Optimization in Structural Design

41 It is fairly accepted fact that one of the most important human activities is decision making. It does not matter what field of activity one belongs to. Whether it is political, military, economic or technological, decisions have a far reaching influence on our lives. Optimization techniques play an important role in structural design, the very purpose of which is to find the best ways so that a designer or a decision maker can derive a maximum benefit from the available resources. The basic idea behind intuitive or indirect design in engineering is the memory of past experiences, subconscious motives, incomplete logical processes, random selections or sometimes mere superstition. This, in general, will not lead to the best design. The shortcomings of the indirect design can be overcome by adopting a direct or optimal design procedure. The feature of the optimal design is that it consists of only logical decisions. In making a logical decision, one sets out the constraints and then minimizes or maximizes the objective function (which could be either cost, weight or merit function). Structural optimum design methods can also be according to the design philosophy employed. Most civil engineering structures are even today designed on the basis of permissible stress criterion. However, some of the recent methods use a specified factor of safety against ultimate failure of the structure. Presently, the approach is based on the design constraints expressing the maximum probability of various types of events such as local or ultimate failure. The objective function is obtained by calculating each event and multiply it by the corresponding probability. The sum of all such products will be the total objective function. The constraints may also be probabilistic. These are suitable in situations when the loads acting on the structure are probabilistic or the material properties are random. During the early fifties there have been considerable advances inàrtànd economy of the structural design through the use of better structural materials and refined knowledge of structural design processes. Thus, the aim was to put structural design on a scientific basis. The need for innovation and optimization arose in the challenging problems faced by the aerospace industry, which gave a Philip to research activities in this area. Requirements for Structural Design The basic requirements for an efficient structural design is that the response of the structure should be acceptable as per various specifications, i.e., it should at least be …