In this slide we have concrete, reinforcement and RCC and their properties.

1. University Institute of Engineering Civil Engineering Department www.cuchd.in
CHANDIGARH UNIVERSITY
DEPARTMENT OF CIVIL ENGINEERING
DESIGN OF CONCRETE STRUCTURES-I
INTRODUCTION TO
Vikas Khandelwal
AP, CIVIL ENGG DEPTT.

2. Concrete:
• is a composite material composed mainly
of water, aggregate, and cement. Often, additives and
reinforcements (such as rebar) are included in the
mixture to achieve the desired physical properties of
the finished material. When these ingredients are
mixed together, they form a fluid mass that is easily
moulded into shape. Over time, the cement forms a
hard matrix which binds the rest of the ingredients
together into a durable stone.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal www.cuchd.in
CHANDIGARH UNIVERSITY

3. Reinforced concrete (RC)
• is a composite material in which concrete's relatively
low tensile strength and ductility are counteracted by
the inclusion of reinforcement having higher tensile
strength and/or ductility. The reinforcement is usually,
though not necessarily, steel reinforcing bars (rebar)
and is usually embedded passively in the concrete
before the concrete sets. Reinforcing schemes are
generally designed to resist tensile stresses in particular
regions of the concrete that might cause
unacceptable cracking and/or structural failure.
Modern reinforced concrete can contain varied
reinforcing materials made of steel, polymers or
alternate composite material in conjunction with rebar
or not.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

4. Reinforcement concrete as
human body:
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
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5. RCC :
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6. Properties of material:
• Properties of concrete:
• Plain concrete is prepared by mixing cement, sand (also
known as fine aggregate), gravel (also known as coarse
aggregate) and water with specific proportions. Mineral
admixtures may also be added to improve certain
properties of concrete. Thus, the properties of concrete
regarding its strength and deformations depend on the
individual properties of cement, sand, gravel, water and
admixtures.
• In plastic state concrete should be:
• 1. workable
• 2. free from segregation
• 3. bleeding
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

7. • (a) Characteristic strength property
• Characteristic strength is defined as the strength
below which not more than five per cent of the test
results are expected to fall. Concrete is graded on
the basis of its characteristic compressive strength
of 150 mm size cube at 28 days and expressed in
N/mm2.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

8. • b) Flexural strength (fcr)
• The flexural and splitting tensile strengths are
obtained as described in IS 516 and IS 5816,
• fcr = 0.7 fck N/MM2
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

9. d) Shrinkage of concrete
• Shrinkage is the time dependent deformation, generally
compressive in nature. The constituents of concrete, size
of the member and environmental conditions are the
factors on which the total shrinkage of concrete depends.
However, the total shrinkage of concrete is most
influenced by the total amount of water present in the
concrete at the time of mixing for a given humidity and
temperature. The cement content, however, influences
the total shrinkage of concrete to a lesser extent. The
approximate value of the total shrinkage strain for design
is taken as 0.0003 in the absence of test data .
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

10. • Shrinkage of concrete is influenced by
• • Water/cement ratio
• • Humidity and temperature of curing
• • Humidity during the period of use
• • Age of concrete at first loading
• • Magnitude of stress and its duration
• • Surface-volume ratio of the member
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

11. • f) Thermal expansion of concrete
• The knowledge of thermal expansion of concrete is very important as it
is prepared and remains in service at a wide range of temperature in
different countries having very hot or cold climates. Moreover, concrete
will be having its effect of high temperature during fire. The coefficient
of thermal expansion depends on the nature of cement, aggregate,
cement content, relative humidity and size of the section. IS 456
stipulates (cl. 6.2.6) page:16 the values of coefficient of thermal
expansion for concrete / oC for different types of aggregate.
• Workability
• It is the property which determines the ease and homogeneity with
which concrete can be mixed, placed, compacted and finished. A
workable concrete will not have any segregation or bleeding.
Segregation causes large voids and hence concrete becomes less
durable. Bleeding results in several small pores on the surface due to
excess water coming up. Bleeding also makes concrete less durable. The
degree of workability of concrete is classified from very low to very high
with the corresponding value of slump in mm (cl. 7 of IS 456).
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

