Abstract: Unlike conventional dynamic calculation inwhich rigid models are used, a serial elastic model of three masses and three degree of freedoms for the trolley frame of container gantry cranes is proposed by taking the large span of the trolley beam into consideration. The precise solutions to the vibrating equations are obtained byusingmodal analysis. The results showthatthe dynamic coefficients ofthe trolleyframe, the gantry structures and the wirerope-pulley system are different