Study On Compositing Mechanical Performance And Bond-Slip Performance Of Concrete Filled Steel Tube

As a concrete-filled steel tube many advantages, it gets more and more applications in engineering. The mechanical performance study of concrete-filled steel tube is one of the hot issues in the engineering study, but most of the research has focused on the capacity of research and the study of seismic behavior. Now the studies of concrete-filled steel tube cooperated work together and bond-slip performance relation are few both at home and abroad. Some of them are not deep enough. On the basis of the domestic and international study summary of the compounding mechanic performance and bond-slip performance of concrete-filled steel tube, this paper study the confining force of concrete-filled steel tube on the elastic stage, from the elastic theory, it derive the formula of confining force of concrete-filled steel tube on the elastic stage and we can know the relation between confining force and steel Poisson's ratio, or concrete Poisson's ratio with confining force, or elastic modulus ratio with confining force, or steel rate with confining force, or stress in the core concrete with confining force. When the column of concrete-filled steel tube loaded in different way, this paper study the concrete-filled steel tube axial direction compressive distribution to get the respective axial direction compressive distribute coefficient. And we get the formula of shearing force transfer length and bond shear capacity within the scope of the shear capacity.Based on the continuum mechanics theory we derive concrete-filled steel tube compounding elastic constitutive relation, the structure of relations provides a theoretical foundation to further study concrete-filled steel tube elastic plastic stability and fatigue issues. We also get the formula of compounding axis direction compressive stiffness of concrete-filled steel considering confining force. Concrete-filled steel tube compounding axis direction compressive stiffness from theory formulas is similar to the results of theoretical calculations.Compounding stiffness of the concrete-filled steel tube is higher than the conversion stiffness that is current widely adopted without considering the effect of hoop. Compounding axis direction compressive elastic modulus is higher than conversion elastic modulus too. Compounding axis direction compressive stiffness is higher than conversion stiffness. With the core rate of steel increases, there are more differences. With the enhancement of the strength of the concrete, there are fewer differences.Based on the energy law and the principle of minimum potential energy in elastic mechanics, we get the tight hoop coefficients of concrete-filled steel under axis pressure and the theoretical calculating formulate of compounding axis direction compressive elastic modulus. The result from the theoretical calculating formulate is similar to the result from the uniform theoretical calculating and the result from theoretical formulate of concrete-filled steel tube's compressive post elastic modulus.The concrete-filled steel tube columns load performance - slip curve have two forms, the first is a clear the peak point of curve and the subsequent decline, the second is without them, but obviously the turning point. The interface bonding of the largest will change with the change of concrete column slendemess ratio, diameter-thickness ratio , the steel rate . In node launched test, bonding strength between the pipe and concrete is higher than in the short column launched test, bonding load corresponding damage is larger than the larger short column. Whenever axial compression test is A loading or B loading, there is less influence to limits strength of the short column.By the 17 concrete-filled steel tube's short columns and node specimen test, the first is that we get the load-slip relation curve of specimen tests launched by nine short columns, so we can get the limit bond load and the limit bond strength of specimen tests launched and we can get some factors of influence to bond strength and the change rule of bond strength according to these factors (slendemess ratio, diameter-thickness ratio, steel rate, tight hoop coefficient, etc.). Also in the pipe wall, we can get the change rule of strain according the change of location and load. We derive change law of bond strength with the change of location and load by further analysis. We can know shearing force transfer length and bond-slip constitutive relations. The second is that we derive load-slip relation curve of 4 axis direction compressive specimen test. In the pipe wall, we can get the change rule of strain according the change of location and load. We derive change law of bond strength with the change of location and load by further analysis. We can know shearing force transfer length and bond-slip constitutive relations. Lastly we derive load-slip relation curve according two nodes launched and the test of two nodes axial direction compressive specimen. In the pipe wall, we can get the change rule of strain according the change of location and load. We derive change law of bond strength with the change of location and load by further analysis. We can know shearing force transfer length and bond-slip constitutive relations.This paper analyzes the pipe stress and the relation of the bond stress between steel pipe and concrete and relative slip from theory. Through mathematical analysis, we derive pipe stress, steel pipe and concrete bonding stress and the relative slip analytical expression and get the change rule of bond stress-slip relation with the changes of different locations.According the results of specimen test launched by 9 round concrete-filled steel tubes and through statistics linear regression, we get the calculation formula about concrete-filled steel tube initial bond load, limit bond load, the initial bond strength, the ultimate bonding strength considering these factors (slendemess ratio, than the diameter thick, steel ratio, tight hoop coefficient, etc). The results obtained from calculation formula and experimental results are compared analysis and error analysis.According to the measurement, we can know the change relation of film with its position change and get the relation formula about the bond stress and strain of steel pipe surface, analyze the distribution rule of the bond stress along the height of circular steel tube concrete columns. Through measurements for strain of circular steel tube, we can found that in general bond stress obey index distribution along the direction of column height.The influence to mechanical properties of components to the pipe of round concrete-filled steel tube is discussed through the formula of limit bond strength from linear regression statistics. Through analysis, we can see the bond strength component size directly affects the length of the shear stress transfer size; But the ultimate strength of concrete-filled steel tube no significant impact, but will make smaller component in the stress was too much under deformation.Through a non-linear finite element analysis of 9 specimen tests launched, the bond destruction load and corresponding slide transplantation can be calculated results. The test results are less than the experimental results. We analyze the reasons for the difference between test results and experimental results. But the ratio of all the specimen calculation results and the test results are very regularity. Generally speaking, this paper using the finite element analysis method gives a more accurate calculation results.In the model introduced by the non-linear finite element analysis, the steel tube-axial stress along the axial load is beginning gradually increasing, the change law along the axial line is close to the straight line change; Concrete axial stress from the maximum loading terminal along the axial began gradually decreasing. Change rules along the axial are nearly a straight line, a steel pipe and concrete change rules of the axial stress are close to the change rules of test results.In bonding surface, the bond stress of the concrete, when the load is small, in the specimen loading terminal certain length (the length of the shear transfer) within the framework of the law changes on a straight-line, and then in the longer remain within the framework of the basic constants do not change.