Chapter 5 - Design approaches

Abstract

This chapter explores “Concepts of Stress on Structural Designs.” Every structural design rests on some uncertainties even though on paper they may appear to be mathematically correct. The basic requirements of safety, serviceability, and economy depend on how well designers maneuver within this probabilistic environment. Structural design approaches can be characterized by the extent to which these uncertainties are made explicit. The simplest approach to designing structures uses a single factor of safety to define allowable stresses for a particular material. If actual (i.e., calculated) stresses do not exceed these allowable stresses, the structure is considered to be safe. A more recent approach to the design of structures explicitly considers the probabilistic nature of loads and the resistance of structural materials to those loads. Strength design pushes the elements to its limits—to the point at which the element fails or otherwise becomes structurally useless—to know the upper limit of stress tolerance. Having acquired this knowledge, it is easier for the designer to stay well within the safety limits.