Dynamic behaviour of multi-span beams under moving loads

In this paper, an exact dynamic stiffness element under the frame work of finite element approximation is presented to study the dynamic response of multi-span structures under a convoy of moving loads. A dynamic model coupled with a FFT algorithm is developed. The model is highly efficient for calculating the response of bridges under multiaxle moving forces. All the vibration frequencies and mode shapes of the beam-structure may be calculated exactly using the Wittrick and Williams algorithm. Examples show that with only one element per span, exact frequencies and modes could be obtained. Some results on the dynamic amplification factor are presented also as a function of the speed of the moving loads. (C) 1997 Academic Press Limited.