SHEET 05 — THE AXES THEMSELVES

Where the Numbers Come From

The axes themselves — tests, standards and the origin of the allowable.

• 22What the Silver Bridge Changed5 min readOne eyebar out of hundreds, one crack a few millimetres deep, and the reason every highway bridge in America is now inspected on a schedule. The 1967 collapse at Point Pleasant told soberly, and the two changes it forced: mandatory inspection, and the phrase 'fracture critical'.
• 23What a Standard Actually Governs3 min readStandards are referred to by number and scope, not reproduced. What a standard is for, who writes one, how it becomes mandatory, and why reading one out of context is worse than not reading it.
• 24How a Test Becomes a Number5 min readThe path from a laboratory result to a design value: repeat testing, statistical treatment, characteristic values and the deliberate conservatism applied at each step.
• 25The Origin of the Allowable3 min readWhere the allowable stress in a code actually comes from, how much of it is measurement and how much is accumulated caution, and why the answer is uncomfortable.