Never manually sync your maths, sketches and 3D models again.

StructArk is a free engineering notebook for structural engineers. One plain-text document holds the inputs, the typeset calculation, the finite-element model, the building model and the dimensioned drawings. Move an input, and everything downstream moves with it.

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Free · No account · Release 0.0.1 · updated 2026-10-02

A piece of a calculation sheet: the earth pressure at the top and the foot of a retaining wall, then the moment and the shear at its base, each written out with the numbers and units put in, and its result under it.

Free: The notebook costs nothing and needs no account. Engineers never pay to open their own calculations.
Reusable: Any finished notebook is a template. The next footing is an input change and a re-print.
Auditable: Every input, formula and result is written out, so a checker follows it line by line and sees what changed between revisions.
Yours: Local files, and no licence to open your own archive ten years from now.

The problem

Concept to software is still typed in by hand.

No engineering notebook supports FEM and BIM

Notebooks like Mathcad and Blockpad typeset maths beautifully, but they cannot analyse a frame or hold a building model. Analysis and BIM live in separate, closed applications.

Every tool needs re-entry from the hand calc

The engineer sketches and solves on paper, then types the same geometry into the analysis package, again into the calc sheet, again into CAD. Each copy can drift, and a changed input has to be chased through all of them.

Existing alternatives

Tool	Strong at	Where it stops
Mathcad	Readable, unit-aware maths a reviewer can follow	No model, no drawings, a closed file, and a licence to open your own work
Blockpad	Spreadsheet and document in one, modern and affordable	General purpose: no FEM, no BIM, no structural drawings
CalcpadCE	Free, text-based calculations with formatted output	Calculation only; the model and the drawings still live elsewhere
Excel · Tedds	Universal sheets; code-checked library calcs	Hidden formulas or a fixed scope; the non-standard part of a job falls back to hand calcs
FEA + CAD + Word	Real analysis, real drawings, a presentable package	Three files, three re-entries; every revision is manual rework

The missing product is not a better spreadsheet. It is one document that can analyse, design, draw and report, and stay consistent when an input moves.

What it does

One set of inputs drives the typeset calculation, the analysis, the building model and the drawings. Change a span or a bar diameter and the whole notebook re-solves and re-draws. Every picture is a document that ships with the app, as the app draws it.

A sheet: a table of six inputs with sliders, a sentence that reads their values, and the earth pressure on a retaining wall written out with its numbers and units. — tank wall.md: the form, the sentence that reads it, and the earth pressure written out.

Inputs and formulas, written out as by hand

An input is a line with its value, its unit and its limits, and the sheet turns it into a form with a slider. A formula is a line too, and the sheet writes it out the way a checking engineer reads it: the symbols, the numbers put in, and the result with its unit.

Every SI and imperial unit, carried through every line and converted where it must be
A comparison is a check, and says OK or FAIL
A value is written into a sentence, so the text follows the numbers
The functions of algebra, trigonometry, matrices and statistics

Open in StructArk

A round tank wall as a mesh in 3D, coloured by its ring stress from blue at the top and the foot to red just above the foot, over a scale from 71.63 to 777.8 kN/m². — fem.md: a round tank 5 m in radius, full of water, coloured by its ring stress. The same document checks the ring force against Timoshenko's closed form.

Frames, plates and shells, solved in 3D

Nodes, members, meshes, supports and loads are one line each. The model is solved in three dimensions, its diagrams and contours are drawn on the sheet, and every result is a value the formulas below it can check.

Members, plates and meshes with openings; round walls, cones and rings for tanks and silos
Springs, settlements, end releases, and soil that lets go where a raft lifts
Load cases and combinations, self-weight, pressure and water loads
Linear or second-order (P-Delta) analysis

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A section through the retaining wall and its footing: hatched concrete with its bars, the fill in layers behind it, dimensions in millimetres, notes with leaders, and the button Export DXF above it. — tank wall.md: the section through the wall at 1:25, as Export DXF saves it.

Dimensioned details, saved as DXF

A detail is drawn in real units on layers, with its hatches, dimensions and notes, from the same values as the calculation. It stands on the sheet, and Export DXF saves it for any CAD program.

