Study On Seismic Behavior Of SRC Frame Columns Based On FLPH Mode

As the main bearing and lateral force resisting members of the composite structure,the steel reinforced concrete frame columns have a good seismic performance,which is an important guarantee for the safety of the composite structure under the earthquake and has a very important effect on the seismic performance of the structure.At present,the research methods for the seismic performance of steel reinforced concrete frame columns are still mainly based on tests,however there are many troubles in experimental research such as large test costs and long test periods,which objectively limit the progress of the research.As an important supplementary means of experimental research,numerical simulation has been favored by global researchers.However,the current numerical model of steel reinforced concrete members,especially frame columns,are still mainly distributed fiber cross-section models.Previous studies have shown that the fiber models can objectively reflect the response of components,but it also has many flaw such as high calculation cost and the convergence of calculation results obtained by iterative algorithms is difficult to guarantee.Therefore,firstly an equivalent plastic hinge length calculation model which is suitable for steel reinforced concrete frame columns was established through theoretical derivation in this paper.The next step is to use a calibration procedure to convert the element restoring force model to a section constitutive,and then to establish the finite length plastic hinge model that can accurately simulate the seismic response of steel reinforced concrete frame columns.Finally,based on the established numerical model,the seismic performance of the steel reinforced concrete frame column is further studied.The main research contents of this paper are:(1)Based on the experiments conducted by the research group early,a limit displacement model and the plastic rotation angle corresponding to the top of the reinforced concrete column and the axis of the column is obtained through the in-depth analysis of the failure process and failure mechanism of reinforced concrete frame columns under horizontal reciprocating loads.Based on reasonable simplification,the expression of each component of the plastic rotation angle of the column axis is established by theoretical derivation,and the calculation model of the equivalent plastic hinge length of the steel reinforced concrete frame column is obtained by mathematical method of curvature integral.The validity of the obtained formula is proved through the displacement curve of the column top calculated by the length of the plastic hinge is compared with the test curve.(2)In order to establish the numerical simulation method of steel reinforced concrete frame columns,based on the full study of the calculation theory of plastic hinge model based on flexibility,in accordance with the existing plastic hinge integration rules,the numerical integration method for the neutral elastic segment is obtained element integration matrix expression for numerical integration.The correction of the element model is achieved by introducing the correction coefficient of the section stiffness at the internal integration point of the element,thereby avoiding the systematic errors generated when the element restoring force model is used to describe the nonlinear behavior of the plastic hinge.The calibrated FLPH frame beam-column element numerical model is used to analyze the examples.The calculation results of the examples prove the validity of the calibrated model.(3)The Modified Ibarra-Medina-Krawinkler cycle degradation model is used as the restoring force model of the unit plastic hinge area,and the relevant parameters in the restoring force model are explained in conjunction with the calculation methods in the existing studies.Numerical simulation is performed on some test pieces in the preliminary test of the research group in the Opensees finite element analysis platform by the finite length plastic hinge model that has been established in this paper.The accuracy of the established numerical model is proved through comparative analysis of the simulation results and the test results.The numerical model established in this paper is used to further study the effect of different steel content and axial compression ratio on the seismic performance of steel reinforced concrete frame columns.