Study On Influence Of Frozen Soil Layer On Seismic Response Of Buildings In Cold Region

Frozen soil is widely distributed in China,permafrost and seasonal frozen soil make up 21.5%and 53.5 of China's land area respectively,and the majority of permafrost region is located in the earthquake area.When the earthquake struck,the existence of permafrost will effect on the seismic response of the building and change the dynamic characteristics of the foundation soil and the predominant period,which directly affects the stability and security of the upper buildings.The current seismic design code(GB050011-2010)for the classification of the field and seismic design shall be carried out in accordance with the ordinary soil,without consideration of permafrost on the structural seismic response and the influence of response spectrum.From the available literature,both at home and abroad under the conditions of frozen soil,considering the dynamic characteristics of frozen soil-structure interaction system for research is extremely limited,the lack of relevant theoretical analysis and experiment data support,led to the understanding of the dynamic characteristics of structure in such venues so rarely.The study of structural seismic response considering the interaction between permafrost and pile has become an indispensable content in analyzing the seismic response law of building structures in cold regions and evaluating their safety performance.It is of great significance to promote the development of seismic design theory of building structures in permafrost regions and enhance their seismic disaster prevention ability.Taking the permafrost-structure interaction system in the cold region as the research object,this paper focuses on the influence law of the existence of permafrost on the seismic response of buildings in the cold region,and establishes the finite element model consistent with the shaking table test by using ANSYS finite element software.The influence of the presence of permafrost on the seismic response of buildings is studied by analyzing the maximum acceleration response spectrum displacement and pile bending moment of the ground surface and the top of buildings.The influence of different seismic waves and different freezing depths on the seismic response of buildings is further studied by changing the freezing depth and other parameters of the seismic wave type permafrost,it can provide reference for seismic performance analysis of building structures in cold areas,and gives preliminary Suggestions for seismic design of frozen ground in current codes.The results show that:(1)When the superstructure is rigid with the presence of proper permafrost,the earthquake damage of the building tends to increase due to the increase of the rigidity of the topsoil layer.(2)With the increase of soil freezing depth,the maximum acceleration of the top layer of the rigid structure tends to increase,while with the increase of soil freezing depth,the shear modulus of the surface soil increases,and the maximum acceleration of the surface tends to decrease.(3)The time corresponding to the response spectrum peak at the top of the structure is the natural vibration period of the structure.With the increase of frozen depth of the permafrost,the natural vibration period of the permafrost-structure interaction system decreases and the vibration frequency of the structure increases,which may lead to the increase of seismic response of the structure due to the resonance phenomenon.(4)From the point of view of the maximum displacement of each floor,different earthquake types have different effects on the maximum displacement of the structure.The existence of frozen soil will reduce the maximum displacement of each floor of the structure,and with the increase of frozen soil depth,the maximum displacement of each floor first decreases and then increases.(5)It can be seen from the bending moment diagram of the pile body that the existence of frozen soil has a constraint effect on the bending moment of the pile body,but the bending moment of the pile body at the junction of frozen soil and unfrozen soil has an obvious abrupt change phenomenon.Therefore,the corresponding position of the pile foundation of buildings in cold areas should be reinforced to reduce earthquake damage.