Analysis of perfect frame (Truss)

 Definition of frame

A structure made up of several bars riveted or welded together is known as frame.



Types of frame

There are two types of frame -

  1. Perfect frame and 
  2. Imperfect frame
Perfect frame -

  • A perfect frame is the which follows the equation n = 2j - 3.

where, n = number of members and 

j = number of joints

  • In this type of frame, the number of members are just sufficient to keep the frame in equilibrium under an external load.
  • There is no extra member is present in a perfect frame.


Imperfect frame -

  • An imperfect frame is one which does not follow the n = 2j - 3 equation.
  • If the number of members in a frame are less than (2j - 3) then the frame is known as deficient frame.
  • If the number of members in a frame are more than (2j -3) then the frame is called redundant frame.


Assumptions made in analysis of frame

The following assumptions are made in finding out the forces in a frame - 

  1. The frame is a perfect frame.
  2.  The frame carries load at the joints.
  3. All the members are pin-joined.
Reactions of supports of a frame
The frames are generally supported on roller support or on hinged support. If the frame is supported on a roller support, then the line of action of the reaction will at right angles to the roller base. If the frame is supported on a hinged support, then the line of action of the reaction will depend upon the load system on the frame.



Analysis of a frame
Analysis of frame includes two steps.
  • Determination of the reactions at the supports and 
  • Determination of the forces in the members of the frame.
   We find out the reactions by considering that the applied load system and induced reactions at the supports form a system of equilibrium.
   To determine the forces in the members, we apply equilibrium condition on every joints.

Thank you.

 

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