Suspension bridges

Suspension bridges

The Hardanger Bridge. Photograph by NTNU/Knut Andreas Kvåle.

Case study: The Hardanger Bridge

The Hardanger Bridge is a 1380 meters long suspension bridge, located on the western coast of Norway. It is the longest suspension bridge in Norway, and the 10th longest in the world, which makes it an interesting case study.  Our research in the field of suspension bridges requires knowledge from several engineering fields; such as aerodynamics, signal processing, finite element analysis and control theory. 

Experimental surveys

A comprehensive measurement system is operating on the Hardanger Bridge to improve the current understanding of the dynamic behaviour of long-span suspension bridges and their interaction with wind. This includes sensors for measurement of both response and environmental excitation. The system is described in detail under Structural monitoring (Structural monitoring - The Hardanger Bridge).

In addition, wind tunnel measurements are used to investigate the behaviour of the bridge girder when subjected to aerodynamic forces.

Bridge girder section of the Hardanger Bridge. Model and illustration by NTNU/Bartosz Siedziako.

System identification and modal analysis

Based on recordings established by the monitoring system, parameters characterizing the system behaviour; typically represented by natural frequencies, damping ratios, and mode shapes; are estimated (system identification). The results are a highly valuable asset for these applications:

  • Studying the dynamic behaviour of the bridge
  • Updating the numerical model, such that it better describes the real behaviour of the bridge
  • Verification and possible improvement of the current state-of-the-art methods used for numerical modelling

Modal shape of the Hardanger Bridge. Model and animation by NTNU/Øyvind Wiig Petersen.

Load modelling and identification

Modelling of the wind-induced forces on suspension bridges is crucially important for accurate prediction of the dynamic response.

The modelling of the environmental wind loads hinges on the description of the spatial and temporal characteristics of the wind field. The wind data from the field measurements will be used to characterize the wind field. It is aimed to test the performance of load models and reveal the uncertainty involved in response prediction.

The models for motion-induced loads most commonly used in bridge aerodynamics are linear engineering approximations. It has been shown in several case studies that the models are working well when the response of the bridge is dominated by one vibration mode in each direction. Taking into account that the principle of superposition does not hold in fluid dynamics, it is unknown if the models will be able to predict reliable results for a more complex motion. Thus, there is a need to test the accuracy of the linear assumption introduced in the modelling of the self-excited forces. This challenging task does not only require development of new experimental setup but also identification techniques able to work with an arbitrary motion.

People:

Postdocs and PhD candidates working with suspension bridges:

Contact bridge

Contact

Professor Ole Øiseth

Phone: +47 735 91 493

E-mail: ole.oiseth@ntnu.no