Methodology Study On Seismic Performance Assessment Based On Deformation And Damage For Frame Structure With Transfer Story

With the rapid economic development in China, the vertical irregular structures withtransfer story have become one trend of high-rise building for meeting the requirement ofmultifunctional building structure. The steel-concrete composite components are commonlyapplied to the building with transfer story due to their good mechanical properties. In the casestudy of this paper, the concrete filled steel tube (CFST) columns and steel reinforcedconcrete (SRC) beams are adopted as the transfer component to improve the seismicperformances of frame structure with transfer story. But the seismic damage investigationsand researches show that the vertical irregular structures with transfer story may fail easilyunder earthquake excitations because abrupt changes of the vertical stiffness causedeformation concentration and energy accumulation at transfer stories. The soft story orcolumn-hinging failure occurring in the vicinity of transfer stories may induce local or globalcollapse of the structure. Although the building with transfer story is designed strictly on thecode for seismic design, when the building is in elastic-plastic state under strong earthquakeexcitation, the seismic damage of the vertical irregular structure with transfer story can’t becontrolled effectively according to the seismic design using the single performance indexbased on the deformation. To solve these problems, considering that the damage of thebuildings are closely related to maximum deformation and cumulative hysteretic energy, aseismic performance assessment method based on deformations (inter-story drift angle of thestructural system) and damages (cumulative hysteretic energy) from structural components tostructural system is proposed to overcome the deficiency of the seismic design using thesingle performance index. The seismic reliability of the vertical irregular structure can beevaluated on the basis of the seismic fragility analysis.The main researches and conclusions are as follow:(1) Considering that the essence of the structure damage is the earthquake input energylarger than energy which the structure can consume, the distribution of cumulative hystereticenergy of the frame structure with transfer story is investigated. The comparison between thedistribution of inter-story drift angle and cumulative hysteretic energy is conducted to identifythe deficiency of the seismic design using the single performance index and provide basis for establishing the dual system of seismic performance assessment method based on thedeformation and damage.(2) The seismic performance assessment method based on the deformation and damageis established on the seismic fragility analysis. The validity of seismic fragility analysis isaffected by the rationality of the ground motion intensity parameter selection. Based on thenonlinear time history analysis results, the log-linear regression analyses between variousground motion intensity parameters and maximum seismic responses of the structure arecarried out. The ground motion intensity parameters, which are mostly related with thestructural seismic responses, are selected according to the correlation coefficient, standarddeviation and regression coefficient. The reasonable ground motion intensity parameter can beprovided to the study on the seismic fragility assessment method based on deformation indexand damage index.(3) Because the influence of the ground motion characteristics on the seismic fragility ofthe structure can’t be reflected sufficiently when the single ground motion intensity parameteris adopted. In order to consider the influence of more ground motion characteristic parameterson the seismic fragility, the seismic fragility surface analysis is conducted on the basis of thestudy on the ground motion intensity parameter selection. The deformation-based (themaximum inter-story drift angle) seismic fragility assessment method is established. Theresults show that the exceedance probability of the frame structure with transfer story insevere damage state is underestimated by the deformation-based seismic fragility analysis. Itis necessary to establish the damage-based seismic fragility assessment method to compensatefor the shortcomings.(4) In the damage-based seismic fragility assessment method, the damage index ofoverall structure is calculated by the damage indices of structural components. Therefore, theseismic damages of structural components will be evaluated firstly. The CFST columns andSRC beam are adopted as transfer components in the frame structure with transfer story.Considering the state-of-art of the damage model and the hysteretic characteristics ofsteel-concrete composite components, an energy-based damage index model proposed byKratzig is selected and modified to evaluate the seismic damages of CFST column. Thedamage index of SRC beam can be calculated through the ratio of the cumulative hysteretic energy of beam to the cumulative hysteretic energy of column. The validity of the modifieddamage index model and the calculation method based on the ratio of the beam damage to thecolumn damage will be verified by some published experiments.(5) Based on the verification of the modified damage index model for structuralcomponent, the damage evolution from the structural component to the story and the overallstructure is investigated. The damage-based (the damage index of overall structure) seismicfragility assessment method is established. In the damage evolution from the structuralcomponent to the story, the weighting method considering the importance coefficient ofstructural component is adopted to calculate the damage index of the story. In the damageevolution from the story to the overall structure, the damage distribution coefficient of storybased on the cumulative hysteretic energy is proposed to simplify the calculation process ofthe damage index of the overall structure. The results show that the exceedance probability ofthe frame structure with transfer story in severe damage state can be evaluated adequately bythe damage-based seismic fragility analysis.(6) The seismic performance assessment system based on the deformation and damage isconstructed. The analysis steps of the new seismic performance assessment method aresummarized. The dual system of seismic performance assessment method will be applied toevaluating the seismic reliability of the frame structure with transfer story. The seismicperformances of frame structure with transfer story can be assessed from the damage of theoverall structure and structural component respectively. The results show that the maximuminter-story drift angle can be adopted as the main evaluation parameter when the structure isin complete state or slight damage state. The damage index of overall structure can be adoptedas the main evaluation parameter when the structure is in moderate or severe damage states.The damage evaluation shows the seismic damages of the frame structure with transfer storyconcentrate on the CFST columns and RC beams in the first and transfer story. The damagesof the CFST columns are aggravated with the increase of seismic intensity. The severedamage occurring in the first and transfer story induces the global collapse of the structure.