or more individual footings connected by a beam called strap. This type of footing is used where the distance between the columns is so great that the trapezoidal footing becomes quite narrow with bending moments.
7. Grillage footings:
This type of footings is used to transmit heavy loads from steel columns to the soils having low bearing power. This type of arrangements prevents deep excavations and provides necessary area at base to reduce the intensity of the pressure.
DEEP FOUNDATIONS
These foundations carry loads from a structure through weak incompressible soils or fills on to the stronger and less compressible soils or rocks at depth. These foundations are in general used as basements, buoyancy rafts, caissons, cylinders, shaft and piles
- Basements
They are constructed in place in an open excavations. They are hollow substructures designed to provide working space below ground level.
2. Buoyancy Rafts
They are hollow substructures designed to provide a buoyant substructure beneath which reduce net loadings on the soil to the desired low density.
3. Caissons
They are hollow s8ubstructures designed to be constructed on or near the surface and then sunk as single units to their required level.
4. Cylinders
They are single small cell caissons.
5. Shaft Foundations
They are constructed within deep excavation supported by lining constructed in place and subsequently filled with concrete.
6. Pile Foundations
The pile foundation is a construction supported on piles. A pile is an element of construction composed of timber, concrete or steel or a combination of them. The piles may be placed separately or they may be placed in form of a cluster throughout the structure.
Brick Bonds – Bonding is the process of arranging brick with mortar to tie them together. The vertical joints provides in the brick masonry should not continue without proper bonding in between bricks, it is not possible to construct the wall
English Bond
In this type of bond there is an alternative course of the stretcher and header. A queen closer is placed just after the header provides a good overlap. The queen closer is not required in the stretcher course.
The English bond is considered as the strongest bond in brickwork and it is generally used in practice. The main features of English bond are as follows.
- The alternative course in English bond shows headers and stretchers.
- The queen closer is put just next to the queen header to develop the face lap.
- The stretcher course does not require any closer. The queen closer will be compulsory only in header course.
- Stretcher supports each alternate header centrally placed over it.
- The bricks do not break the joints with each other in the same course. The joints are straight.
- It is necessary to place a queen closer after the first header in each header course for breaking the vertical joints in the consecutive course.
- All the headers of a header course are centrally placed over stretchers of the stretcher course.
- If the wall thickness is even multiple of half-brick, a particular course will show either header or stretcher on both the face of the wall.
- For wall having a thickness of two bricks or more, the interior filling is entirely done with the headers.
- Nearly double the number of joints of header course than that in stretcher course.
- As queen closer is liable to get displaced in this position, a header course should never start with a queen closer.
Flemish Bond
In this type of bond, the headers are distributed evenly and hence, it creates a better appearance than the English bond. Following are the features of the Flemish bond:
- In every course, the headers and stretchers are placed alternatively.
- The queen closer is placed next to the queen header in alternative course to develop the face lap.
- Every header is centrally supported over a stretcher below it.
- For breaking vertical joints in successive courses queen closers are inserted in alternate courses next to the queen header.
- In-wall having their thickness equal to the odd numbers of half bricks the bats are necessary to be used.
- It gives a better appearance than the English bond.
Ashlar masonry
Stone is a very strong building material. Cultures around the world have known this for centuries. In some places like Egypt and Peru, people made walls from layers of uniformly shaped stones. This building method is called ashlar masonry.
In ashlar masonry, all the stones are cut and dressed, or worked, so they have the same shape, size and surface texture. When stone is first hewn out of a quarry, which is really nothing more than a giant sold rock wall, it's rough and random. Stoneworkers have to use chisels and other tools to refine the stone to a more finished appearance. The stone blocks used in ashlar masonry are very different than random uncut stones, which are sometimes called rubble. In fact, ashlar masonry is sometimes referred to as 'dressed stone'.
Rubble masonry
In rubble masonry, the blocks of stones that are used are either undressed or comparatively roughly dressed. The masonry has wide joints since stones of irregular size are used.
Steel trusses
Structural steel trusses are the metallic support mechanism, found under the roof to provide support.
Generally, roof trusses are made out of two materials, steel and timber. Trusses made out of steel structures are a common choice among commercial, industrial and large residential complexes.
Roofing for industrial buildings
Thermoplastic Polyolefin
Thermoplastic polyolefin (TPO) is a type of single-ply membrane roofing. It’s made up of a blend of ethylene, propylene, rubber, and fiberglass. TPO has several benefits which make it a favorite choice for many commercial buildings. Some of the benefits include:
- High durability
- Fire resistance
- Wind resistance
- UV resistance
- Resistance to chemical exposure
- Puncture resistance
- 20+ year lifespan
Thermoset Roof Membrane
Thermostat roofing – also known as EPDM roofing – is another kind of single-ply membrane roofing. It’s constructed from a rubber material and has been considered a reliable roofing option for many years. The benefits of EPDM roofing include:
- Fire resistance
- Cold resistance
- UV resistance
- Acid resistance
- Alcohol and solvent resistance
- Easy installation, maintenance, and repair
- EDPM is generally black, but it can still be made to be a “cool roof,” meaning it helps deflect the sun’s rays and keeps your building cooler.
3. Metal Roofs
Metal is often what people think of when they imagine an industrial building’s roof. Its high level of durability makes it an obvious choice for buildings that need to be protected against damage. People often worry about rust and dents when it comes to metal roofs, but metal roofing is not really susceptible to denting, and many are built to resist rust for 40 years. Benefits that draw people to metal roofs include:
- High fire resistance
- Versatility
- High durability
- Wind resistance
- Hold up well under snow
Built-Up Roofing
Built-up roofs (BUR) are named after their application method rather than the materials used to make them. These kinds of roofs have been used for decades, and will likely be found on any old building that you purchase. If you’ve ever stood upon a roof with a gravelly appearance, it’s a BUR.
- Waterproof seal
- UV resistance
- Low maintenance
- High durability
- Low cost
5. Modified Bitumen
Modified bitumen roofs are sometimes regarded as built-up roofs due to their similar application method. They also can only be applied to roofs with little-to-no slope. Unlike a BUR, however, the layers in a modified bitumen roof are solid when they’re applied, not liquid. The layers of a modified bitumen roof are made up of bitumen (naturally-occurring solid petroleum) mixed with another material such as fiberglass. Benefits of modified bitumen include:
- Resistance to severe weather conditions
- High durability
- Resistance to cracking during freezing temperatures
- Low maintenance
- Durable under heavy foot traffic
