ES-110 Frames and Machines
Frames are structures which contain multiforce members. Frames differ from trusses (see S120) specifically by
  1. Members can be continuous through joints.
  2. Loads can be applied anywhere.
  3. Forces do not have to be along members.
Note: Frames may contain truss members (two force bodies).


To solve for forces in members the following steps (illustrated by examples) should be taken...

All possible reactions should be found. For this case, A and D are pinned connections, therefore, it seems as though four reaction unknowns exist. However, inspection shows that AC is a truss member (it is a two force body), therefore, the reaction at A must be along AB (Ax and Ay are dependent), or

       (1)

Hence,

        (2)

Solution of (1) and (2) yield Ax and Ay.

The force equations yield the independent components Dx and Dy.


The forces in member AC are just the reaction at A. The forces in BCD are as shown...

Analysis of machines is identical to analysis of frames.


While frames are designed for static application, machines are designed for transmittal or modification of forces. Analysis of machines in this course is limited to their static behavior.

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