Research On Seismic Reinforcement Technology Of Existing RC Frame Structure Reinforced By Additional Diagonal Bracing

The existing buildings in China are huge and with the continuous improvement of seismic fortification requirements,some existing buildings cannot meet the requirements of existing specifications.As an effective way to improve structural performance,seismic reinforcement technology is of great significance to solve this problem.With the rapid development of China’s economy,the losses caused by earthquakes will become more and more serious.Therefore,in addition to the safety requirements of building structures,it is also required to have better seismic resilience or post-earthquake repairability.The damage is relatively slight in the earthquake,and its use function can be restored after simple repair after the earthquake.Based on this,this paper puts forward the seismic strengthening technology of existing reinforced concrete frame structure with additional cable-stayed support,that is,the existing reinforced concrete frame beams and columns are strengthened by increasing the cross-section method,and the steel rods are arranged crosswise along the diagonal in the frame plane.The ends of the steel rods are anchored in the core area of the beam and column joints,and the prestressing force is applied to the steel rods to make them become the interlayer lateral support structure.The reinforcement method can not only improve the lateral stiffness of the frame structure,but also enhance the self-centering ability of the lateral deformation between layers.In order to verify the effectiveness of the reinforcement technology,the seismic performance is studied by quasi-static test and ABAQUS finite element analysis :(1)Combined with the principle of performance-based seismic reinforcement design,the seismic reinforcement design of additional diagonal bracing is carried out.Three single-story and single-span plane frame structure specimens are made and the quasi-static test is carried out.One of the specimens is an unreinforced contrast specimen,and the other two specimens are frame structure specimens reinforced by additional diagonal bracing structure.The test results show that the ultimate bearing capacity,energy dissipation capacity and stiffness of the reinforced concrete frame structure are greatly improved after the reinforcement of the additional cable-stayed support structure.At the same time,after the horizontal load is removed,the residual displacement rate of the reinforced specimen is significantly smaller than that of the unreinforced specimen,and the deformation self-centering ability of the structure is obviously enhanced.The damage of the strengthened specimens is relatively slight and the residual displacement is very small within the given inter-story drift angle range,and the repairability after the earthquake is significantly improved.(2)The influence of the initial prestress of the prestressed steel tie rod,the cross-sectional area of the prestressed steel tie rod,the concrete strength of the reinforcement layer and the cross-sectional thickness of the reinforcement layer on the seismic performance of the specimens after the seismic reinforcement of the additional diagonal bracing was analyzed by ABAQUS software.The simulation results show that the increase of the above four parameters can improve the bearing capacity,initial stiffness and energy dissipation capacity of the reinforced structure.Increasing the initial prestress of the prestressed steel tie rod and the crosssectional area of the steel tie rod can effectively improve the self-centering ability of the reinforced structure.The increase of the concrete strength of the reinforced layer and the increase of the cross-section thickness of the reinforced layer lead to a slight decrease in the self-centering ability of the structure.(3)Based on the calculation formula of normal section flexural bearing capacity given by the specification,the stress of the specimen after the seismic strengthening technology of the existing RC frame structure with diagonal bracing is analyzed.The theoretical calculation formula of the initial stiffness and yield flexural bearing capacity of the strengthened member is established by theoretical derivation.The calculation results are in good agreement with the experimental results,which has guiding significance for the application of this strengthening technology.