In this post you will learn:
| The support reaction, also known as the reaction at the point of support, is a force in the form of a vector that occurs at the point where a body (such as a beam, frame or truss) is connected to its support when it is disconnected from that support. |
It all starts with Newton's principles of dynamics... But, so as not to bore you too much I have recalled below the short definition he gives Wikipedia :
If body A acts on body B with a force F (action), then body B acts on body A with a force (reaction) of the same value and direction, but with opposite direction.
That is, if we press on the support with some force or moment, then the support gives us back. And this force with which the support gives us back is just reaction.
Thanks to the fact that the forces of interaction balance each other, we can talk about static, that is, the body remains at rest.
Types of supports and their support reactions
Mechanics defines the reactions of supports depending on the type of support. Below you will find a description of the most common types of supports.
| You can find all the supports listed below in the app Beam calculator Where you can test ways to support beam systems and get a complete step-by-step beam solution. |
Pin support
The first type of support we will discuss is a non-sliding (fixed) pivot support. Such a support blocks our ability to move horizontally (x-axis) and vertically (y-axis). There is, however, the possibility of rotation around the joint. That is why it is called a support articulated non-sliding. The circle at the top of the triangle in which the reactions are hooked is the joint.
You often ask if it matters which way the reaction feedback takes (which way the arrow of the force vector is pointing)?
| We can assume any turn we want, the important thing is that there is a constant direction. |
Roller support
Another type of support is the sliding pivot support. In this support we have one reaction in the vertical direction. It is in this direction that no movement is possible. The horizontal direction is freed, which is symbolized by the gap between the ground and the support or the circles symbolizing the possibility of movement.
| You may encounter in tasks with a support rotated by some angle. Then remember to turn the direction of the reaction perpendicular to the ground of the support, as I have shown in the figure above. |
Fix support
Restraint is another type of support you may encounter. Here, in addition to blocking movement in the vertical and horizontal directions, the possibility of rotation at the point of restraint is blocked. In restraint we have three degrees of freedom taken away, so we have three reactions: horizontal, vertical and moment.
Sliding bracket - vertical skate
The vertical skate is a support much less common in mechanics assignments. The vertical skate has two degrees of freedom taken away through horizontal reaction and moment. This support does not have the ability to move horizontally and rotate.
Sliding bracket - horizontal skate
The horizontal skate also has two degrees of freedom taken away from it, with the difference that it has vertical reaction and moment. This support does not have vertical movement and rotation.
Joint
And finally, the joint. How many degrees of freedom does the joint take away? As you can see in the figure above there are two degrees of freedom. Horizontal and vertical reaction just like in a non-sliding pivot support.