The impact of reasonable PGA modulation and spatiotemporal variability of far-field long-period ground motion on continuous rigid-frame bridges

Far-field long-period (FFLP) ground motion and their spatiotemporal variability are detrimental factors in seismic analyses of large-span long-period structures. Adjusting the peak ground acceleration (PGA) of FFLP ground motion according to design specifications can lead to an overamplification of structural response without practical significance. To ensure the accuracy of the response of long-period structures under FFLP ground motion, this paper introduces an amplitude modulation method suitable for seismic analysis of FFLP ground motion-the Improved Amplitude Modulation Method (IAMM). This method optimizes the PGA calculation formula in the specifications by introducing a scaling factor Sf. Taking a continuous rigid-frame bridge as an example, the influence of the traveling wave effect of FFLP and ordinary ground motion on the structure is analyzed based on the IAMM. The results indicate that using the IAMM can reflect the non-stationarity of FFLP ground motion, ensuring that structural responses are realistic and reasonable. The traveling wave effect causes a redistribution of internal forces within the structure, which is closely related to the type of ground motion, apparent wave velocity, and structural characteristics. For continuous rigid-frame bridges, the traveling wave effect is beneficial for piers but detrimental to the mid-span region of the main beam. Under ordinary ground motion action, the sensitivity of internal force response to apparent wave velocity is higher than that of FFLP ground motion. Additionally, under low apparent wave velocity conditions, structural response is prone to underestimation, thus necessitating the rational determination of apparent wave velocity based on site characteristics.