Abstract: In this paper,the seismic response of the high-flexible structure under coupled horizontal,tilting and vertical ground motion is investigated.First,a dynamic equation under the coupled ground motion is derived,in which the additional second-order effects of gravity caused by the foundation tilt under the tilting ground motion is taken into consideration.Then,the influence of the vertical ground motion on the second-order effects of gravity is discussed.Finally,by taking a 210 m television tower as the prototype,the shaking table test of a reduced scale model is carried out under the coupled ground motion.The comparison between the theoretical analysis results and the test ones show that (1) the results of the shaking table test accord well with the theoretical ones obtained through the derived dynamic equation,which testifies the rationality and accuracy of the theoretical analysis; (2) the vertical ground motion can cause the change of the conventional second-order effects of gravity to change,and it has an significant impact on the additional second-order effects of gravity caused by the tilt; and (3) as compared with the single horizontal ground motion,the coupled ground motion causes the geometric rigidity to change with time and results in a larger asymmetric displacement，which means that the structure capable of resisting the hori- zontal ground motion originally may get destroyed.

Key words: shaking table test, tilting ground motion, earth quake, high-flexible structure, dynamic response