Research On Seismic Performance Of New Abnormal Joint With Changed Beam Section

With the rapid development of the world economy,the functional and aesthetic demands of buildings are getting higher and higher and the form of building structure is increasingly complicated and diversified.What’s more,abnormal joint with changed beam section occurs frequently in building structure.In order to further optimize the seismic performance of the abnormal joint with changed beam section,this thesis intends to undertake an improvement on it by utilizing the Polyvinyl Alcohol Fiber-Engineered Cementitious Composites(PVA-ECC)material to take the place of ordinary concrete material in the column part of the abnormal joint with changed beam section.In this way,the thesis aims to form a new type of the abnormal joint with changed beam section,namely,PVA-ECC column-reinforced concrete beams abnormal joint.To compare it with the ordinary reinforced concrete abnormal joint with changed beam section,Quasi-static test and finite element analysis of the two test specimens were carried out.The main research contents of this paper are as follows:(1)A new type of abnormal joint with changed beam section,namely PVA-ECC column-reinforced concrete beams abnormal joint and an ordinary reinforced concrete abnormal joint with changed beam section are designed simultaneously to conduct a comparison.A quasi-static test of the two test specimens was carried out to compare their bearing capacities,hysteretic curves,skeleton curves,displacement ductility,stiffness degradation,energy-dissipation ability,crack development and failure patterns.The test result shows that PVA fiber can well restrict the development of the core region and the column crack of abnormal joint with changed beam section.Under the same reinforcement,the plastic hinge damage appears at the bean-end of the PVA-ECC column-reinforced concrete beams abnormal joint,while it appears at the column-end of ordinary abnormal joint with changed beam section.Using PVA-ECC materials in the whole column can enhance the bearing capacity,ductility and energy dissipation capacity of the abnormal joint with changed beam section to a certain extent,and in the same time it can improve the stiffness degradation phenomenon of the abnormal joint with changed beam section,thus,effectively improving the seismic performance of the abnormal joint with changed beam section.(2)The finite element model of the test component is established by finite element software OpenSees and the numerical simulation is carried out.The results of the model basically match the actual experimental results,which indicate the rationality of the model and the effectiveness of the seismic performance test.On this basis,a parameter analysis of the anti-seismic performance of the abnormal joint with changed beam section is conducted by OpenSees to analyze the influence of the core area stirrup ratio and the axial load ratio on the seismic performance of the abnormal joint with changed beam section.The result of finite element analysis shows that the bearing capacity of the abnormal joint with changed beam section is significantly reduced with the increase of stirrup spacing.However,when the axial load ratio is too small,the axial load ratio has little impact on the bearing capacity of the abnormal joint with changed beam section.At that time,the replacement of ordinary concrete material by PVA-ECC material applied to the column part of the abnormal joint with changed beam section can reduce its core area stirrup ratio.When the axial load ratio exceeds a certain value,the decrease range of the bearing capacity will increase and the ductility of the test specimen will decrease with the further increase of the axial load ratio.