CONSTRUCTION CLASSIFIED BASED
UPON MATERIALS ANDTECHNIQUE

CONSTRUCTION CLASSIFIED
BASED UPON MATERIALS AND
TECHNIQUE

CHOICE OF BUILDINGTYPES -WEATHER

CHOICE OF BUILDING
TYPES -WEATHER

CHOICE OF BUILDING
TYPES -
EARTHQUAKE

CHOICE OF BUILDINGTYPES
– URBANISATION &
AFFLUENCE

REQUIREMENTS FOR BUILDINGS
Where should be:
Residential?
Administrative?
Recreational?

REQUIREMENTS FOR SITE SELECTION

REQUIREMENTS FOR
SITE SELECTION

WHAT IS A STRUCTURE?
 A structure is a system of inter connected elements that define either a
hierarchy or a process flow from top to bottom.
 In Civil Engineering: A structure is a system of inter connected elements to
carry loads safely to under ground earth.

WHAT ARE LOADS?
 Corporate: Demands / Deadlines / RevenueTargets; Electric Transmission
System: Energy (kW / units) demand etc
 Civil Engineering: Forces (measured in Newtons and its higher units) that need to
carried by the structure without failing i.e., breaking / sliding / toppling etc

LOADS CLASSIFICATION
 Dead: Ever-
present,
unmovable,
unmodifable etc
 Live: Modifiable
(even if
stationary),
movable
 Wind, Snow &
Earthquake
 Temperature
 Erection Loads
Roofing system and
sheets
Mezzanine floor
Passengers and
seating
Gates

HOWTO DETERMINE
LOADS?
For Deadloads: Unit weights (densities) available in IS:875-
1987 (part I)
For Live Loads: Distributed floor and roof loads available in
IS:875-1987 (part II) for various occupancies and type of
buildings

HOWTO DETERMINE LOADS?
For Wind Loads:
1. Basic Wind Speed Map
available for India in IS:875-
2015 (part 3)
2. Correction factors k1, k2,
k3 for importance of building,
height of building, terrain
(obstructions to wind) and
slope of the land.
3. Conversion (empirical) from
wind speed (m/s) to pressure
(Pa).
4. Pressure coefficients for
surface (roof or wall) shape
and openings through which
wind can flow across

Inertial Force opposes direction of motion!
Earthquake is a movement (shake) imparted to the ground,
and not a force applied directly on building!
Inertia -> mass & sudden acceleration
-> Earthquake force distributes to each floor in
proportion to mass of the storey.
-> the storey ‘drifts’ in relation to the ‘stiffness’
of the storey

For Earthquake Loads:
1. Seismic Zone Map in
IS:1893 -2016 (part I)
2. Z – zone factor, Sa-spectral
acceleration, R – reduction, I –
Importance, Ah - acceleration
slope of the land.
3. Every building has a natural
time period (T), like a
pendulum.The acceleration
will be smaller if ground
below is softer
4.Total Earthquake force (VB,
called base shear) distributes
to each floor in relation to
storey mass and height

HOWTO DETERMINE
LOADS? EXAMPLE
Determine the load to be carried by
each column.The roof on top is
accessible. (Drawing not to scale)
Method:
1. Find volumes of each material
separately – concrete, steel, water
2. Multiply these volumes by unit weights
3. Add the load from accessible part of
roof (roof area minus area occupied by
tank)
4. Since everything is symmetric, divide
total load by number of columns (4). Deeper question: If concrete crushes at a stress of 25
N/mm2, are the size of the footings enough?

SUBSTRUCTURE AND SUPERSTRUCTURE
Reference level is the ‘finished ground level’ (FGL).This
includes the foundations and basement levels, if any
In a bridge, reference level is the bottom of the support
bearings. Everything below the ‘pier cap’ is classified as
substructure.
Pier cap
Pier
Pile cap
Piles
Girders
Deck
Tip: All parts which can be loaded are generally
superstructures.All parts which are not themselves
loaded, and just function to carry loads to ground are
substructures

GENERAL BUILDINGS COMPONENTS
 Structural parts: Essential elements for carrying
loads
 Non-structural parts: Parts for protection,
convenience etc (curtain walls, windows, doors
etc)
 Some parts may be both: e.g., a building can
stand without a staircase (non-structural). But if
user needs a staircase, the staircase needs
supporting beams or slab (structural)
 Everything, whether structural or non-structural
part, adds to the load (due to weight) of entire
structure. But share of non-structural parts in
taking this load is comparatively negligible.

