The Experimental Research On The Soil-multilayer Frame Structure Dynamic Interaction

The analysis of structural earthquake responses in seismic resistant architectural structure design is commonly based on the rigid foundation assumption. A vast number of experimental studies and theoretical analyses demonstrate that actual seismic responses and soil-structure dynamic interaction influences dynamic response of structures on a large scale. Therefore, the research on the soil-foundation-structure interactions dynamic interaction is of great significance for accurately predicting structural seismic response, and has been a subject of great interest and difficulty in earthquake engineering over the last two or three decades.A series of experimental studies were carried out in order to understand the effects and rules of the soil-structure dynamic interaction, based on "Research and Demonstration on Energy-saving and Key Seismic Resistant Technology of Rural Buildings"(2011BAJ08B02)supported by the National Key Technology R&D Program during the Twelfth Five-year Plan period, and one of the major scientific research projects of Hunan Province entitled "Study on Practical Rural Residential Seismic Resistant Technology and Related Policies"(06sk4057). The thesis is divided into four chapters. The details of each chapter are as follows:Chapter I introduces the importance of the soil-structure dynamic interaction, as well as the necessity of the research. It reviews the study of the history of theories, research methods and some of the major research question concerning the soil-structure dynamic interaction, and particularly introduces how the research results apply to the seismic resistant design.Chapter II addresses general situation of the steel frame vibration test. After determining the test site, physical characters of the soil at test site could be obtained through tests. Then, the working status and test solutions of the steel frame model test of three or six layers could be identified. By changing the stiffness of the superstructure and inputting different excitation waveform toward the structure, comparative analysis could be made with the structure response on rigid foundation.Chapter III compares the vibration excitation tests of steel frame model on the rigid foundation and soil bin respectively to demonstrate that the soil-structure interaction must be taken into consideration on site II, which could provide correct dynamic analysis for structural seismic resistant design. As the soil has certain seismic absorption effects to the superstructure, reduction factor of lateral seismic shearing force decreases with the increasing superstructure stiffness. The test reveals SSI patterns of the soil on site II that natural vibration period of the structure is closed to characteristic cycle of soil at site when the stiffness of superstructure approaches toward certain value; therefore, resonances are created between the structure and the soil ground and the experimental structure will increase the seismic effect of the superstructure in a large degree and its shearing force at the bottom. The results also reflects that the top layer acceleration and displacement responses change regularly with varying stiffness. By changing the superstructure stiffness, steel frame with six or three layers are similar with their dynamic responses, which could demonstrate the patterns of soil-structure dynamic interaction on site II. Besides, the soil-structure interaction is not only related to the stiffness ratio of the structures and the soil, but also to the structures quality and height-width ratio.Chapter IV deduces equivalence relationship between the upper vibration of equivalent single degree freedom and seismic response input, to explain that the upper vibration could reflects the soil-structure interaction as well. The vibration theory could also indicate the effects of the SSI at the floor, which verifies the experiment. Different working conditions of the experiment were analyzed, considering three factors which affect the SSI effect:the stiffness ratio, quality ratio and height-width ratio. The period ratio of varied working conditions calculated with the SR model of single particle system is similar to the period ratio of the actual measurement to some extent, though there is still certain deviation. Analyzing the working conditions of the steel frame with similar stiffness ratio indicates the effects of height-width ratio; In the cases of different height-width ratio, the relationship of the stiffness ratio to shearing force of substructure, the top layer acceleration, and the top layer displacement respectively are fitted and reflects certain patterns, which provides significant reference for considering the soil-structure dynamic interaction.