Truss Analysis Calculator

A free 2D solver that shows its work: draw any truss — nodes, members, supports, loads — and get reactions, displacements, and member forces in tables you can verify by hand, line by line.

The Solver’s Three Tables — What Each One Tells You

Every truss analysis ends in the same three tables. This matrix maps each table to the question it answers, how to read it, and how to verify it by hand.

Highlight verify column

Output	Answers	How to read it	How to verify	Units
Reactions	What do the supports actually push back with?	One row per support: vertical always, horizontal at the pin only	Total vertical reactions must equal total applied load	kip / kN
Displacements	How far does every joint move under load?	One row per node: x and y movement, tiny numbers by design	Scale with 1/E — swap the material inputs and watch them move	in / mm
Member forces	Which members stretch and which squeeze, and by how much?	One row per member, plus the diagram: red vs blue coloring	Check any member with the method of joints at its nodes	kip / kN (tension +, compression −)
Determinacy audit	Will the frame solve at all — and is it stable?	Node and member counts against the determinacy rule	m + r = 2j means one clean answer per member	count
Load path	Where does the force actually travel to reach the ground?	Follow the diagram's colored members from load point to support	Remove a suspect member and watch the load reroute or fail	visual

Model Any Truss in 2D: Nodes, Members, Supports, Loads

Every truss model — from a four-member classroom triangle to a sixty-member barn roof — is built from the same four moves. Do them in order and the solver takes over from there; the whole loop takes about two minutes on a first attempt.

Place the nodes

Every joint of the frame is a point you drop onto the canvas — supports included. Start from the two bearing points and work inward, keeping spacing regular; the node coordinates become the geometry the whole solve hangs from. A truss needs at least two nodes and one member before the solver will run, but useful models start at five.

Connect members

Members join node to node — never mid-span, never crossing without a joint. The moment you draw a member it becomes a two-force body: pure push or pure pull, no bending. That single assumption is what makes a truss light for its span, and it is also why the solver's answer is one number per member instead of a stress diagram.

Set the supports

A pin holds a node in both directions; a roller holds it vertically only. One pin plus one roller is the classic stable pair — the pin absorbs horizontal force, the roller lets the frame expand and contract. Two pins over-span quietly build in horizontal force the drawing never shows; the reactions table exposes it immediately.

Apply the loads

Loads attach to nodes too. Push down with vertical load for gravity, sideways for wind or braking force. The convention matches hand calculations: downward load is positive input, and the reactions table shows the supports pushing back the other way. Enter loads at panel points the way the real structure would collect them.

Open the Preloaded Starter Model

A 30 ft Warren-profile truss — 7 nodes, 11 members, 6 kip on each interior bottom joint — small enough to check by hand, real enough to show every solver feature. Use it as your sandbox for the experiments below.

▶ Load the starter model

Truss Analysis With Steps: Reading the Full Calculation Report

“With steps” is the whole promise here: no result appears that you cannot re-derive. The report unrolls in the same order a hand solution would — equilibrium first, stiffness second, member forces last — and every row stays small enough to audit against the method of joints or a textbook example.

Step 1

Reactions — the balance sheet

The solver first finds what the supports must supply. The check is total and instant: vertical reactions added together equal the applied load, always. On a roller-and-pin frame the horizontal number appears only at the pin — and if it reads large with no horizontal load applied, your geometry is arguing with your supports.

Step 2

Displacements — the stiffness story

Next, how the frame actually moves: every node’s x and y movement under load, computed from member areas and material elasticity. These are the numbers that change when you swap wood for steel, deepen a chord, or double a member’s area — the force table barely moves while the displacement table tells the whole stiffness story.

Step 3

Member forces — the deliverable

One line per member: tension positive, compression negative, mirrored in the diagram’s coloring. This is the table you export to the supplier conversation, sort by magnitude to find the critical members, and verify at any joint with two hand sums. Sorted descending, the top rows are your design’s headline.

💡 Why the report stays auditable: the solver runs the stiffness-matrix method — the same equilibrium bookkeeping at every joint, executed in bulk. That means the "steps" are not narrative decoration: each member line closes the same force balances you would write by hand, and any disagreement between the table and your hand check points to a specific joint to inspect. Errors localize instead of hiding.

Use It as a Truss Simulator: Six Experiments That Teach the Most

The solver recalculates live as you edit — which makes it a simulator by default. Each experiment below runs in under a minute on the starter model and teaches a structural concept that lectures usually take a week to land.

Delete one web member

Remove a single diagonal from the preloaded model and re-solve. On a determinate truss the solver refuses: the frame becomes a mechanism, and the error message names the condition instead of pretending to compute. It is the fastest determinacy lesson available.

Swap the roller for a pin

Change the right support from roller to pin and reload. Displacements change barely at all, but the reactions table now shows horizontal force fighting at both supports — real thrust that a drawing-only review would never surface.

Push sideways, not down

Replace a vertical load with a horizontal one at the same joint. Reactions split asymmetrically, one diagonal group flips from tension to compression, and the diagram recolors panel by panel — wind load behavior in one click.

