Test: Trusses -2 - Civil Engineering (CE) MCQ

At join D, the equilibrium shows the force in member CD is 50 kN tensile.

For plane truss assumptions are:
(i) Weight of all members are neglected. All members are straight.
(ii) All connections are smooth, frictionless pins.
(iii) External loads are applied directly to the pin joints.
(iv) All frames are perfect, hence statically determinate.

Cutting a section through members CA, CD, DEand EB and taking moment of the upper part about E.

∴ F_ca x 6 + 10 x 6 - 20 x 3 = 0
∴ F_ca = 0

Force in AB or AC [Consider joint B],

So in case I force in members will be less than that in case II.
From symmetry, there will be only vertical deflection of joint B.

Six members having zero forces are obvious and seventh member can be from top chord member between the applied loads.

At joint C there is no external force so force in member BC is zero.