Study On Seismic Behavior Of RC Columns With High Strength Steel Bars

The frequent occurrence of large earthquakes and mega earthquakes beyond the normal design and continuous strong earthquakes have brought new challenges to structural engineering over the past decades.In China,the ductility structure design is adopted in the current codes.However,encountering strong earthquakes exceeding the standard fortification level,the ductile concrete frames can only ensure that the structure does not collapse,with the buildings already suffering from serious damage and excessive residual deformation.It is so difficult to restore the damaged buildings that they have to be demolished and rebuilt.Meanwhile,the seismic performance of the structures under large earthquake and long-period earthquake motion has not been fully studied in the current code design.In order to ensure that new structure has enough seismic performance and the damage can be repaired,the concept of resilient concrete structure is put forward.The resilient concrete structure should have at least two characteristics: 1)a stable large earthquake response----even under high axial compression,the bearing capacity of the structure will not be reduced until the large deformation stage.In other words,the structure should have a positive rigidity under large deformation;2)the residual deformation of the structure should be controlled within 2% over the seismic level specified in the current seismic design specification,so as to ensure that the structure can be repaired and quickly resume function.In this study,an ultra-high strength steel bar(HB)with low bond-strength is used as the longitudinal reinforcement to realize resilience of RC columns under large earthquake.6 RC columns are tested under the reversed cyclic lateral loading.The effects of longitudinal reinforcement type,shear span ratio and confinement on hysteretic curves,bearing capacity,deformation capacity and energy dissipation capacity of the columns are analyzed.Through the mechanism analysis and numerical fitting,a self-centering RC skeleton curve model is established.The feasibility of restoring damaged concrete columns after earthquake is quantitatively evaluated by the maximum crack width and the residual crack width.Compared with conventional RC columns,the RC columns with HB show obvious post-yield stiffness.The maximum crack width is only 1.2mm before the 2%,the minimum residual crack width is only 0.4mm,and the residual drift ratio before 6% is less than 2%.The lateral force increasing by more than 50% and when reaching 6%,it still shows good self-centering ability and seismic performance.For the combined specimen with steel plate constraint and HB,it has higher bearing capacity and better self-centering performance.By studying the seismic behavior of reinforced concrete columns with HB,it can be seen that the use of low bonding HB can effectively control the residual deformation of components under large deformation,improve structural damage,and achieve self-centering of columns.Therefore,the use of HB can provide an effective and concise way for the development and application of self-centering RC columns in high-rise buildings in earthquake areas.