A truss
In this step, we meet axially loaded members - referred to in Structure Bench as truss members. These are structural elements that only carry axial load, rather than the frame members we've been using up to this point that resist bending and axial load.
Truss members, unsurprisingly, are most commonly used to model pin-jointed truss structures. They're also commonly used to model bracing elements in larger structures, something we'll see in a later step.
Our focus in this step will be how to use axially loaded elements and read the results returned from Structure Bench's solver. Our case study structure will be a simple Pratt truss. The common manual analysis techniques that we can use for pin-jointed structures like this are the method of sections and the method of joints. If you need a refresher on these techniques, take a look at this EngineeringSkills tutorial, Truss Analysis using the Method of Joints and Method of Sections.
1.0 The idea
A truss member is pinned at both ends, which means no moment can be transmitted into the member. When we connect enough of these members together, we can form triangulated structures - trusses. These act to resist externally applied loads by developing axial forces within the members of the structure.
Because each member in a truss structure only develops axial force, truss structures tend to be structurally efficient because all of the fibres in the member develop the same magnitude of axial stress. In other words, all of the fibres in the cross-section of an individual member are equally utilised. This is in contrast to a member that bends or flexes and develops linearly varying normal stresses, maximally utilising the outer fibres with zero stress at the neutral axis.
For each structural member in Structure Bench, we assign a member type - frame (flexural) or truss (purely axially loaded). Once a model has been solved, we can visualise the axial forces that develop in each member.