ABSTRACT

Juha Kilkki

AUTOMATED FORMULATION OF OPTIMISATION MODELS FOR STEEL BEAM
STRUCTURES

Lappeenranta 2002
85 pages and 14 appendices at 30 pages
Acta Universitatis Lappeenrantaensis 140
Diss. Lappeenranta University of Technology
ISBN 951-764-713-1, ISSN 1456-4491

Over 70% of the total costs of an end product are consequences of decisions that are made during
the design process. A search for optimal cross-sections will often have only a marginal effect on
the amount of material used if the geometry of a structure is fixed and if the cross-sectional
characteristics of its elements are property designed by conventional methods. In recent years,
optimal geometry has become a central area of research in the automated design of structures. It
is generally accepted that no single optimisation algorithm is suitable for all engineering design
problems. An appropriate algorithm, therefore, must be selected individually for each optimisation
situation.

Modelling is the most time consuming phase in the optimisation of steel and metal structures. In
this research, the goal was to develop a method and computer program, which reduces the modelling
and optimisation time for structural design. The program needed an optimisation algorithm
that is suitable for various engineering design problems. Because Finite Element modelling is
commonly used in the design of steel and metal structures, the interaction between a finite element
tool and optimisation tool needed a practical solution. The developed method and computer
programs were tested with standard optimisation tests and practical design optimisation cases.
Three generations of computer programs are developed. The programs combine an optimisation
problem modelling tool and FE-modelling program using three alternate methdos. The modelling
and optimisation was demonstrated in the design of a new boom construction and steel structures
of flat and ridge roofs.

This thesis demonstrates that the most time consuming modelling time is significantly reduced.
Modelling errors are reduced and the results are more reliable. A new selection rule for the
evolution algorithm, which eliminates the need for constraint weight factors is tested with optimisation
cases of the steel structures that include hundreds of constraints. It is seen that the tested
algorithm can be used nearly as a black box without parameter settings and penalty factors of the
constraints.

Keywords: optimisation model, steel structure, differential evolution, evolution algorithm, optimisation
UDC 519.85 : 624.014.2