Study On The Static Load And The Seismic Performance Degradation Of The Old Reinforced Frame Joints

Since the reform and opening-up, concrete frame structure system has been widely used. However, most of the frame structures of our country have entered a stage of old age and degradation with the passage of time. Various reasons causes of reinforcement corrosion, and then lead to the degradation of the ability of resisting the load and resisting earthequake. As we all know, the node in the frame structure is the most sensitive part. Therefore, the aging problem of node in concrete frame structure has attached more and more attention of scholars and engineers. In the construction process of these old buildings, the quality accidents of stirrups in frame node have been put less or miss is occurred frequently.In this paper,based on the actual situation of the project, we do simulate reasearchs of static and seismic performance degradation countered the frame nodes which have different corrosion rate of reinforcement.Using the methods of combining with theoretical analysis and numerical simulation, this paper studies frame nodes of degradation on strength, ductility, stiffness, energy dissipation capacity, with different axial compression ratio and different corrosion degrees of steel bars, which is under monotonic loading and low cyclic loads. In this paper ABAQUS finite element analysis software is used to establish the model of frame node with no stirrups in its core area. It simulates the corrosion of steel bars through putting radial displacement load on the concret around steel bars. Finally I get the load-dispalcement curves, hysteretic curves,skeleton curves and so on, observe the stress nephogram of frame nodes, make the analysis of the influence of steel bars corrosion and axial compression ratio on the mechanical properties and the seismic performance of frame nodes, and find the degration laws of strength, ductility and other performances of frame nodes with the corrosion rate of steel bar and axial compression ratio increasing.The corrosion of steel bar has also led to big loss of the ultimate bearing capacity and the ultimate displacement when the old frame nodes under low cyclic loading. When the corrosion of steel bar is seriously, the degradation of the strength of frame nodes is nearly 50%. Moreover, the component stiffness decreased rapidly, the loss of the seismic is also huge.Through the comparison of stress conditions of frame nodes under monotonic loading and low cyclic loading, I think appropriate axial compression ratio is good to mechanical properties and seismic performance of frame nodes, the smaller axial compression ratio can not make the node strength better, but the bigger compression ratio can cause premature failure.