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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 77
PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON CIVIL AND STRUCTURAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping
Paper 134

Optimal Design of Curved Pre-Stressed Box Girder Bridges

N. Maniatis and V. Koumousis

Institute of Structural Analysis and Aseismic Research, National Technical University of Athens, Greece

Full Bibliographic Reference for this paper
N. Maniatis, V. Koumousis, "Optimal Design of Curved Pre-Stressed Box Girder Bridges", in B.H.V. Topping, (Editor), "Proceedings of the Ninth International Conference on Civil and Structural Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 134, 2003. doi:10.4203/ccp.77.134
Keywords: optimal design, bridges, box girder.

Summary
In this work the problem of optimal design of curved prestressed box girder bridges is addressed. The design variables are the coordinates of the nodes that define the single cell box girder cross-section and the prestressing forces of the internal and external web of the cross-section. The entire design corresponds to a level of preliminary design and takes into account all loading cases specified in DIN 1072 for vehicle SLW 60/30 and the main strength and serviceability constraints based on DIN 4227.

The analysis is based on stresses developed from a longitudinal analysis that considers the bridge as a 3D frame and a lateral analysis that is based on a frame model of the cross-section appropriately supported. The mechanical properties of the box section are determined on the basis of a refined theory based on boundary element method, or simplified formulas. The tendon loads are determined at a number of closed spaced sections by first solving the geometrical problem that defines the projection of a parabola at the vertical chord plane to the internal and external web and then determine the concentrated load in the plane of three consecutive nodes. These nodal loads are transferred to the axis of every section as statically equivalent loads and moments under the assumption of non deformable section. All loading cases that produce min-max stresses are defined and are used to determine the constraints of the problem.

The optimization problem considers a combined objective that accounts for both the cost of the concrete and the cost of the prestressing tendons based on unit prices using a micro GA algorithm. Numerical results are presented that verify the main design rules of thump that exist among experts in bridge design.

References
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Goldberg, D.E., "Genetic algorithms in search, optimization, and machine learning" Addison-Wesley, Reading, Mass., USA, 1989.

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