How to draw a shear force diagram - 01

Drawing a Shear Force diagram is a very important task is solid mechanics. A simple example of SFD for a point load is explained below.

Figure 01

Consider Figure 01: A point load is applied in the middle of the beam and the reactions in the two supports are given in the figure 01. 

Figure 02

01. Figure 02: Starting from the left side of the beam; the reaction at A is upward (see figure 02). As the shear force remains constant between A and B so the shear force diagram is constant between these points (figure 3).

Figure 03

• Note: actually when a structure / beam is in equilibrium then the shear force would be equal to the external load applied to a specific point. If a load in applied (fig 4.a) in a beam. In this point the shear would be the same (fig 4.). If the structure is in equilibrium then there would be an equal and opposite force to resist it (fig 4.c). Similarly, likewise of figure 4 (d) there will be an opposite force similar to the applied external load on the beam. This is the reason why the shear force are same/horizontal when there is no change of applied load between two points.

02.In the point B, there is a P load downward and we have a positive load of P/2 at this point. So the shear at B point would be - +P/2 – P = -P/2. Actually, the total amount of shear at B would be equal to the load applied on that point (P).

Figure 05

03.  Figure 6 is as Same as Number 01

Figure 06

04. A reaction at C, hence upward trend of the load meets the zero point (figure 07).

Figure 07