Research On Some Basic Problems Of Shape Memory Alloy Auxiliary Cable-cable System

Stay cables are main functional elements of a cable-stayed bridge to support the bridge deck and transmits vehicle loads to bridge tower. Due to light weight, low inherent damping and slenderness characteristics, cables are vunlerable to environmental excitations such as wind and wind/rain. Harmful vibrations may cause uneasiness of pedestrians and drivers. Excessive long-time vibration may also induce damage of protective system of stay cable and the high-strength wires would contact directly to corrosive air and water. Corrosion and fatigue-corrosion of the high strength will greatly shorten the anticipated service life of stay cables. Aerodynamic countermeasures, damping devices and cross-ties are applied to suppress these harmful vibrations. And these methods may hybrid applied for better mitigation effects. Due to the favorable characteristics of super elasticity and fatigue resistance,Shape Memory Alloy(SMA) has the potential to be applied for cable vibration mitigation as high damping cross-ties. However, the application of SMA cross-ties on cable vibration mitigation is still not well investigated yet; damping effects of cable with SMA cross-ties and influence of environmental temperature still needs further experimental studies. Particularly, the design methods for cable system with additional SMA cross-link are not established yet.This paper researched the prediction of low mode vibration frequency and modal damping ratio of the system using the linear functions, based on the previous research about theoretical research of parallel spring-damper-cable system, the relevant test data about free vibration test of pre-tensioned SMA wire-single(short cable, 3.2m)cable model system and mechanical properties test of SMA wire. Then free vibration of a single(long cable, 15.15m) cable model and additional single pre-tensioned SMA wire-single(long cable, 15.15m) cable model were tested, the effect of test temperature on the 1st and 2nd mode vibration frequency and modal damping ratio ofthe system was mostly studied. Filtered the displacement-time curves to obtained logarithmic attenuation value and the system vibration frequency. At the same time,based on this experiment, the creep test is made on the pre tension SMA wire to study the effect of cable creep on the system vibration. Finally, establish the additional damper-two cable system model, for simplicity, the effect of flexural rigidity of cable would not be considered in the study, and the cable was simplified into a taut cable.The separation of variables was used to deride the characteristic equation, and the relevant limit solutions are analyzed. Finally, the effect of mass-tension ratio,frequency ratio, length ratio and installation location are studied. The influence of the change of the non- dimensional damping coefficient on the system mode shape was discussed.