TYPES OF BEAMS -- Based on reinforcement

Singly Reinforced Beams:

A singly reinforced beam is a beam provided with longitudinal reinforcement in the tension zone only.

The analysis and design of a reinforced concrete member subjected to bending are based on the following assumptions: 

1) Plane sections transverse to the centre line of a member before bending remain plane sections after bending.

2) Elastic modulus of concrete has the same value within the limits of deformation of the member.

3) Elastic modulus for steel has the same value within the limits of deformation of the member.

4) The reinforcement does not slip from concrete surrounding it.

5) Tension is entirely by steel.

6) The steel is free from initial stresses when embedded in concrete.

7) There is no resultant thrust on any transverse section of the member.

Doubly Reinforced Beams:

Beams reinforced with steel in compression and tension zones are called Doubly reinforced beams.  

CONCRETE SAMPLES

Sampling Procedure: 

         A random sampling procedure is adopted to ensure that each concrete batch shall have a reasonable chance of being tested i.e., sampling is done to the entire period of concreting and cover all mixing units.

Frequency:

The minimum frequency of sampling of concrete of each grade shall be accordance with the following:

Quantity of concrete in the work (m3)	Number of samples
1-5	1
6-15	2
16-30	3
31-50	4
51 and above	4 Plus one additional sample for each additional 50 m3

Strength test of concrete (IS 456):

          Samples from fresh concrete shall be taken and cubes shall be made and tested at 28 days. The test strength shall be the average of the strength of 3 specimen. The individual variation should not be more than 15 percent (+15% or -15%) of the average.

Different Grades of Concrete -- Concrete Mix Design

Different grades of Concrete:

          Based on different concrete mix proportions (or) mix ratio’s, concrete mixer is divided into different grades. As per IS 456:2000, concrete mix design has the following mix proportions:

Type of Concrete	Concrete Grade	Mix Ratio (or) Proportion	Characteristic Compressive strength of Concrete @ 28 Days in N/mm2
Ordinary concrete	M5	1:5:10	5 N/mm2
	M7.5	1:4:8	7.5 N/mm2
	M10	1:3:6	10 N/mm2
	M15	1:2:4	15 N/mm2
	M20	1:1.5:3	20 N/mm2
Standard Concrete	M25	1:1:2	25 N/mm2
	M30	Design Mix	30 N/mm2
	M35	Design Mix	35 N/mm2
	M40	Design Mix	40 N/mm2
	M45	Design Mix	45 N/mm2
	M50	Design Mix	50 N/mm2
High Strength Concrete	M55	Design Mix	55 N/mm2
	M60	Design Mix	60 N/mm2
	M65	Design Mix	65 N/mm2
	M70	Design Mix	70 N/mm2

Note:-

In Example: M5

M represents "Mix"

5 represents the compressive strength achieved after 28 days of curing.

GRADES OF CONCRETE