- [Instructor] So the first special element
we're going to look at is the truss element.
And we're going to remind ourselves what is a truss element.
It's a 1D line element.
There's no representational space in this element.
It just knows area as a parameter taken from
a geometry interpretation.
It only carries end loads,
there are no moments, shear forces, or torsion.
Each end is pin-jointed.
Now we've already seen some examples,
such as in the building industry,
where they're actually described as trusses.
Then we have crane jibs, which are truss-like.
We have cables in tension.
And finally tension links.
The SOLIDWORKS Setup to produce these elements
requires constant section geometry,
typified by Boss-Extrude, or Loft-type operations.
We can also use Weldments,
which have a constant cross-section.
The finite element analysis mesh that results
has one element per body,
and a pin joint at each end.
So in this example, there are only two elements,
in this truss assembly, and three joints.
The area is obtained from the geometry of the body.
Now in this SOLIDWORKS Setup,
constraints, or fixtures as they call them,
can only be applied at joints.
There's no meaning to applying a fixture on the body.
Out of plane, degrees of freedom are also no constrained.
Loading can only be applied at joints.
There's no meaning to load being applied along the truss.
And finally, no moments can be applied at the joints.
When we look at the output from a truss element,
we have to be careful about the sign convention,
for the stress on the force within the element.
The sign convention used is dependent
on the element orientation.
Now in some cases,
that might conflict with the conventional load
balance diagram.
In the example shown, the external load to the right,
is going to result in tension in the left hand member,
and compression in the right hand member.
So we have to use engineering judgment
to confirm the sense of the stresses and the forces.