Floors are the horizontal
units of a building structure which divide the building into different levels.
The purpose of separation or division is to create more accommodation within a
restricted space one above the other for different purposes, viz., to provide
support for the occupants, to allow space for furniture and equipment, etc.
Strictly, the division of vertical occupation is called floors and the exposed
top surfaces of floors are termed as floorings. But in usage, both the terms
reflect the same meaning.
Thus the floor of a
building immediately above the ground is known as the ground floor. The
construction below the ground level or the building has a basement, the floor is
termed as the basement floor. The top portion of a ceiling forms the first floor or
an upper floor. Any subsequent top portions of ceilings form upper floors.
The major problems of
ground and basement floors are dampness removal and protection from heat.
Generally, there will be no problem regarding strength and stability for ground
and basement floors as they get full support from the ground. The major
problems of upper floors are strength and stability.
FUNCTIONS OF A FLOOR
A floor consists of a sub-floor and a floor covering.
Sub-floor may be a base-course or a sub-grade. This is
required to impart strength and stability to support a floor covering and all
other super-imposed loads including live loads. Floor covering or paving or
simply as flooring is the one constructed over the sub-floor and is intended to
provide a hard, clean, smooth, impervious, durable and impressive surface to
the floor.
The functional requirements of floors, in general, are as
follows:
(i) Strength and stability
(ii) Damp prevention
(iii) Heat insulation
(iv) Sound insulation
(v) Fire resistance
(vi) Durability
SELECTION OF FLOORS
In order to select a suitable type of floor construction
in a building, certain factors have to be considered. Although certain points
may be common for ground, upper and basement floors, some distinct different
points are to be observed in certain cases.
Ground Floors
For ground floors, the selection of the type of the
wearing surface is important and the other factors which need consideration are
given below:
(i) Initial
cost
(ii) Appearance
(iii) Durability
(iv) Cleanliness
(v) Thermal
insulation
(vi) Dampness
(vii) Indentation
(viii) Noiselessness
(ix) Maintenance
(x) Fire
resistance
Upper Floors
Selection of a suitable type of construction for upper
floors of a building depend on the following main factors:
(i) Initial
cost
(ii) Floor loads
(iii) Type of
construction
(iv) Plan of the
building
(v) Function of
the building
(vi) Fire
resistance
(vii) Sound
insulation
(viii) Type of
ceiling
(ix) Wearing
surface
(x) Weight and
position of floors
Basement Floor
It is not a routine type of floor provided in every
building. It is provided for a particular type of buildings like apartments,
hotels and restaurants, cinema halls, etc. The selection of basement floors depends
on the following factors:
(i) Initial cost
(ii) Availability of ventilation
(iii) Drainage of water from the floor
(iv) Adequate safety against fire
(v) Groundwater level
TYPES OF GROUND FLOORS
As the ground floor directly rests on the ground, there
is no need for a sub-floor. In order to drain the water outside completely,
adequate drainage arrangements have to be made beneath the floor.
In normal practice, the space above the ground, up to a
height of about 25–30 cm below the plinth level, called the basement, is filled
with some inert materials like sand, gravel, crushed stone, cinder, etc. Over
this course, a damp-proof course if needed is laid. Otherwise, the floor
covering is laid directly on the uniform bed.
The materials used for ground floor construction are:
bricks, stones, concrete, hollow concrete blocks or wooden blocks.
The materials generally used for floor coverings are
bricks, concrete, terrazzo tiles, marbles, stones, mosaic, wood, etc.
Stone Floors
Usual sizes of stones of 30 cm × 30 cm, 45 cm × 45 cm or
60 cm × 60 cm with a thickness of 2–4 cm are used. Generally, square stone slabs
of the above sizes are used but the slabs can be rectangular or oblong in
shape with square edges. Stone slabs are laid on concrete bedding.
Before laying the slab a base is prepared after
excavating to the required depth and the earthen base is levelled, rammed and
watered. A layer of lime concrete of thickness 10–45 cm is spread over which
the concrete bed or sub-grade is laid.
After setting the stone floor with a slope of 1 in 40,
the mortar joints are raked out to a depth of 2 cm and flush pointed with
cement mortar of 1 : 3.
