Research On Seismic Behavior Of Reinforced Concrete Short Columns Under Biaxial Horizontal Cyclic Loading

The failure mechanism of rectangular section column under biaxial shearing is very complex and research on this topic is not sufficient.Frame columns not only bear the axial loads,but also bear the horizontal loads under earthquakes.Data from the past earthquakes show that,the failure of reinforced concrete short frame columns for which the shear span ratio is less than 2 is very serious and the plastic deformation ability is poor.The brittle ruptures always lead to sudden collapse on the structures,and make serious economic losses.With reinforced concrete columns being widely used in high-rise buildings,the study of columns under bidirectional shearing has gain widespread attention.In this thesis,the seismic performances of five reinforced concrete short columns with rectangular sections under bidirectional cyclic shearing were tested.The main research works are as follows:(1)Five rectangular section reinforced concrete short columns subjected to lateral cyclic load under different loading paths were experimentally investigated in this article.Five loading paths were used in the experiment,including X direction,Y direction,45 ° diagonal direction,the square in the first and third quadrant in the form of an eight and expanding square.The effects of different loading paths on the energy dissipation capacity,strength,stiffness and ductility of specimens were mainly analyzed.(2)Combined with the test data,on the base of the existing calculation methods on the shear capacity of bidirectional shearing columns which considering the superior design factors,proposing the calculation method on the shear capacity of columns under earthquakes.(3)Simulations were conducted using finite element analysis software ABAQUS,and the load-displacement curves and failure characteristics of specimens were obtained.Compare with the result of finite element analysis and test,and by analyzing the causes to verify the feasibility of finite element analysis in the bidirectional shearing short column.The results of tests indicate that the loading paths have a great impact on the seismic behavior of reinforced concrete short columns.The columns under bidirectional loading show significant two-way coupling;the ultimate capacity of the columns is greatly reduced compared to the case in unidirectional loading condition.The bearing capacity of short columns decreases by 40% in the strong axis and 20% in the weak axis.The loading paths do not affect the ductility and stiffness degradation significantly,but have a significant effect on cumulative hysteretic dissipation energy..The calculation result of considering the superior design factor differs in 2% to 18% with the test result,indicating that this calculation method can be applied for short columns under biaxial cyclic loading.The result of the finite element analysis and test are in good agreement when the displacement is no more than 8mm.It indicates that using finite element analysis can accurately analyze the mechanical behavior of the specimen when a small displacement.