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CALCULATORS / BEAMS, PLATES AND STRUCTURAL SCREENING

Planar truss forces calculator

Symmetric two-bar pin-jointed truss; only axial forces.

structures-truss.napkin / editable
✓ checks pass

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

ScenarioaxialNstressMPa
707.1077.07107
565.6855.65685

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

axial stress budget7.07 MPa✓ passes

BASELINE INPUTS

CALCULATED

axial707.11 N
stress7.0711 MPa

Edits change the baseline source.

Calculated from your source · not saved
Baseline · Baseline
axial stress budget7.07 MPa ✓ passes
alternative · alternative
axial stress budget5.66 MPa ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

axial
axial = load/(2*sin(angle)) [N]
stress
stress = axial/area [MPa]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

load
1000 N
angle
45 deg
area
100 mm^2

Calculated

axial
707.107 N
stress
7.07107 MPa

Assumptions and limits

Symmetric two-bar pin-jointed truss; only axial forces.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Planar truss forces. Inputs: nodes; members; supports; loads. Outputs: member forces; reactions; mechanism detection. Model scope: Linear elastic idealizations and stated boundary conditions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

  • Inputs: nodes, members, supports, loads
  • Outputs: member forces, reactions, mechanism detection
  • Modes: calculate, compare, sweep
  • Drawing: Deflection and stress diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS

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