Following aspects are kept in mind while laying stone
slabs, Fig. below:
(i) To begin with two stone slabs from diagonally
opposite corners are laid. A string is stretched touching these corner slabs so
as to fix top level of the floor.
(ii) Intermediate slabs are placed from both sides
taking care that the tops of stone slabs are touching the string which ensures
the provision of proper grade.
(iii) All stone slabs should be of uniform thickness,
strength and well-drained on edges for residential and public buildings.
(iv) Width of joints between the slabs should not exceed
0.5 cm.
(v) Rough surface stone, may be used for godown, sheds,
stores, etc.
Stone
flooring
Brick Floors
This type of flooring is used in case of warehouses,
stores and godowns. This is a cheap construction and used in areas when stones
are not available but good quality bricks are available.
This flooring may be laid flat or on edge. They may be
arranged in a herringbone pattern or at right angles to the walls. Brick on edge
is preferred compared to bricks laid flat as the brick on edge is less liable
for crack under pressure because of the higher depths. The bricks, in both the
cases, are laid on ordinary mortar and pointed with cement or set in hydraulic
mortar.
The construction of brick flooring is done as explained
below, Fig. below:
(i) An excavation of about 40 cm depth below the
intended level of the floor is made.
(ii) The earth surface is levelled, watered and well rimmed
until it is dry and hard.
(iii) Over the earth, above a sub-grade of 25 cm depth
consisting of rubble or brickbats is laid.
(iv) Over this, a 10 –15 cm thick layer of lime concrete
or lean cement concrete (1:3:6) is laid.
(v) Upon this prepared sub-grade, bricks are laid in the
desired shape.
Brick
flooring
Concrete Floors
Concrete floorings are mostly used in all residential,
commercial and public buildings. The flooring is constructed adopting either
monolithic or non-monolithic construction.
In the monolithic construction, after laying the base
course layer, immediately a concrete topping is provided. In this type of
construction, only a small thickness is needed for the wearing surface as the
bond between the base course and the wearing surface is good.
But this type of flooring has got several disadvantages
as explained below:
(i) The wearing the surface is susceptible for damage due to subsequent floor use.
(ii) As the base
course if undergoing only a small settlement immediately, there is a possibility
for hair cracks.
(iii) Repairing
the damaged top surface is difficult.
(iv) The
progress is slow as the base course has to settle.
Non-monolithic construction is sound as the wearing
surface is laid only after adequate drying of the base course. The floor finish
generally used is an ordinary concrete finish of 1:11:3 (Fig. 23.3). Under
controlled conditions, a mix of 1:2:4 ratio with carefully selected aggregates may be used.
For non-monolithic construction, the surface of the base
concrete is brushed with a stiff broom and cleaned thoroughly. The surface is
wetted and excess water removed. The floor is laid in rectangular panels not greater
than 2 × 2 m. Generally, alternate bays are concreted so as to avoid initial
shrinkages. When the concrete layer is even, the surface is rapidly compacted
by remaining or beating and screeded to a uniform level. Then trowelling is
done to give a level smooth surface. Adequate curing is done for 7 days by
spreading a layer of wet sand or special membrane may be used.
Concrete
Floors
Granolithic Floors
It is a concrete flooring
with a different type of floor finish called granolithic. Granolithic finish is
concrete made of specially selected aggregate. The thickness of the layer varies
from
1.25 to 4 cm. When it is
greater than 4 cm this may be laid monolithically or after the base concrete
has hardened.
This flooring is made with
very hard and tough quality aggregate in rich concrete of 1:1: 2. Generally, hard fine-grained granite, basalt, limestone and quartzite stones are suit-
able for coarse aggregate. In order to get a better granolithic finish, the aggregate may be crushed and used. The fine aggregates are the natural or
crushed sands with a suitable gathering. Non-slippery surfaces can be obtained
by adding suitable abrasives. In case of non-monolithic construction, the base
course may be prepared as done in concrete flooring. Granolithic flooring has
all the advantages of concrete flooring.
Terrazo
Floors
Terrazo is a special type of concrete flooring
containing marble chips as aggregates. Any designed colour and designs can be
obtained by using marble chips of different shades and colour cement.
Terrazo mix of 1: 2 or 1: 3 (1 cement to 2–3 marble
chips) is used depending on the size of marble chips. Terrazo finish is of 10
mm thick. The terrazzo finish is laid over the concrete base course (as
explained in concrete flooring) by two methods.
