The Compression Fatigue Research About Concrete Filled Steel Tube

Since19th century, people began to dicover and study the fatigue issue of concrete. Withthe continuous inprovement of world technoledge and rapid development of China’s economy,a growing number of basic facilities including high ways, cross-sea bridges, airports and portsof large scale and high intensity have been erected and put into use, which hold the importantand prominent position in national economy. In the actual project, the cyclic loading of thebuilding accelerate the damage to the structure. Thus, the security of the project is directlyrelated to the fatigue performance and fatigue life of the structures and materials in civilengineering. As a result, the fatigue properties including fatigue life and residual intensity ofthe project draw increasing attention and concern from the scholars and engineers in currentera.With the advances in special structure technoledge such as high rise and long span,ordinary concrete materials gradually cannot meet the needs of the new structure, andconcrete filled steel emerges as a new structure. The structure has several advantages such asconvient construction, large capacity, high tenacity, excellent stability of fire resistance, gooddurability. Etc. Then it can be predicted that this structure may have the good fatigueperformance. This paper use the fatigue resistance performance test of concrete filled steelunder constant amplitude loading as the basis, studies the properties such as residual pressureresistance intensity combined with the code for design of concrete structure and fatigue failurecriterion. In conclusion, the experimental process, the collection and analysis of the data, andthe theoretical research includes the following aspects:To achieve the ultimate compressive strength of concrete filled steel tube columnsthrough static loading experiments, and carefully study the various phenomena and propertiesof concrete filled steel tube being destroyed to obtain the ultimate fracture section of concretefilled steel tube.To carry out the fatigue tests and get the double logarithmic relationship between thefatigue stress level and fatigue life of concrete filled steel tube after the accurate data for theinitial ultimate compressive strength of CFST is obtained, to fit out the S-N curve equation,and draw the S-N curve.To use the reliability theory as a research tool to study the compressive residual strengthof CFST, and get the P-R-N curve for the compressive fatigue of CFST. The curve shows theresidual strength degradation and at the same time provides an accurate Guarantee rate offatigue damage to CEST. The fatigue life of CFST can be predicted through P-R-N curve.To introduce the maximum strain in fatigue to define the decay rate of CFST, obtain theempirical formula for the decay rates of CFST, find that the damage variable and compressiveresidual strength showed a good linear relationship, and to verify the internal damage is theimportant reason resulting in the residual strength degradation of CFST. To construct a constitutive model for uniaxial compressive residual fatigue strength ofCFST through the theories of boundary face and continuum damage mechanics.