The Experiment Research On Strengthening Of R.C Frame Joints Injured In Beam Ends

The joint of the reinforced concrete frame structure is the intersection of beam and column, including the joint core and beam ends and column ends. The stress of structure to stand is complex. They should withstand the bending moment and shear coming from beams and columns, playing the role of passing and the allocating internal forces and maintaining integrity of structureJoints are the weakest parts of the frame structure.There are many cases that earthquake results in the loss of bearing capacity even collapsing of the entire structure due to the destruction of the joints. When the joint was designed incorrectly, constructed with unreasonable methods or the intensity of seismic defence in the region of the structure has raised, the seismic performance of the bearing capacity, ductility, stiffness of the structure may do not meet the requirements of specification.The seismic performance can be improved through reinforcement.In this paper, the seismic performance of reinforced concrete frame flat cross-shaped joints are analysed systematically through experiment, and the effect of strengthening injured joints with carbon fiber are studied.Four joints are loaded by low cyclic load in the experiment to study the seismic performance of them, and structural performance parameters was analysed systematically.The experiment was simulated with ANSYS finally, on the test.The content includes the following aspects:(1) the common several methods of structural reinforcement are introduced briefly, including their research achievements and respective advantages and disadvantages;(2) The whole scheme of the experiment designed, load systems, and the purpose of the experiment was introduced in detail;(3) The cracking load, ultimate load, ultimate displacement,ductility, stiffness degradation, capacity of energy dissipation before and after strengthened are analysed according to the data of the experiment,and the relevant conclusions are gained;(4)numerical analysis models are built with finite element software ANSYS on the basis of the experiment, then the conclusions gained by ANSYS are contrasted with the experiment.The main conclusions from the experiment are following:(1) The yield displacement, maximum displacement in the column ends of injured specimens after strengthened has raised in varying degrees. But the carrying capacity is not improved significantly and ductility and stiffness remained unchanged. Reinforcement has greatly improved the performance of strength degradation,stiffness degradation and energy consumption.(2) The axial pressure ratio has some effects on the seismic behavior of the specimen before and after reinforcement. With the axial pressure ratio increasing, the yield load, maximum load, ultimate load has improved in varying degrees, while the yield displacement, maximum displacement and limit displacement reduced in different degrees. The increasing of the axial pressure ratio improves the performance of strength degradation, stiffness degradation, increases the energy dissipation capacity of the specimen, while does not effect on the performance of specimen ductility.(3) The yield load, maximum load, ultimate load of specimens with direct reinforcement are greater than those strengthened after injured, while the yield displacement, maximum displacement, the ultimate displacement of the former are smaller than the latter. The degradation and stiffness degradation performance of specimen with undamaged reinforcement are better than the specimen with damaged reinforcement; the ductility factor of the former and the latter are almost the same, but the energy dissipation capacity of the former is stronger than the latter.