17.8 : שיקול עיצובי

While designing a structure, the considerations start with the ultimate strength of a material, which is determined through tests, measuring changes under increased load until it reaches its limit or breaks.

The maximum load beyond which the material breaks is the ultimate load. The ratio of the ultimate load to the original cross-sectional area provides the ultimate normal stress or ultimate strength.

The other important consideration is the factor of safety, which is the ratio of ultimate to allowable load, ensuring a reserve of load-carrying capacity for safe operation.

The factor of safety selection involves considering variations in material properties, loadings, potential failure types, uncertainties in analytical methods, future deterioration, structural importance, and risk to life and property.

The conventional allowable-stress method groups all uncertainties into a single safety factor, but an alternate method called the Load and Resistance Factor Design method distinguishes between uncertainties associated with a structure and its load and differentiates between live and dead loads.