Genex Systems, LLC

FHWA-HRT-14-067

Tech Report

United States

United States. Federal Highway Administration. Office of Infrastructure Research and Development

Cable-stayed bridges have been recognized as the most efficient and cost effective structural form for medium to long span bridges over the past several decades. With their widespread use, cases of serviceability problems associated with large amplitude vibration of stay cables have been reported. Stay cables are laterally flexible structural members with very low inherent damping and thus are highly susceptible to environmental conditions such as wind and rain/wind combination. Recognition of these problems led to the incorporation of different types of mitigation measures on many cable-stayed bridges around the world. These measures included surface modifications, cable crossties and external dampers. Modification of cable surfaces has been widely accepted as a means to mitigate rain/wind vibrations. Recent studies have firmly established the formation of a water rivulet along the upper side of the stay and its interaction with wind flow as the main cause of rain/wind vibrations. Appropriate modification of exterior cable surface effectively disrupts the formation of a water rivulet. The objective of this study was to supplement the existing knowledge base on some of the outstanding issues of stay cable vibrations and develop technical recommendations that may be incorporated into design guidelines. Specifically, this project focused on identification of in-situ cable dynamic properties and performance of external viscous dampers on the Penobscot Narrows Bridge. Forced vibration tests were conducted on the stay cables during the latter stages of construction, just prior to and following installation of viscous dampers. Cable properties, such as vibration frequencies and damping levels, were established and compared with design targets.

PDF

DTFH61-07-D-00034

Federal Highway Administration
US Transportation Collection