Experimental Study On Seismic Behavior Of High-strength Concrete Filled Steel Tube Column With Column Connections

With the development of modern engineering technology,high-strength concrete with strength around 100 MPa has been applied to high-rise buildings.The concrete filled steel tube is combined with the advantages of steel and concrete.It has good bearing capacity and seismic performance.The concrete filled steel tube column with high strength concrete can effectively reduce the section size.At the same time,because of the strong restraining effect of the steel pipe,the steel tube high strength concrete column can ensure good seismic performance by reasonable design.However,there is no design method for concrete filled steel tubular columns above C80 in China’s existing design codes.In recent years,China has set off a wave of the development of assembly architecture,the state has put assembly architecture into the "13th Five-Year" plan,and assembly architecture will become an important direction for the development of China’s construction industry.The components of the assembly structure are concentrated in the factory and transported to the construction site for assembly and connection.The connection performance between the components has a great influence on the aseismic performance of the assembly structure.There are few studies on the assembly of concrete filled steel tube structures.Therefore,it is very important for the development of the assembly architecture to put forward the convenient construction operation,less field wet work,fast construction speed and excellent seismic performance.In this paper,a concrete-filled steel tube column-column connection method using C80 strength concrete is proposed,and concrete filled steel tube columns can be produced and poured in the factory.The construction site is connected directly to the column-column connection between the upper and lower beam and column joints to reduce the wet operation in the field.In this paper,the static test of 4 high strength concrete filled steel tube reinforced concrete columns and 1 full cast steel tube high strength concrete columns is completed.The failure mode,hysteresis curve,skeleton curve,displacement ductility,energy dissipation capacity and steel tube strain of each prefabricated column under low cyclic loading are studied.The related calculation methods are put forward.The design proposal provides reference for the practical engineering to adopt the assembled concrete filled steel tubular column-column connection form.Through statistical analysis and experimental research,the following conclusions can be drawn:(1)By collecting 123 steel tube ordinary concrete columns and 85 steel tube high strength concrete columns,the following conclusions are obtained: when the concrete filled steel tube columns above C80 are calculated according to the standard design method,the safety coefficient is slightly higher than that of the ordinary steel tube concrete column,with the ratio of length to length increased.The safety factor will be slightly reduced.(2)In this paper,34 ordinary concrete columns and 32 steel tube high strength concrete columns have been collected in this paper.The results show that the factors affecting the ductility of the steel tube high strength concrete column are the same as the factors that affect the ductility factor of the ordinary concrete filled steel tube columns,and the ductility coefficient decreases with the increase of axial compression ratio,and the coefficient decreases with the axial compression ratio.Based on the ductility data of test members,the displacement ductility factor formula for high strength concrete filled steel tubular columns is derived.(3)the experiment completed in this paper shows that the assembly connection method of the inner steel pipe can reliably transfer the horizontal and vertical forces.The inner steel pipe can improve the shear capacity of the joint surface,prevent the horizontal slip of the joint surface and enhance the integrity of the connection area.The test results show that the hysteretic curve of the prefabricated column used in this paper is full,and the normalization treatment is basically the same as the skeleton curve of the cast-in-place column,and the energy dissipation performance and the deformation ability are equivalent to the cast-in-place column.(4)The test results show that the variation of ductility coefficient of steel tube high strength concrete column is similar to that of steel tube ordinary concrete column.That is,with the increase of axial compression ratio,the ductility coefficient of the deformation capacity of the specimen is reduced,but its peak bearing capacity and energy dissipation capacity are increased,and the stiffness of the small slender member is larger and the corresponding horizontal bearing capacity becomes larger.The coefficient of stiffness is smaller,the horizontal bearing capacity is smaller,and the ductility coefficient decreases.This article has the following two innovative points:(1)A new type of high strength concrete filled steel tubular column-column connection method was proposed,and the corresponding design method of connection area was proposed.The low cycle repeated test was carried out on the prefabricated steel tube high strength concrete column with this connection.(2)By collecting and analyzing the compression test and pseudo static test of the ordinary steel tube concrete column and the steel tube high strength concrete column,the calculation method of the bearing capacity of the concrete filled steel tube column with high strength concrete above C80,and the calculation formula for the displacement ductility of the steel tube high strength concrete column have been put forward by statistical regression.