# How to Calculate flexural strength of concrete? | Flexural strength formula

## What is flexural strength of concrete ?

The flexural strength of concrete is indirectly the tensile strength of the concrete. There are different ways of calculating the flexural strength of concrete. We will discuss here two flexural strength of concrete formula to calculate the flexural strength of concrete.

## Difference between flexural strength and compressive strength of concrete

It is very easy to calculate the flexural strength of concrete by using a simple flexural strength formula which is given below. Let us discuss the process of calculation.

The flexural strength of concrete is an alternate method for measuring the tensile strength of concrete. The test is made on the beam of size (Depth, Width, and Length) (15 * 15 * 7) millimeters.

or 100 mm * 100 mm * 500mm

The flexural strength of concrete is determined by either central point loading or two-point loading. The typical machine used for this test is shown below.

The bed of the testing machine is be provided with two steel rollers of 38 millimeters in diameter the rulers are mounted at the distance from center to center is 600 millimeters for 150 millimeters specimens and 400 millimeters for 100 millimeters specimens.

The Loads applied through a similar roller mounted at the top in case of 2 point loading. The rollers are spaced at 200 centimeters or 133 centimeters center to center.

The concrete is prepared as per the required grade of concrete and placed on the mold in layers and tamp 25 blows for each layer. After a day. the mold is removed and the specimen is placed in the curing tank at a temperature of 27 plus or minus 2 degrees Celsius depending upon the requirement.

The test specimen is removed from the tank and dried at 14 and 28 days for testing. The specimen is placed on the rollers and centred with the longitudinal axis of the specimen.

The load is applied at a rate of loading of 400 kilograms per minute for the 150 millimetres specimens and at a rate of 180 kilograms per minute for the 100 millimetres specimens.

Finally, note down the load at which the cylinder fails by developing cracks. Now measure the distance between the line of fracture and the nearest support consider this as (I ). if (I) is greater than 200 millimetres for 150 millimetres and 130 millimetres for 100 millimetres specimen.

Then flexural strength or modulus of rupture FB is calculated by equation given below.

## Flexural strength of concrete formula

If (I) is less than 200 millimeters and greater than 170 millimeters for 150 millimeters and less than 133 millimetres and greater than 110 millimeters for the 100-millimetre specimen.

Then flexural strength or modulus of rupture FB is calculated by the equation given below.

Where,

(b) is the width of the beam in millimeters

(d) is the failure point depth in millimeters

(L) is the supported length in millimeters and

(Pa) is the maximum load applied to the beam in kilograms and

(a) is the distance between the line of fracture and nearest support in millimeter.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Ranjeet Sahani