Input earthquake ground motions considering the orientation with respect to the most significant characteristic of its response spectra

It was commonly ignored that the effect of observation-orientation on the characteristics of response spectra of strong-motion recordings which be selected as input earthquake ground motions for seismic analysis and design of structures in previous studies and practices. The recordings obtained from Wenchuan Wolong Station in Ms8.0 Wenchuan Earthquake in 2008 were applied, named as 051WCW recordings in the paper. The two orthogonal acceleration time-series were rotated in horizontal plane and the pseudo-spectra acceleration S_a was calculated. For each oscillation period, the relationship between rotation angles and S_a was established. It was shown that S_a was highly dependent on the rotation angles, that was to say the observation-orientation had significant effect on the S_a of recorded ground motions. Therefore, the scheme of selecting seismic input was suggested, which considered the orientation with respect to the most significant characteristic of response spectra of recorded ground motions. Then for determining this orientation, we designed an index function and detailed computation procedure. Finally, it was used for gaining the orientation of 051WCW recordings as E42°S, which means that before 051WCW recordings being input into interest structure, rotate it to orientation E42°S essentially.