| With the rapid development of economy,the number of high-rise buildings or super high-rise buildings is increasing,and the requirements for building functions are becoming more and more complicated.The traditional three level-two stage seismic design concept and the structural design method based on rigid foundation assumption are out of date.In practice,engineers and researchers have gradually realized the necessity of considering the influence of soft soil foundation on the seismic response of structures.However,there are no perfect design specifications in the current codes in China and abroad for the interaction between soft soil foundation and superstructure.The relevant research in this field is mainly theoretical research and lack of experimental verification.Based on this background,shaking table tests and numerical simulations were carried out to study the interaction of soft soil foundation and steel frame structure under horizontal earthquake.The differences between seismic responses of steel frame structures under frequent earthquakes and rare earthquakes when considering different foundation conditions were revealed.The calculation formula for seismic response of steel frame structures when considering the interaction of soft soil foundation was proposed.In this paper,a series of mechanical properties tests were carried out on Q235 steel and sand materials.Static standard tensile test was carried out on Q235 steel,and the mechanical properties such as elastic modulus,yield strength and ultimate strength and the stress-strain curve were obtained.The conventional physical property test were carried out on the sand,and the category,specific gravity,relative compactness and grading curve of the sand were obtained.Through the direct shear test,the internal friction angle of the sand was obtained.The shear wave velocity and the maximum dynamic shear modulus of sand were obtained by bending element method.The bending element test results show that the shear wave velocity of soil increases with the increase of soil compactness.Through the indoor dynamic triaxial test,the dynamic shear modulus and damping ratio of sand were obtained.The results of dynamic triaxial tests show that:(1)with the increase of soil shear strain,the dynamic shear modulus decreases and the damping ratio increases;(2)the factors affecting the dynamic mechanical properties of sand are confining pressure and water content,consolidation ratio;(3)Davidenkov foundation model agrees well with dynamic triaxial test results.Experimental results of mechanical properties of Q235 steel and sand materials provided important data for subsequent finite element analysisBased on the test results of mechanical properties of materials,three seismic waves,including EL wave,Kobe wave and Taft wave,were used to carry out shaking table tests with different seismic wave amplitude excitations ranging from small to large,The shaking table tests consisted of four parts: the laminar shear soil container test,free field test,rigid foundation with a 1:10 steel frame structure test,and soft soil foundation with a 1:10 steel frame structure test.The experiment mainly investigated the influence of time domain and frequency domain characteristics of seismic waves on the structural seismic response and explored the influence of rigid foundation and soft soil foundation on the structural seismic response.Through the shaking table test of the laminar shear soil container,its natural vibration frequency and damping ratio were obtained.Through the free-field shaking table test,the laws of the time domain and frequency domain of seismic waves in the soil propagation process were obtained,respectively.Through the shaking table test of steel frame structure under rigid foundation and soft soil foundation,the natural vibration frequency and damping ratio,acceleration and interlayer displacement of steel frame structure were obtained.The test results show that:(1)the laminar shear soil container designed in this paper meets the requirements of the infinite domain of soil;(2)The soft soil foundation has a double influence on the time domain of seismic waves.For the frequency domain of seismic waves,soft soil foundation will magnify low frequency and reduce high frequency;(3)Soft soil foundation and steel frame structure have interaction.The steel frame structure reduces the seismic response of the soft soil foundation.The soft soil foundation will prolong the natural vibration period of the steel frame structure,increase the damping,and change the structural acceleration and interlayer displacement.In this paper,ABAQUS finite element software was used to simulate and contrast various soil boundaries.The results show that the viscous-spring boundary meets the requirements of soil infinite domain better.At the same time,the ground motion input method based on viscous-spring boundary was derived,and the seismic wave time history was transformed into the equivalent seismic load time history.Based on the secondary development platform of ABAQUS,the equivalent linear viscoelastic constitutive model of soil was developed by using Fortran programming language.The automatic iterative calculation of soil was realized by MATLAB program and Python program.Based on the above soil boundary,soil constitutive model and ground motion input method,the finite element simulation analyses of steel frame structure under rigid foundation and soft soil foundation were carried out.The numerical results were compared with the experimental results to verify the accuracy of the finite element models of rigid foundation / soft soil foundation-steel frame structure.At the same time,the free field test was used to verify the accuracy of the EERA free-field seismic response model,which prepared for the parametric analysis of seismic response of free-field seismic,rigid foundation-steel frame structures and soft soil-steel frame structures.Based on the validated EERA free-field seismic response model,the parameterized dynamic time-history analyses of two factors(site shear wave velocity and overburden thickness)affecting seismic wave propagation in free-field were first carried out.The results show that:(1)The soil has the dual effect of amplifying and reducing the seismic wave,and the effects are different under different shearing wave velocity and thickness of the covering layer.(2)The soil has the function of amplifying low frequency and reducing high frequency on the frequency domain of seismic waves.The smaller the shear velocity of the site is and the greater the thickness of the cover layer is,the more significant this function will be.Based on proven rigid foundation-steel frame structure and soft soil foundation-steel frame structure finite element model.In this paper,the parametric dynamic time history analyses of three factors(seismic wave,soft soil foundation stiffness,steel frame structure stiffness)affecting the interation of soft soil foundation-steel frame structure were carried out.The results show that:(1)The soft soil foundation reduces the natural vibration frequency of the structure and increases the damping.The smaller the shear wave velocity of the soft soil foundation,the lower the natural vibration frequency of the structure.(2)The inter-layer shear ratio and inter-layer displacement are consistent along the structural height under rigid foundation and soft soil foundation,and the inter-layer shear ratio and inter-layer displacement of the soft soil foundation are larger than the rigid foundation.(3)Structural seismic response(structural modality,acceleration,inter-layer shear force and inter-layer displacement)are closely related to the time and frequency domain characteristics of seismic waves,steel frame structural stiffness,and soft soil foundation stiffness,etc.The three factors are coupled to each other.In combination with current specifications,the concept of stiffness ratio was introduced.Based on the parametric analysis of numerical simulation,when considering the influence of soft soil foundation,the calculation formulas were fitted for the additional cycle and stiffness ratio,interlayer displacement adjustment coefficient and stiffness ratio of steel frame structure.The effect of soft soil foundation on structural seismic response(self-vibration period,interlayer displacement)was quantified.Comparing the calculation results of fitting formulas with the experimental results,the accuracy of the fitting calculation formulas was verified,which will provide an important theoretical basis for the subsequent research on the interation of soft soil foundation and steel frame structure under horizontal earthquake. |
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