IB Design Technology Topic A3.2.10: Load-bearing Design in Structures Notes

Load-Bearing Design Makes Sure A Structure Safely Carries Every Load It Meets

1. In practice it means three things:
   1. Identify the loads the structure will face.
   2. Choose materials with the right strength, flexibility and durability.
   3. Analyse how the loads travel through the structure so nothing is overstressed.
2. The loads come in three kinds:
   1. Dead loads are permanent and static, above all the weight of the structure itself.
   2. Live loads are temporary and moving, the people, furniture and vehicles a structure carries as it is used.
   3. Environmental loads come from nature: wind pushing on the walls, snow resting on the roof, or the shaking of an earthquake.

What A Safety Factor Of 1, And Above 1, Means

1. The safety factor, defined and calculated in A3.2.9, compares the load a structure can bear with the load it must actually carry.
2. Its value tells you how much margin there is.
3. Reading the ratio:
   1. SF = 1: the structure is designed to fail at exactly the expected load, with no margin at all.
   2. That is only safe if the material is flawless, no unexpected load ever arrives, and nothing degrades with age, which is rarely true.
   3. SF greater than 1: a buffer against material variability, loads that turn out larger than predicted, and small errors in the design calculations.
4. Why most structures use a safety factor above 1:
   1. Safety and reliability: it prevents failure and protects users even when unexpected forces occur.
   2. Uncertainty: it covers unknowns in materials, usage and construction accuracy.
   3. Regulations: building codes and safety standards require it.