Getting started

Build your first truss — a simple triangle — and read off its reactions and member forces.

Last updated 2026-09-24

The classic first truss: three nodes forming a triangle, two supports, one load. It's built on a 3-4-5 triangle, so every number that comes out of it — reactions, member forces — is a clean whole number instead of a decimal.

New to the toolbar itself? Take the interactive tour first — it points out where everything is before you start building.

A video walkthrough of this exact example is on its way — check back soon.

1. Draw the triangle

Pick the Draw member tool. Click once to place a node, then click again to place the next one — that finishes one member. Use a 3-4-5 ratio: base 6 m, apex 4 m above the midpoint. That makes each sloped side exactly 5 m — a Pythagorean triple, so the shape has no irrational lengths or odd angles to begin with.

1. Bottom-left node → bottom-right node (the base, 6 m)
2. Bottom-right node → apex node (5 m)
3. Apex node → bottom-left node, closing the triangle (5 m)

Press Esc any time to cancel a member you're still placing.

2. Add supports

Pick the Support tool. In its panel, choose a type, then click the node you want it on:

• Pinned on the bottom-left node — fixes it in both directions.
• Roller on the bottom-right node — fixes it vertically, lets it slide sideways.

A pin plus a roller is the standard way to support a truss: together they hold it in place, without a third restraint fighting the other two.

3. Add a load

Pick the Nodal load tool. Set Fy to -8 kN and click the apex node to apply it. 8 isn't arbitrary — it's 2 × 4, and 4 is the triangle's height leg, which is what makes the reactions below come out even.

4. Read the reactions

There's no calculate button — results appear immediately. Each support already shows an arrow for its reaction force; hover one for the exact numbers.

The triangle is symmetric and the load sits on its axis, so the 8 kN splits evenly: 4 kN up at each support. The pin's horizontal reaction is 0 — nothing pulls the structure sideways, so nothing has to resist it.

5. Read the normal force in each member

Every member shows its internal force on the canvas — red for tension, blue for compression. Hover a member for the exact number and a Tension/Compression label.

• Each sloped side carries 5 kN compression. That force runs along the member's own 3-4-5 direction, so it splits the same way the geometry does: 4 kN straight down into the support beneath it, 3 kN sideways, outward, at the base.
• The base carries 3 kN tension. It isn't carrying load down to a support — it's a tie, stopping the two sloped sides from spreading apart. The 3 kN it resists is exactly the sideways 3 kN the diagonals pushed outward.

Same ratio, twice: 3-4-5 in the geometry, 3-4-5 in the forces. That's why this particular triangle is the one every course starts with — pick any other angle and the same reasoning still holds, but the numbers stop being whole.

Why the forces balance

A truss doesn't move, so none of its nodes do either: the forces meeting at every node are in balance. That's what makes the numbers above come out the way they do.

Support reactions works through this exact triangle step by step, with an interactive version you can drag and change.

Now try it in the app

Once the basics make sense, open the same truss in Truzme and change it — tilt the load to an angle, move the supports, add more members.

Then open the stability indicator in the top toolbar. It checks the same balance for the whole structure at once — every load (action) and every support reaction add up to zero:

Action + Reaction = 0

Behavior notes

Everything is live. Drag a node, move a support, or change the load, and every reaction and member force updates immediately — no calculate button anywhere.

Color is consistent everywhere. Tension is always red, compression is always blue, on every diagram and every check in the app — worth learning early.