The earthquake motion has non-stationarity both in strength and frequency

and it make the dynamic responses of multi-span bridges be complex and severe.To study the responses of continuous bridges under multi-support excitations

three indexes are presented:the standard deviation of absolute amplitudes

the direction dispersion and the crossing-zero rates.The significance of the general matrix of modal participation factor is represented according to the characteristics of the structural motion equations under multi-support excitations.The regularity of the responses of different span continuous bridges under excitations is studied by applying the displacements or accelerations with different directions or amplitudes on each supports.The results show that the responses become more complex and various with the increasement of the span number and the non-stationarity in earthquake excitations.