Armature — Karamba-style Frame Analysis

Structure

Draw & edit

Point load20 kN

Any edit forks the preset into a custom model (the parameter sliders hand over to your geometry). Draw chains members click by click — Esc ends a chain; nodes snap to 0.25 m. The Load tool paints the Point-load value on nodes and the Deck-load value on members.

Loads

Deck load

Lateral load

Self-weight (from the sections)

Deck load is kN per metre of member on the deck members; lateral loads push at the frame joints. Self-weight is computed from each member's real section area × density — resize a section and the structure gets heavier.

Materials & sections

One material + section per member group, like Karamba's cross-section assignment. Click any member in the view to pin / free its ends (pinned ends carry no moment — a truss member).

Optimize (the Karamba move)

Target utilization1.00

Walks each group's catalog to the lightest section that meets the target, re-solving as the stiffness (and the self-weight) redistributes — Karamba3D's "Optimize Cross Section".

Display

Exaggeration

Peak-value labels

Import / Export

Import takes three formats: this tool's JSON, an OBJ line model (Rhino: export curves as OBJ — 3D input is flattened to the best axis plane and the discarded depth reported), and a Relax structural-net hand-off (same file Truss reads — its members arrive pin-ended; click them rigid and a chain stands as a bent beam). Imports without supports get pins at the low corners — move them with the Support tool. CSV lists every member with N / V / M, stress and utilization plus the reactions; OBJ writes centrelines back out for Rhino.

Vs. professional FEA — read this

What this shares with the pro tools: the first-order matrix displacement method is the same math SAP2000, RFEM or Karamba3D run first — the diagrams, reactions and deflections here are exact within that theory, not cartoons.

What a professional analysis adds that this does NOT have: the third dimension (out-of-plane behaviour, lateral-torsional buckling, torsion); second-order P–Δ effects and sway stability; design strengths with γ-factors and code load combinations (ASCE 7 / Eurocode — here γ = 1 on characteristic values); member imperfections and real buckling curves (here: bare Euler, k = 1); connection and joint design; dynamics, vibration and seismic; shells, plates and concrete. And a licensed engineer who signs it. Use this to develop structural intuition and rough proportions; never to size a real structure.

Sources & method

What is actually solved. A linear-elastic first-order plane-frame finite element analysis: 2-node Euler–Bernoulli beam-columns (3 dof per node) with real E, A and I from the material and catalog section you chose; end releases by exact static condensation (a member pinned both ends is a truss bar); uniform member loads via consistent fixed-end forces; K·u = f by Gaussian elimination. Deflections, diagrams and reactions are exact within that theory — the same math as Karamba3D's first-order Analyze.

The catalogs. IPE properties are the standard European table values (masses check against the published tables within 1%); CHS / SHS / timber / rod sections are computed from exact geometry — except that SHS ignores the corner radii, so those sections run a few percent heavy (never light). Timber strengths are EN 338 / EN 14080 characteristic values.

Utilization is σ = |N|/A + |M|/W_el measured against the material strength (steel/aluminium: yield; timber: separate tension / compression / bending values from EN 338 / EN 14080), γ = 1 — characteristic, not design, values. Compression members also get a Euler buckling check N_cr = π²EI_min/L² with effective length k = 1 and the member's weak axis; the governing value colors the view.

Optimization re-runs the analysis while walking each group's catalog to the lightest adequate section (Karamba's "Optimize Cross Section"). If even the heaviest section fails, it says so — never silently.

Not solved: second-order (P–Δ) effects and sway buckling, lateral-torsional buckling, out-of-plane behaviour (this is a PLANE frame), connection design, code load combinations and safety factors, cracked concrete (no concrete in the catalog on purpose). A learning + preliminary design tool — a licensed structural engineer must analyse and size any real structure.

Sources. Matrix displacement method: Hibbeler, Structural Analysis; McGuire, Gallagher & Ziemian, Matrix Structural Analysis — free 2nd ed.. Section tables: EN standard IPE ranges. Timber strengths: EN 338 / EN 14080. The tool this imitates: Karamba3D (parametric structural engineering for Grasshopper) — use it when the real project starts.