Frames

Frames are generally rigid, stationary structures often consisting of pin-connected members to form a stabilized system to support externally applied loads.

Trusses are made of two-force members that withstand axial forces like tension and compression, operating along the axis of their members.

In comparison, frames are composed of two-force members and at least one multi-force member, which is acted upon by three or more forces.

They are widely used as structural support in beams and columns of buildings, chassis in automobiles, and construction equipment like cranes and excavators.

To analyze a frame, consider an example of a crane in equilibrium lifting a load W.

A free-body diagram of the crane is drawn to determine the external forces acting on the frame.

Further, each member of the free-body diagram is separately analyzed to identify the known and unknown forces. Generally, two-force members are considered first.

Then, the forces acting at each end and connecting point of multi-force members are determined.