- Assume that locomotion proceeds from left to right,
and compute the bending moment
Study shows that Mb increases as the system moves until the rear load is at C, the front
load being 14 ft (4.3 m) to the right of C. Calculate the corresponding value of M 6. Thus,
Mb = 22.50(24) + (22.50 - 3/8 x 14)(6) = 6435 ft-kips (872.59 kN-m). .'. Mb max = 664.5
ft-kips (901.06 kN-m). - Determine the maximum force in the member
Cut the truss at plane YY. Determine the maximum force in BC by considering the equi-
librium of the left part of the structure. Thus, ^Mb = Mb- 2QBC = O; BC = 664.5/20 =
33.2-kips (147.67-kN) compression.
INFLUENCE LINE FOR BENDING MOMENT
IN THREE-HINGED ARCH
The arch in Fig. 52a is hinged ZtA 9 B, and C. Draw the influence line for bending moment
at Z), and locate the neutral point.
Position of unit load
for zero moment
at D(a) Three-hinged arch(b) Influence line for bending moment at D
FIGURE 52