The influence of input angle of excitation on structural response is significant

apractical response spectrum method for analyzing the behaviors of this kind of structure is studied.Firstly

based on the achievements about the multi-components accelerations power spectra matrix

a rational formula

considering the input angle of excitation

is deduced by using stationary random vibration principle.Secondly

apractical formula is proposed by introducing the displacement response spectrum considering the non-stationarity of excitation.Finally

the practical formula is used in a typical case:a spatial steel structure with L shape plane

and the comparison between the results from the formula and ones from time-history method with some earthquake ground motions is conducted

which proved the practical formula is reasonable and could be a reference for design and analysis of structures under seismic actions.