3D Beams and frames

In the Beams and frames pathway, we worked through the 2D modelling canvas from first principles: nodes, members, sections, supports and loads, the diagrams and the probe, load cases and combinations, and what a linear elastic solve does and doesn't tell you. All of the structures in that pathway were planar, existing exclusively in a single 2D plane.

In this 3D Beams and frames pathway, we'll take those same skills into three dimensions. The 3D canvas has a toolset of its own, and some of it may not be familiar even if you've used other 3D analysis software.

A section now has a roll angle, and a load can act in any of three directions, in global or local axes. Supports and releases work on six degrees of freedom rather than three. We’ll also meet behaviour that only exists in 3D, such as strong and weak axis bending, biaxial bending, torsion, space trusses and lateral load paths in two directions.

We'll start where the 2D pathway started, with a simply supported beam, and see the 3D canvas give the same numbers. Then we'll add the 3D ideas one at a time, finishing with a two-storey braced building frame, built from a grid.

In this pathway, we'll work through ten steps with nine models. The model for each step can be opened alongside the pathway page, so you can orbit it, read its results and probe its members as you read. If you're a member, you can copy any of the models into one of your own projects and try the changes each step suggests. As before, you'll learn far more by poking and prodding the models yourself than by reading about them! By the end of the pathway, you'll be able to:

• build a beam or a frame in the 3D canvas, orbit around it, select what you mean to select, and read its results in six components,
• say which way a member's local axes point, set a roll angle on purpose, and predict what it does to the stiffness,
• apply a load in global or local axes, in any of the three directions, and get the per-metre convention right on a sloping member,
• read bending moments in both planes and torsion, and work out the worst fibre of a section by hand,
• choose a release, a hinge or a support's six degrees of freedom to match the connection you're modelling,