BUILDING DRAWING
BASIC DDEEFFINITIONS
Concrete
Concrete is a mixture of stone particles and some suitable binding material. While in
fresh state, concrete is plastic or fluid-like and may be molded in any shape but, with
time, it hardens and becomes an artificial stone-like material. Because small stone
particles may be “assembled” at site to provide any desired architectural shape and
because of the relatively lesser cost, concrete is used for most of the construction. The
main constituents of concrete are described below:
(A) Binding Material: It is usually a paste of cement in water and is the relatively
costly constituent of the concrete. Lime and some other materials may also be used as
binding material.
(B) Filler Material: It is required to reduce the cost and, at the same time, to provide
sufficient strength. Most commonly filler material is composed of natural round
gravel or crushed stone but other materials like brick-ballast, bloated clay and iron
chips may also be used in certain cases. Filler material may also be termed as
“Aggregate”.
Within a particular aggregate, particles of all the sizes must be present in a suitable
proportion. In other words, the size of aggregate particles should gradually reduce to
minimum so that the smaller particles may fill spaces between the larger particles to
give a dense mass. It is quite clear that the larger particles must be present in greater
proportion. Depending upon the particle size, the aggregates may be classified into
two categories, Coarse and Fine Aggregates. The portion of aggregate having
particle size greater than 3/16-in (5 mm) is called Coarse Aggregate while the portion
having particle size lesser than or equal to 3/16-in is called Fine Aggregate (or
Sandy).
There are two main types of concrete to be used for construction purposes namely
Plain Cement Concrete and Reinforced Cement Concrete.
Plain Cement Concrete: It is abbreviated as P.C.C. and is the simple concrete
without the provision of embedded steel bars (or reinforcement). It is sufficiently
strong in compression (internal force corresponding to push on a body) but is weak
in tension (internal force corresponding to pull on a body). Ratio of the constituent
materials is also written with a particular P.C.C. to be used in the following standard
way:
P.C.C. (Part of Cement : Part of sand : Part of Coarse Aggregate)
For example, P.C.C. (1:2:4) means that cement content by weight is one out of 7
parts, sand is 2 out of 7 parts and coarse aggregate is 4 out of 7 parts.
Fig. 6.1 Aggregate Particles in Concrete
a ) Lean Concrete: If the cement content in concrete is lesser than about 10%, the
concrete is called lean concrete and is commonly used under the floors and
foundations. P.C.C. (1:4:8) and P.C.C. (1:6:12) are the examples of lean concrete.
b ) Normal Concrete: If the cement content is 10 to 15%, the concrete is called
normal concrete, the example being P.C.C.(1:2:4). Normal concrete is used in D.P.C.,
RC.C. and floor finishes.
c) Rich Concrete: In rich concrete, the cement content more than about 15%, as in
P.C.C. (1:1.5:3). It is used for RC.C. (Reinforced Cement Concrete) when smaller
structural members are required in support heavier loads for architectural reasons.
Reinforced Cement Concrete: It is abbreviated as R.C.C. and is defined as the
concrete with the addition of steel bars or reinforcement to resist tension, -as
explained in paragraph 6.1.3. R.C.C. is used for beams, lintels, roof-slabs and concrete
columns, etc.
Mortar
Mortar is a material used for plastering of walls and roofs and to join bricks in
masonry. Mud mortar and lime mortar were initially used but now-a-days cement
sand mortar is most commonly used abbreviated as C/S mortar. Its constituents are
cement and sand and the ratio of these materials is also specified. For example, (1:2) C/s mortar means that cement is one part out of three by weight and sand is two parts
out of three by weight.
Beam
Beam is a structural member used to provide support to upper part of the building
leaving clear space underneath and to transfer the imposed loads to supports at its
ends. Its width is lesser that main dimensions of the building which distinguish it
from a roof-slab. Usually the load acts at right angle to the longitudinal axis of the
member. Main deformation of the beam with the loads is bending. For the beam
shown in Fig. 6.2, bending is associated with elongation of the bottom layers and
shortening of the top layers. Shortening of the material shows that “push” is acting
over it or compression is produced in it. Concrete is sufficiently strong to develop
that much compression. Elongation of the material at the bottom shows that “pull” is
acting over it or tension is produced in it.
