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

US Transportation Collection
Federal Highway Administration