• François Coignet was a French industrialist of the
nineteenth century, a pioneer in the development of structural,
prefabricated and reinforced concrete.
• In 1853 Coignet built the first iron reinforced concrete structure, a four story
• Ernest L. Ransome, was an innovator of the reinforced concrete techniques in
the end of the 19thcentury
Uses of RCC
• It is used in the construction of Columns, Beams, Footings, Slabs etc.
• It is used in storage structures like Dams, Water Tanks, Tunnels etc.
• It is used to build heavy structures like Bridges, Walls, Towers, Under water
• It is used in tall structures and skyscrapers.
Why it is essential?
• High relative strength
• High toleration of tensile strain
• Good bond to the concrete, irrespective of pH, moisture, and
• Thermal compatibility, not causing unacceptable stresses in response
• Durability in the concrete environment, irrespective of corrosion or sustained
Merits of Reinforced Concrete
• Good Binding Between Steel and Concrete
there is a very good development of bond between steel and concrete.
• Stable Structure
Concrete is strong in compression but week in tension and steel as strong in
tension so their combination give a strong stable structure.
• Less Chances of Buckling
Concrete members are not slim like steel members so chances of
buckling are much less.
concrete structures are aesthetically good and cladding is not required
• Lesser Chances of Rusting
steel reinforcement is enclosed in concrete so chances of rusting are
Short Reinforced Concrete Compression Members
Short - slenderness does not need to be considered–column will
Only axial load
As =Area ofsteel
Ac =Area of
concrete Ag =
Fs =stress in
Fc =stress in
P =Acfc +Asfs
If bond is maintained εs = εc
Mechanism of Load
Function of structure is
to transfer all the loads
safely to ground.
A particular structural
member transfers load
to other structural
“The loads which do not change their magnitude and
position w.r.t. time within the life of structure”
Dead load mainly consist of superimposed loads and self
load of structure.
It is the load of structural member due to its own weight.
It is the load supported by a structural member. For
instance self weight of column is self load and load of beam and
slab over it is superimposed load.
Design Loads (contd…)
“Live loads consist chiefly of occupancy loads in buildings
and traffic loads on bridges”
They may be either fully or partially in place or not present at all, and
may also change in location.
Their magnitude and distribution at any given time are uncertain, and even
their maximum intensities throughout the life time of the structure are not
known with precision.
The minimum live loads for which the floor and roof of a building should be
designed are usually specified in the building codes that governs at the site
Objectives of Designer
There are two main objectives
The structure should be safe enough to carry all the applied
throughout the life.
Structures should be economical. Lighter structures are more
Economy α1/self weight (More valid for Steel Structures)
In concrete Structures overall cost of construction decides the
economy, not just the self weight.
To combine various loads in such a way to get a critical situation.
Load Factor = Factor by which a load is to be increased x probability of
1. 1.2D + 1.6L
3. 1.2D + 1.6L + 0.5Lr
4. 1.2D + 1.6Lr + (1.0L or 0.8W)
D = Dead load
L = Live load on intermediate floors
Lr = Live load on roof W
= Wind Load
“Shrinkage is reduction in volume of concrete due to loss of water”
Coefficient of shrinkage varies with time. Coefficient of shortening is:
0.00025 at 28 days
0.00035 at 3 months
0.0005 at 12 months
Shrinkage = Shrinkage coefficient x Length
Excessive shrinkage can be avoided by proper curing during first 28
days because half of the total shrinkage takes place during this period
“creep is the slow deformation
of material over considerable
lengths of time at constant
stress or load”
Creep deformations for a given
concrete are practically
proportional to the magnitude of the
applied stress; at any given stress,
high strength concrete show less
creep than lower strength concrete.
(MPa) 10-6 perMPa
Plain & Reinforced Concrete
How to calculate shortenings due to creep? Consider a column of 3m
which is under sustained load for several years.