Fig. 6.2 A Typical Beam
Fig. 6.3 A Typical Column
Concrete is very weak in tension and if no reinforcement is provided, the beam will
crack at the bottom and will fall down. Another example of material strong in
compression and weak in tension is an ordinary piece of chalk. When it is pressed
from both ends with the fingers, it is very difficult to break it but very little resistance is
offered when it is pulled. Remember that push is a force acting towards the
material whereas pull is a force acting away from the material.
If we provide steel bars at the bottom of the beam under consideration, it becomes safe as steel is sufficiently strong in tension. When concrete is provided to resist
compression and steel to resist tension, the combination may resist any type of load and is called reinforced cement concrete.
Roof Slab
The term roof slab is used for the actual load carrying part of the roof present as the
lowermost layer.
Column
Column is structural member which provides a continuous support for upper part of the
building and carries the load directly up to the foundations. In case of a column,
the load acts along the longitudinal axis of the member. Column may be made up of
bricks, R.C.C. or steel. Its dimensions are lesser than main dimensions of the building
which distinguish it from a wall.
Damp Proof Course (D.P.C.)
Bricks have a porous structure and the pores are interconnected to form capillaries. As
a result, bricks suck dampness from the soil underneath and pump it to upper parts of
the building under the action of capillary force. With dampness mortar and concrete
deteriorate reducing the strength of the structure. With time plaster falls down and
surface treatments like white-washing and painting are damaged leading to unpleasant
appearance. Further these damp conditions are subject to insect and germ growth and
are not good from hygienic point of view. A continuous water proof layer is provided
above the ground level to prevent the moisture to come up which is called damp
proof course or simply DPC. If there is any direct contact between the underneath
soil and brickwork of the super structure, even for a very small part, whole of the
building will be affected. DPC to be provided in walls consists of 1 -in to 3-in thick layer
of P.C.C.(1:2:4) over which two coats of hot bitumen are applied. Sometimes, for load
bearing walls, polythene sheet is also provided. The top of DPC is made in level with the
ground floor top of the building.
Brick
It is a structural unit made up of properly burnt clayey soil having the nominal
dimensions (including the mortar thickness) as shown in Fig. 6.4.
Fig. 6.4 Nominal Dimensions of a Standard Brick
Possible thickness of brick walls is always an integral multiple of 4 1/2-in or 1/2 brick.
Ceiling Height (C.H.)
Bottom of roof slab is called ceiling. Height of the ceiling from the finished floor level is called ceiling height which normally varies from 8 to 12 ft. In other words, the clear height available inside a building is known as ceiling height. Smaller ceiling height is preferable for multistorey buildings and for buildings where artificial air-conditioning is to be used.
Size of air-conditioners or heaters depend upon volume of the building. Bigger
ceiling height is preferable for single storey buildings for better natural air-
conditioning.
Sill Level (S.L.)
It is the level of bottom of main windows generally 3 ft. higher than the floor level. In the past, a sill or slab was provided at the bottom of the windows projecting from the wall from which the term S.L. is derived. Now a days this type of sill is not used but the term S.L. is still there and is also important for some other definitions.
Finished Floor Level (F.F.L.)
Top level of floor in any part of the building is called finished floor level. It may be
different for rooms, verandahs and open areas of a building. Further it is different for
different storeys.
Plinth Level (P.L.)
It is the level of the ground floor top in main part of the building. It is made higher than
the ground level by an amount depending upon the following factors with a minimum
Of 1 ft.
a) The building must be prevented from the rainwater to come inside the
building.
b) Drainage of the used water from the building must be easy.
c) Future trends in the locality like raising of street and road levels is to be kept
in mind.
Ground Level (G.L.)
