About
This is a growing collection of illustrated essays about how structures carry load. Each one takes a single idea and draws it until the argument is visible.
What this is not
It is not a textbook, not a code of practice, and not a design guide. Nothing here should be used to size anything. There is no syllabus, no problem sets, and no obligation to cover anything in particular. An essay exists because there is a figure that explains something better than a paragraph can — and if there is no such figure, there is no essay.
The figures are solved, not sketched
Every illustration is generated as SVG at build time by code in this repository. None are photographs, none are exported from a drawing program, and none are bitmaps. The consequence that matters is not that they are sharp or small, though they are both:
- They are correct by construction. The member forces in a truss figure come from assembling the joint equilibrium equations and solving them, so the members coloured for tension really are in tension. A shear diagram is the integral of the load, computed. A deflected shape is the second integral of the moment.
- They are parameterised. The same generator draws the truss as a Pratt, a Howe or a Warren, at any number of panels and any depth, and the essay picks.
- They respond to the light and dark themes, because they reference colour roles rather than colours. Vermilion always means applied load; green always means reaction.
The full set of generators is listed on the figure library page.
Nothing here is measured directly
Statics is a science of things that do not move. Every quantity in it is obtained by imagining a motion that does not happen and insisting the sums cancel — a free body is cut where nothing has been cut, and forces appear on the cut face that no instrument ever recorded. This site tries to keep that visible: where a number is quoted, the essay says which body was drawn and which equation produced it.
Where the model stops
The subject is a stack of assumptions, each excellent inside a range: rigid bodies, small deflections, linear elastic material, pinned joints, plane sections staying plane. Every one of them fails somewhere, and several of them fail exactly where structures actually collapse. Where a figure relies on one, the essay names it.
On being wrong
Corrections are welcome and will be made. A figure that is beautiful and wrong is worse than no figure, because it is more persuasive.