In the allowable strength design method, what must the actual calculated stress not exceed?

In the allowable strength design method, the critical aspect is that the actual calculated stress must not exceed the allowable stress. This concept ensures that structures are designed within safe limits to avoid failure during service conditions. Allowable stress is derived from material properties and safety factors, accounting for uncertainties in the material and loading conditions.

By ensuring that the actual stress remains below this threshold, engineers can provide a margin of safety against potential failure mechanisms such as yielding, buckling, or cracking, which could occur if the material is subjected to excessive loads. Using allowable stress as the standard allows for a systematic approach to design and helps maintain structural integrity through a balance of strength and safety.

The other terms listed, such as ultimate stress and yield strength, are related to material properties but do not represent the specific criteria used in the allowable strength design framework. Design strength is also influenced by various factors, including safety factors, and does not straightforwardly define the limit for actual stress in the way that allowable stress does.