Compressive strength, fc’ = 30 MPa
Sustained stress due to load = 10 MPa
Specific creep for 28 MPa fc’ = 116 x 10-6 per MPa Creep
Strain = 10 x 116 x 10-6 = 116 x 10-5
Shortening due to creep = 3000 x 116 x 10-5
= 3.48 mm
Specified Compressive Strength Concrete, fc’
“28 days cylinder strength of concrete”
The cylinder has 150mm dia and 300mm length.
According to ASTM standards at least two cylinders should be tested
and their average is to be taken.
ACI 5.1.1: for concrete designed and constructed in accordance with ACI
code, fc’ shall not be less than 17 Mpa (2500 psi)
Building A :- has thick and stiff floors and
During a earthquake, the whole building will pancake. the bottom columns
receive the largest forces and bend; wallscrack
Building B :- has a ductile floordesign.
During Earthquake, Floors will be waving and cracking, but the building
How to avoid corrosion?
⚫ Careful detailing to protect from water
⚫ Use stainless steel
⚫ Protect steel with galvanizing (zinc coating) or other
Corrosion of Steel
Every 90 seconds, across the world, one ton of steel turns
to rust; of every two tons of steel made, one is to replace
• Most concrete used for construction is a combination of
concrete and reinforcement that is called reinforced
• Steel is the most common material used as reinforcement, but
other materials such as fiber-reinforced polymer (FRP) are also
Reinforcement in aconcrete column
REINFORCEMENT USED IN RCC BUILDING
Fiber-reinforced concrete (FRC) is concrete with the addition of discrete
reinforcing fibers made of steel, glass, synthetic(nylon, polyester, and
polypropylene), and natural fiber materials.
Synthetic fibers can be delivered to the mixing system in preweighed, degradable
bags that break down during the mixing cycle. Steel fibers are introduced to the
rotating mixer via conveyor belt, either at the same time as the coarse aggregate or
on their own after all the conventional ingredients have been added.
1. The major applications of FRC are slab-on-grade construction, precast concrete, and
2. Some examples of slab-on-grade construction are airport runways, residential,
commercial, and industrial floor slabs, and hydraulic structures
3. Fiber- reinforced shotcrete is used for rock slope stabilization, tunnel liners,
hydraulic structures, and maintenance of existing concrete.
4. FRC is also used in repair applications, such as repair of bridge decks, piers, and
Steel reinforcement:-Steel reinforcement is available in the form of plain steel
bars, deformed steel bars, cold-drawn wire, welded wire fabric, and deformed
welded wire fabric.
Deformed steel bars:—Deformed bars are round steelbars with lugs, or
deformations, rolled into the surface of the bar during manufacturing
Threaded steel bars:—Threaded steel bars are made by several
manufacturers in different grades They are used as an alternative to lapping
standard deformed bars when long bar lengths arerequired
Welded wire fabric:—Welded wire fabric reinforcement also known as welded
wire reinforcement is a square or rectangular mesh ofwires.
Typicaldeformed reinforcing bar
Welded wirereinforcement sheets
TYPES OF CONCRETE
Prestressed concrete is structural concrete in which internal stresses have
been introduced to reduce potential tensile stresses in the concrete
resulting from loads.
a. Toresist internal pressures in circular structures like tank,pipe
b. To limit cracking in bridge decks and slabs-on-grade.
c. To improve capacity of columns and piles.
d. To reduce long-term deflections.
Plain concrete is structural concrete withoutreinforcement
It is sometimes used in slabs-on grade ,pavement, basementwalls,
small foundations, and curb-and-gutter.
Pretensioning is usually performed in a factory (or precasting yard). The
tendons are held in place and tensioned against the ends of the casting
bed before the concrete is placed.
Advantages of pretensioned concrete are that it
tendons are bonded to the concrete over theirentire length.
Post-tensioning is usually performed at the job site. Post- tensioning tendons
are usually internal but can be external.
