Structural Analysis MCQ Questions & Answers | Civil Engineering

Plastic Moment Capacity: This is the maximum bending moment a structural section can withstand before it starts to deform permanently.
Shear Force: Shear force acts parallel to the cross-section of a structural member.
Effect of Shear Force: When shear force is present, it reduces the area available to resist bending. Think of it like some part of the section is already 'busy' resisting shear, so it can't contribute as much to resisting bending. Therefore, the plastic moment capacity decreases.
Axial Force: Axial force acts along the longitudinal axis of a structural member (either tension or compression).
Effect of Axial Force: Axial force also reduces the area available to resist bending. If there's compressive axial force, some of the material is already stressed in compression, leaving less capacity for resisting compressive stresses from bending. If there's tensile axial force, it can similarly reduce the effective area for resisting bending. Therefore, the plastic moment capacity decreases.
In summary, both shear force and axial force reduce the plastic moment capacity of a structure.

The correct answer is Option C: 3.
Here's why:
In a rigid jointed plane frame, each member is subjected to three internal forces:
* Axial Force: The force acting along the longitudinal axis of the member (tension or compression).
* Shear Force: The force acting perpendicular to the longitudinal axis of the member.
* Bending Moment: The internal moment that causes bending in the member.
Therefore, there are three unknown internal forces in each member of a rigid jointed plane frame.