Marcel Poser

This article explains the various phenomena and technology surrounding cable vibration, as observed in medium to long-span cable-stayed bridges. The author describes how vibration occurs in bridges, noting such phenomena as galloping, which is caused by aerodynamic instability involving airflow around an unsymmetrical cross-section. The author also discusses the long-term effects of cable vibration. These can include reduced safety in general or even complete cable failure, due to multiple cycles of bending fatigue stress that accumulate at the anchorages. Countermeasures, including the use of a helical rib on the outside of the cable surface, and supplemental damping devices (e.g., hydraulic dampers, mechanical friction dampers) are discussed.

Ein Ankerkorper (3) ist von Offnungen (4) zur Aufnahme einzelner Seilstrange (1, 1', 1'') durchsetzt, wobei die Seilstrange durch Verankerungsmittel (5) verankert sind. Innerhalb eines Sockelrohrs (6) ist im Abstand zum Ankerkorper eine mit Offnungen (9) versehene Fuhrungsscheibe (8) gehalten. Zwischen den Offnungen des Ankerkorpers und den Offnungen der Fuhrungsscheibe erstrecken sich Fuhrungsrohre (10), in denen je ein Seilstrang gefuhrt ist. Wenigstens im Bereich der Austrittsoffnung (7) des Sockelrohrs weisen die Fuhrungsrohre einen elastischen Wandabschnitt (11) auf. Dadurch konnen im Seilstrang auftretende Querkrafte durch Auslenkung elastisch aufgenommen und direkt oder indirekt auf das Sockelrohr ubertragen werden.

Large amplitude stay-cable vibrations have been observed numerous times in the past few years in two long-span cable-stayed bridges in Texas: the Veterans Memorial Bridge near Port Arthur and the Fred Hartman Bridge near Baytown. In most cases, these vibrations have occurred in combination with light rain and relatively low winds. The rainwater forms rivulets on the cable that change the aerodynamic cross section of the smooth cable stays. This paper describes the field measurements, analytical models of vibration, fatigue tests carried out in Japan, and the development of planned laboratory fatigue tests that will be carried out at Ferguson Laboratory during 2001. The full-size cable fatigue tests will assess the relationship between the amplitude of cable vibration and fatigue damage. A future paper will relate these experimental results to the stays of the Veterans Memorial and Fred Hartman bridges in order to provide an estimate of the fatigue damage that may develop in their stays.

This article explains the various phenomena and technology surrounding cable vibration, as observed in medium to long-span cable-stayed bridges. The author describes how vibration occurs in bridges, noting such phenomena as galloping, which is caused by aerodynamic instability involving airflow around an unsymmetrical cross-section. The author also discusses the long-term effects of cable vibration. These can include reduced safety in general or even complete cable failure, due to multiple cycles of bending fatigue stress that accumulate at the anchorages. Countermeasures, including the use of a helical rib on the outside of the cable surface, and supplemental damping devices (e.g., hydraulic dampers, mechanical friction dampers) are discussed.