Structural Design
The design of structures involves the systematic study of their stability, strength, and rigidity.
Structural Design
The design of structures involves the systematic study of their stability, strength, and rigidity. It is the basic objective of structural analysis and design to produce a structure that is capable of resisting all applied loads without failure during its intended lifetime. A structure’s primary function is to transmit or support loads. The structure may not perform its intended function if it is improperly designed or fabricated, or if the actual applied loads exceed the design specifications. A well-engineered structure greatly reduces the likelihood of costly failures.
The planning phase involves consideration of the various requirements and factors affecting the general layout and dimensions of the structure, resulting in one or more alternative types of structure, which offer the best general solution. A primary consideration is the function of the structure. Other factors such as aesthetics, sociology, law, economics, and the environment may also be considered. In addition, structural and constructional requirements and limitations can affect the type of structure to be designed.
Structural design begins with determining the loading conditions and other design conditions that must be supported by the structure and that must therefore be considered as part of its design. Then comes the analysis and computation of internal gross forces (i.e., thrust, shear, bending moments and twisting moments), as well as stress intensities, strain, deflection, and reactions caused by loads, temperature changes, shrinkage, creep, and other design conditions. Following this is the proportioning and selection of materials for the members and connections to respond adequately to the effects produced by the design conditions.
Elastic design is traditionally based on allowable stresses, which are chosen in accordance with the concept that stress or strain corresponds to the yield point of the material and should not be exceeded at the most stressed points of the structure, selection of failure due to fatigue, buckling, or brittle fracture, or consideration of the structural deflection allowed.
In reinforced concrete literature, a newer approach is called strength design, and in steel literature, plastic design. The anticipated service loading is multiplied by a suitable load factor, the magnitude of which is dependent on the uncertainty of the service loading, the possibility that it may change during the life of the structure, and for a combination of service loadings, the likelihood, frequency, and duration of that combination.
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The structural design process can be divided into three phases, namely planning, design, and construction.