STRUCTURAL COMPONENTS
 Slabs: Generally the first and directly loaded structural component in general buildings e.g.,
floors and roofs

STRUCTURAL
COMPONENTS
Prevent!

STRUCTURAL
COMPONENTS
Provision of proper detailing (steel reinforcement bars)
according to engineering design principles, safeguards
against bending cracks and uplift
Tension cracks from
excessive bending of slab.
This roof would have
fallen if not for the steel
reinforcement just about
holding it.

STRUCTURAL
COMPONENTS
Steel slabs (like chequered plates) are used only for
temporary constructions and footbridges, walkways etc.
Unsuitable for permanent full scale floors and roofs.
Steel is used in
composite
form (with
concrete) for
floor slabs.
‘Profile steel
sheet’ and
concrete layer
on top.
Lighter than
pure concrete
slab. More
ductile – holds
concrete from
collapsing

Beams receive the load which are taken by the slab
Beams are also elements that undergo mainly
bending
Slab edge
reaction
Load on
beam
Load on
slab

End can rotate
End is fixed,cannot rotate
Beams are classified
based on how their
ends are supported
1.Vertical and
horizontal
movement of ends
2. Rotation of the
ends

l
>l
<l
When bent, concave
side becomes shorter
and convex side
becomes longer
i.e., compression and
tension
The middle, where
the length does not
change is called
‘Neutral Axis’ and has
zero stress
‘Euler-Bernoulli’
theoram

Find the load carried by beams
which are loaded from slabs
carrying 8 kN/m2 of load:
a. Slab size 5 m x 5 m
b. Slab size 6 m x 2 m
For design purpose:
Two way slab:
Longer side/shorter side < = 2.0 & Loads transfer at 45 deg to all beams
One way slab:
Longer side/shorter side > 2.0 & Load transfer only to the longer beams

Crack is going vertically up from the mid-length of
the beam.
Common in beams which are quite long (i.e.,
length / depth of beam >6, for concrete beams)
This is failure by bending
Crack is going diagonally up from the end of beam
to mid-length of beam
Common in beams which are not long (i.e., length /
depth of beam <2.5, for concrete beams)
This is failure by ‘shear’

Tension
reinforcement
bars to resist
cracks by
bending failure
Shear
reinforcement
hoops (stirrups)
to resist cracks
by shear failure
Rectangular beam –
common for regular
buildings
T – beam – common as
bridge girders

STRUCTURAL
COMPONENTS
Beams cast-in-situ
Precast beam (cast in factory)
Transported to site and erected
Plinth / Grade beam – beams at the finished ground level.
Demarcates superstructure from the foundation
Secondary beam – beam between two primary beams

Beam-slab system for modern bridges:
- Segmental construction with launching
cranes
- “Post-tensioned” girders

Common ‘rolled steel’ section shapes
I-section and Channel for main beams / rafters
Channel, angle and Z for ‘purlins’, though I –
section also can be used
The connection of steel beams, bolting or welding, is very
important in steel frame construction.
Often steel frames fail because of bad connections only.
Rafter – the inclined I-section beams on top of sheds and
warehouses
Purlin –The beam spanning from rafter to rafter and holds
the roofing sheet

Columns transfer loads from the ends of beams
(beam reactions) to the foundation
- Mainly ‘axial’ loads (compression)
- In conventional concrete building construction
beam ends are rigidly joined to columns by
suitable detailing
- Then some bending also needs to be carried
by column and transferred

Reinforcement bars are called
longitudinal reinforcement and
help taking the compression along
with concrete
The hoops (or helix in circular
columns) are called ‘lateral ties’
and help in keeping the
longitudinal reinforcement
together before concrete is
poured.

In concrete columns,
proper connection with
beam achieved by
extending
reinforcement bars
from beam into the
column for sufficient
length
In steel columns,
connection with beam
by suitable
arrangement of plates,
bolts and welds.

