Study On The Influence Of Sand And Gravel Cushion On Seismic Response For The Tall Buildings

Ground treatment of cushion method is an ancient method, and much attention was paid on, so much experience was accumulated. Sand and gravel, as a kind of natural building material with higher performances, is widely used in a great number of cases such as dams, railway subgrade, bridge pier, and weak ground treatment used as sand and gravel cushion. In ground treatment, however, research is still expected in the studies of cushion's actual bearing capacity, deformation capacity, dynamic properties, shearing performance, and especially, the properties of the superstructure under seismic actions. In this paper, based on a practical subject, a chimney built on sand and gravel cushion is analyzed with the static and dynamic finite element methods to consider the influence of the cushion upon superstructure under earthquake, and the attempts that have been done are as follows:First of all, the strength mechanics of the sand and gravel cushion as well as their influence factors are discussed in this paper;Secondly, modal analysis is employed in a chimney of 240m height located on the cushion to yield its frequencies and periodicities when the characteristics of the under cushion is changed. This indicates that the structural natural vibration period is lengthened when the effect of the sand and gravel cushion is considered. And also, as it is anticipated, when the weakness of the foundation soil is changed, the seismic response of superstructure varies too.Results of horizontal seismic time-history response of the chimney are given at last. It shows that the displacement and acceleration decrease at the top of the structure. At the base, however, the displacement and acceleration increase in some degree, but the relative displacement and relative acceleration is reduced, which means the sand and gravel cushion can limit the deformation in the tall buildings and effectively reduce the superstructure's seismic response.