Dynamic Interaction between Towers and Cables of a Long Suspension Bridge During Construction

Abstract

This chapter provides a three-dimensional finite element modal analysis to investigate the dynamic interaction between the towers and cables of the Tsing Ma long suspension bridge during its construction. The two bridge towers, made up of reinforced concrete columns and deep prestressed concrete beams, are modeled by three-dimensional Timoshenko beam elements with rigid arms at the connections between columns and beams. The main span cables and side span cables are modeled by three-node cable elements accounting for geometric nonlinearity and large deflection. The chapter explores the natural frequencies and modes of vibration of the free-standing towers, and the isolated main and side span cables are first computed. Modal analysis of the three-dimensional tower-cable systems is then carried out. The results show that the in-plane dynamic characteristics of the bridge towers with cables are significantly different from those of the free-standing towers. Out-of-plane dynamic characteristics of the towers with cables, however, remain almost the same as those of the free-standing towers. Both in-plane and out-of-plane dynamic interactions between the towers and cables are significant at global natural frequencies, but there are many local natural frequencies at which the cables vibrate but the towers remain still or have relatively small modal motion.