Calculate the Axial Forces of the Truss Members

Find the axial forces of the members 2-3, 9-3 of the truss for the given loads.

Solution

From the equilibrium of the forces on the truss we have:

ΣF_x = 0 -> H₁ = 0

ΣM₁ = 0 -> 200 * 4 - B₅ * 8 = 0 -> B₅ = 100KN

ΣF_y = 0 -> B₁ + B₅  = 200KN -> B₁ = 100KN

We consider the cross section T so as to calculate the axial forces on member 2-3 and 3-9. We consider the equilibrium of moments to the node 9.

ΣM₉ = 0 -> 2 * 100 - S_2-3 * 2 = 0 -> S_2-3 = 100KN

From the quilibrium of forces at Y direction

ΣF_y = 0 -> -S_9-3 * sin45 + 100 = 0 -> S_9-3 = 100 / sin45 KN