Definition and Application of Allowable Stress
Allowable stress is a term used to describe the maximum amount of stress that a structural component or material can withstand before it begins to suffer permanent deformation or failure. It is applied to the design of structures and components in order to prevent premature failure of an assembly or component due to excessive stresses during operation. Allowable stresses are determined by the designer, or codes of practice or ultimate strength of the material used.
Allowable stress is an important concept in the design and analysis of structures. In engineering calculations, the value of the allowable stress is used to calculate the dimensions and sizes of components in order to ensure that the component or structure as a whole can withstand the loads and environmental conditions that it will experience during its intended service life. For example, allowable stresses are often specified for components of bridges and buildings in order to ensure that these structures can withstand wind, vibration, and other, more severe loads.
In most cases, the calculation of the allowable stress for a particular component or structure is based on a combination of two factors: the expected stresses during service and the strength characteristics of the material. Generally, the expected stresses are determined by considering the load conditions, loads induced by environmental factors, and other design considerations. The strength of the material is found through tensile or compression testing, or by applying a certain amount of stress to the material and measuring its response over time.
The type of allowable stress used in the design of structures will depend largely on the requirements of the intended application. For example, if a structure is intended to remain in a static condition, such as a beam in a building, then the designer might use a low allowable stress that is based on ultimate strength of the material used. On the other hand, if a structure is intended to experience dynamic conditions, such as components of a bridge, then the designer might use a higher allowable stress based on yield strength of the material used.
Allowable stresses are not only used to determine the structural integrity of components and structures, but also to limit deflection, vibration and fatigue. Limit stresses can be established by applying a certain amount of stress and measuring the response over time. If a component or structure is expected to experience dynamic loading conditions, then an engineer may choose to limit the allowable stress to ensure that the structure does not experience fatigue, vibration or deflection issues during extended exposure to dynamic loading.
In conclusion, allowable stress is an important concept in the design and analysis of structures. It is the numerical value used to determine the dimensions and sizes of components, as well as the maximum stress that a component can withstand before it begins to suffer from permanent deformation or failure. The allowable stress calculation is based on the expected stress during service and the strength characteristics of the materials used. Allowable stresses are also used to limit deflection, vibration and fatigue of components and structures.
