Summary

This study presents an evolution strategy integrated parallel solution algorithm for efficient size optimum design of large steel space frame structures, in particular high-rise steel buildings. An optimum design achieved for such systems is not of much practical value unless structural members are selected from a discrete list of ready sections according to strength, stability and serviceability requirements of a chosen code of practice. Besides, geometric compatibilities between beam and column members framing into each other at rigid joints have to be considered for practicality of the application. These points are observed in the solution algorithm developed such that the provisions of the Allowable Stress Design Code of the American Institute of Steel Construction (ASD-AISC [1]) are adopted for steel frames which are subject to vertical and horizontal loads, and standard wide flange hot-rolled sections are used to size the structural members. The algorithm has two novel attributes associated with the integrated optimization method and its parallel computing environment. It implements a very effective adaptive discrete evolution strategy method recently developed by Hasançebi [2]. The serial version of the solution algorithm, which allows for its implementation using a single processor, is first computerized using Borland Delphi source code. Next a master-slave configuration based parallel version of the algorithm is developed, where the sequential code is modified and reorganized with the advanced techniques of parallel processing to operate within a parallel computing system, which can be multiprocessors of a single computer or a cluster of computers connected via a local area network. The uniqueness of the parallel computing environment generated for the algorithm lies in the point that unlike FORTRAN and C++ programming languages, Delphi is not naturally supported by any MPI (Message Passing Interface) implementation. In order to implement MPI for the algorithm, special Pascal headers for MPICH2 [3] provided by the Lazarus Project [4] are revised according to the requirements of the algorithm.

The efficiency of the parallel algorithm in the optimum design of high-rise steel buildings is assessed using three examples. These examples are a 1040-member steel space frame with 60 member groups, a 3590-member steel space frame with 109 member groups and a 7648-member steel space frame with 198 member groups. The optimum designs are achieved for these frames using a cluster of computers with 32 processors in all. It has been shown that a maximum speedup ratio between 12.2 and 16.8 can been achieved for these examples. The performance of parallel computing system versus the number of processors employed is also examined in each example.

References

1 Manual of Steel Construction, “Allowable Stress Design”, 9th edition, AISC, American Institutes of Steel Construction, Inc, Chicago, Illinois, USA, 1989.
2 O. Hasançebi, “Discrete Approaches in Evolution Strategies Based Optimum Design of Steel Frames”, Structural Engineering and Mechanics, 26(2), 191-210, 2007.
3 MPICH2 Library, “High-Performance and Widely Portable Implementation of Massage Passing Interface (MPI) standard”, http://www.mcs.anl.gov/research/projects/mpich2, 2009.
4 Lazarus Project, “Visual Programming Environment for the Free Pascal Compiler”, http://www.lazarus.freepascal.org, 2009.

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