Research On Seismic Performance Of New Fully Precast Repairable RC Frame Beam-column Joint

To improve the post-earthquake repairable performance of reinforced concrete(RC)frame nodes,reduce the residual deformation of the structure,and achieve rapid post-earthquake rehabilitation of building functions,this study based on the mortise-tenon construction in ancient Chinese architecture,and adopted the lap joint method to form a new fully precast repairable RC frame beam-column joint(RBCJ),which has the advantages of controlled plastic hinge position,small residual deformation,and easily repairable performance after the earthquake.Two 1/2 scale RBCJ specimens were designed and fabricated,and the main difference between the two specimens was the difference in the lap lengths of the joints.The damage mechanism,hysteresis performance,energy dissipation capacity,stiffness degradation,residual displacement of the RBCJ,and the effect of the lap length on the seismic performance of the RBCJ were studied by conducting low cyclic loading tests on the specimens.The postearthquake repairable performance of the joints was investigated by replacing the damaged connecting steel plates and reloading the damaged specimens.The ABAQUS finite element software was used to establish the model,17 RBCJ finite element simulation specimens were established on this basis for variable parameter analysis,to study the effects of parameters such as the lap length of the joint,the distance from the lapped seam to the column surface,the thickness of the energy-dissipating steel plate and the concrete strength grade on the seismic performance of the RBCJ.The theoretical equations of the yielding load and ultimate load that the joint could withstand were derived by using the theoretical energy method of the Timosinko thin plate,and the relationship between the ultimate bearing capacity and the thickness of the energy-dissipating steel plate was given;the local force and damage mechanism of the lap joint was analyzed,and a control formula was given so that the concrete lap joint of the RBCJ would not be damaged when the energy-dissipating steel plate yields,The shear and tensile strength of the bolts in the RBCJ were tested,and they all met the safety requirements.Finally,to better reflect the ability of the joint to recover its original shape after unloading,the restoring force model of RBCJ was established based on the test results of model RBCJ-3.This restoring force model could better describe the hysteresis characteristics of RBCJ and provide a reference basis for the subsequent theoretical analysis of the joint.The test results showed that: the short-lap RBCJ specimen had better seismic performance than the long-lap RBCJ specimen;and the maximum tensile stress at the root section of the long-lap RBCJ specimen reached the cracking strength of the concrete.In the late loading period,the concrete of the precast beam cracked locally.After the loading drift of the short-lap RBCJ reached 1/50,the repairing work was completed by replacing the energy-dissipating steel plate,and the seismic performance of the joint did not drop significantly after the repair.The results of the ABAQUS analysis showed that the lap length had a certain influence on the seismic performance of the joint,except for the flat-lap specimens,the positive and negative bearing capacity of the remaining specimens became higher with the increase of the lap length,but the increase was not obvious.Although the bearing capacity of the flat-lap specimens was higher,the concrete damage at the joint was more serious.Penetration lap length of 1/4 beam height and meet the minimum support length can prevent serious damage to the concrete.With the increase of the distance from the lap seam to the surface of the column,the maximum bearing capacity of each specimen gradually increased,but the increase was not obvious.The distance from the lap seam to the surface of the column should not be too long,generally,3/4height of the beam is more reasonable,which could effectively avoid more serious damage to the concrete.The thickness of the energy-dissipating steel plate had a significant impact on the seismic performance of the joint because the energy-dissipating steel plate is the main forcebearing member of the structure.The effect of concrete strength grade on the seismic performance of RBCJ was not very obvious,but the effect on the damage mode of RBCJ was more significant and the size control formula of the lap joint was derived,which provided a theoretical basis for the design of following joints.