Strength & utilisation

How Truzme checks a member's stress against its material's strength, and how to read the Utilisation panel and diagrams.

Last updated 2026-09-15

Quickstart

1. In the Utilisation panel, find the Max strength chip and turn its switch on.
2. The chip shows the most-utilised member as a percentage, with a red/amber/teal bar — 100% means it has reached the material's limit.
3. Click DETAILS to see the numbers behind the check for that member, or hover the ⓘ next to a value for its formula.
4. On the canvas, switch the diagram mode to Stress to see raw stress per member, or Strength [%] to see every member's percentage of its limit at once — not just the single worst one the panel shows.

What it is

Every member carries an internal axial force. Stress turns that force into a number that accounts for how thick the member is — the same force through a thin rod produces far more stress than through a thick one. The strength check then compares that stress to the material's own limit, so a member fails not because the force is "big" in some absolute sense, but because it's too big for that specific member's material and cross-section.

The formulas

Stress is the internal force spread over the member's cross-sectional area:

σ = Nx / A

Nx is the member's internal axial force, A is its section area. The utilisation ratio then compares that stress to the material's strength:

u = |σ| / fMax

fMax is the material's strength — the maximum stress it can take before it breaks (see the materials & sections guide). u ≥ 1 means the member has reached or passed that limit.

Turned around, the same check tells you how big a member in tension needs to be. The smallest section area that keeps it within the limit is:

Amin = Nx / fMax

If the member's area A is at least Amin, it passes the strength check — the same as its utilisation staying under 100%. This only applies to members in tension: a member in compression can also buckle, so a big enough area alone doesn't make it safe (see Buckling).

A member over the limit fails one of two ways, depending on its internal force's sign: tension (being pulled apart) can tear, while compression (being pushed together) can crush. The Utilisation panel shows which one applies to the member it's currently flagging.

Reading the diagrams

Three diagram modes cover this check, and they show different things:

• Stress — the raw axial stress in every member (force ÷ area), independent of any material. Useful for comparing members directly, even before you've decided what they're made of.
• Strength [%] — stress divided by that member's own material strength, i.e. how close each member is to its own limit. This is what actually turns red once a member is overloaded — two members can show the same stress but a very different percentage if they use different materials.
• Tension [%] — the same percentage, but only for members in tension; members in compression are greyed out with "—". Use it to size the members that could tear: change their sections until every one is under 100%. Hover a member to see the area it needs (Amin) next to the area it has.

Open this truss and switch between the Strength, Tension and Buckling diagrams — its members fail in different ways, so each diagram points at different ones:

Behavior notes

Opt-in, like buckling. Strength and buckling are two separate checks, each with its own switch in the Utilisation panel, both off by default — see the buckling guide for the other one.

Two checks, one governing member. With both switches on, a Governing badge shows which check is currently closer to failing, since strength and buckling can easily point at different members.

Always computed, opt-in to flag. The diagrams and stress values exist regardless of the panel's switches — the switch only controls whether an over-limit member is treated as a problem worth flagging.