Dynamic Factor of Bridges Subjected to Linear Induction Motor Train Load

The linear induction motor (LIM) has been used in urban rail transit systems in China and other parts of the world. However, specialized specifications for design or assessment of bridges in urban rail transit systems have not yet been established. The electromagnetic force of LIM complicates vehicle-bridge interaction. In this paper, a typical bridge on the Guangzhou metro line 4 is evaluated both experimentally and theoretically to determine vehicle-bridge interaction characteristics. The LIM vehicle is represented by a model of secondary suspension with 6 degrees of freedom, and the bridge is modeled using standard beam elements. The coupled motion equation is formulated using the principle of total potential energy with stationary value in an elastic system and solved by using the Newmark-β method. Field dynamical tests were also performed on the bridge. The calculated and experimental vertical displacement time-histories for LIM trains crossing the bridge were obtained and dynamic factors were developed. A formula for determination of the dynamic factor, which can provide an engineering basis for design and evaluation of bridges in urban rail transit system, is proposed.