Dynamic interaction between towers and cables of a long suspension bridge during construction

摘要

A three-dimensional finite element modal analysis is performed to investigate 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 modelled 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 modelled by three-node cable elements accounting for geometric nonlinearity and large deflectin. 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 system is then carried out. The results show that 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, almost remain 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.