Tuesday, 28 March 2017

BASICS OF SHEAR FORCE AND BENDING MOMENT DIAGRAMS

BASICS OF SHEAR FORCE AND BENDING MOMENT DIAGRAMS

We were discussing meaning and importance of shear force and bending moment and also sign conventions for shear force and bending moment in our recent posts. We have already seen the various types of beams and different types of loads on beam during our previous posts.

 
Today we will see here the basics of shear force and bending moment diagrams in subject of strength of materials with the help of this post.

As we know very well that shear force diagram i.e. SFD will tell you the variation of shear force along the length of the beam and bending moment diagram i.e. BMD will tell you the variation of bending moment throughout the length of the beam.

Now we will see here few points those are very important to consider while drawing shear force diagram i.e. SFD and bending moment diagram i.e. BMD.

We will have to divide the loaded beam with section X-X and we will have o consider either left or right part of the section.

Length of shear force diagram i.e. SFD and bending moment diagram i.e. BMD will be equal to the length or span of the given loaded beam.

 
Shear force diagram i.e. SFD will be drawn below the given loaded beam and bending moment diagram i.e. BMD will be drawn below the SFD.

We will have to remind the sign conventions for shear force and bending moment during drawing the SFD and BMD.

We will have to add all the forces including reaction forces too normal to the beam on left or right portion of the section. We may select left portion of the section or right portion of the section of the beam according to our choice, but we will select left portion of the section during drawing the SFD and BMD.

If inclined load is acting on beam, we will have to resolve the inclined load in vertical and horizontal components and only vertical component of the inclined load will cause the shear force and bending moment. Horizontal component of the inclined load will cause the axial thrust in the loaded beam.

If a beam will be subjected with a couple at a section then bending moment will be changed suddenly at the section but shear force will remain same at the section.

We must have to note it here that positive values of shear force and bending moment will be drawn above the base line and negative values of shear force and bending moment will be drawn below the base line.

 
We will have to determine shear force and bending moment at each critical point.

In case of simply supported beam, bending moment will be zero at end supports.

In case of cantilever beam, bending moment will be zero at free end.

In case of overhanging beam, bending moment will be positive between two supports and bending moment will be negative for the overhanging portion.

Shear force will be constant between two vertical loads or we can also say that if there is no load between two points then shear force will be constant and will be represented by a horizontal line.

Above points must be considered during drawing shear force diagram i.e. SFD and bending moment diagram i.e. BMD.

Do you have any suggestions? Please write in comment box

Reference:

Strength of material, By R. K. Bansal
Image Courtesy: Google

We will see another important topic i.e. concept to draw shear force and bending moment diagrams for a cantilever beam with a point load or force acting at free end in the category of strength of material.

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