Research On Seismic Performance Of Steel Reinforced Concrete Frame With Macroscopic Flexible Joints

The steel reinforced concrete structure has high bearing capacity,high rigidity and good seismic performance.It is widely used in engineering practice,especially in high-rise buildings and large-span buildings.At present,the study of steel reinforced concrete structures in China mainly focuses on the seismic performance of frame structures.It is rare to use the macro-flexible node units for the detailed modeling and analysis of steel reinforced concrete frames.In this paper,on the basis of studying the mechanical mechanism of the macro-flexible node model,using the macro-flexible node elements and bond-slip models already existing in the finite element software OpenSEES to establish the finite element calculation model of the common concrete frame and steel reinforced concrete structure with the macro-flexible node model,and using this model to perform non-linear analysis of ordinary concrete frames and steel reinforced concrete frames subjected to low-cycle cyclic loading,finally,the author analyzes some major factors that affect the seismic performance of SRC frames,and obtains some conclusions and suggestions that can be used to guide the design of steel SRC frames.The main tasks completed are as follow:(1)On the basis of extensive reading of literature at home and abroad,summarize the research status of the experimental research and finite element analysis of ordinary concrete frames and steel reinforced concrete frames at home and abroad.Put forward the existing problems in the study of the seismic performance of ordinary concrete frames and steel reinforced concrete frames and discuss the significance of further research on these issues.(2)Explain the nonlinear analysis theory of concrete frames based on macro flexible node units in detail.Based on the existing macro-flexible node units and bond-slip models in the finite element software OpenSEES,a finite element model of the concrete frame considering the macro-flexible node units is established,and based on the consideration of the macro-flexible node and without consideration of the macro-flexible node,the finite element model of domestic researchers have completed4 single-layer and single-span concrete frame concrete frame under horizontal low cyclic loading was analyzed.The calculation results in the situation agree well with the test results,that verifies the applicability and reliability of the concrete frame finite element model considering the macro-flexible node model.(3)Based on the OpenSEES software,the finite element model of the steel reinforced concrete frame considering the macro-flexible node model was established.And using the finite element model to calculate and analyze the low cycle repeated load test of 9 single-layer and single-span steel reinforced concrete frames which domestic researchers have completed.The calculation results show that the skeleton curve,load-displacement hysteresis curve,displacement ductility and energy dissipation capacity of the simulation frame are in good agreement with the experimental results.The calculated curve better simulates pinched images,ultimate bearing capacity,strength degradation,and stiffness degradation of the steel reinforced concrete frame,which verifying the applicability and reliability of the finite element model of the steel reinforced concrete frame with the macro-flexible node model.(4)By analyzing the four main influencing factors affecting the seismic performance of steel reinforced concrete frames,the concrete strength,the profile steel ratio,shear span ratio and axial pressure ratio,the thesis designed 28 steel reinforced concrete frames and 4 ordinary reinforced concrete frame,from the ultimate bearing capacity,displacement ductility and energy dissipation ability three aspects has carried on the finite element analysis of the seismic performance.Analysis results show that in order to make steel reinforced concrete frames has enough ductility and energy consumption,suggested the stirrup characteristic of concrete frame joints should not be more than the calculated value of seismic shear bearing capacity calculation formula of code,at the same time,suggest that the profile steel ratio of the steel reinforced concrete frame should be controlled between 5% and 8%;when the axial pressure ratio is higher than 0.5,the ductility of the frame is slightly reduced and the energy consumption capacity is not changed much.The specification of steel reinforced concrete composite structure(JGJ138-2001)suggests that the column axial compression ratio is not more than 0.65.Combining with the calculation results in this paper,it is recommended that the column axial pressure ratio should be controlled at 0.5.