Simultaneous
contribution
of both steel
section and
concrete.
No need for
separate
formwork
Initial cost is
more

STRUCTURAL
COMPONENTS
How a column fails depends on its ‘slenderness’
(a measure of height vs width). For concrete
columns ratios shown above.
Short columns & long columns
A short column fails by crushing (typical
in concrete columns.A long column fails
by buckling (typical in steel columns)
Columns can
buckle in different
shapes depending
on how the ends
are supported

400
mm
500 mm
200
mm
300 mm
18 mm
10 mm
300
mm
600 mm
The concrete can resist upto
25 N/mm2 stress while steel
can resist upto 250 N/mm2.To
be safe reduce, concrete
strength by 1.5 times and
steel strength by 1.15 times.
How much load can it take?
The concrete can resist upto 30
N/mm2 stress while steel can resist
upto 415 N/mm2. There are six 12
mm diameter bars.To be safe
reduce, concrete strength by 1.5
times and steel strength by 1.15
times. [No need to consider the
hoops]. How much load can it take?
Easily calculated by parallel
load taking action of steel
and concrete:
1. Find area of steel and
concrete separately.
2. Divide the mentioned
resistances by the factors
mentioned.
3. Multiply the found steel
areas by the reduced
strength and for concrete
also respectively. [N/mm2 x
mm2 = N]
4. Add the two load
capacities

Foundation is the final terminal for all the
loads that will be taken by the ground.
Soil becomes a deciding factor
Why else do Indian Engineers do ‘Bhumi Pooja’
before starting to excavate??
The cost of excavation and foundations can
be even upto 25-30% of the total construction
cost

STRUCTURAL COMPONENTS - SOIL
For cheaper
foundations:
- Stiffer soil (higher
‘subgrade modulus’)
- Stronger soil (higher
‘safe bearing
capacity’)
- At a close depth to
ground level
- Water table – Bad!
- Rock strata – Good!
(mostly except EQ)

Geotechnical investigations reveal the
strata underneath:
1. Bore holes are drilled and samples
extracted at different depths
2. Samples tested at laboratories
(welcome to visit our lab in Civil
Engineering Department)
3.What depth to place the foundation
4. Any improvement need to be made to
soil before construction?

STRUCTURAL
COMPONENTS - SOIL
The Standard PenetrationTest (SPT) is a
common sight in construction sites. It
gives data used to calculate safe bearing
capacity.
Samplers with bore drilling (left) and
cores (above) are methods to extract soil
samples for testing soil properties in
laboratories

STRUCTURAL
COMPONENTS - SOIL
Some key soil properties of interest:
1.Water content; 2. Angle of friction; 3. Consistency limits*;
4. Permeability; 5. Cohesion; 6. Grading
*Variation of soil state (dry particle – semisolid – flowing)
with change in water content – Liquid, Plastic, Shrinkage

These tests help determine the nature of soil from the extracted sample:
1.What is the basic type of soil?Clay, Silt, Sand? Organic, Inorganic?
2. How well is it graded (i.e., distribution of different soil particle sizes) and what do these sizes mean?

Depth where sufficient SBC soil is present is a primary decision factor in deciding foundation type
- Excavating low depths – required SBC may not be encountered
- Excavating to large depths to get required SBC – expensive
Shallow foundations – those that can be built at depths possible by excavation
Deep foundations – those that are built to large depths, by driving and not by excavation

Wall footing – below walls
Isolated footing – below columns,
good SBC soil
Combined footing –When columns
are close to each other, good SBC
soil
Strap footing – One footing heavily
loaded, so other footing assists
Raft or Mat – Insufficient SBC soil
requiring large area per footing, so
all footings are combined into one
mat or raft

Driven Piles – Directly driven in with a ‘cutting edge’ or by hammering if soil is soft enough

Cast in-situ Piles –
Bored to required
depth (with help of
bentonite slurry for
reducing friction).
Outer casing of pile
(if decided to give) is
inserted in.
Pile reinforcements
are inserted into the
casing.
Concrete is poured
in layers.

If rocky / gravely strata is
reachable (by within 20 m
usually) end bearing piles good
- Load is transferred to stata
from tip of the pile
If rocky / gravely strata not
encountered within possible
depth (like on river beds for
bridge foundations) friction pile
is adopted
- Load is resisted by the
opposing friction between pile
surface area and soil friction

A square column needs to
transfer 2000 kN to a soil of SBC
150 kN/m2. Decide the area of
footing. Are two adjacent
columns possible at 4 m spacing?
[10% adjustment for footing
weight and soil on top of footing]
- Increase the load by 10% for the
adjustment
- Divide load by SBC to get
required footing area
- See if column spacing > footing
width
A circular column of diameter 450
mm needs to transfer 2500 kN to
rocky strata by end bearing pile. If
concrete pile going to be used,
decide the diameter of pile if 20
numbers 20 mm diameter
longitudinal reinforcement used.
- Do just like column problem
- Use concrete strength 35/1.5
N/mm2 and steel strength 500/1.5
N/mm2
- Find area of concrete pile for sum
of steel and concrete loads to equal
2500 kN.

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