Experimental Study On Biaxial Seismic Behavior Of Prefabricated Concrete Columns With Different Reinforcement Connection Forms

Research on earthquake disaster surveys in the past showed that the response of the structure under the actual earthquake action shows a multi-dimensional,random motion state,and the inter story of the structure may appear in any direction.Reinforced concrete(RC)column bears the main vertical load in the frame structure,and is in a complex stress state under the load of different horizontal angles.At the same time,due to the different conne ction structures,the mechanical properties of prefabricated Concrete(PC)structure have certain differences compared with the cast-in-situ RC structure,especially when facing natural disasters such as earthquakes.Most of the existing tests have studied the seismic performance of RC structures in single direction or multi-dimensional direction,and there are few studies on the impact of bidirectional earthquake on the seismic performance of PC structures.In this paper,PC columns with different reinforc ement connection modes(sleeve grouting connection and mortar anchor lap connection)are taken as the main research objects.Through the pseudo static test,the influence of different horizontal loading angles on their seismic performance is analyzed,and the test conclusion is supplemented by the numerical simulation parameter expansion analysis and theoretical analysis.The main research contents are as follows:1.In this paper,four PC column specimens(three sleeve grouting connection PC columns and one mortar anchor lap connection PC column)and one RC column specimen were designed and manufactured.The pseudo static tests were carried out under constant axial force.The effects of different horizontal loading angles and reinforcement connection methods on the seismic performance of PC columns were investigated.At the same time,the differences between the seismic performance of PC columns and RC columns under 45° horizontal loading angle were compared.The results show that:(1)When the axial compression ratio is 0.3,the horizontal bearing capacity of PC column connected by sleeve grouting decreases gradually with the increase of the angle between the horizontal loading direction and the section principal axis,which should be considered in the actual engineering design and application;(2)Compared with the PC column connected by sleeve grouting,the horizontal bearing capacity and ductility of the PC column connected by mortar anchor lapping are improved to a certain extent.The limit displacement angle of the prefabricated column connected by two types of reinforcement can reach 3.0% and3.4%,meeting the requirements of the 2% displacement angle limit under the rare earthquake in the code;(3)Compared with RC column,the horizontal bearing capacity of PC column connected by sleeve grouting and PC column connected by mortar anchor lapping are increased by 7.0% and 10.3% respectively.2.Based on ABAQUS finite element software,the finite element models of the test results in this paper are established.The hysteresis curve,skeleton curve,reinforcement strain distribution and crack development obtained by finite element analysis are close to the test results,which proves the accuracy and app licability of the modeling method and the selection of modeling parameters in this paper.Based on the above verified modeling and analysis method,the parameter expansion analysis of the finite element model of PC column connected by sleeve grouting is carried out with the loading angle,axial compression ratio and concrete strength as the research parameters.The numerical simulation results show that:(1)When the axial compression ratio is 0.3,the horizontal peak bearing capacity of PC column connected by sleeve grouting is the highest when the loading angle is 0°,and the peak bearing capacity gradually decreases with the increase of horizontal loading angle;(2)With the increase of axial compression ratio,the horizontal bearing capacity of PC columns with different horizontal loading angles first increases and then decreases.When the axial compression ratio is 0.2,the effect of horizontal loading angle on the horizontal bearing capacity of PC columns is not obvious;When the axial compression ratio is less than 0.2,the horizontal bearing capacity of PC column increases with the increase of horizontal loading angle;When the axial compression ratio is greater than 0.2,the horizontal bearing capacity of PC column decreases with the increase of horizontal loading angle.With the increase of horizontal loading angle,the critical axial compression ratio of PC column becomes smaller,and it is more necessary to control the axial compression ratio to avoid small eccentric compression failure;(3)When the horizontal loading angle is 0° and45°,the horizontal bearing capacity of PC column increases with the increase of concrete strength;(4)Under the same parameters,the bearing capacity of PC column is higher than that of RC column.3.The possible failure section at the root of PC column is discussed.The bearing capacity of PC column at the joint and the top section of sleeve or bellows is calculated and compared with the test results.The results show that the bearing capacity calculated according to the section at the joint of PC specimen is conservative,and the bearing capacity calculated according to the top section of sleeve is close to the test results,indicating that the existence of sleeve increases the section stiffness at the root of PC column.Thus,the failure section is transferred.The load isoline method is used to calculate the biaxial eccentric compression bearing capacity of the Chinese,American and European codes.The results show that the biaxial eccentric compression bearing capacity calculated by the codes of various countries retains a certain safety reserve,and the safety reserve of the Chinese code is the largest.