Support reactions:
If a support prevents
translation of a body in a given direction, a force is developed on the
body in that direction.
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Constraints |
Type and direction of forces produced |
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The connection point on the bar can not move
downward. |
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The joint can not move in vertical and horizontal
directions. |
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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. |
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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:
- FBD:
