The net forces acting on a body must be zero for equilibrium

In order for a body to be in equilibrium, the net forces acting on it must be zero. This means that the vector sum of all the forces must be equal to zero. If there is a non-zero net force acting on a body, it will accelerate in the direction of that force.

Applicability of this principle to simply supported structures

This principle is also applicable to simply supported structures. Simply supported structures are those that are supported at two points, such as a beam supported on two pillars. The support reactions at these points play an important role in determining the equilibrium of the structure.

Support reactions are counted in making the net force zero

The support reactions at the points of support in a simply supported structure are considered external forces acting on the body. These support reactions are typically in the form of normal forces and moments.

When analyzing the equilibrium of a simply supported structure, the support reactions must be taken into account. These reactions contribute to the net force acting on the structure and must be included in the calculation of the net force.

For example, consider a simply supported beam with a point load applied at the center. The support reactions at the two ends of the beam will contribute to the net force acting on the beam. If the magnitudes and directions of these support reactions are properly determined, they can be added to the applied load to ensure that the net force acting on the beam is zero.

Conclusion

In conclusion, the net forces acting on a body must be zero for equilibrium. This principle applies to simply supported structures as well. The support reactions at the points of support in a simply supported structure are considered external forces and must be included in the calculation of the net force. By properly determining the magnitudes and directions of these support reactions, the net force acting on the structure can be made zero, ensuring equilibrium.