Date of Award

2010

Degree Type

Thesis

Degree Name

Doctor of Philosophy

Department

Civil and Environmental Engineering

First Advisor

Dr. El Damatty A. A

Second Advisor

Supervisory Committee

Abstract

Owing to their excellent structural characteristics, aesthetic appearance, low maintenance cost, and efficient use of structural materials, cable-stayed bridges have gained much popularity in recent decades. Stay cables of a cable stayed bridge are post-tensioned to counteract the effect of the bridge dead load. The solution for an optimum distribution of post-tensioning cable forces is considered one of the most important and difficult tasks in the design of cable-stayed bridges. A novel approach that utilizes the finite element method, B-spline curves, and real coded genetic algorithm to determine the global optimum post-tensioning cable forces is developed. The effect of geometric nonlinearity on the determination of the post-tensioning cable forces is assessed. The study is further extended to develop the first surrogate polynomial functions that can be used to evaluate the post-tensioning cable forces in semi-fan cable stayed bridges. The developed post tensioning functions are then used to investigate the optimal geometric configurations, which lead to the most uniform distribution of the post-tensioning cable forces. Details of an optimization code developed in-house specifically to optimize the design of composite cable-stayed bridges with semi-fan cable arrangement are then reported. The optimization design code integrates a finite element model, the real coded genetic algorithm, the post tensioning polynomial functions, and the design provisions provided by the Canadian Highway Bridge Design Code. An extensive parametric study is then conducted using this optimization code to develop a database for the optimum design of semi-fan cable stayed bridges. The database covers bridge lengths ranging from 250 m to 700 m. It describes the variations of the optimum design parameters, such as the main span length,height of the pylon, number of stay cables, and cross-sectional dimensions with the total length of the bridge.

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