12. Workability of concrete:
PLACING CONDITION DEGREE OF WORKABILITY SLUMP (mm)
Blinding concrete Very low Compaction factor : 0.75-0.85
Mass conc., lightly rcc section
beam, slab,wall
low 25-75
Heavy RCC section slab,
beam, column.
medium 50-100
75-100
Pumped conc, in-situ piling high 100-150
Terime work Very high Ease of flow is good.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

13. (c) Durability of concrete
• A durable concrete performs satisfactorily in the working
environment during its anticipated exposure conditions during
service. The durable concrete should have low permeability with
adequate cement content, sufficient low free water/cement ratio
and ensured complete compaction of concrete by adequate
curing. For more information, please refer to cl. 8 of IS 456
• Factor influence the durability of conc.
• 1. the environment
• 2. cover to embedded steel.
• 3. types and quality of material used.
• 4. water/cement ratio of concrete.
• 5. workmanship, to obtain full compaction and efficient curing.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

14. • Properties of steel:
• As mentioned earlier in sec. 1.2.2, steel is used as the reinforcing
material in concrete to make it good in tension. Steel as such is
good in tension as well as in compression. Unlike concrete, steel
reinforcement rods are produced in steel plants. Moreover, the
reinforcing bars or rods are commercially available in some
specific diameters. Normally, steel bars up to 12 mm in diameter
are designated as bars which can be coiled for transportation.
Bars more than 12 mm in diameter are termed as rods and they
are transported in standard lengths.
• Like concrete, steel also has several types or grades. The four types of steel
used in concrete structures as specified in cl. 5.6 of IS 456 are given below:
• (i) Mild steel and medium tensile steel bars conforming to IS 432 (Part 1)
• (ii) High yield strength deformed (HYSD) steel bars conforming to IS 1786
• (iii) Hard-drawn steel wire fabric conforming to IS 1566
• (iv) Structural steel conforming to Grade A of IS 2062.
• Mild steel bars had been progressively replaced by HYSD bars and
subsequently TMT bars are promoted in our country. The implications of
adopting different kinds of blended cement and reinforcing steel should be
examined before adopting.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

15. Steel bar
FROM FIG-2 PLAIN BAR
–MILD STEEL BAR
DEFORMED-HYSD BARS
FIG: 1
FIG:2
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16. Stress-strain curves for reinforcement:
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17. • The characteristic yield strength fy of steel is
assumed as the minimum yield stress or 0.2 per
cent of proof stress for steel having no definite
yield point. The modulus of elasticity of steel is
taken to be 2x105 N/mm2.
• The two grades of cold worked bars used as steel
reinforcement are Fe 415 and Fe 500 with the
values of fy as 415 N/mm2 and 500 N/mm2,
respectively.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

18. The grades of concrete:
• designated by one letter M (for mix) and a number
from 10 to 80 indicating the characteristic
compressive strength (fck) in N/mm2.
• As per IS 456 , concrete has three groups as
• ordinary concrete (M 10 to M 20),
• standard concrete (M 25 to M 55)
• high strength concrete (M 60 to M 80). The size of
specimen for determining characteristic strength
may be different in different countries
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

19. Permissible Stresses in material:
• Permissible Stresses in concrete:
• The permissible stresses of concrete in bending
compression σcbc,
• in direct compression σcc and
• the average bond for plain bars in tension τbd are
given in Table 21 of IS 456 for different grades of
concrete.
Grade of concrete Direct tension σtd (N/mm2 ) Bending compression σcbc
(N/mm2 )
Direct compression σcc (N/mm2
)
Average bond
τbd for plain
bars in tension (N/mm2 )
M 20 2.8 7.0 5.0 0.8
M 25 3.2 8.5 6.0 0.9
M 30 3.6 10.0 8.0 1.0
M 35 4.0 11.5 9.0 1.1
M 40 4.4 13.0 10.0 1.2
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

