The basic requirement for shear reinforcement is to strengthen the shear load capability that members can bear. However, another important condition that must be met is that, unlike the sudden brittle failure behavior of the member that occurs after reaching the maximum shear force, the ductile behavior must be improved by using shear reinforcement.

Improved shear resistance performance (P₂) is secured compared to the shear resistance capacity (P₁) when unreinforced. (See [Figure 1] on the left)

It has the effect of reducing the width of cracks that occur. This is due to the effect that the displacement value (d₂) is reduced compared to the value (d₁) when not reinforced. In particular, the enlarged head type shear reinforcement ‘SRD’ has the characteristic of a significantly reduced displacement value (d₂) compared to the bending anchorage type

This is a truss model composed of Struts, Ties, and Nodes that transmit the cross-sectional force of the Struts and Ties to a Node or nearby area. Reinforced concrete members can be designed according to traditional shear design methods or the Strut-and-Tie model.

The strut responsible for compression corresponds to the concrete, and the tie refers to the surrounding concrete having the same central axis, including reinforcing bars, tendons, or these. Additionally, the surrounding concrete is also used to define nodal areas where the forces of struts and ties can be anchored. In particular, in the Strut-and-Tie model of reinforced concrete members, the ties must be firmly anchored (in the node area) by mechanical devices, post-tension anchoring devices, standard hooks, extensions of reinforcing bars, etc. in order to effectively exert tensile force.

Quotations : R. Beutel, J. Hegger / Germany / Cement & Composiete 24 (2002) 539-549

Shear reinforcement is placed across the shear crack location, and it plays a role in confining the concrete to prevent the shear crack widening. (See [Photo 2] on the left)

And the performance of shear reinforcement can be ultimately evaluated by comparing the anchorage characteristics with a pull-out tensile test, as shown on the left [Figure 2].

The general classification of shear reinforcement methods includes 1) Bending anchorage type represented by Stirrup, 2) Shear head type in which steel beams are arranged in a lattice form, and 3) Enlarged head type introduced in the revised domestic structural standards in 2012. In particular, it can be explained in two types. The main features compared to the bending anchorage method and the enlarged head method are summarized as follows.

Bending anchorage method

Bending anchorage method

Method of securing anchorage performance	· ⓐ Bending part + ⓑ Penetrating rebar + ⓒ Bonding force · Secure anchorage performance through the 3-factors · Rebars must be tightly surrounded.
Anchorage displacement (slip)	· (relatively) large
Cracks and peeling	· The width of cracks is (relatively) large. · Structural performance degradation when the peeling
Whether yield strength is reached	· Not reaching yield strength (thin slab, etc.)
Type	· Closed, single-stranded, multi-stranded stirrups, etc. (see figure below) · This method also includes the use of steel wires or thin plates instead of rebars
Example

『Concrete Structure Standard Design Commentary KDS 14 20 22, 4.11.5 (1)』

According to the results of an experimental study (Joint ACI-ASCE Committee 421 1999), the studs with mechanical anchorage that are as close to the top and bottom of the slab as possible effectively resist punching shear. Compared to shear reinforcing bars with hooks at the ends, the enlarged heads of shear studs have less slip, so the shear crack width is relatively small.

The enlarged head method has the characteristic of maintaining anchorage performance with little deformation (slip) by using the enlarged head alone without the help of adhesion even in situations where cracks progress or the coating peels off.

This means that the performance of the structure can be stably maintained even in unexpected situations such as sudden shocks, and this can be said to be a very necessary feature, especially in public SOC structures where safety is important.