The Research On Soil-structure Dynamic Interaction About Steel Frame With Raft Foundation

China is a country often suffered from earthquake, which leads to great damageevery year. The vast majority of architecture are built on the soil and few are directlybased on the bedrock. Soil-structure interaction(referred to as SSI)will affect thestress of the structure when the foundation contact with soil. When the foundation ofthe structure shocks, the soil-structure interaction is also called soil-structure dynamicinteraction(referred to as SSDI).The effect of SSDI is signifcant to the structure thefoundation of which contacts with soft soil. That whether the effect is beneficial orharmful depends on the relative characteristics of structure and soil, such as therelative stiffness ratio between superstructure and ground soil (referred to as relativestiffness ratio). At present the seismic code of our country about soil and structuredynamic interaction is rough. It simply uses a period related reduction coefficient tocalculate the dynamic response of a structure under the earthquake, which does nottake the relative characteristics of the structure and soil into account. This will reducethe calculation response of the structure (compared with the response of the structureof rigid foundation assumption), but the reality is that the response of the structurealso has the possibility of increasing. It will make the structure dangerous whenconsidering soil-structure dynamic interaction.Considering the present situation, the main research of this thesis is the influenceof relative stiffness ratio of the structure to the structure’s dynamic characteristics anddynamic response, the point is the correlation between natural period and the relativestiffness ratio, and the correlation between bottom shear of the structure and therelative stiffness ratio. The test model is a steel frame with6layers, the rigidfoundation model test and soft foundation model test was done to make a contrast. Bychanging the diagonal brace of each layer to change the stiffness of the upperstructure, so as to change the relative stiffness ratio.The two contrast model test areexactly the same in addition to the foundation, and the difference dynamic reaction ofof the two model is caused by soil-structure dynamic interaction. Test results showthat the natural vibration period and the structure of the bottom shear is related to therelative stiffness ratio. When the relative stiffness ratio is greater than0.3, the groundsoil is softer than the superstructure, which leads the bottom shear to reduce; when therelative stiffness ratio is less than0.3, the resonance is easy to occure between structure and soil, which leads the bottom shear to increase, and should get enoughattention.