20. • Permissible stresses in steel reinforcement
Type of stress in steel reinforcement Mild steel bars, Fe 250, (N/mm2 ) High yield strength deformed bars, Fe
415, (N/mm2 )
Tension σst or σss
(a) up to and including 20 mm diameter
(b) over 20 mm diameter
140
130
230
230
Compression in column bars σsc 130 190
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

21. • Working stress method
• The method is designated as working stress method as
the loads for the design of structures are the service
loads or the working loads. The failure of the structure
will occur at a much higher load. The ratio of the failure
loads to the working loads is the factor of safety.
Accordingly, the stresses of concrete and steel in a
structure designed by the working stress method are
not allowed to exceed some specified values of stresses
known as permissible stresses. permissible stresses are
determined dividing the characteristic strength fck of
the material by the respective factor of safety. The
values of the factor of safety depend on the grade of
the material and the type of stress.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

22. • Assumptions for Design of Members by Working Stress Method
• As mentioned earlier, the working stress method is based
on elastic theory, where the following assumptions are made, as
specified in cl. B-1.3 of IS 456.
• (a) Plane sections before bending remain plane after bending.
• (b) Normally, concrete is not considered for taking the tensile
stresses except otherwise specifically permitted. Therefore, all
tensile stresses are taken up by reinforcement only.
• (c) The stress-strain relationship of steel and concrete is a straight
line under working loads.
• (d) The modular ratio m has the value of 280/3σcbc, where σcbc
is the permissible compressive stress in concrete due to bending
in N/mm2 . The values of σcbc are given in Table 21 of IS 456. The
modular ratio is explained in the next section.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

23. • Modular Ratio m In the elastic theory, structures having different
materials are made equivalent to one common material. In the
reinforced concrete structure, concrete and reinforcing steel are,
therefore, converted into one material. This is done by
transformation using the modular ratio m which is the ratio of
modulus of elasticity of steel and concrete. Thus, m = Es/Ec.
where Es is the modulus of elasticity of steel which is 200000
N/mm2 . However, concrete has different moduli, as it is not a
perfectly elastic material. The short-term modulus of concrete Ec
= 5000 fck in N/mm2 , where fck is the characteristic strength of
concrete. However, the short-term modulus does not take into
account the effects of creep, shrinkage and other long-term
effects. Accordingly, the modular ratio m is not computed as m =
Es/Ec = 200000/(5000√𝑓ck ) The value of m,i.e., 280/3σcbc,
partially takes into account long-term effects. This is also
mentioned in the note of cl. B-1.3 of IS 456.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

24. • Ultimate load method (ULM)
• The method is based on the ultimate strength of reinforced
concrete at ultimate load is obtained by enhancing the
service load by some factor called as load factor for giving a
desired margin of safety .Hence the method is also referred
to as the load factor method or the ultimate strength
method. In the ULM, stress condition at the state of in
pending collapse of the structure is analysed, thus using, the
non-linear stress – strain curves of concrete and steel. The
safely measure in the design is obtained by the use of
proper load factor. The satisfactory strength performance at
ultimate loads does not guarantee satisfactory strength
performance at ultimate loads does not guarantee
satisfactory serviceability performance at normal service
loads
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

25. • Limit state method
• The term “Limit states” is of continental origin where there are three
limit states - serviceability / crack opening / collapse. For reasons not
very clear, in English literature limit state of collapse is termed as limit
state. As mentioned in sec. 1.1.1, the semi-empirical limit state method
of design has been found to be the best for the design of reinforced
concrete members. More details of this method are explained in
Module 3 (Lesson 4). However, because of its superiority to other two
methods (see sections 2.3.2 and 2.3.3 of Lesson 3), IS 456:2000 has
been thoroughly updated in its fourth revision in 2000 taking into
consideration the rapid development in the field of concrete technology
and incorporating important aspects like durability etc. This standard
has put greater emphasis to limit state method of design by presenting
it in a full section (section 5), while the working stress method has been
given in Annex B of the same standard. Accordingly, structures or
structural elements shall normally be designed by limit state method.
University Institute of Engineering Civil Engineering Department Vikas Khandelwal (E3177) www.cuchd.in
CHANDIGARH UNIVERSITY

26. Thanks
Queries are welcome
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