Research On The Effects Of Key Parameters To Axial Behavior For Pre-stressed Concrete Filled Tube

In this paper,the hydraulic method for pre-stressing and concrete-filled steel tube are combined together which forming hydraulic pre-stressed concrete-filled steel tube.The pre-stressed concrete filled steel tube based on the characteristics of the ordinary concrete filled steel tube,using the applied stress increases the restriction in steel tube on core concrete before loading.It can solve the defect of common concrete filled steel tube,which is the lack of steel tube on core concrete constraint.It can also solve the disadvantage of self-stressing concrete filled steel tube,which can't apply active stress.Based on project supported by the natural science foundation of the colleges and universities in Jiangsu province of the experimental research on behavior of hydraulic pre-stressed concrete filled steel tubes columns under axial compression and numerical simulation(15KJB560001),following work has been carried out in this paper.(1)Three deformation tests of ordinary concrete filled steel tube columns were carried out.The experimental results indicate that concrete filled steel tube column can produce expansive deformation in the first 4 days after pouring concrete,then shrinkage deformation appeared.Ultimate lateral strain is about-108??,ultimate longitudinal strain is about-46??.(2)To compensate the shrinkage of core concrete,concrete filled steel tube columns were made 5 groups with different expansion agent dosage,then analyzing shrinkage and mechanical properties of the specimens.The results show that the optimal expansion agent content of compensating shrinkage is 12%.The specimen can have an expansive deformation within 28 days when expansive agent content is 12%.Compared with other specimens.The stiffness of elastic stage and ultimate bearing capacity of the specimen are the maximum when expansive agent content is 12%.(3)The Loss of pre-stress tests for a long time of 4 hydraulic pre-stressed concrete filled steel tube was tested.The results show that the pre-stress loss is less than 20% at the time of 28 days as for adding 12% expansive agent.At the same time ordinary specimen is about 45%.It shows that adding 12% expansion agent can effectively reduce the loss of pre-stress.Therefore,the optimal value is 12%.(4)The axial compression tests of 6 hydraulic pre-stressed concrete filled steel tubes were carried out.The main parameter in the study is expansion agent(0?12%)and pre-stress value(0MPa?2.5MPa?5MPa?7.5MPa).The experimental results indicate that the stiffness of elastic stage and maximum axial force of elastic stage of specimen increases obviously.With the increase of pre-stress value,it increases more obviously.Compared with ordinary concrete filled steel tube column,the maximum axial force of elastic stage of pre-stressed specimen can reach 95.6% of the ultimate bearing capacity,the stiffness of elastic stage can increase 612%.Compared with the pre-stressed specimens without adding expansive agent,maximum axial force of elastic stage of the pre-stressed specimen can be increased about 16%,the stiffness of elastic stage can increase about 94% with a maximum of 12% expansion agent.The ultimate bearing capacity of the pre-stressed specimens changed little.(5)Axial compression model of hydraulic pre-stressed concrete filled steel tube was established using ABAQUS software.Software was used to simulate the hydraulic method for pre-stressing and the whole process of axial compression.The test results are in good agreement with those obtained in the software.