Research On Seismic Vulnerability Of Steel Frame On Soft Soil Foundation Considering Group Effect

Earthquake disaster can bring huge loss of life and property to mankind,so it is urgent to carry out earthquake risk analysis.However,for coastal urban areas with wide distribution of soft soil,seismic vulnerability analysis without considering soil-structure interaction is difficult to reasonably evaluate the seismic performance of structures,which leads to the reduction of reliability of seismic risk analysis.At the same time,the rapid development of urbanization leads to the dense distribution of buildings,so the study of vulnerability of soil-structure dynamic interaction considering group effect is becoming more and more important,because it is helpful to evaluate earthquake risk reasonably and reduce the loss caused by earthquake effectively.In this paper,the effect of group effect on seismic vulnerability of steel frame structure is studied by finite element simulation.In this paper,vulnerability is the ultimate research goal,and the influence of group effect is studied by comparing the soil-structure dynamic interaction of single structure and group structure.Firstly,the finite element model of comparative analysis is established,then the parametric dynamic analysis is used to verify the model,and the influence rules of each influencing factor on the group effect is explored.Then the probabilistic seismic demand analysis is carried out based on incremental dynamic analysis,and the effect of group effect on structural seismic response is studied from the perspective of statistics.Finally,the seismic vulnerability function of the structure is obtained by combining the seismic capacity analysis,and the effect of the group effect on the seismic performance is evaluated from different aspects.The main research contents and conclusions based on the specific calculation examples in this paper are as follows:Firstly,the numerical simulation of the interaction system is carried out.The upper steel frame structure,soft soil foundation in finite area,raft foundation and pile foundation are simulated by finite element method.The soft soil foundation-steel frame model and soft soil foundation-group steel frame model are established by coupling each part to lay the foundation for the subsequent dynamic analysis.The non-linearity of soil is emphatically considered,which is realized by the UMAT subroutine of equivalent linear constitutive of soil,and an automatic iterative calculation program for multi-layer soil was developed.Secondly,dynamic parametric analysis is carried out.Based on the established model,three typical seismic waves are input to carry out dynamic time history analysis.Taking the inter-story displacement angle and inter-story shear force of the structure as the contrast index,the analysis results are compared with the existing literature research results to verify the reliability of the model.For the benchmark model in this paper,the group effect can reduce the seismic response of the structure,which can reach 12.0%.However,when the the soil stiffness and the structure stiffness are changed,the opposite effect may occur,while the spacing of the structure has no obvious influence.Thirdly,the probabilistic seismic demand analysis is carried out.The IDA curve cluster is obtained by incremental dynamic analysis,and the percentile curve is obtained by statistical analysis.Then the spectral acceleration intensity S_a（T₁,5%）of the defined performance points is obtained based on the percentile curve.Finally,the probabilistic seismic demand model is obtained by linear fitting of seismic demand as the basis of subsequent vulnerability analysis.The results show that the S_a（T₁,5%）of the soft soil-steel frame model is about 0.88 times that of the soft soil-group steel frame model when the same performance point is reached.Finally,the seismic vulnerability analysis is carried out.Based on the existing research results,the parameters of the seismic capacity model are obtained,and the seismic vulnerability function of the structure is obtained by combining the probabilistic seismic demand model.The influence of group effect on the seismic performance of the structure is evaluated in three ways:failure state probability,three-level seismic fortification requirement and performance margin ratio.Based on the results of vulnerability analysis,a seismic design method considering group effect is proposed.The results show that the group effect reduces the seismic vulnerability of the structure,the difference can reach 11.2%,and the collapse margin ratio is increased by13.4%.Even if the favorable influence of the group effect is considered,the structure in soft soil foundation can not meet the requirements of three-level seismic fortifications.