**Follow the load.**

Every truss you have ever walked past is asking you a question: which of these members is
being pulled apart, and which is being crushed? This app 📱 is built around answering it.

Pick a span and you get bare line geometry — no illustration, no decoration, just chords,
webs, supports and the loads on them. Before a single number 🔢 appears, you commit: tap 👆 a
member once to call it **tension**, twice for **compression**, three times for **zero
force**. Then you press LOAD, and the structure judges you instead of a message box.
Members you called correctly ignite and are redrawn with their stroke width proportional
to the force they actually carry, so the load path appears as thickness. Members you
called wrongly buckle sideways or snap at the joint, and the span sags. Nothing tells you
that you were wrong ❌ — you watch 👀 it happen.

Behind the drill sits a real engine, not a quiz ❓ script:

- **Truss solver** — a genuine 2D pin-jointed solver (equilibrium at every joint, solved
by Gaussian elimination) with support reactions, determinacy checking and a live
redraw as you drag ✋ span, depth and bay count.
- **Joint by joint** — the method of joints played back one joint at a time ⏱️, with the
force triangle drawn as it resolves and both equilibrium equations written out in real
numbers 🔢.
- **Section cut** — drag ✋ a cut across the span, move the moment centre to any joint, and
watch 👀 the arithmetic rewrite while the answer stays the same.
- **Supports and reactions** — swap pin for roller, drag ✋ supports along the chord, see 👀
what each one can and cannot resist, and push the span sideways to prove it.
- **Shear and moment** — build 🔨 a beam, add point and distributed loads, and read V and M
anywhere along it with the two diagrams live under the deflected shape.
- **Buckling** — Euler's critical load against a live curve: drag ✋ a strut longer and
watch 👀 its capacity collapse, with end conditions, slenderness and the governing
failure mode called out.
- **Member sizing** — assign real stock sections, or auto-size the whole truss, and grade
every member's utilisation with a slenderness cap on the compression members.
- **Determinacy** — add and remove members until 2j = m + r balances, with twelve
hand-built challenges and an unstable frame that genuinely wobbles.
- **Load cases** — flip between dead, snow, wind, uplift and point loading, predict which
members will reverse sign, and see 👀 each member's governing case.

Plus a reference library 📚 of 24 truss types with live thumbnails and the story of what each
was invented to do, 30 written explanations of the mechanisms behind the answers, a
99-term glossary that cross-links itself, spaced review that brings back exactly the
members you keep mis-signing, and a specimen file where you can photograph a real roof
truss or footbridge, trace its joints onto the picture and solve that structure — or work
on a blank grid, because the camera 📷 is always optional.

174 drill structures across eight load cases. Force in kN, lbf or kgf; length in metres or
feet; change it once and every number 🔢 in the app 📱 re-labels itself instantly ⚡. Orange is
always tension, blue is always compression, teal always carries nothing — nothing here is
coloured for decoration.

No accounts, no adverts, no sound. Everything you model stays on your device 📱.

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Crystal Castle Games Studio

Additional Information