It is the level of ground in or near the building which may be natural or developed
ground level.
Super-Structure and Sub-Structure
The portion of a structure which is visible or which is above the ground level is called
super-structure. The portion of the structure present underground is called
substructure including the foundations and the basements, if present.
Parapet
Small wall provided on periphery of the roof for safety and privacy purposes is called
parapet wall having a height of 1′-0″ to about 5-0″ from top of the roof slab.
One foot height is only recommended in those buildings where access to the roof is not
available and is only used to retain the filling materials on the roof surface.
Boundary Wall
It is the outermost wall of a building marking the boundary of the area used to
provide safety and privacy inside the building. In undeveloped localities, height of the
boundary wall should be higher than eye-level of a common person but should not be
so high that it blocks the passage of the wind or the sun. This height is about 5 to 7 ft.
from the G.L. In developed areas, according to the bye- laws of the controlling
authorities, the plot is to be kept open on at least three sides and inside a constructed
block is made having its own outer wall with one or two entrances. This constructed
portion is separately safe and provides privacy. So, in such cases, we may reduce the
height of the boundary wall. Sometimes boundary wall is replaced by plantation only.
Riser and Tread
The height covered in one step of a stair is called riser and the width of horizontal
platform required for one step of stair is called tread or going. For public buildings,
riser is usually made equal to 6-in while the tread is kept equal to 12-in.
Flight of Stairs
A series of stair-steps arranged together usually in a single line is called a flight.
Maximum number of steps in a single flight must not exceed 12 to 14. Longer flight
may be dangerous and uneasy for the person using it. Further it requires a longer
space which is generally not available inside a building.
Number of treads in a flight of stair is always one lesser than the number of risers
because the top horizontal surface serves the purpose of one tread. Number of steps
required for a stair may be found out as follows:
Having decided the values for the riser and the tread, number of risers are then
decided using the above relation rounding the answer. The value of riser may then
be adjusted accordingly.
Landing in Stairs
The horizontal platform provided between two flights of a stair is called landing. It
enables us to change the direction of stairs so that these may be accommodated in a
lengthwise smaller space. Further it provides an opportunity for taking rest during the
use of the stair.
Foundation
The portion of a structure under columns and walls which transfers load of the
structure to the soil underneath ‘in a safe way without excessive settlement is called
foundation. The load concentration within walls and columns is generally much
greater because these structural elements resist the load of greater part of the
building transferred to them by the beams and the roof-slabs. The function of a
foundation is to re-distribute this load over a larger area reducing the load per unit
area (load intensity) until it becomes equal to the safe bearing capacity of the soil
underneath (0.5 to 1.5 tons/sq.ft).
Consider the example of an object weighing 100 kg which is required to be lifted and
carried by some distance. If one labourer is employed, it will be very difficult for him to lift the load. Suppose the same load is to be lifted by employing ten labourers, the work will be completed quite easily. What happens in the second case? Although the total load remains the same, the load per person (called load intensity) S reduced from 100 kg in the first case to 10 kg in the second case.
In case of a stepped foundation, brick wall is expanded below ground level in
different steps. The increase in thickness of the wall in one step should be 2 1/4-in (1/4
brick) on either side with a total of 4 1/2-in (1/2 brick). The height of each step may vary in multiples of 3-in depending upon the required depth of foundation from the ground level. At the bottom of each foundation, lean concrete or a compacted mixture of brick-ballast with 257. sand is to be provided; offset of this layer must be lesser than or equal to its depth. (6″ or 9″). If detailed calculations of the loads is not possible, the
number of steps are found out by dividing the wall thickness in inches by 4-1/2″.
Depth of foundation from the G.L. must be sufficient so that the foundation reach to a
hard and durable strata with a minimum of 2-ft to take care of the possible erosion
by the rain and to avoid the top soil layer having organic matter in it (like roots of
trees and grass, etc.)
Lintel
Lintel is a small usually concealed beam provided over openings in walls like doors,
windows and ventilators.
