Generate faces form single mesh edge? My first post, and no im not suck in edit mode!

I downloaded a model of an oil rig from blend swap created by "B M." as i'm hoping to model one of my own.

Upon opening the blend file i noticed that the beam like support structures pictured below are modeled in a particular way where it looks to be single verts with edges that then somehow generates faces around it.




This don't seem to be the work of a modifier. Something seems to be going on under the 'Shape Tab' within 'Data Object' options, as when i tweak the 'Fill values' and the 'Bevel Factor' the geomerty generated around the faces of the single Vert and Edge begins to take shape / deform. 

In sum


What is going on here?
how do i achieve this type of modeling?
what other applications could this type of modeling be used for?


Thank you in advance.
There are three distinct ways to do this.


Either use Bezier Curve objects. They have the advantage of being simple to edit for tubular structures, can easily bend and make curves, and can have custom sections





Use a mesh with a Wireframe modifier. It is fast to process and is a mesh, so can have a lot more modifiers on top than a bezier curve





Use a skin modifier. It is slower to process and computationally heavy to handle, but will generate cleaner topology and have proper intersections at the joints.