fundamental concepts of reinforced concrete members

Fundamental Conceptsof

Reinforced Concrete Members

Pooja JainAssistant Professor

Department of Civil Engineering

SKITM&G, Jaipur

28-12-2020 Pooja Jain, Assistant Professor, SKITM&G, Jaipur 5CE4-03: DESIGN OF CONCRETE STRUCTURES

CONTENT

• REINFORCED CEMENT CONCRETE

• SALIENT FEATURES

• WORKABILITY OF CONCRETE

• EXPOSURE CONDITION

• ACCEPTANCE OF CONCRETE

• REINFORCEMENT

• SIZE OF REINFORCEMENT

• REFERENCES


R.C.C. (REINFORCED CEMENT CONCRETE)

• It is made up of cement concrete and reinforcement bars.

• Cement concrete consists of cement, sand (F.A.), stone chips (C.A.), water and admixtures.

Cement Concrete

Cement

F.A.

C.A.Water

Admixture

Reinforcement bars


SALIENT FEATURES

Grade of concrete (As per IS 456:2000 Table-2, pg.16):

Here, M denotes Mix of Ingredients and the number represent characteristic strength of concrete in

N/𝑚𝑚2 or MPa after 28 days of curing.

• For RCC minimum grade of concrete is M20.

• For construction exposed to sea water minimum grade for RCC is M30 & for PCC is M20.

• Two types of design mix: Nominal mix ( volumetric ratio of fixed proportion of ingredients) and Design

mix (as per specifications of IS 10262:2019).

• Modulus of elasticity and brittleness of concrete is increased with increase in grade of concrete.

Ordinary Concrete Standard Concrete High Strength Concrete

M10 to M20 M25 to M55 M60 to M80

Lean Concrete RCC Prestressed Concrete


WORKABILITY OF CONCRETE (As per IS 456:2000 Clause-7, pg.17):

S.No.Degree of

WorkabilitySlump (mm)

Compaction

FactorUse

1. Very Low - 0.75 – 0.80- Road Construction

- Shallow Section

2. Low 25 -75 0.80 – 0.85

- Mass Concreting

- Light reinforced

section

3. Medium 50-100 0.85 – 0.92

- Heavily reinforced

section

- Pumped concrete

4. High 100 – 150 More than 0.92 - Piling

5. Very High More than 150 More than 0.92- Tremie concreting

- In-situ piling


EXPOSURE CONDITION (As per IS 456:2000 Table-3,5&16):

S.No. Environment Exposure conditionMinimum grade

of concrete

Nominal

cover

1. Mild• Protected against weather

• Not exposed to rainM 20 20 mm

2. Moderate • Exposed to rain & protected from severe rain M 25 30 mm

3. Severe

• Exposed to severe rain

• Alternate wetting and drying

• Completely immersed in sea water

M 30 45 mm

4. Very severe

• Exposed to sea water

• Severe freezing

• Exposed to subsoil water (foundation)

M 35 50 mm

5. Extreme• Surface of members in Tidal zone

• Structure exposed to chemicalsM 40 75 mm

Nominal Cover (As per IS 456:2000 Clause-26.4.3, Pg-46) : Minimum design depth of concrete cover

of normal-weight aggregate concrete required for all types of reinforcement including links.


ACCEPTANCE OF CONCRETE (As per IS 456:2000)

Quantity of Survey No. of Sample

1 to 5 m3 1

6 to 15 m3 2

16 to 30 m3 3

31 to 50 m3 4

Above 50 m3 4 + 1 Sample for each additional 50 m3

• For M 20 and above (As per table 11, pg-30): Mean of the Group of 4 Non-Overlapping Consecutive

Test Results in N/mm2 >= fck + 0.825*S established standard deviation (rounded off to nearest 0.5

N/mm2) fck + 4 N/mm2 , whichever is greater.

* In the absence of established value of standard deviation, the values given in Table 2 (of IS10262-2019)

may be assumed, and attempt should be made to obtain results of 30 samples as early as possible to

establish the value of standard deviation.

* Here, 1 Sample equal

to set of cubes casted

from same concrete at

same time.


ACCEPTANCE OF CONCRETE (As per IS 456:2000, pg.-29):

• The test results of the sample shall be the average of the strength of three specimens. The individual

variation should not be more than ±15 percent of the average. If more, the test results of the sample

are invalid. (Clause 15.4, pg-29)

• Flexural Strength (Clause 16.2, pg-29): The strength determined from any test result is not less than

the specified characteristic strength less 0.3 N/mm2.

Characteristic Load is that value of load which has a 95 percent probability of not being exceeded

during the life time of the structure.

Characteristic strength (fck): The value of strength of material below which not more than 5% of test

results are expected to fall.


REINFORCEMENT

• It is used for increase the tensile property of the concrete.

• Reinforcement made of materials like Steel, Copper, Aluminium, Plastic Fibre, Bamboo etc. is used.

S. No. Type of Reinforcement Characteristic strength

(Yield Strength)

Permissible Stress

In Tension In Compression

1 Mild Steel Bars Fe250, fy = 250 N/mm2

High ductility

For ≤ 20mm ϕ σst =140 N/mm2

For > 20mm ϕ σst =130 N/mm2

σsc = 130 N/mm2

2 Medium Tensile Steel 190 N/mm2 σsc = 130 N/mm2

3 Cold Twisted Deformed

Bars (CTD)

Fe415

Fe500

Fe550 or higher

σst = 230 N/mm2

σst = 275 N/mm2

σst = 0.55*fy

σsc = 190 N/mm2

4 High Yield Strength

Deformed Bars (HYSD)

High Strength, Low

ductility

Same as above. σsc = 190 N/mm2

5 Thermo Mechanical

Treated Bars (TMT)

High Strength, High

ductility and Anti corrosive

Same as above. σsc = 190 N/mm2


SIZE OF REINFORCEMENT

S.No. Diameter (mm) Cross Sectional Area (mm2)

1. 6 20.27

2. 8 50.26

3. 10 78.54

4. 12 113.09

5. 16 201.6

6. 20 314.15

7. 25 490.87

8. 28 615.75

9. 32 804.24

10. 36 1017.87

11. 40 1256.63

12. 45 1590.43

13. 50 1963.49


REFERENCES

• IS 456 (2000): Plain and Reinforced Concrete - Code of Practice

• “Design of Reinforced Concrete Structures” by S. Ramamrutham of “Dhanpat Rai Publishing

Company”

• “RCC Designs” by B.C. Punmia, A.K. Jain & Arun K. Jain of “Laxmi Publications”.

• “Reinforced Concrete Design” by Pillai & Menon of “Tata McGraw Hill Publication”


THANK YOU


fundamental concepts of reinforced concrete members

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