Keywords: ANGEL heuristic method, simultaneous sizing-shaping optimization, steel bridges.

In this paper a new hybrid metaheuristic ANGEL algorithm is presented for continuous and discrete optimization of steel bridges with combined sizing and shaping variables. The ANGEL algorithm combines ant colony optimization (ACO), genetic algorithm (GA), and local search (LS) strategy. The main procedure of ANGEL follows the repetition of these two steps: (1) ACO with LS and (2) GA with LS. The initial population is a totally random design set. In other words, firstly ANGEL generates an initial population, after that, in an iterative process ACO and GE search alternately and cooperatively on the current design set. According to the systematic simplification, the algorithm consists of only three basic operators: random selection, random perturbation (ACO), and random combination (GA). The proposed method has been presented first time for space trusses [1] and later extended for sensitivity analysis of shallow dome structures [2], and shaping and sizing problems of space trusses [3].

The shaping and sizing optimization of steel bridges where the design variables are the cross-sections and nodal coordinates is very complex problem. The different nature of the design variables usually causes unacceptable numerical instability for a single optimization algorithm. To solve this problem it is necessary to adequately combine different optimization algorithms, depending on the different types of design variables of the problem. The separate treatment of the two kinds of design variables is not an obligation but a simplification.

In this paper, the discrete solutions are computed by an optimal rounding algorithm according to the given catalogue values. A simple but efficient local search procedure is proposed as well, which is able to improve the quality of the discrete solutions. Experimental results are presented for shaping and sizing optimization of steel bridges.

1

Csébfalvi A., Csébfalvi G., "A new hybrid meta-heuristic method for optimal design of space trusses with elastic-plastic collapse constraints", in Proceedings of The Eighth International Conference on Computational Structures Technology, Edited by B.H.V. Topping, G. Montero and R. Montenegro, Civil-Comp Press, Stirling, UK, paper 199, 2006. doi:10.4203/ccp.83.199

2

Csébfalvi A., Csébfalvi G., "Optimum Design and Sensitivity Analysis of Shallow Space Structures using an Improved Meta Heuristic Method", in Proceedings of the 15th UK Conference of the Association of Computational Mechanics in Engineering, B.H.V. Topping (Editor), Civil-Comp Press, Stirlingshire, UK, paper 59, 2007. doi:10.4203/ccp.85.59

3

Csébfalvi A., Csébfalvi G., "An ANGEL meta-heuristic method for combined shape and sizing truss optimization", in Proceedings of the 7th World Congress on Structural and Multidisciplinary Optimization, Seoul, Korea, 98550, 2007.

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