Fig. 286. Princess Truss.
The main truss is made up of the cross beam (D), rafters (E, E) and thrust beam (F). Purlin posts (G, G) are placed at an angle intermediate the ends of the rafters, and the purlin plates (H, H) support the roof rafters (A, B, C); I, I are the vertical tie rods.
This type is probably the oldest form of truss for building purposes, and it has been modified in many ways, the most usual modification being the substitution of posts for the tie rods (I, I).
Following out the foregoing forms, we may call attention to one more type which permitted ornamentation to a considerable degree, although it still required the tie beam. In fact the tie beam itself was the feature on which the architect depended to make the greatest effect by elaborating it.
This is shown in Fig. 287, and is called the Arched, or Cambered, Tie Beam Truss. It is a very old type, samples of which have been found which take it back to a very remote age.
Fig. 287. Arched, or Cambered, Tie Beam.