About
About StiffStruct
A structural-analysis web app that shows its working.
What StiffStruct is
StiffStruct analyses beams, 2D and 3D trusses, and 2D and 3D frames with the direct stiffness method, the same matrix method that sits inside commercial structural software. You describe the structure; it returns reactions, member forces, shear, moment and deflection diagrams, and, if you want it, the complete step-by-step calculation behind every number.
It runs entirely in your browser. There is no server to wait for, and your models stay on your device unless you choose to share a link.
Who it is for
Students
Check homework, see how a stiffness matrix is assembled, and compare a hand solution with a computed one.
Teachers
Show the method on real examples, share a model as a link, and export a Python script students can read and modify.
Engineers
Run a quick independent check of a beam, truss or frame, and keep a printable record of the calculation.
The method in short
Each member has a known stiffness relation between its end forces and end displacements. StiffStruct writes that relation in global coordinates, assembles all members into one system K u = f, applies the supports, solves for the unknown displacements, and then recovers reactions and member forces. Internal forces and deflections along each member come from the exact piecewise solution of the beam equation, so no extra meshing is needed.
The full derivation, the element matrices and the sign conventions are in the theory notes.
What it can and cannot do
It can
- Linear-elastic, first-order analysis of prismatic members
- Euler–Bernoulli bending, axial and (3D) torsion behaviour
- Many support types, springs, settlement and internal releases
- Point, distributed, temperature and fabrication-error loads
- Load cases, combinations and envelopes
It cannot
- Second-order (P-delta) effects or buckling
- Shear deformation (Timoshenko beams) or warping torsion
- Material non-linearity, plates, shells or solids
- Dynamic or seismic analysis
- Code checks of members or connections
Every result is traceable
StiffStruct is built so that you can follow the calculation. The step-by-step report shows each member matrix, the assembled system, the supports applied, the solved displacements and the recovered forces, and the theory notes explain the formulas behind them. A Python script or a MATLAB/Octave function that reproduces the analysis can be exported for your own work.