The Study On Local Site Effect Of The Seismic Response Of Frame Structures Located On Slopes And Supported By Foundations With Different Elevations

There are more and more structures on a slope with application in multi-storey and high-rise buildings.The structure supported by foundations with different elevations is a typical structural form of structure on slope.This structure has a geometric distance among foundations at different elevations,in addition,the foundation may also have complex overlay,which will have an influence on the amplitude and spectral characteristics of the ground motion when it comes to the upper and lower surface of the slope,namely,the local site effect of slope.In the case of the structure supported by foundations with different elevations,the earthquake ground motion imported at the upper embedding is not the same as that at the lower embedding end,which will have an influence on the seismic response of the structure.There is no specific provision in current codes on the seismic input of mountain building structure,and if the non-uniform excitation of the earthquake ground motion is not carefully considered in the design,the seismic response of structures will be seriously underestimated,which will affect the structural safety.In this paper,the effect of the slope site effect on the seismic response of the structure of the frame structure supported by foundations with different elevations is carried out,and the seismic response analysis of the slope free field with slope height and soil condition as variable is carried out.Then,a comparative analysis of seismic response of frame structure supported by foundations with different elevations under uniform excitation and non-uniform excitation of earthquake ground motion is performed.Finally,the influence of slope site effect on the seismic response of the frame structure supported by foundations with different elevations is summarized.Also,The extent of influence of the site effect of slope on the seismic response of the frame structure supported by foundations with different elevations is studied by the direction of earthquake action,structure arrangement,and structural height changes.Based on the structural response amplification law,the seismic action considering the site effect of the slope on frame structure supported by foundations with different elevations is suggested.The main conclusions of this paper are shown as follows:(1)In the sloping field,there is a difference between the earthquake ground motions on the upper embedding end and lower embedding end,and the excellent period of the amplitude and response spectrum of the ground motion on the slope are affected by the differences in slope height and soil conditions.(2)The effect of local site effects on the earthquake response of frame structure supported by foundations with different elevations on slopes is mainly caused by the soil conditions and slope height.When the soil condition changes from soft soil to medium-hard soil,the amplification of structural seismic response weakens gradually.Response magnifying part transfers from the upper structure to the floors under the upper embedding end.When the slope height changes from 3m to 15 m,response magnifying part keep the same,but the amplification of the response increases with the increase of slope height.(3)The influence of the direction of earthquake action,structure arrangement,and structural height on the seismic response of frame structure supported by foundations with different elevations under sloping site effects is not obvious.(4)When the slope height is less than 3m or the soil condition is medium hard soil,the adverse effects of local site effects can be considered by multiplying the earthquake ground motion parameters with the amplification factor.When the slope height is greater than 3m and the soil conditions are soft soil or medium soft soil,the multi-point excitation of ground motion should be adopted to consider the site effect of the slope.The adverse effects of earthquake ground motion variability caused by slope site effects on the structure cannot be fully considered by only multiplying the earthquake ground motion parameters with an amplification factor.