What is a shear key in steel structures?

 In steel structure engineering, the column base connection serves as the pivotal interface linking the superstructure to the concrete foundation below. It must safely and reliably transmit various loads from the upper structure: vertical pressure, uplift forces, bending moments, and horizontal shear forces. When horizontal shear forces become substantial, the friction alone between the column base plate and the concrete foundation surface proves insufficient to resist them. At this juncture, a critical small component becomes indispensable—the shear key.

Shear keys, as the name suggests, are structural steel connection components specifically designed to resist and transmit horizontal shear forces. Essentially, they are short steel members.

Installation location:

Typically welded or anchored to the base plate of a steel column (or other load-bearing components such as equipment supports), with its lower end embedded in the concrete foundation or concrete structure cast beneath.

Common forms:

1. Cylindrical-headed studs: Resembling short nails with enlarged heads, these are factory-welded to base plates. They represent the most widely used type with high standardisation.

2. Short sections of structural steel: Such as angle bars, T-bars, channel bars, and I-beam segments. Offering high load-bearing capacity and rigidity, they are frequently employed in heavy-duty structures or equipment foundations subjected to immense shear forces.

3. Shear plates: Thick steel plates with openings or embedded reinforcement bars, pre-embedded within concrete and welded to the column base plate.

Key Features:

It is no ordinary anchor bolt. While anchor bolts primarily resist uplift forces and secure positioning, the core mission of shear keys is to counteract horizontal shear forces. They serve as the “anchor” in structural safety, preventing slippage.

In essence: Shear keys are steel ‘bolsters’ or ‘pins’ embedded within concrete and welded to steel column bases, specifically designed to prevent horizontal displacement between steel structures and foundations.