Shear connections are designed to absorb shear forces caused by loads applied to structural elements. The most debated element related to shear connections are concrete beams. There are no beams without connections, although other elements may have connections omitted as design requirements.
A load applied to a structural element is transferred to its supports in the form of stresses. We take them into account in different ways in our projects. These are the bending moment and the shear forces. The shear force is the force that transfers the load applied to the column.
As explained above, shear amplification in the beam is inevitable. According to structural design standards, we must provide at least minimum shear reinforcement in the beams.
Let's discuss why we need shear connections
As we can see in the figure above, the shear fracture plane is angular. However, we provide shared connections in the vertical direction because, in practice, this is the easiest way to maintain them.
There are other ways to attach shear reinforcement. Upward-facing bars contribute most effectively to shear strength and are placed perpendicular to the plane of shear failure.
However, due to the density of the reinforcement, it is very difficult to place the bent bars as shear reinforcement inside the beams. They are also used in areas where shear stress is critical.
As we can see in the image above, bent bars can be placed in the beams, with the main reinforcing bar continuing as a bent bar in the beam.
Let's specifically discuss the type of shear reinforcement in beams.
Beam Shear Connections
When shear reinforcement is provided for beams, we need to follow the standard reinforcement detailing method. Most standards like BS 8110, ACI 318, Eurocode 2 etc. follow almost similar shear reinforcement arrangements.
The bundle of articles Shear design For more information on the design process, reference can be made to Eurocode 2.
Furthermore, the reinforcement provisions for seismic requirements are more similar.
The following figure of the standard detailing method shows the type of connections and their arrangement in the beams.
Depending on the detailing and reinforcement requirements of the project, shear connections are provided. Furthermore, constructability aspects are also taken into consideration when detailing the reinforcement.
The following figure was also taken from the same pattern. It shows some of the most important aspects that are taken into account in detail according to Eurocode 2.
These guidelines must be strictly followed when detailing shear reinforcement. Furthermore, the detailing is not limited to the above methods and reference should be made to the relevant standards.
In summary, the following can be highlighted
- No shear connections may be overlapped as specified
- If twisting moments occur, attention must be paid to the shape of the connecting link
- Compression bars must be secured by fasteners in accordance with the requirements of relevant guidelines.
- Compression rods must also be secured by shear connections in accordance with specified standards.
Plate Shear Connections
Making shear joints in panels is not a common practice. However, we normally use shear joints in flat plates. Flat plates are shear critical depending on the magnitude of applied loads.
Unlike beams, shared members have special types of shear member assemblies and shear members that are used to transmit the shear forces.
Additionally, bent bars can also be used to support shear forces.
The following figure, created for the standard drill-down method, shows some important things that need to be considered in detail.
The above values are based on the detailing requirements of Eurocode 2. However, this provision and technical information may be used where appropriate.
In addition, the following statements can also be used to obtain more details about the arrangement of shear connections.
Column Scissor Connections
There are two main purposes for providing shear connections in columns
- To avoid bending
- To absorb shear forces
To prevent buckling of column under load, minimum number of connections should be provided in a column.
Buckling failure of columns is a well-known phenomenon. If connections are provided and reinforcement designs are carried out with adequate effective heights in mind, buckling failure can be avoided.
On the other hand, we create connections to supports to absorb shear forces. As in the article on Structural forms frame structures, in which there are no shear walls, support shear forces.
In this type of structure, the pillars support the shear forces that pass lateral loads .
It is mandatory, good Systems for absorbing lateral loads in buildings. In frame structures, however, the frame transfers lateral loads to the foundation.
Columns have different verbosity requirements. For normal structures, we provide shear connections in accordance with relevant standards. However, when we design/detail for seismic purposes, earthquake safety details must be expelled.
In relation to this area, the following important points can be highlighted.
- If the distance from a bar to the restraining bar (the bar with shear connection) exceeds 150 mm, a shear connection shall be provided to restrain that bar.
- The distance between the links must be in accordance with the relevant standards
- Most often, connection spacing is maintained at 150 mm to satisfy seismic requirements near beam-to-column connections. You could read the article on Seismic Detailing for better understanding.
Raft Shear Connections
Installing shear connections in individual slabs or foundations is not as common as they can be avoided through several methods.
We can increase the depth where the shear forces are greatest, or we can increase the area of the tensile reinforcement to increase the shear capacity.
However, increasing depth is not always possible, as it has limitations. According to BS 8110, increasing depth above a certain depth (400mm) does not directly contribute to increasing shear capacity.
As indicated in the figure above, these options can be followed to avoid shear joints. However, due to the construction difficulties of option 01 and the curb obstruction of option 02, this is not always the preferred option.
Anyway, let's assume we provide shear connections.
Therefore, we need to provide shear connections in the areas where the design shear is greater than the allowable shear.
Concepts or arrangements similar to those for flat slabs are also used for slab foundations.
However, the arrangement of the shear connections is slightly different.
The following image shows the details of a typical share link.
Links are provided around the loaded area and the number of links must meet the project requirements.
Shear connections in walls
There are basically two types of walls that require shear connections.
- retaining walls
- Shear walls
retaining walls
Retaining walls are exposed to out-of-plan actions. Due to out-of-plane loads, shear forces and bending moments arise.
Therefore, shear connections must also run in the shear direction to avoid shear errors. A similar type of shear connection as indicated above for slabs can also be used for retaining walls.
Links can be placed horizontally between vertical bars.
The number of connections to be provided in vertical and horizontal directions depends on the project requirements.
The method for calculating the number of shear connections can be found in the article on Punching Shear Design .
Shear walls
Shear walls are designed to accommodate lateral loads. Furthermore, the effect of the in-situ shear wall is utilized to resist the forces.
Therefore, the members of the actions are provided in the cutting direction. Closed links are usually provided. However, open links are also used, as shown in the following figure.
The number of watertight joints depends on the shear forces acting on the shear wall. The Shear Walls article could be more related to shear walls.
