ABSTRACT
This chapter is concerned with two-dimensional pin-jointed frames, or trusses. It considers three useful methods for analysing them to deduce the effects of externally applied loads: graphical methods; the method of joints; and the method of sections. Many framed structures are designed as pin-jointed frames. There are three methods available for use in determining the forces in the members of a pin-jointed plane frame. The Maxwell Diagram consists of a force diagram which contains within the one figure the force polygons for every joint in the framework. The pattern of loading is important for the two chords; it is preferable for loads to be applied at the joints, rather than between the joints. In a roof truss which supports purlins, for example, the spacing of joints along the upper chord is ideally related to the purlin spacing. The method of joints is a general-purpose method; it provides a speedy solution for parallel-chord trusses, but can be slower for pitched trusses.
