Shear Force and Bending Moment
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For both the concentrated loads experiment and non-symmetrical loads experiment, as the load increases, the bending moment and the shear force also increases. If there is the presence of a graph for the two experiment, we can observe that as the shear force increases(with decreasing x),the slope of the bending moment also increases. However, for the symmetrical loads experiment, as the load increases, the shear force does not show many changes in the value and almost all the readings are nearly zero yet the bending moment increases. The bending moment is maximum when its derivative, the shear force is zero. Zero shear force will lead to the zero principal stress at the neutral axis as the shear force are equal to the integration of the shear stress over the section.
There are some errors occur during this experiment and cause the experimental values of the shear force and bending moment for the three experiments above are different from the theoretical value. Wind is the main factor that cause the readings to be inaccurate. This is because wind will shake the hanger of the loads and make it unstable. For concentrated loads experiment, the loads are not properly place in the center of the beam also cause the readings of the shear force and bending moment to be less accurate and make the beam to be unstable which also will affect the readings. The readings of the shear force and bending moment on the screen which are always change and make us to difficult to take the readings also is one of the errors. This is because the dynamometer is so sensitive to the surrounding condition such as wind and the digital indicator is not too accurate. The disturbance of the load by applying force also can cause the readings of the shear force and the bending moment on the screen to be inaccurate. For the symmetrical loads experiment, the factor that cause the error to occur is the distance between loads and support is not exactly equal and same. Moreover, the beam is too sensitive as when we want to put the load, the beam is moving. The beam is no more at the original position when we try to change the holder of the hanger to another size. Therefore, the experimental value for the shear force and bending moment are different compare with the theoretical value.
There are some precautions need to be taken during this experiment. In order to prevent the disturbance from surrounding such as wind, this experiment must be done at a less windy place. This is because wind is able to affect the readings and make the results inaccurate. Make sure that the beam is aligned horizontally when each load is added to the hanger so that the beam is balanced and an accurate results can be obtained. Moreover, the load must place in the exact center of the beam in order for it to balance. We also must ensure that we do not cause the unbalancing of the beam when we align the beam horizontally or add load to the hanger.