Truss-One

Forty-five screens of structural analysis: section properties and principal axes, shear flow and the shear centre, the plastic section and its shape factor, axial members, plane stress and Mohr's circle, strain rosettes, elastic constants, yield criteria, thin-walled pressure vessels, beam diagrams, bending stress, transverse shear, transformed sections, combined axial and bending, deflection by standard case and by integration, trusses by joints and by sections, force diagrams, a model canvas, matrix solution of plane frames, circular torsion, non-circular and thin-walled torsion, combined bending and torsion, Euler columns with seven end conditions, the column strength curve, columns that started bent, columns loaded off centre by the secant formula, inelastic buckling by both the tangent and the reduced modulus, effective length for a column in a frame, plate buckling with its scalloped envelope, beam-columns, the movement of one chosen joint by virtual work, energy methods with Castigliano beside the unit load, supports on springs and beams bedded on soil, the classical methods -- slope-deflection and the force method -- checked against the matrix answer, second-order analysis with the buckling load found by counting pivots, plastic collapse by minimising over mechanisms, torsional and lateral-torsional buckling, the approximate methods bracketed from both sides, the whole model's own buckling mode, and a gravity retaining wall with its three failure modes. Every screen opens on a worked example rather than an empty form, and every number redraws as you type. There is no calculate button and nothing to wait for. Drag a span, a thickness or a load and watch the results and the figure move together — which is the thing a single static answer cannot show you. WHAT MAKES IT DIFFERENT Each result names the relation that produced it. A stress that came from combined axial and bending is labelled as such, so you can see which relation you are looking at instead of trusting a table. Where more than one answer is right, the app asks instead of deciding. A fixed-ended column braced against sway and one free to sway have the same end conditions on a drawing and critical loads four times apart; the app makes you say which, and tells you why it matters. Where a relation genuinely has no value — a bore as wide as the shaft, a column of no length — it shows a dash or an infinity sign and puts the reason beside it, rather than a zero you might act on. Where a model is near the edge of its range, it says so next to the number. A member too stubby for beam theory gets a note, not a footnote. HOW IT WAS CHECKED Every relation is verified against sixty-digit reference values computed independently of the app itself, from public-domain sources: NACA and NASA technical reports, MIL-HDBK-5J, and the Forest Products Laboratory's wood handbook. The macOS and iPadOS implementations are compared against the same reference values, so both give the same answer to the last few digits. The theory manual on the support site lists every relation, every assumption, and every limit. It is worth reading before you buy. WHAT IT IS NOT This is a mechanics tool, not a design-code checker. It applies no national or regional standard, computes no allowable stress, and applies no load factors. It will not tell you whether a member passes; it will tell you what the mechanics says, and show you the working. REQUIREMENTS macOS 14 or later, iPadOS 17 or later. Works entirely offline: no network connection is used, no account is needed, and nothing is collected.