Analysis of Damping System for Cable Stayed Bridges Under Dynamic Loading

Abstract

ABSTRACT The study deals with static, dynamic (earthquake response) analysis, and seismic analysis of cable stayed bridges. The analyses include the effect of using damping systems on the response of bridge to various directions of earthquakes. The bridge of semi-fan type cables is considered in this study. Detailed analysis aspects of modeling, loading, boundary conditions (deck as simply supported beam and towers were fixed at base in all directions), and solution ar components were idealized as three dimensional modeling with shell, link and beam elements having six degree of freedoms. The cables are modeled in two schemes; First scheme as single link element, and second scheme as multi- beam elements. Gravity load is applied on all nodes of cable stayed bridge. Accordingly, static and free vibration analyses of the cable stayed bridge are studied for cases of gravity load. It was found that, deflections of deck in first scheme were less than 30% those in second scheme. The results of first scheme were more realistic than those of The cable stayed bridge is analyzed for earthquake excitations acting independently in three directions, longitudinal, transversehorizontal and transverse- vertical directions. It was found that earthquakes in transverse- horizontal direction have greater effects on 50% than earthquakes in other directions because of its danger to the collapse of towers. Damping effects on reduction deflections, resulted from earthquakes, are studied. The effect of changing number, direction and value of damping coefficient on reduction response to earthquake, are analyzed. Results show that inclined dampers were more effective than vertical dampers in longitudinal and lateral earthquakes. Damping effect of eight inclined dampers was 80% in deck deflections at lateral earthquake component. four vertical dampers have damping effect 50% on deck deflections with lateral earthquake