What is a Shear Key in Construction?

Shear key is a structural element that is installed in a structure to make it stable against lateral loads like wind and earthquake. The application of shear key varies based on the type of construction, loads and structure. It is generally used as a connection between two structural elements. We will discuss the important features, purpose and application of shear key in various structures.

Purpose of Shear Key in Structures

Shear key serves the purpose to maintain the integrity of the structure. The shear key only allows to transfer the shear stress and not the transfer of bending moment. Hence, its objective is to transfer the shear force caused due to applied loads or lateral loads between the structure and the shear key provided.

Shear keys can be provided in beams, retaining walls, columns, foundation etc. For example, in the case of a foundation, a shear key is provided below the footing in order to stop the sliding of the foundation. This would help to increase the factor of safety for sliding.

Consider a retaining wall as shown in figure-1. It is subjected to lateral earth pressure Fs that is created due to backfill on retaining wall. This Fs can result in sliding. If Fr is the force that is needed to stop sliding, 

when Fs =Fr, the cantilever will stay as such. 

When we consider IS: 456-2000, 

Fr ≥1.4Fs

When Fs > Fr, then it causes sliding. This will demand shear key. This means, when the factor of safety is less than 1.4, we provide shear key.

The shear is provided and constructed below the ground, on the base slab of the retaining wall, which stops sliding. This shear key creates extra passive earth pressure  (Ps)(which is much higher compared to active pressure), which stop the retaining wall from sliding.

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