Explore the Truss Bridge Builder & Load Tester
Build a truss bridge from a template or from scratch, drive a truck over it and watch real tension, compression, stress, buckling.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
See it in action
The Truss Bridge Builder & Load Tester with sample data entered and the result showing.
What is the Truss Bridge Builder & Load Tester?
Build a truss bridge from a template or from scratch, drive a truck over it and watch real tension, compression, stress, buckling and collapse from a stiffness-method solver. It runs in your browser, so a change to a setting or a drag on an object shows up at once.
Highway and railway bridges, roof trusses, cranes, transmission towers and aircraft structures are analysed with the same stiffness method, member checks for yield and buckling, and moving-load studies used here.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Members in tension are pulled and members in compression are pushed: a truss carries load only through axial force in its members.
A stable truss is built from triangles. Remove or cut a member and it can become a mechanism that collapses.
Stress is force divided by cross-section area, and the factor of safety compares it with the material's yield strength.
Drag the truck along the deck and watch which members swap between tension and compression.
Press Test to failure, see which member buckles first, then thicken only that member.
Compare Warren, Pratt and Howe with identical members and read the maximum truck load and mass.
Used for
Pick one to see how it fits.
Engineering learners
Engineering and technology students, makers, robotics clubs and teachers of design and technology.
Try it freeTeachers
For teachers: project the Truss Bridge Builder & Load Tester on the board, let students predict the result, then run it together and test this: Press Test to failure, see which member buckles first, then thicken only that member. For students: change one thing at a time and write down what changes.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This simulation | Textbook diagram | |
|---|---|---|
| Interactive | Drag, tap and change settings | Fixed picture |
| Install | Nothing to install | Not needed |
| Cost | Free to use | Depends on the book |
Questions people ask
Why are trusses made of triangles?
A triangle cannot change shape without changing the length of a side, so it is rigid. A four-sided frame can fold flat like a chair, which is why the solver reports a mechanism when triangles are missing.
How does the simulator calculate the forces?
It uses the direct stiffness method used by structural analysis software. Each member gets an axial stiffness EA/L, these are assembled into K u = F, the supports are applied, and the solver finds the joint displacements, then the member forces, stresses and support reactions. It was checked against a NumPy solution and agrees to rounding error.
What is the difference between yielding and buckling?
Yielding is the material giving way under stress, which depends on cross-section area. Buckling is a slender member in compression bowing sideways at the Euler load, which depends on stiffness EI and length. A long thin compression member buckles first.
Which is stronger, a Warren, Pratt or Howe truss?
It depends on span, height and loading, so use the Compare designs tab to test them under the same load. A Pratt truss puts its long diagonals in tension and a Howe in compression, so with identical members the Pratt is usually the stronger.
Can I use this for an engineering class?
Yes. There are Beginner, Engineering and Instructor levels, design challenges with mass, safety factor and deflection limits, a show-your-working calculation view, influence lines, and a printable report. It is an educational simulation, not a certification for a real bridge.
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Try the Truss Bridge Builder & Load Tester now
Build a truss bridge from a template or from scratch, drive a truck over it and watch. Free to use.
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