Calculating flexture modulus3/19/2023 ![]() ![]() In the third cycle, the load from zero position to 1/3rd of the cube strength plus 1.5 kg/cm 2 is divided into 10 intervals. The reading of extensometer is noted and the load released slowly till it reaches to a value of 1.5 kg/cm 2 on the cylinder specimen. In the second operation, the reading of the extensometer is noted and it is again loaded till the load reaches to 1/3rd of the cube strength plus 1.5 kg/cm 2. ![]() After sustained loading for one minute the load is released gradually at a rate of 1.5 kg/cm 2. The load on cylinder increased till it reaches to 1/3rd of cube strength plus 7 kg/cm 2. ![]() In this method the extensometer is fixed on a 15 cms x 30 cms cylinder and placed in compression testing machine and loaded at a rate of 140 kg/cm 2 per minute. The measurements of strains in concrete are not easy, but within limits it can be determined by Lamb’s roller extensometer. Stress-strain relationship of aggregate, cement paste and concrete are shown in Fig. Thus the stress-strain curve continues to bend faster than the increase of stress. This failure of bond at the interface increases at a faster rate than that due to applied stress. Perhaps this is due to the development of fine or micro cracks at the interface of the aggregate and cement paste. However upto about 10 to 15% of the ultimate strength of concrete, the stress-strain curve is not much curved and more accurate values of modulus of elasticity may be obtained. It has been observed that even under short term loading concrete does not behave as an elastic material. The modulus of elasticity so obtained from actual loading is called static modulus of elasticity. A stress-strain curve is drawn with the help of values of stress and strain obtained. The stress will be obtained by dividing the load by the area of cross-section of the specimen. The value of strain is calculated by dividing the gauge readings by gauge length. (Universal testing machine) and measuring the strains or deformations by strain gauges or dial gauges fixed at certain gauge length. The modulus of elasticity is determined by subjecting a cylinder of 15 cm diameter and 30 cm length or 15 cm cube to uniaxial compression usually in U.T.M. Hence the degree of nonlinear behaviour is also very small. When the load is applied extremely rapidly, the recorded strains are greatly reduced and the curvature of stress strain curve is reduced to a very small value.īy slowing down the rate of loading i.e., by increasing the time of loading from 5 seconds to about 2 minutes, the increase in the strain is found to go up by 15%, but at normal rate of loading, normally 2 to 10 minutes time is required to test a specimen in an ordinary testing machine, the increase in strain is very small. The magnitude of the observed strains and the curvature of the stress-strain relation depend on the rate of application of stress. The terms elastic modulus or Young’s modulus of elasticity can be applied strictly to linear relationship i.e., straight part of stress strain curve. It is a measure of stiffness or resistance to deformation of a material. Thus the deformation behaviour of concrete is quite complex. The deformation of concrete depends upon the magnitude of the load, the rate of applying the load and the time elapsed after which the observations are recorded. In case of concrete, it deforms on the application of load, but this deformation does not follow any set rule. On the other hand if the curve is as shown in Fig.15.2 then the material is not perfectly elastic. If the stress-strain cure is straight as shown in Fig.15.1 then the material is elastic. By definition of elasticity, strain appears on the application of stress or force and disappears on removal of stress. Actually none of these assumptions is strictly true and concrete is not perfectly elastic material. In the theory of reinforced concrete, it is assumed that concrete is elastic, isotropic and homogeneous and obeys Hooke’s law. Determination of Modulus of Elasticity 3. In this article we will discuss about:- 1. ![]()
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