Five structure types
Beams, 2D trusses, 2D frames, 3D trusses and 3D frames, all from one model format.
Free plan available · 3-day free trial on paid plans
Structural analysis with the direct stiffness method
Beams, 2D and 3D trusses, and 2D and 3D frames. Reactions, shear, moment and deflection diagrams, and the full step-by-step stiffness-matrix calculation for your own model — nothing to install.
No installation. Your models stay in your browser. The free plan shows the diagram shapes; Student and Pro show every value, with a 3-day free trial.
Solving the example in your browser…
5structure types: beam, 2D/3D truss, 2D/3D frame
45 / 45closed-form benchmarks reproduced
49 / 49models agree with an independent Python implementation
3 daysfree trial on paid plans; cancel any time
Features
Everything a first-order structural analysis needs
One tool for the beam in your homework and the 3D frame in your project — with the working shown.
Supports and releases
Fixed, pinned, roller, inclined, guided and spring supports, support settlement, internal hinges and member end releases.
All load types
Nodal and point loads, uniform, triangular, trapezoidal and partial distributed loads, temperature, lack of fit and self-weight.
Exact SFD, BMD and deflection
Closed-form equations per segment, with maxima, minima, zero-shear and contraflexure points — no meshing needed.
Step-by-step report
Degrees of freedom, element matrices, assembly, the solution and an equilibrium check for your model. Print to PDF, HTML or LaTeX. Student and Pro plans.
Python and MATLAB export
Download a self-contained script that reproduces the analysis, so you can check it or build on it. Student and Pro plans.
SI, US and custom units
Switch between kN·m, kip·ft, tf·m or your own unit per quantity without changing the physics.
3D viewer
Orbit, inspect and edit 3D trusses and frames, with deformed shape and member diagrams. Values for 3D models: Student and Pro plans.
Load combinations
Any number of load cases, ASCE 7 and EN 1990 combination generators, and envelopes. Student and Pro plans.
Sections and materials
AISC W, IPE, HEA and HEB shapes, a section calculator with formulas shown, and steel, concrete, aluminium and timber presets.
Save and share
Autosave in your browser, JSON files, and share links that carry the model in the URL.
Free plan, paid plans
Model and see the diagram shapes without an account. The free plan shows the shape of every diagram. Student and Pro show all the values and unlock everything, with a 3-day free trial.
How it works
Model, analyze, report
Model
Describe the geometry, supports, sections and loads with the beam wizard, the drawing canvas or the spreadsheet tables.
Analyze
The direct stiffness method runs in your browser in milliseconds. Read reactions, member forces, diagrams and deflections.
Report
Open the full calculation, print it to PDF, or export Python and MATLAB code that reproduces every number.
Why StiffStruct
StiffStruct vs typical online calculators
Typical online calculators hide the numbers behind a monthly subscription. StiffStruct gives you a free plan, and the whole product for a fraction of the price.
| Feature | Typical online calculators | StiffStruct |
|---|---|---|
| Reactions and diagram values | Often behind a paywall or an e-mail wall | Diagram shapes free; all values from $24/year (3-day free trial) |
| Deflection and slope diagrams | Often paid or missing | Included |
| Step-by-step stiffness-matrix report for your own model | Canned examples only, or a single member | Yes, for every structure type (Student and Pro) |
| 3D trusses and frames | Rare, or paid | Included in Student and Pro |
| Load cases, combinations, envelopes, self-weight | Usually paid | Included in Student and Pro |
| PDF report | Paid | Print to PDF, HTML or LaTeX (Student and Pro) |
| Python and MATLAB code export | Almost never offered | Included in Student and Pro |
| Springs, settlement, temperature, lack of fit, inclined supports | Limited or paid | Included |
| Pricing | $10–$139 per month, or payment per calculation | A free plan, then low yearly prices with a 3-day free trial. See pricing |
Based on a survey of popular online beam and truss calculators; features and prices vary by site and change over time.
Verification
Checked against textbooks and an independent implementation
The solver is checked against 45 closed-form benchmarks and against an independent Python implementation on 49 models. You can re-run the tests yourself, in your browser.
45 / 45
closed-form benchmarks (reactions, moments, deflections, truss forces) reproduced.
49 / 49
models and 53 load cases agree with an independent Python implementation to 10-6 or better.
19 / 19
built-in example models match the textbook answers printed with each of them.
Traceable results
Read the theory, run the tests, and follow every matrix and every step in the calculation report.
Run the benchmark tests Read the theory
An educational tool. StiffStruct performs first-order, linear-elastic analysis. Results must be checked by a qualified engineer before they are used for final design or construction. See the terms.
FAQ
Frequently asked questions
Is there a free plan?
Yes. The Free plan has no time limit: you can build any model and see the shape of its diagrams. The numbers (reactions, diagram values, tables), 3D, the step-by-step report, code export and load combinations come with Student or Pro, which you can try free for 3 days. See the pricing page.
How does the free trial work?
Student and Pro start with a 3-day free trial. You add a card at checkout, nothing is charged for 3 days, and then the plan you chose is charged automatically unless you cancel before the trial ends. Cancel any time and you keep access until the end of the period you paid for. See the refund policy.
Do I need an account?
No account is needed to build a model, run the analysis and see the shape of the shear and moment diagrams. To see the numeric values you sign in (with Google or an e-mail address); the account is free, and paid features need a Student or Pro plan.
Is it accurate?
For linear-elastic, first-order analysis of prismatic Euler–Bernoulli members, yes: the element formulas are exact, and the solver is checked against 45 closed-form benchmarks and an independent Python implementation. It does not model second-order effects, buckling or shear deformation. Always verify results before using them for design.
Which units can I use?
SI (kN·m, N·mm, kN·mm), MKS (tf·m), US (kip·ft, kip·in, lb·ft, lb·in) or a custom unit for each quantity. Switching units never changes the physics.
Can I run it offline or export the calculation?
The analysis runs entirely in your browser. You can export the model as JSON, print the report to PDF, and download a Python (NumPy) script or a MATLAB/Octave function that reproduces the analysis on your own computer.
What sign conventions are used?
Axial force is positive in tension. Bending moment is sagging-positive for a horizontal member, and shear is defined by V = dM/dx, so a simply supported beam under gravity has positive shear at its left end. Gravity acts in −Y and rotations follow the right-hand rule. The details are in the theory notes.
Pricing
Simple pricing. A fraction of what other tools charge.
Start free. Try Student or Pro free for 3 days, then keep the plan that suits you. Prices are in US dollars.
Analyze your structure now
Open the calculator, start from an example or a blank model, and see the result in seconds.