Research Of Strengthening On Reinforced Concrete Frame Beam-column Joints In High-rise Buildings

As an important component of the frame structure, Beam-Column joints play a role in transferring the internal force and ensuring the integrity of the structure. Once the joints are damaged, the beam and column components connected to them will lose the bearing capacity, which are likely to cause the whole structure to collapse. This article takes a high-rise building in ShenYang as an object, in the construction process of joints the steel fabric around the core sector of joints was not fastened or even not set before the concrete pouring, results in the collapsed concrete. The height of high-grade concrete in joints was reduced because of the concrete that flow into the template. This formed a sandwich layer that contains low-grade concrete after the followed beams and slab pouring. In the self-inspection, it is found out that the concrete strength of most beam-column joints has not reached the design requirements, which makes the joints become a vulnerable part in the structure. Therefore it is necessary to take further research and reinforcement on such low bearing capacity joints. This article is aimed to solve the engineering problems by FEM numerical analysis.In order to investigate the influence of low-grade concrete on the joint bearing capacity, the paper used the ANSYS software to apply finite element simulation on 5 beam-column joint specimen with different low-grade concrete-ratio. The stress nephogram of each finite model indicates that the higher the low-grade concrete ratio in the joint, the greater the stress will occur on the reinforcing steel and concrete. Besides, the peak stresses appear also in the sandwich layer. The analysis results show that the presence of the sandwich layer has negative effect on the joint rigidity and bearing capacity.This article takes the external joint and internal joint as objects to research the reinforcement with enlarging section method. The joint specimen uses 50% ratio as the worst case scenario. The methods discussed in the article are intent to restore the bearing capacity loss caused by joint failure. This paper uses the finite element numerical simulation to analyze two types of joints reinforced by enlarging section method by comparing the changes of stress nephogram of concrete and reinforcing steel and the joint deformation path graph, the results showed as follows:Both external joint and the internal joint have certain increments on rigidity and bearing capacity after reinforcement, which indicates that the enlarging sections method provides satisfied reinforcement to the joints. Finally, the article discussed the general applicability of this research in engineering and further concerns of finite element simulation on joint analysis.