The larger number of roof trusses are of this class, and, as a rule, the loads are considered as acting vertically, as is always the case with dead loads, so that the computations for the supporting forces are very simple.
In every truss with end supports and vertical loads symmetrically disposed with reference to the span, the supporting forces are equal, and each is equal to one-half the sum of the loads.
By symmetrically disposed, we mean that every load on one side of the center must be balanced by an equal load on the other side, and applied at the same distance from the center. It does not matter whether or not the truss itself is symmetrical nor what its shape may be, provided that the loads are symmetrical.
The trusses shown in Figs. 249, 252, 253, and 256 are both symmetrical and symmetrically loaded, and this is true of most of the trusses that have been shown thus far. Fig. 116 is an example of an unsymmetrical truss, symmetrically loaded.