(i) The cement concrete base is covered uniformly by a 6
mm thick sand cushion and a tar paper is placed on this. Over this paper, a
layer of rich mortar (1 : 3) about 30 mm is placed uniformly.
(ii) A thin coat of cement is spread over the wet
concrete base. This layer is cleaned and a layer of cement mortar 12 mm thick
is spread evenly over it. When the mortar bed has hardened the terrazzo mix (1
cement : 3 marble chips) of 6 and 12 mm is laid after adding water and making the workable mix.
After curing for several days, the surface is polished
by means of a grinding machine fitted with a carborundum grinding stone disc.
During grinding the surface is kept wet and small holes or pores are filled
with a suitable cement paste matching the surface configuration. The surface is
then washed with a weak solution of soft soap in warm water. Such a finished
surface gives a pleasing appearance and a clean environment.
This type of floor is used in public buildings like
banks, hotels, offices, etc., because of its decorative appearance and
excellent wear-resisting properties.
Mosaic Floors
For the construction of this type of flooring, a hard
concrete base is laid first. When the base is wet, a 2 cm thick layer of cement
mortar (1: 2) is evenly laid. Over this layer, small pieces of broken tiles are
arranged in different patterns. After this, the inner space between tiles is
filled with coloured pieces of marble in the desired fashion.
Following this cement or coloured cement is sprinkled at
the top to get a complete floor without pores. Then the surface is rolled by a light stone roller till an even surface is obtained. After 24 hours of drying
the surface is rubbed with a pumice stone of 20 cm × 20 cm × 7 cm fitted to a
long wooden handle. This polished surface is allowed to dry for 2 weeks before
put into use.
Tiled Floors
In this type of flooring tiles either of clay or cement
concrete, manufactured in different shapes, are used. A 15 cm thick layer or
lime or cement concrete is laid over the levelled ground. In order to receive
the tiles at 25 mm thick layer of lime mortar (1: 3) or cement mortar (1:1) is
laid. A cement slurry is spread over the hardened mortar. Tiles are laid flat
on this bed and a cement paste is applied on the sides. Joints are rubbed with
carborundum stone after allowing 2–3 days for setting. The entire surface is polished
with a pumice stone (Fig below).
Tiled
Floors
Tiled floorings are used in residential buildings,
hotels, offices and other public buildings. These floors can be constructed in a very short time with a pleasing appearance and good durability.
Asphalt Floors
Asphalt floorings are of two types, viz., (i) using
asphalt tiles and (ii) using mastic asphalt. Asphalt tiles are made from
asphalt, asbestos fibres and other materials and pressed under pressure.
Asphalt mastic is a mixture of fine aggregates and natural or artificial
asphalt.
Asphalt tiles are used to cover wooden or concrete
floors. These tiles are resilient, non-absorbent, moisture-proof and cheap.
They are used in schools, offices and hospitals, etc.
Asphaltic mastic can be mixed hot and laid in continuous
sheets or pressed into blocks which can be used for flooring. As an alternative, it may be mixed with oil and asbestos and applied cold. An ordinary concrete or
wood base may be used for laying this mixture.
Marble Floors
High quality marble slabs
in the required sizes and colours are available in the market. The construction
procedure is the same as that of mosaic flooring except for that marble slabs or pieces
are used instead of mosaic tiles or pieces. This type of flooring is preferred
when sanitation and cleanliness are required as in the case of hospitals,
temples, theatres and another superior type of works. Nowadays some quality
marbles are used for residential buildings also.
Timber Floors
Timber flooring is not generally preferred for ground
floors. If it is used as a ground floor, the prevention of dampness is most
important. Timber floorings can be provided in any one of the following
methods. Strip flooring consists of narrow and thin strips of wood joined to
each other by tongue and groove joint. Planked flooring is one type in which
wider planks are used and they are also of tongued and grooved type. Wooden
block flooring consists of small square or rectangular blocks with tongue and
groove joints, Fig. below
Timber flooring should have a concrete base or should
rest on joints spanning across dwarf walls which are constructed at suitable
intervals. For fixing the timber floors on concrete slabs, longitudinal nailing
strips are provided. Planked flooring should be laid with spaces of metals
spaced 1 mm apart temporarily for providing expansion joints. Strip flooring is
used in thickness of 2–2.5 cm and width of 6–10 cm.
