Design of Concrete Structures Introduction

By Amritansh Mishra|Updated : December 2nd, 2021

Through Champion Study Plan for GATE Civil Engineering (CE) 2022, we are providing Design of Concrete Structures Introduction study notes and other important materials on every topic of each subject.

These topic-wise study notes are useful for the preparation of various upcoming exams like GATE CivilIESBARCISROSSC-JEState Engineering Services examinations and other important upcoming competitive exams.

The article contains fundamental notes on the "Introduction"  topic of the "Design of Concrete Structures" subject. 

Design of Concrete Structures Introduction 

IMPORTANT CODE

byjusexamprep

Table- Permissible Limit for Impurities in the water

 (IS 456:2000)

Impurity

Maximum permissible limit

( mg/l)

Organic

200

Inorganic

300

Sulphates (as  )

400

Suspended matter

2000

Chloride as Cl

2000- plain Concrete

500- Reinforce concrete work

IMP TEST ON CEMENT

1-  Consistency- Vicat apparatus

2-  Initial and final setting time- Vicat apparatus

3-  Soundness test- Autoclave test

4-  Specific gravity- Le chatelier flask

5-  Fineness by specific surface- Blaine air permeability test

  •  Concrete is graded according to its compressive strength.
  • A grade lower than M20 should not be used in Reinforced cement concrete.
  • For prestressed concrete, the minimum grade is M40 for pretension work, and M30 is used in the case of post-tension work.
  • For foundation, the Minimum grade of Concrete is M35.
  • The water-cement ratio affects the compressive strength of concrete.

 

IMPORTANT CRITERIA USED IN RCC

Comparison of workability by various methods  

byjusexamprep

Minimum cement contents and maximum w/c ratio for durability

byjusexamprep

Exposure conditions

Environment

Exposure condition

Mild

Concrete surfaces protected against weather or aggressive conditions, except those situated in the coastal area

Moderate

Concrete surfaces sheltered from rain or freezing whilst wet

Concrete exposed to condensation and rain

Concrete continuously underwater Concrete in contact or buried under non-aggressive soil/groundwater

Concrete surfaces sheltered from saturated salt air in the coastal area

Severe

Concrete surface exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation.

Concrete completely immersed m seawater. Concrete exposed to the coastal environment

Very severe

Concrete surfaces exposed to seawater spray. corrosive fumes or severe freezing conditions whilst wet concrete in contact or buried under aggressive subsoil groundwater

Extreme

The surface of members in the tidal zone. Members in direct contact with liquid/solid aggressive chemicals

 

NOMINAL COVER

It is minimum clear cover required for the outermost layer of steel reinforcement.

Minimum Nominal cover

Member

Mild (mm)

Moderate (mm)

Severe (mm)

Very severe (mm)

Extreme

(mm)

Slab

20

30

45

50

75

Beam

25

30

45

50

75

Column

40

40

45

50

75

Foundation

40

50

50

50

75

 

CHARACTERISTIC STRENGTH OF CONCRETE (fck)

1-The strength below which 5% of test result are expected to fail is called characteristic strength of concrete.

2- fck value gives compressive strength at 28 days after casting.

If fm is targeted mean strength and fck is characteristics strength, then

                  fm = fck + 1.65 × ∝

∝  = standard deviation

 Value of standard deviation

Grade

standard deviation ()N/mm² )

M10- M15

3.5

M 20-M25

4

M 30 & Higher

5

 

ACCEPTANCE CRITERIA FOR CONCRETE

As per IS code 456:2000

1- The avg. strength of four non overlapping consecutive test should not be

fav ≥ (fck + 0.825 × ∝)  or favg ≥ (fck + 3) {whichever is more}             

2- For individual test result

ITR ≥ (fCK─ 3)

3- Test result should be obtained after testing on at least three cubes. The difference in each test block strength and average strength should not be more than 15%.

*****

If you are preparing for ESE/ GATE or other PSU Exams (Civil Engineering), then avail Online Classroom Program for ESE and GATE CE:

Online Classroom Program for ESE/GATE CE

You can avail of BYJU'S Exam Prep Test Series specially designed for all Civil Engineering Exams:

BYJU'S Exam Prep Test Series ESE/GATE CE

Thanks

All the Best

Comments

write a comment

Featured Articles

Follow us for latest updates