Innovative structural concepts for motorway flyovers
Author: Louis Bauer
Language: English
Abstract
This thesis investigates and evaluates innovative structural concepts for motorway flyovers in Switzerland, with a focus on achieving designs that are more economical, low-maintenance, and sustainable while minimising traffic disruptions during construction. The study focuses on optimising materials, structural systems, and construction methods to meet these objectives.
Using steel-concrete composite members helps to enhance structural efficiency. The system is low weight and compatible with prefabrication. This eliminates the need for falsework and enables efficient construction within tight clearance profiles. Additionally, composite girders allow for the use of prefabricated girders that can be lifted into place, minimising traffic disruptions to an absolute minimum.
The study employs finite element analysis (FEM) to analyse the flexural behaviour of composite cross-sections using different materials. Key findings reveal that steel grade S355 provides the optimal balance of strength, stiffness, and ductility for composite girders. Ultra-high-performance concrete (UHPC) significantly enhances flexural behaviour and reduces self-weight. However, the cost and environmental impact of UHPC outweigh the benefits of weight reduction, making it unjustifiable as a primary material for flyover construction. The study highlights the challenges posed by strict height limitations, which complicate the achievement of adequate flexural stiffness. Additionally, higher-grade steels, such as S460, do not offer notable advantages in the examined design scenario.
The proposed frame bridge design utilises cast-in-place frame corners to enhance rigidity and enable efficient load transfer. The lightweight composite girder spans the central gap, reducing self-weight while maintaining strength and stiffness. This approach optimises force distribution, reducing stress at the midspan and improving overall structural efficiency.