Some of the advantages of post-tensioning are that it does not require the
large temporary anchorages required for pretensioning,
It allows for larger members than are possible in aprecasting plant.
Plain & Reinforced Concrete
Reinforced Cement Concrete (RCC) contd..
Cement : Sand : Crush
1 : 1.5 : 3
1 : 2 : 4
Water Cement Ratio (W/C)
1 : 4 : 8
W/C = 0.5 – 0.6
For a mix proportion of 1:2:4 and W/C = 0.5, if cement is 50 kg
Batching By Weight
= 2 x 50 = 100 Kg
= 4 x 50 = 200 Kg
= 50 x 0.5 = 25 Kg
It is better to provide a max spacing of 200mm(8”) for main bars and
250mm(10”)in order to control the crack width and spacing.
A min. of 0.24% shall be used for the roof slabs since it is subjected to higher
temperature. Variations than the floor slabs. This is required to take care of
It is advisable to not to use 6mm bars as main bars as this size available in
the local market is of inferior not only with respect to size but also the
quality since like TATAand SAILare not producing this size of bar.
A min. of 0.2% is to be provided for the compression bars in order to take care of
The stirrups shall be minimum size of 8mm in the case of lateral load resistance .
The hooks shall be bent to 135degree.
Minimum size of foundation for a single storey of G+1building, where
soil safe bearing capacity is 30 tonnes per square meter, and the oncoming
load on the column does not exceed 30tonnes.
Reinforcing bar details
Arrangement of reinforcement in various
structural members :
R.C.C. is used as a structural element, thecommon structural elements in
R.C.C. is used are:
(a) Footings (b) Columns
(c) Beams and lintels (d) roofs and slabs.
1) Footings :
• In rectangular footing the reinforcement parallel to the long direction shall be
distributed uniformly across the width of the footing.
• In short direction, since the support provided to the Footing by the column is
concentrated near the middle, the moment per unit length is largest i.e., the
curvature of the footing is sharpest immediately under the column and
decreases in the long direction with the increasing distance from the column.
• For this reason larger steel area is needed in the central portion and is
determined in accordance with the equation given below.
2) Columns :
The main reinforcement in columns in longitudinal , parallel to the direction
to the direction of the load and consists of bars arranged in square,
rectangular or spherical shape.
Main steel is provided to resist the compression load along with the
The bar shall not be less than 12mmin diameter
Nominal max. Size of coarse aggregte is 5mm.
The no of bars in columns are varies from 10,12,14,16 with varyingdiameter.
3) Beams :
Generally a beam consists of following types of
Longitudinal reinforcement .
Side face reinforcement in the web of the beam isprovided
when the depth of the web in a beam exceeds 750mm.
Arrangements of bars in a beam should confirm to the requirements of
clause given in 8.1and 8.2of SP34.Bars of size 6,8,10,12,16,20,25,32,50 mm are
available in market.
Thickness of the slab is decided based on span to depth ratio . Min
reinforcement is 0.12% for HYSD bars and 0.15% for mild steel bars. The
diameter of bar generally used in slabs are: 6 mm, 8 mm, 10mm, 12mm and 16
The maximum diameter of bar used in slab should not exceed 1/8 of the total
thickness of slab. Maximum spacing of main bar is restricted to 3 times
effective depth . For distribution bars the maximum spacing is specified as 5
times the effective depth .
4) Slabs :
Minimum clear cover to reinforcements in slab depends on the durability
criteria . Generally 15 mm to 20 mm cover is provided for the main
Torsion reinforcement shall be provided at any corner where the slab is
simply supported on both edges meeting at that corner.
It shall consist of top and bottom reinforcement, each with layer of bars
placed parallel to the sides of the slab and extending from the edges a
minimum distance of one fifth of the shorterspan.
Mr. VIKAS MEHTA
School of Mechanical and civil engineering
Village Bajhol, Solan (H.P)