TYPES OF UPPER FLOORS
Upper floors should be strong to take heavy loads,
should have sound insulation and fire resistance and also have a good wearing
resistance. The upper floors are generally classified based on the materials of
construction arrangement of beams and girders or materials used.
Commonly used floors are explained below.
Timber Floors
Timber floors are used only
in areas where more timber is available at a reasonable cost. Further, they are
used for residential buildings where the span is less and load on the floor is
less.
The floors may be of a single
joist, double joist or triple joist. Joists of floors should be strong enough
and not deflect too much causing any cracking of plaster of the ceiling. Further
long joists need strutting to avoid buckling. The planking consists of wooden
boards of 4 cm thickness and 10–15 cm wide. The figure below shows the details of a single joist timber floor, and the details of the joist’s joint are shown
separately.
Details
of single-joint timber floor
Jack Arch Brick Floors
Bricks and plain concrete can not be used directly as a flooring system without proper strengthening. Either reinforcement can be
provided or provision can be made so as to develop arch action.
Rolled steel joists (RSJ) are used to build arches so as
to form jack arch floorings. The arches have spares varying from 1.25 to 2 m
and the rise is 1/12th to 1/16th of the span. In order to accomplish the end
thrusts the rods of 2–2.5 cm are run at 2–2.75m apart as shown in Fig below.
The rods are encased in the wall along with an RSJ. The spandulus are filled
with concrete.
Brick jack arches are constructed by bringing up the
arches by laying the bricks on edges starting from the ends where the bottom of
an RSJ is concreted. Lime or cement mortar is used. After laying the brick from
ends, the key brick is introduced to set the arch action. Next layer is laid by
pushing the centring ahead. This operation is continued till the work is
completed.
Brick
jack arch floor
RCC Slab Floors
All modern buildings are invariably constructed with
reinforced cement concrete. For small spans a simple RCC slab floor is
generally suitable. For rooms, with the ratio of length of the room to its
width is greater than 1.5, slabs are designed to span along the shorter width.
That is, the main reinforcements are placed to the shorter width. The thickness
of the slab depends on the type of concrete used, the span, floor loads, etc.
These slabs are considered along with a frame then it is made monolithically
with the supporting frames (Fig. below).
RCC
slab floor
If the spans of rooms are
approximately equal then the slab is designed as a two-way slab (i.e., main
reinforcements are placed parallel to both the spans). At corners suitable
reinforcement is provided at top and bottom to take the stresses due to partial
fixity.
Reinforced concrete slabs
are laid adopting the routine mixing, laying, finishing and curing. The slab
provides a very smooth surface at the bottom and a pleasing appearance. It also
accommodates all lighting arrangements. The RCC slabs are restricted up to 4 m
span beyond which beam and slab construction has to be adopted.
The following is the construction procedure:
(i) A centring of steel or timber is erected to support
its own weight and the superimposed load.
(ii) The reinforcement is placed on the centring before
coating a thin layer (2–5 cm) of cement concrete.
(iii) The required mix of cement concrete is then
prepared and poured around the reinforcement up to the required thickness of
the slab.
(iv) The concrete is well consolidated by ramming or
using a vibrator.
(v) The concrete is cured for a minimum period of 2
weeks to attain its full strength.
(vi) After the concrete has sufficiently hardened, the
formwork is recovered.
(vii) The upper and lower surfaces of the slab are plastered
and required finish is given.
RCC Beam and Slab Floors
For larger spans and heavy loading conditions, RCC beam
and slab construction is generally resorted to. This type of construction is
commonly used for most of important buildings (Fig. below).
RCC T-Beam Slab Floors
In this type of floor,
beams and slabs are designed as rectangular sections and the slabs are
supported on beams. It is a monolithic construction both the beams and slabs
are cast together. The beam used in monolithic construction is called a T-beam
(i.e., a part of the slab acts as a flange of the T-beam).
The main reinforcement of
the slab runs parallel to the short span. However, some reinforcement is
provided on the other, as in RCC slab floor, as distributors. In the case of equal
spans, two-way slabs may be constructed with reinforcement provided on both
directions. Sometimes the projecting beams are covered by providing a false
ceiling underneath it (Fig. below).
