Enrichment · STEM Explorations · Engineering

Find the weakest
link before the
shelf does.

List each part with what it can take and what it will carry. The calculator gives every factor of safety, checks them against the required one, names the weakest part and tells you how much stronger it needs to be.

Check the designWhat you get

The safety factor calculator

The worked example is made up: a classroom library shelf with a bracket, wall anchors, screws and a plywood board. Nothing you type leaves this browser.

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What you get

Enrichment · STEM ExplorationsFree

What you finish with
Each part’s factor and margin of safety, whether it meets the requirement, the weakest link and the capacity or load that would fix it. It prints as a summary and downloads as a spreadsheet.
Who it is for
Engineering and technology students, robotics and bridge-building clubs, STEM and CTE teachers and families doing build projects.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Up to 30 parts. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The STEM Explorations space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Name the design, its unit and the required factor of safety.
  2. Add each part with its capacity and the load it will carry.
  3. Read the weakest link and which parts fall short.
  4. Change a part and watch the factors update.
  5. Print the summary or download the spreadsheet for your design notebook.

Check the design

How the factor is worked out

What it can take, over what it will carry.

The worked example: the plywood shelfShelf can take620 Nfrom a bending testShelf will carry250 Nbooks, about 25 kgFactor of safety2.48620 ÷ 250Required 3750 Ncapacity needed: 250 × 3The worked example: the plywood shelfShelf can take620 Nfrom a bending testShelf will carry250 Nbooks, about 25 kgFactor of safety2.48620 ÷ 250Required 3750 Ncapacity needed: 250 × 3
Every other part clears the required factor of 3; the shelf board itself does not, so a thicker board or a center bracket is the fix.

The arithmetic

A factor of safety divides a part’s capacity, the load or stress at which it fails, by the load or stress it carries in use. A factor of 3 means it could carry three times its working load. The margin of safety, the factor minus 1, is the extra beyond the working load. A design fails at its weakest part, so the smallest factor is the one that counts.

Choosing a requirement

Designers ask for larger factors when loads are uncertain, materials vary, failure would hurt someone or parts wear over time; aircraft parts use small factors with careful testing, while ropes and lifting gear use large ones. Building codes and standards set factors for real structures. In class, the brief or teacher sets it.

Sources

  1. NASA. Factor of safety and margin of safety in structural design, NASA-STD-5001 (standards.nasa.gov).
  2. OpenStax. University Physics Volume 1 (2016), chapter 12, Static Equilibrium and Elasticity: stress, strain and failure (openstax.org).
  3. Occupational Safety and Health Administration. Rigging and sling safety factors, 29 CFR 1926.251 (osha.gov).
  4. Next Generation Science Standards, MS-ETS1 and HS-ETS1 Engineering Design: criteria and constraints (nextgenscience.org).

The worked example is made up. This page does arithmetic on your figures; it does not certify a design as safe. Your figures stay in this browser. Support: team@caveatacademic.com.