Seismic Analysis Of The Frame Structure Reformed By Cutting Off Column And Jacking Based On Stiffness Ratio

The construction of reinforced concrete frame structure occupies a large proportion in the existing buildings in our country.Along with the development of times,many existing buildings need to be modified to meet the functional requirements.The cutting off column and jacking technology is a method for increasing story height,which has been widely used and paid much attention in engineering.The stiffness will be changed after the process of cutting off column and jacking,which directly affect the overall seismic performance.It is usually necessary to take seismic strengthening measures to enhance the stiffness.But its design method is not mature enough,the design code is far from perfect and the construction technology is not standardized.Engineering practice is more than theoretical research and engineering experience is dominant in the design and construction.However,it is irregular construction affect the seismic performance of structures.The stiffness of structures will be changed after the jacking.So the reinforcement design is very important.So it has important engineering significance to carry out the research which is about the seism ic performance of structures after cutting off column and jacking.In this paper,through the study of the models which are before jacking,after jacking and the reinforced of a five story frame structure in Jinan New and High-tech Zone.Study on the seismic performance based on stiffness ratio in this paper,start the following work and draw the following conclusions:(1)The paper takes a five story frame structure jacking project in Jinan High-tech Zone as an example,discusses the construction method and procedure of cutting off column and jacking technology.The key technical problems are analyzed and the reinforcement scheme is proposed for the lifting structure in this paper.The main research content is a series of problems,such as the combination of the new-old concrete interface and the steel bar connection.The theoretical calculation and numerical simulation is conducted for the force and bearing capacity at the old and the new-old concrete interface.(2)Study on the calculation process and modeling method of dynamic time-history analysis method by ABAQUS.The finite element models are established which contains the before and after lifting model and the reinforced model.Based on the stiffness,the dynamic time-history analysis is carried out to research its seismic performance under the EL-Centro seismic wave,the Taft seismic wave and the Tianjin artificial seismic wave.(3)The height of the first floor increases after lifting and the stiffness becomes smaller,which resulting in reduced seismic performance.It is necessary to do some reinforcement.In this paper,the method of enlarging section is used to reinforce the column.Some beams are reinforced by some carbon fiber.After reinforcing,the stiffness ratio of the second and first layer is reduced and the seismic performance of this structure is improved obviously.(4)Through the comparison of the calculated data between the nun lifting and the reinforced,the stiffness ratio of the second and first layer is controlled by the reinforcement.So the seismic performance of the lifting structure can meet the seismic requirements.Through the seismic analysis of the frame structure reformed by cutting off column and jacking based on stiffness ratio,It provides some guidance for the design and construction of the entire jack lifting structure.