Difference between frame and truss

Many times in our daily engineering work life the words truss and frame are used in place of each other, though they have many similarities but there exist some differences between truss and frame.

Truss and frame both are constructed by some triangular members and connected at joints.
In truss, joints are of pin joint type and the members are free to rotate about the pin. So, truss cannot transfer moments. Members are subjected to only axial forces (tensile and compression).
On the other hand, members of frames are jointed rigidly at joints by means of welding and bolting. So the joints of frame could transfer moments also in addition to the axial loads.

Practically, you may see trusses with no flexibility in joints, but still the analysis could be acceptable, if you assume it as a perfect truss.

  • Rebecca Brannon

    The elegant and rigorous definition of a truss is “a structure composed entirely of two-force members.” With this definition, there is no requirement that the links be straight or to form triangles. The need for frictionless pins and and for loads to be applied only at joints are consequences of this definition. Any load-bearing structure that is not composed of two-force members is called a frame. It’s that simple.

  • Rebecca Brannon

    The elegant and rigorous definition of a truss is “a structure composed entirely of two-force members.” With this definition, there is no requirement that the links be straight or to form triangles. The need for frictionless pins and and for loads to be applied only at joints are consequences of this definition. Any load-bearing structure that is not composed of two-force members is called a frame. It’s that simple.

  • MechGuru

    Thanks Rebecca for sharing your knowledge