Experimental Study On Shrinkage And Creep Of High Strength Concrete-Filled Steel Tube

In high-rise buildings and long-span bridge structures,the use of concrete-filled steel tubes is more and more extensive.Concrete-filled steel tubes have many advantages such as high bearing capacity,convenient construction,good seismic performance,etc.However,the characteristics of concrete's shrinkage and creep are time dependent,and the deflection and internal force of the concrete-filled steel tube structure are changed with time,which will directly affect the performance of the concrete-filled steel tube structure.Scholars at home and abroad have begun to study the shrinkage and creep of concrete-filled steel tubes,but the strength of the concrete is generally low.With the continuous development and application of materials science,the use of high-strength materials are used more and more,and the use of high-strength steel-filled high-strength concrete will have a great prospect,so this paper carries out an experimental study on the shrinkage and creep properties of high-strength CFST.The main work content is as follows:(1)The bearing capacity of ordinary and high-strength CFST was studied experimentally.The relationship between the force and longitudinal displacement and the failure mode of the two specimens under axial compression were observed and studied.The actual bearing capacity of the specimen was obtained for use in determining the loading value of the creep test.(2)By comparing the creep test data of concrete specimens with four existing calculation models,it is found that the AFREM calculation model considering the influence of silica fume is more accurate in predicting the creep of high strength concrete,while other models without considering silica fume consistently overestimate the creep change of the specimens.(3)Modified model of four creep calculation models are obtained by considerting the effect of size and humidity,and the influence of internal force redistribution of steel tube and concrete.Compared with the high-strength steel tube concrete specimens,it was found that each theory has a certain deviation.The improvement of the theory of concrete filled steel tube is proposed to include the steel rate parameter.The calculation results are in good agreement with the experimental data after modification.