Resolving forces in truss

We can now remove bars 1 and 2 from the model as well, replacing them with their internal forces. We can see all the resulting axial forces inside the member and the reactions at the supports. For them to take an axial load, they would have to deform along their axes, but since both extremities are constrained, they can't deform and therefore will never take a load.

Accordingly, there can be no force in Member 2 or else the point will become unbalanced and no longer static. Accordingly, since the sum of forces must be zero, that member can have no force associated with it. And that's that. Accordingly, we know that member 1 must be causing a force in the upwards direction to keep the point static.

The load is vertical and only bar 2 has a vertical component, so it will have to absorb the entirety of the external force. Again, if we look at summing the forces in the x-direction, we can see there is only one member that has any force in the x-direction.

Since bar 5 is rigid, the central node won't suffer any horizontal displacements from the horizontal force applied by bar 2. Since we know this force occurs at this point, we will consider just this point in isolation. We do this by ignoring all the members and just looking at the forces and supports in the structure.

These forces are known as Axial Forces and are very important in truss analysis.

how to solve trusses by method of joints examples
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Tutorial for Truss Method of Joints