COST OPTIMIZATION OF STEEL STRUCTURES

While the weight of a steel structure is a major component of the total cost, the minimization of the cost should be the final objective for optimum use of available resources. The total cost of a steel structure includes (a) the material cost of structural members such as beams, columns, and bracings, (b) the fabrication cost including the material costs of connection elements, bolts, and electrodes and the labor cost, (c) the cost of transporting the fabricated pieces to the construction field, and (d) the erection cost including the material costs of connection elements, bolts, and electrodes and the labor cost. In this article, a chronological review of the journal articles on cost optimization of steel structures is presented. Articles on deterministic, reliability-based, and fuzzy logic-based optimization of steel structures are reviewed. Research on cost optimization can encourage the use of the optimization approach in structural steel design practice by providing a more realistic way of modeling structural steel design and resulting in additional savings compared with the weight optimization problem.     

A Heuristic Approach for Interactive Analysis of Bridge Trusses under Moving Loads

A heuristic approach is presented for interactive analysis of statically determinate and indeterminate bridge trusses subjected to moving loads such as the American Association of State Highway and Transportation Officials (AASHTO) specifications live loads. These loads consist of two-axle truck loading, two-axle truck plus one-axle semitrailer loading, and uniform lane loading. The procedure is based on using the information about the shape of the influence line diagrams (ILDs) for members of a truss. This information may be obtained through numerical experimentation for any given type of truss. A methodology is presented for classifying the ILDs for member axial forces of a bridge truss. The procedure is applied to Pratt trusses. Heuristic rules are developed for finding the maximum compression and tensile forces in the members of a Pratt truss based on its characteristic influence line diagrams and the type of the AASHTO live load. The procedure presented in this article results in substantial savings in structural analysis computations, and is specially suitable on microcomputers in an interactive environment.     

Heuristic Analysis of Bridge Trusses Under AASHTO Live Loads

In a recent article, Adeli and Balasubramanyam [2] presented a heuristic approach for analysis of bridge trusses subjected to American Association of State Highway and Transportation Officials (AASHTO) moving loads. This procedure is based on the recognition of patterns of influence line diagrams (ILDs) for various members of a bridge truss. The procedure was applied to Pratt trusses. This arricle extends and generalizes the previous work of the authors by applying it to other classes of trusses, i.e., the statically determinate K-trusses and the statically indeterminate Parker trusses. This approach is significantly more efficient than the bruteforce method of generating the nodal load vectors due to the moving loads positioned at numerous locations along the span and performing numerous structural analyses. Thus, it is particularly suitable for microcomputers. The heuristic approach presented in this article can be easily extended to other classes of bridge trusses.     

Interactive Optimization of Multispan Plate Girders

An efficient and robust optimization algorithm is presented for minimum weight disign of continous multispan steel plate girders using the general geometric programming technique. The loading on the girder can consist of any number of concentrated and uniformly distributed loads. The nonlinear programming problem is formulated on the basis of the last edition of the American Institue of Steel Construction (AISC) specification. The desing variables are the flange width and thickness, teh web depth and thickness, and the dimensions and spacings of the transverse stiffeners for stiffened plate girders. In the optimization algorithm, the nonlinear primal problem is transformed to and via double condesation. The algorithm is quite general and can be applied to stiffened of unstiffened, homogeneous or hybird plate girders. The girder may be fully restrained agained lateral torsional buckling or may haae lateral supports only at selected locations along the length ofthe girder. The algorithm id implemented in FORTRAN 77 in an interactive computing environment with graphic capabilities. The grogram can display the plate girder elevtion, various cross sections, and loading on the girder. Three examples are presented, a two-span homogeneous, a three-span hybird, and a five-span homogeneous plate girder.     

Automatic Partitioning of Frame Structures for Concurrent Processing

An efficient 3-stage algorithm for automatic partitioning of frame structures is presented. Once the input data of the structure is fed into the computer, the domain is partitioned into a number of subdomains equal to the number of the specified processors. The underlying concept is to preprocess the input data in such a manner that subsequent analysis and optimal design steps can be carried out efficiently on multiprocessor computers. Emphasis is directed towards attaining a balance of workload among the processors, minimizing the bandwidth within each subdomain, and minimizing the number of linear equations to be solved for the interface degrees of freedom. All the vectors involved in the partitioning algorithm are integers, requiring a small storage and resulting in calculations that can be processed fast. The algorithm is specially suitable for analysis and design of large structures such as space stations. The algorithm presented is hardware independent. Our applications, however, are limited to the Encore Multimax shared memory computer. The efficiency of the algorithm is demonstrated through partitioning several truss and frame problems, for a variable number of processors.