How can you distinguish a pinned connection from a moment connection in a structural frame?

• A. Pinned connections rotate freely and transfer minimal moment; moment connections resist rotation and transfer moment.
• B. Pinned connections rotate freely and transfer moment; moment connections resist rotation and transfer minimal moment.
• C. Pinned connections resist rotation and transfer moment; moment connections rotate freely.
• D. Pinned and moment connections behave the same.

Answer: (A)

Understanding how a joint handles rotation and bending moment is how you tell pinned from moment connections. A pinned connection allows rotation freely, so it does not resist turning about the joint and transfers only forces like shear and axial load with negligible bending moment. A moment (or rigid) connection, on the other hand, resists rotation; it provides continuity between members and transmits the bending moment, making the joint stiff under load.

So the best description is that pinned connections rotate freely and transfer minimal moment, while moment connections resist rotation and transfer moment. In practice, pinned joints often use simpler bolting without welding across the faces, whereas moment connections are welded or bolted with plates to lock the rotation and carry bending moments.

The other statements don’t fit because they reverse these roles or claim no difference at all.