Research Of Creep On Concrete Filled Steel Tubular Compressed Member In The Natural Environment

Since used in the piers of the Severn railway bridge in the UK in1879, concrete filled steel tube (CFST) is widely used in practical engineering because of its unique structural features. As time goes by, creep is produced in CFST, which makes the concrete occur stress relaxation and the stress of steel pipe increases significantly, affecting the normal work of the structure components. Design control standard of the previous works in this area is not particularly stringent, theoretical research is relatively lagging behind; However, the emerging high-speed rail requires the track structure with high ride comfort and stability,which improves the design control standard in this area. Therefore, the theoretical study on the creep characteristics of CFST is of great importance.In this thesis, based on the project of the Zhenjiang Continuous beam arch bridge (90+180+90m) which crosses Jing-Hang Canal on the Beijing-Shanghai high-speed railway, the CFST which is as consistent as possible with the performance of its concrete is used for the creep test in the natural random environment. The main research contents are as follows:(1) Compare and analyze the domestic and foreign common concrete creep prediction models, creep computing theory and methodology briefly, introduce the creep characteristics of the core concrete of CFST.(2) According to the long-term observation of CFST test components in the natural random environment, obtain the rules and characteristics of CFST under different steel ratio and different ages, and the law of stress redistribution of CFST cross-section.(3) Based on the further analysis of test data, obtain the creep coefficient calculation expression of plain concrete and CFST by the use of MATLAB software, and compare with excited theories.(4) Use the finite element analysis software MIDAS CIVIL to establish the spatial calculation model of the Zhenjiang Continuous beam arch bridge (90+180+90m) which crosses Jing-Hang Canal on the Beijing-Shanghai high-speed railway, analyze the influence to the structure of taking or not taking creep into consideration in construction phase and using different creep computing models in operational phase.