RCC
T-beam slab floor
The construction procedure is same as that of RCC slab
floor, except for the type of centring or formwork required for the floor.
Flat Slab Floors
This type of floor is called a beamless slab floor.
This flat-slab floor is directly supported on columns without any intermediate
beams. This type of floor is preferred where heavy loads are anticipated and
where there is headroom restriction. The columns supporting the floor are
invariably circular in cross-section and the tops of the column are flared or
tapered, which is called as capital. Sometimes a certain portion of the slab,
symmetrical with the column, is thickened which is called drop panel (Fig. below).
Flat
slab floor
The flat slab floors have several advantages which are
given below:
(i) As there is no projection of beam, there is no need
for an additional ceiling.
(ii) More clean headroom is available.
(iii) Better ventilation and lighting is available.
(iv) Even for heavier loads only thin slab thickness is
needed.
(v) The construction is comparatively easier.
The flat slab floors are preferred under the following
conditions:
(i) When large equal number of panels are required.
(ii) Where clear large spans are required.
(iii) Where there is a limitation in headroom.
(iv) The ratio of length to breadth of panels is to be
more than 4 : 3.
(v) The difference between the length and breadth of any
two adjacent panels should not be more than 10% of the greater of the two.
The following two types of systems of reinforcement are
in use: (i) two-way system and
(ii) four-way system.
In the two-way system of reinforcement, the
reinforcement is provided between the columns and perpendicular to the columns.
The area left is considered as supported on four sides.
In the four-way system of reinforcement, the
reinforcement is placed in four directions. That is two rows of main steel from
column to column and other two rows placed diagonally across the panel from
column to column.
Resilient Floors
Floors made from materials such as PVC, linoleum,
rubber, etc., are called resilient floors. Resilient floors are soundproof and
dust free and are used in libraries, offices, computer rooms, showrooms, etc.
The three important resilient floors are: (i) PVC (Vinyl floors), Linoleum
floor and Rubber floor, which are briefed below.
1. PVC
Floor
The material in PVC floors is the thermoplastic binder
which can be vinyl chloride poly- mer or vinyl chloride copolymer or both. The
floor covering is backed with hessian or other woven fabric. Vinyl asbestos
tiles have 40% of chrysotile asbestos fibre together with powdered mineral
fillers and pigments. The thickness of normal PVC floor coverings are 1.5, 2.0,
2.5, 3.0 and 4.00 mm and the thickness of back floor coverings come in 2.0,
2.5, 3.0, 4.0 and 5.0 mm sizes. In roll form it is
usually available in 1.0, 1.5 and 2.0 m and lengths of 10 m.
2. Linoleum
Floor
Linoleum is a covering materials generally laid over
wooden or concrete floors. Linoleum material is lubricated by mixing oxidised
linseed oil with gum, resin, pigments, wood floor, cork dust and other filler
materials. It is available as rolls of 2 or 4 m width with 2–2.5 m thick and
both in plain and printed forms. Linoleum coverings are fixed to the sub-floor
by means of suitable adhesive in order to have adequate bond and high durability.
In some cases, it is nailed at the edges.
3. Rubber
Floor
It is composed of natural rubber with various filling
compounds. As the cost of rubber is high, their type of floor is expensive.
They are produced in sheets and also in tile form. A sub-floor is essential.
Hollow Block and Rib Floors
In this type of floors, to reduce the total weight of
the floor hollow blocks of clay or concrete are used. In one type, the blocks
are placed at 10 cm apart and in this space, mild steel bars are placed (Fig. below).
Suitable flooring at top and ceiling finish are provided. In order to develop
enough bond with the concrete, the blocks are provided with rough or grooved
surface.
Hollow
block and rib floor
The structural hollow clay floor tiles should be free
from cracks and of uniform colour and texture. Projections of tiles are kept on
one of the external face of such tiles so as to facilitate the application of
plaster. The dimensions of length, 45–90 cm, width, 19–24 cm and height 70–90
mm. The weight per metre length of structural hollow clay tiles does not exceed
140 N.
Thanks! For reading the article...
SOURCE: Basic Civil Engineering
Fourth Edition
MS. Palanichamy
Vice-Chairman
Tamil Nadu State Council for Technical Education Chennai, Tamil Nadu
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