| Precast Concrete(PC)structure is a kind of building structure advocated by our country.Our country is in the earthquake-prone zone.While promoting the development of PC structure,we must also consider the problem of PC structure damage caused by strong earthquakes in the future.In order to mitigate the economic losses caused by the earthquake,some PC structures with lighter damage and no need to be knocked down and rebuilt need to be repaired and strengthened to continue their service.As an important way of transmitting force for PC structures,PC nodes are easily destroyed in earthquakes because of their complex forces.It is very important to study how to repair and strengthen damaged PC joints and verify the seismic performance of the repaired and strengthened PC joints.(1)The quasi-static preloading tests of two full-scale PC frame beam-column joints were designed and completed,and the crack development process,failure mode and hysteretic curve of PC joint specimens were obtained.The test results show that all PC joint specimens were damaged by plastic hinge at the beam end.In addition to the cross shear inclined cracks in the core area of the joint,horizontal and vertical shear cracks were also generated along the interface between precast beam and column and the core area of the joint.The displacement ductility coefficients of the two PC nodes are 6.5 and 5.82 respectively,which shows that the designed PC nodes have excellent displacement ductility.(2)Based on the failure characteristics of pre-damaged PC joints,a method of strengthening earthquake-damaged PC joints with CFRP and axillary combination at beam end was proposed.The shear strength and stiffness of damaged PC joints can be improved by adding axilla at the beam end,while the flexural and shear bearing capacity of damaged PC joints can be improved by pasting CFRP,and the displacement ductility and energy dissipation capacity of damaged PC joints can be improved.(3)The quasi-static test of PC joints strengthened by seismic damage has been completed.The crack development process,failure mode and hysteretic curve of PC joint specimens strengthened with seismic damage were obtained.It is found that the PC joints strengthened by seismic damage form plastic hinge failure at the axillary end of the beam,and there are cross shear inclined cracks in the core of the joints.Except for the initial horizontal shear crack of GJ-1 joint with low axial compression ratio at the joint surface between the upper column bottom and the joint area,there are no shear cracks at the other joints.By comparing and analyzing the failure modes and seismic performance of PC joints before and after seismic damage reinforcement,it is proved that the shear strength and stiffness of PC joints with seismic damage are effectively improved along the interface between precast beam and column and the core area of the joints due to shear cracks,thus avoiding the occurrence and development of shear cracks at the interface,and the plastic hinge area at the end of the beam moves from the position close to the core area to the axilla of the beam.End,.The cumulative energy consumption of GJ-1 and GJ-2 joints strengthened by seismic damage is 88.1% and49.4% higher than that of original joints J-1 and J-2 respectively;the bearing capacity of GJ-1 and GJ-2 is 25.2% and 67.8% higher than that of J-1 and J-2 respectively;and the initial stiffness of GJ-1 and GJ-2 is 27% and 34% higher than that of J-1 and J-2respectively.The displacement ductility of damaged PC joints is also basically restored.The displacement ductility coefficients of GJ-1 and GJ-2 are 6.5 and 5.42,respectively.They are 100% and 93.1% of the original PC joints J-1 and J-2. |
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