Example 4.10

Determine the force in each member of the compound truss shown in Fig. 4.25(a).

Solution

Static Determinacy The truss has 11 members and 7 joints and is supported by 3 reactions. Since m þ r ¼ 2j and the reactions and the members of the truss are properly arranged, it is statically determinate. The slopes of the inclined members, as determined from the dimensions of the truss, are shown in Fig. 4.25(a). Reactions The reactions at supports A and B, as computed by applying the three equilibrium equations to the freebody diagram of the entire truss (Fig. 4.25(b)), are

With FAB now known, the method of joints can be started either at joint A, or at joint B, since both of these joints have only two unknowns each. We begin with joint A.
Joint A The free-body diagram of joint A is shown in Fig. 4.25(d).