Fuzzy discrete multicriteria cost optimization of steel structures using genetic algorithm

A great majority of optimization works on steel structures deal with minimum weight design. But in reality minimum weight design is not necessarily a minimum cost design. The price of commercially available rolled steel shapes in the market does not necessarily depend only on its weight but also on some other factors including demands and grades. In cost optimization, however, additional difficulties are encountered. They include the definition of cost function and uncertainties and fuzziness involved in determining the cost parameters. As a result only a small fraction of the structural optimization papers published deal with the minimization of the cost.; In this work a fuzzy discrete multicriteria initial cost optimization model has been developed by considering three criteria: (1) minimum cost, (2) minimum weight, and (3) minimum number of section types. This discrete cost optimization procedure is preceded by a fuzzy genetic continuous variable minimum weight design as a preliminary design. In this design the uncertainty or fuzziness of the AISC code based design constraints are considered. Furthermore, the fuzzy multicriteria initial cost optimization model is extended to perform a life cycle cost optimization of steel structures.; For optimization of large steel structures more than 99% of computation time is spent on the minimum weight design using the fuzzy Genetic Algorithm. Sequential processing of this optimization work in a single processor is very inefficient resulting in huge numbers of page faults and cache misses even in a supercomputer like Origin 2000. In this work two bi-level parallel processing algorithms are developed by using (1) data parallel procedure using OpenMP API at inner level and (2) message passing distributed parallel processing procedure by using function calls from MPI message passing library at outer level. Significant performance enhancement has been obtained in comparison to the traditional data parallel or distributed message passing parallel processing.