Double one joint load

Concentrate twice the load at a single bottom node instead of spreading it. Chord forces near that panel jump while far-side members barely move — proof that load path is local before it is global.

Stretch the height

Halve the truss height and keep everything else. Bottom-chord tension roughly doubles, exactly as the lever-arm argument predicts — and the displacement table agrees with the force table this time, since geometry changed for both.

Zero a member

Load only one panel of the Warren starter model and inspect the far web members: some read 0.000. Zero-force members are not mistakes — they are the frame keeping itself stable for the loads you did not apply yet.

Steel roof truss framework under construction showing nodes and members of a real 2D truss

Every real frame is a 2D analysis waiting to be checkedPhoto: Unsplash

⚠️ Where simulation ends: the 2D model assumes pin joints, straight members, and node loads — excellent for member forces, silent on connection design, buckling capacity, and out-of-plane bracing. Treat the force table as the start of the sizing conversation, not the stamped end of it. The simulator's job is to make the structural behavior obvious; the engineer's stamp is what makes it official.

Truss Analysis Calculator FAQ

How do I calculate the forces in a truss with steps I can check?▼

The solver on this site produces exactly that artifact: a full calculation report where every row is one member and every number is reproducible by hand. The workflow: build or load a model, read the reactions (they must balance the applied loads — that is your first check), then open the member force table and pick any member. At its start node, sum forces horizontally and vertically; the member force you read from the table is the one that closes both sums. The report's ordering — reactions, then displacements, then member forces one line each — mirrors the way a hand solution unfolds, which is what 'with steps' means here: not a black box, a checklist you can audit line by line.

Is this online truss analysis calculator really free?▼

Yes — no account, no install, no export watermark, no member-count cap. The full solver runs in your browser: any 2D truss you can draw with nodes and members, up to the tool's practical canvas limits, solves at full accuracy with all three output tables and the share-link feature. Browser-side solving also means your geometry never leaves your machine — relevant for consulting work under NDA. The free tool covers the same determinate and indeterminate frames desktop packages solve at this scale; what it deliberately does not do is member code-checking (AISC/NDS capacity tables), which remains the fabricator's or engineer's stamp job.

What is the difference between a truss solver and a truss simulator?▼

A solver answers one question — given this frame and these loads, what are the numbers? A simulator invites the follow-up — and what happens if I change something? The tool on this site is both. The solver part is the report: reactions, displacements, member forces, all recomputed live as you edit. The simulator part is the editing canvas: drag a node, delete a member, flip a support, and the numbers update before your cursor settles. That live-recalculate behavior is the difference between checking an answer and understanding a structure — the five experiments on this page are built entirely on it.

What does a negative member force mean in the calculator?▼

Negative means compression — the member is being squeezed, its joints pushed toward each other. Positive means tension — stretched, joints pulled apart. The diagram encodes the same thing in color, typically red for compression and blue for tension (or the reverse depending on the theme), so a glance at the picture tells you which members would buckle and which would snap first. Sign conventions matter most when comparing against hand work: if your method-of-joints calculation assumed tension and the solver agrees with a positive number, both of you said 'tension'; a negative number where you guessed tension means the member is really in compression.

Why do some members show zero force?▼

Zero-force members are real, correct, and routinely misunderstood. A member shows 0.000 when, under the specific loads applied, the joint it serves is already balanced without it — typically at an unloaded joint where two members are collinear and a third meets them at an angle. The member still matters: it stabilizes the frame against the loads you did not apply, prevents buckling of long members it braces, and becomes active the day a load lands somewhere else. The classic exam trick asks which members are zero-force under one load case; the simulator approach is faster — load one panel, read the table, and watch the zeros appear far from the action.

Can the calculator handle indeterminate trusses?▼

Yes — that is what the stiffness-matrix method underneath is for. The determinacy rule (members plus reactions equals twice the joints) marks the boundary: at or below it, unique member forces exist and simple joint methods can find them; above it — extra supports, redundant web members, a torus of triangles — forces depend on member stiffness, and joint methods can no longer separate them. The solver builds the full stiffness matrix either way, inverts the stable ones, and reports forces that account for how stiffness shares the load. Practical use: add a redundant diagonal to a determinate frame and watch the forces redistribute — the extra member quietly takes work from its neighbors, proportional to relative stiffness.

How accurate is a 2D truss analysis compared to real structures?▼

Within its assumptions, exact — the accuracy question is about the assumptions, not the arithmetic. The model treats every joint as a frictionless pin, every member as straight and two-force, every load as applied at nodes. Real welded joints carry some bending; real members sag, and real roofs collect load along members rather than at points. For truss work those effects are second-order: axial forces from a pin-jointed analysis routinely land within a few percent of measured values on clean frames, which is why the method has run bridges for 150 years. The numbers you should not take from any 2D tool are connection forces and member buckling capacity — both live in the specialty software and stamp stage that follows.