Box type section is the most preferable section to be used at places where torsion occurs.

Explanation:

Torsion is a twisting force that tends to cause rotation in an object. In structural engineering, torsion can occur in various elements such as beams, columns, and shafts. When designing these elements, it is important to select a section that can effectively resist torsional forces.

Types of Sections:

1. Angle Section: Angle sections are commonly used for resisting bending moments. However, they are not ideal for torsional loads as the flanges of the section are relatively thin. This makes them less effective in resisting torsional forces.

2. Channel Section: Channel sections have a shape resembling a U, with a flat base and two flanges. While they are commonly used for resisting bending moments, they are also not the best choice for torsion. Similar to angle sections, the flanges of channel sections are relatively thin, making them less effective in resisting torsional forces.

3. Box Type Section: Box type sections, also known as hollow sections, have a closed rectangular or square shape. These sections are highly effective in resisting torsional forces due to their closed shape. The closed cross-section provides a greater resistance to twisting forces compared to open sections like angles and channels.

Advantages of Box Type Section:

- Increased torsional rigidity: The closed shape of the box section provides higher torsional rigidity, making it more resistant to twisting forces.

- Uniform stress distribution: The closed shape allows for a more uniform distribution of stress throughout the section, reducing localized stress concentrations.

- Greater strength-to-weight ratio: The hollow nature of the box section allows for efficient use of material, resulting in a higher strength-to-weight ratio compared to other sections.

- Easy integration: Box type sections can be easily integrated with other structural elements, providing flexibility in design and construction.

In conclusion, the box type section is the most preferable choice at places where torsion occurs due to its superior resistance to twisting forces, uniform stress distribution, and higher strength-to-weight ratio.