Support reactions:
If a support prevents translation of a body in a given direction, a force is developed on the
body in that direction.
Constraints Type and direction of forces produced
The connection point on the bar can not move
downward.
The joint can not move in vertical and horizontal
directions.
The support prevents translation in vertical and
horizontal directions and also rotation,
Hence a couple moment is developed on the body in
that direction as well.
Free body diagrams considering supports:
Example:
Draw the FBD for the following beam (the trusses are imposing the same forces on the
beam):
Solution:
• A pin can be considered for left support (A); no motion in 2 directions,
• A roller can be considered for right support (B); no vertical motion,
• Weight of the beam is generally neglected (when not mentioned and) when it is
small compared to the load the beam supports.
• Replace each truss with force F:
