The following trusses are considered in this section: Three-hinged trusses, trusses with a hinged chain, and complex trusses. Each of the above-mentioned trusses has some peculiarities.

Three-Hinged Trusses

A three-hinged truss is actually two trusses connected by the hinge C as shown in Fig. 3.20a. Both supports are pinned. The fundamental feature of this structure is that horizontal reactions appear even if the structure is subjected to a vertical load

Having the influence line for the thrust allows us to determine the internal force in any member due to arbitrary load. Assume for example, that the right half of the truss is loaded by uniformly distributed load q. In this case,

After that, finding the internal force in any member is a matter of elementary calculation. So the influence line for thrust should be regarded as a key influence line