Every construction must be supported in such a way that the construction cannot move freely.
The Construction must also be supported in the directions where there are no applied forces.
If a construction is not properly supported the no calculations can be performed.
A junction point may be supported in three direction:
* Horizontally
* Vertically
* Rotated
A support to a nodal point exists if that nodal point can no longer move in a certain direction.
The load in that direction (reaction force or moment) is unknown and will be calculated be the program.
In the table below you can see the most common forms of support and their directions.
After applying supports to the junction points the rafter may not be allowed to move or rotate.
In the next diagram two incorrect constructions have been drawn. The first example is a construction still able to move along the X-axis. In the second the construction has a part still allowed to move on its hinge. Even if on both constructions there were no horizontal forces these constructions would still be incorrect.
