Shear centre – definition of the special load application point In an open thin-walled section, the shear centre is the unique point through which if the resultant transverse load acts, the member will experience no:

Introduction:
Open, thin-walled sections (e.g., channels, angles, Z-sections) loaded by shear often twist if the shear load is not applied through a special point. That special point is the shear centre. Recognizing its role prevents unintended torsion and warping in beams and stiffeners.

Given Data / Assumptions:

• Linear elastic behavior; Saint-Venant torsion concepts apply.
• Transverse shear flows develop in walls of open sections.
• Load is applied at a point in the cross-section; bending about centroidal axes is allowed.

Concept / Approach:

The shear flow distribution in an open section generates a resultant that generally does not pass through the centroid. If the external shear force is applied away from the shear centre, a torque results. The shear centre is defined as the point where application of the resultant shear produces zero net torque, so the section bends without twisting. For doubly symmetric sections (e.g., rectangles, circles), the shear centre coincides with the centroid; for most open asymmetric sections, it lies outside the material boundaries.

Step-by-Step Solution:

Verification / Alternative check:

Classic results place the shear centre outside for channels and angles; experiments confirm no twisting when loading through this point.

Why Other Options Are Wrong:

Bending still occurs under transverse loads; tension/compression refer to axial effects; “shear” is present by definition.

Common Pitfalls:

Assuming centroid equals shear centre for any shape; ignoring warping torsion in thin-walled members.

Final Answer:

Torsion