Lines, polylines with arcs, circles, ellipses and multilines
Hatches of concrete, earth, gravel and lines, and patterns of your own
Linear, radius, diameter, angle, ordinate and arc-length dimensions
Notes with leaders, and blocks at any scale and angle

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A 3D model of a small building on three levels: columns, beams, a curved balcony beam, two floors with a stair hole, masonry walls, pad footings, piles and a round water tank on the roof, with its grids and levels named. — bim.md: a small building on three levels, with an arc wall, a curved beam, a stair through the floor, pads, piles and a tank on the roof.

A building model, saved as IFC

Levels, grids and elements are written with the values of the calculation, so the model follows the form. It is drawn in 3D on the sheet, opens as large as the window, and IFC saves it for any BIM program. Its quantities come back as values.

Columns, beams, braces, walls, slabs, footings, rafts, piles and stairs
Curved walls, beams and slab edges, and openings through walls and slabs
Rectangle, circle, I, channel, tee, angle, box, tube and any polygon section
The volume, weight, area and length of an element, or of all of a material

Open in StructArk

A plot of the reinforcement a wall needs against its retained height, rising past the level line of what Y12 at 200 gives, with this wall marked at 2 m. — tank wall.md: the reinforcement a wall needs against its retained height. The curves cross at 3.787 m, the height these bars are good for.

Figures drawn from formulas

A curve is a formula over a range, drawn with its axes, units and legend. What the figure shows is published as a value: its largest value, a root, an area, or the point where two curves cross.

Curves, parametric paths, measured points, bars, and surfaces in 3D
Limit lines, marks, notes and shaded areas
Maximum, minimum, roots, areas and crossings, published to the text

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The first printed page of the tank wall calculation: its heading, the inputs as a table, the earth pressure written out, the check of the bars marked OK, and the start of a figure. — The first page of tank wall.md, printed.

The sheet is the calculation report

What the sheet shows is what prints: numbered headings, the inputs as a table, the calculation line by line, and every check with its verdict. The browser's own print makes the PDF, and a 3D view prints as a picture of it.

Nothing is copied into a word processor: the document is the report
The formulas stay text in the PDF, sharp at any size
Paper on screen and paper in print: the same page

Open in StructArk

A sheet in Hebrew: its heading and text run from the right, and its table of inputs, its formulas and its check marked OK read from the left. — rtl.md: a simple beam in Hebrew, with its formulas and its check.

Hebrew and Arabic, right to left

One line turns a document right to left. The text and the sheet run from the right, and formulas, numbers and units still read from the left, as they do on paper.

Set once for the document, or ticked in File › Right to left
Each line of the text runs the way its first letter is written
A value in a sentence stays whole: 6 m, never m 6

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Verification

The analysis engine is tested against textbook results. Each row is one of its tests, run on every change, with the tolerance the test holds it to.

Benchmark	Reference	Agreement
Axial bar, end load: extension	PL / EA	Exact
Cantilever, tip load: deflection	PL³ / 3EI	Exact
Cantilever, tip load: base reactions	P and PL	Exact
Simple beam, uniform load: midspan deflection	5wL⁴ / 384EI	Exact
Fixed beam, uniform load: end and midspan moments	wL² / 12 and wL² / 24	Exact
3D frame: joint displacements and rotations	Logan, A First Course in the Finite Element Method, example 5.8	Within 2 %
Cantilever column, second order (P-Delta): sway	The exact solution, with tan kL	Within 4 %
Simply supported square plate, uniform pressure: centre deflection	Timoshenko, Theory of Plates and Shells, table 8	Within 5 %
Simply supported square plate, uniform pressure: centre moment	Timoshenko, Theory of Plates and Shells, table 8	Within 10 %
Ring plate held at its outer edge: deflection at the hole	The plate equation, solved in closed form	Within 2 %

Exact: equal to the closed form to the 8th decimal place or better.

The other engines are held the same way. Every row of the language reference is a test of the calculation engine: what each word computes, and the formula the sheet draws for it. Every drawing test reads its DXF file back, every building-model test reads its IFC file back with an independent reader, and every document that ships with the app is computed in the tests.

Planned

Beside the notebook, three tools are planned.

Revit export saves the building model straight into the project's Revit model. An assistant turns a hand sketch and a hand calculation into a document, for you to check and sign. Cloud sync keeps your notebooks in your account and opens them on any machine. If you want to be told when each is ready, join the waitlist.

One email when each tool is ready. Your address is used for nothing else.

Follow the work as it happens.

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