Engineering Mechanics

(^278) „„„„„ A Textbook of Engineering Mechanics
13.18. MISCELLANEOUS STRUCTURES
In the previous articles we have been analysing the regular frames subjected to vertical, hori-
zontal and inclined loads. We have been solving such examples by the methods of joints and sections.
But sometimes we come across irregular structures.
Such structures may be analysed in the same way as that for regular structures. The casual look
at such a structure, gives us a feeling that it is complicated problem. But a patient and thoughtful
procedure helps us in solving such problems. The following examples will illustrate this point.
Example 13.17. Figure 13.54 shows a bridge truss of 130 m span subjected to two points
loads.
Fig. 13.54.
Determine the forces in the members 1, 2 and 3 of the bridge truss by any suitable method.
Solution. The whole structure may be considered to consist of two cantilever trusses
supporting an intermediate truss. As a matter of fact, the two point loads acting at the intermediate
truss are transferred to the ends of the cantilever trusses.
Since the two cantilever trusses are symmetrical and the point loads on the intermediate truss
are also symmetrical, therefore each cantilever truss is subjected to a point load as shown in Fig.
13.55 (a).
Fig. 13.55.
Let VB = Vertical reaction at the support B.
Taking moments about the support A and equating the same,
VB × 30 = W × 50 = 50 W