**Circular Section and Reverse Stress Condition**

In the field of structural engineering, the circular section is often encountered, particularly in the design of columns and shafts. When analyzing circular sections, it is important to consider the reverse stress condition, which refers to the occurrence of compressive stresses on one side of the section and tensile stresses on the opposite side. This condition can lead to structural instability and failure.

**1. Middle Third Rule**

The middle third rule is a widely used concept in structural engineering for analyzing circular sections. According to this rule, the neutral axis of a circular section lies within the middle third of the section's depth. In other words, the maximum tensile and compressive stresses occur within the middle third of the section. This rule provides a conservative estimate of the stress distribution and helps prevent the development of reverse stress conditions.

**2. Bending Equation**

The bending equation, also known as the flexure formula, is a fundamental equation used to calculate the stresses in a beam or column subjected to bending. It relates the bending moment, section properties, and distance from the neutral axis to the stresses in the section. However, the bending equation does not directly address the issue of reverse stress conditions in circular sections.

**3. Middle Quarter Rule**

The middle quarter rule is an alternative to the middle third rule for analyzing circular sections. It suggests that the neutral axis of a circular section lies within the middle quarter of the section's depth. This rule provides a more conservative estimate of the stress distribution than the middle third rule and ensures that the reverse stress condition is avoided.

**4. Parallel Axis Theorem**

The parallel axis theorem is a principle used to calculate the moment of inertia of an area about an axis parallel to its centroidal axis. It states that the moment of inertia about an axis parallel to a given axis is equal to the sum of the moment of inertia about the centroidal axis and the product of the area and the square of the distance between the two axes. While the parallel axis theorem is a useful tool for calculating the moment of inertia, it does not directly address the reverse stress condition in circular sections.

In conclusion, of the given options, the middle third rule and the middle quarter rule are the most relevant concepts when dealing with circular sections and the reverse stress condition. The bending equation and the parallel axis theorem, although important in structural analysis, do not directly address the issue of reverse stress conditions in circular sections. It is crucial for engineers to consider these rules and principles to ensure the stability and safety of circular sections in structural designs.