Free Truss Analysis Calculator
Draw your truss joint by joint, add the members, supports and loads, and get the support reactions and the axial force in every member, marked as tension or compression. Works for determinate and indeterminate 2D trusses: roof trusses, Pratt, Howe and Warren trusses, bridges and any custom geometry.
- ✓Member forces table: tension, compression and zero-force members
- ✓Axial forces diagram drawn on the truss
- ✓Pinned and roller supports, loads at the joints
- ✓Metric (kN, m), MKS (ton, m) and imperial (kip, ft) units
- ✓Save your models and share them with a link
Free with a Google account · daily free credits · Premium for unlimited use
Worked example: a statically indeterminate truss
This is the truss from the video tutorial, in imperial units: five joints, seven members with two sections and three supports, loaded with a horizontal force of 100 kip at joint E. With three supports it has one more reaction than a determinate truss (m + r = 7 + 4 = 11 > 2j = 10), so the member areas affect the result. Chords AB, BC, AD and DC have A = 3 in², the web members DB, DE and EC have A = 1 in², and E = 29,000 ksi for all of them.
Joints and supports
| Joint | x [ft] | y [ft] | Support |
|---|---|---|---|
| A | 0 | 0 | Roller |
| B | 20 | 0 | Roller |
| C | 40 | 0 | Pinned |
| D | 20 | 15 | — |
| E | 40 | 30 | — |
Support reactions
| Support | Reaction [kip] |
|---|---|
| A | Ay = 47.97 ↓ |
| B | By = 54.06 ↓ |
| C | Cy = 102.03 ↑ |
| C | Cx = 100.00 ← |
Check: the vertical reactions add up to zero and the moments about C balance the load (47.97 × 40 + 54.06 × 20 = 100 × 30 = 3,000 kip·ft).
Member forces
| Member | A [in²] | Force [kip] | State |
|---|---|---|---|
| AB | 3.0 | −63.96 | Compression |
| BC | 3.0 | −63.96 | Compression |
| AD | 3.0 | 79.95 | Tension |
| DC | 3.0 | −45.05 | Compression |
| DB | 1.0 | 54.06 | Tension |
| DE | 1.0 | 125.00 | Tension |
| EC | 1.0 | −75.00 | Compression |
Positive force is tension, negative is compression.
Video tutorial: analyze a truss step by step
Joints, members with two sections, supports, the joint load and the results, in about three minutes.
How truss analysis works
Method of joints
Every joint of a truss is in equilibrium: the sum of horizontal forces and the sum of vertical forces are zero (ΣFx = 0, ΣFy = 0). Starting from a joint with at most two unknown member forces, you solve joint by joint until every member is known. A member that pulls on the joint is in tension; one that pushes is in compression.
Determinate or indeterminate?
With m members, r support reactions and j joints, a stable truss is statically determinate when m + r = 2j and indeterminate when m + r > 2j. If m + r < 2j it is a mechanism and cannot carry load. The calculator handles both determinate and indeterminate trusses.
Zero-force members
At an unloaded joint where two members meet at an angle, both carry zero force. At an unloaded joint with three members, two of them collinear, the third carries zero force. They still brace the truss, and the results table marks them as zero force.
Assumptions
Members are straight and joined by frictionless pins, loads act only at the joints, and the material is linear elastic with small displacements. Under these assumptions every member carries only axial force.
Frequently Asked Questions
What does the truss calculator give me?
The support reactions, the axial force in every member with its state (tension, compression or zero force) and the axial forces diagram drawn on the truss. You can work in metric (kN, m), MKS (ton, m) or imperial (kip, ft) units.
Can it solve statically indeterminate trusses?
Yes. The calculator uses the stiffness method, so it solves both determinate and indeterminate trusses. In indeterminate trusses the member areas and the modulus of elasticity change how the forces are shared, so enter the real sections.
Why does it say my truss is unstable?
The truss moves like a mechanism: a joint is held by too few members or the supports cannot restrain the structure. Check that every panel is triangulated, that no joint hangs from a single member and that the supports prevent horizontal and vertical movement.
Which supports and loads can I use?
Pinned and roller supports. In a truss every joint is a hinge, so there are no fixed supports. Loads are applied at the joints, in the horizontal and vertical directions.
Is the truss calculator free?
Yes. Sign in with your Google account and calculate for free with daily credits. If you need unlimited calculations, Premium removes the limit.