What is a shear key and its role?

• A. A shear key is a decorative feature used for aesthetics.
• B. A shear key is a device that prevents lateral movement entirely.
• C. A shear key provides a roughened interface to improve shear transfer between deck and girder, enhancing composite action.
• D. A shear key provides a roughened interface to improve shear transfer between concrete deck and steel girder, enhancing composite action.

Answer: (D)

In composite bridge construction, you want the concrete deck and the steel girder to act together as one structural system, which means shear must be effectively transferred across their interface. A shear key provides a roughened or interlocking surface at that interface, creating mechanical friction and interlock that resist sliding between the deck and the girder. This enhances shear transfer and locks the two components together, enabling the deck and girder to share loads and behave as a single unit under bending and overall loading.

This is specifically about the concrete deck and steel girder pairing, which is why describing the interface as between concrete and steel is important. The other options miss that this feature is for a concrete deck-steel girder connection and/or use an absolute statement about preventing any movement, which isn’t how shear keys function in practice.