Analysis And Research On Seismic Vulnerability And Applicability Of Ground Motion Parameters Of Concrete Filled Steel Tubular Piers

As a new type of composite structure,concrete-filled steel tubular(CFST)columns are widely used in building construction,bridge construction and other fields because of its intuitive structure force and simple section form.Vulnerability analysis of(CFST)piers in bridge structures has always been a research hotspot,which can predict the exceeding probability of damage of CFST piers according to the intensity of earthquake,and provide a reliable basis for the pre-earthquake fortification and post-earthquake repair of structures.At present,most of the research on the vulnerability of CFST piers stays on the single parameter of PGA or Sa,while the analysis of other ground motion parameters is less.Therefore,based on the fitting results of damage index and ground motion parameters,the applicability of ground motion intensity parameters of CFST piers with different natural periods and diameter-thickness ratios is analyzed in this paper.The main work and conclusions are as follows:1.In this paper,the frequency statistical method,the capacity demand ratio and the direct regression fitting method are compared and analyzed.Based on the comprehensive consideration of the advantages and disadvantages of each calculation method,the direct regression linear fitting method is selected as the vulnerability research method of CFST piers.2.A typical CFST pier project is taken as the research object,and it is simplified as a multi-degree of freedom structure system.The incremental dynamic analysis of the simplified structure system is carried out by using the verified finite element method,and the seismic response of the CFST pier under 400 seismic waves is analyzed from the displacement of the pier top,the curvature of the pier bottom and the hysteretic energy dissipation.The height of plastic hinge is obtained from the distribution of curvature and displacement of the pier shaft,which is in good agreement with the empirical formula.3.An axial force-moment-curvature numerical simulation method is proposed based on the section stress state of CFST piers,and the numerical simulation is carried out by Opensees software,and the simulation results are in good agreement with the test results.The proposed numerical simulation method is used to analyze the failure process of a CFST pier under increasing axial force,and the damage limit is divided according to the material properties.Referring to the existing bridge specifications,the quantified curvature and displacement are calculated,and the vulnerability curve based on displacement and curvature is obtained.4.Six CFST piers were designed with natural vibration period and diameterthickness ratio as the main influencing parameters.Four damage indexes and 20 ground motion parameters were selected,and 480 times of linear logarithm fitting were carried out between the structural seismic response and the ground motion parameters.The applicability of the structural parameters and the ground motion parameters were analyzed from the four aspects of correlation,validity,practicability and benefit of the ground motion parameters.The results show that the short period structure is suitable for VSI,the medium period structure is suitable for HI,the long period structure for SED,the structure with steel pipe wall thickness t = 15 mm is suitable for HI,the structure with steel pipe wall thickness t = 20 mm is applicable to HI,and the structure with 25 mm steel tube wall thickness is applicable to VSI.