Concrete Pressure And Internal Diaphragm Shape Optimization Of Concrete-filled Rectangular Steel Tubular Column During Bottom-up Pumping Construction

In recent years,in the construction of super high-rise buildings,the application of pumping concrete from bottom to up is more and more common.Pumping concrete from bottom to up can not only ensure the quality of concrete in the steel tube column,especially ensure the density of concrete between the transverse diaphragms in the beam-column joints,but also avoid the cross operation of steel column installation and concrete pumping,which is conducive to accelerating the construction progress and reducing the safety risk.However,in the process of pumping concrete with box-shaped steel columns,expansion deformation is easy to occur once the construction is improper.Over-expansion deformation column is extremely difficult to handle,and will cause great economic losses,which will have a very adverse impact on the construction.Therefore,it is of great practical significance to determine the pressure limit in the column during pumping construction,determine the maximum safe height of pumped concrete and control the expansion deformation of concrete-filled steel tube.In this paper,experimental research,finite element numerical simulation and theoretical analysis are carried out on concrete-filled square steel tubular columns with the concrete pumping method from bottom to up.The main research contents and conclusions are as follows:(1)The concrete pumping test of concrete-filled square steel tube column with diaphragm inside was carried out to study the pressure distribution,column wall strain and expansion deformation of steel tube.The test results show that the concrete-filled square steel tube column with diaphragm will produce local pressure loss during concrete pumping construction,which makes the internal pressure of the steel tube column significantly greater than the hydrostatic pressure;(2)According to the results of the concrete pumping test of the CFRST column,the calculation method of the internal pressure of the square steel tube concrete column with the barrier of the diaphragm is proposed when concrete pumping construction method is adopted,and it is verified by the test,the results show that the proposed formula has certain accuracy;(3)The test results show that the diaphragm set inside the steel tube column is beneficial to the resistance of the steel tube column to lateral deformation.In this paper,the finite element analysis is carried out for the reasonable strengthening distance of the steel tube column.The results show that it is best to set the distance of the strengthening measures close to the section width of the steel tube;(4)Based on the finite element numerical simulation and theoretical analysis,the factors affecting the pumping height of concrete-filled rectangular steel tubular columns are studied,and the calculation method for determining the safe pumping height is proposed.The analysis results show that the width-thickness ratio of the steel column section,the internal strengthening measures of the steel column and the external strengthening measures will have an impact on the pumping height,and the finite element analysis verifies that the proposed calculation method of the concrete pumping height has certain accuracy;(5)In order to solve the problem of pressure loss in the concrete-filled steel tubular column due to the internal structural block during the concrete pumping construction,an optimization method for the internal diaphragm of the CFRST column is proposed.Through parameter analysis,it is determined that the main factors affecting the opening rate of the diaphragm inside the steel tube column are the relative size of the beam-column section and the thickness of the diaphragm,and the optimization formula is fitted based on the finite element analysis results.Through verification with the specification,the proposed optimization formula conforms to the calculation requirements of the bearing capacity;(6)Based on the principle of equal strength design,two new types of internal diaphragms are proposed.Through finite element analysis,the two new diaphragms proposed can further increase the opening rate,thereby reducing the blocking effect of the internal diaphragms on the pumping concrete,and is conducive to reducing the construction risk.