Wind Tunnel Investigations of An Inclined Stay Cable With A Helical Fillet

CHAPTER 1: INTRODUCTION

In response to concerns expressed in the wind engineering community with regards to the aerodynamics of inclined stay cables with helical fillets, NRC-IAR, in collaboration with the University of Bristol and the University of Stavanger, was mandated to conduct an experimental study in its 3-by-6-m Propulsion and Icing Wind Tunnel. This project was initiated by the Federal Highway Administration (FHWA), which has undertaken the task to fill the knowledge gap on aerodynamics of stay cables with helical fillets. The main objective of the investigation was to define the sensitivity of stay cables with helical fillets (such as those commonly used on cable-stayed bridges in the United States and Europe) to galloping. For this purpose, a small helical fillet was affixed to an existing stay cable model composed of a steel core covered with a HDPE tube, typical of actual bridge stay cables. The aeroelastic stability of the cable as well as the nature of underlying aerodynamic forces were investigated.

The investigation was divided in two phases. In phase I, the aerodynamic stability of a cable with helical fillets was studied with a spring-supported cable model in smooth flow for a cable inclined at 60 degrees from the horizontal. The dynamic response of the model and the cross-sectional wind-induced surface pressures were monitored as a function of Reynolds number.

In phase II, different cable orientations were studied (45 and 60 degrees). For the cases where important cable vibrations were observed in smooth flow, tests in turbulent flow for conditions representative of field conditions were carried out.

This report documents the work undertaken by NRC-IAR and presents the results of the investigation. The approach adopted was to carry out the test in a 3-by-6-m wind tunnel on a 6.7-m-long sectional model built at a geometrical scale of 1:1 and free to respond on an eight-spring suspension system. The tests took place from May 2, 2011, to June 24, 2011.

The main findings of the investigation for both rounds of tests are presented in this report. The documentation of the tests also includes video recordings, still images, and all the experimental data in electronic form.