Experimental Research On Size Effect Of Concrete-filled Steel Tubular Stub Columns Under Axial Compressive Load

With the development of economy and technology, modern engineering projectsare developing with longer span, heavier service load and higher altitude. The concretefilled steel tubes have been widely used due to high bearing capacity, excellent seismicperformance in super high-rise buildings, long-span arch bridges and special structures.With the continuous increase of buildings height and bridge spans, the sizes of thecross-sections of the CFSTs have been creating new records. The interaction betweenthe steel tube and the core concrete makes the size effect more complicated. Theexisting rules of calculation methods for size effect are conclusions of research based onsmall size columns, which may lead to an overestimation on the load carrying capacityof the large size members. However, present research on the size effect of concretefilled steel tubular members is quite limited. Therefore, it is necessary to investigate thesize effect of CFST members to ensure the reliability of large size component. In thisdissertation, the size effect of CFST columns is studied with the specific work listed asfollows:(1) Two groups of short CFST columns, which satisfy both geometric similarityconditions and mechanical property conditions, are axially loaded to failure to study thesize effect of carrying capacity, failure mode, stiffness, lateral deformation coefficient,peak strain and ductility.(2) The diameter of plain concrete columns is totally the same as the core concretecolumns of in CFST columns. The plain concrete columns are also axially loaded tofailure to study the size effect of carrying capacity, failure mode, stiffness, lateraldeformation coefficient, peak strain and ductility. These results are used as a basis ofinvestigating the size effect of CFST columns.(3) Through the analysis of the carrying capacity of both the CFST columns andthe plain concrete columns, the relationship between the proportion of increasedcarrying capacity and size is obtained. In addition, the relationship between ultimatestress and lateral confinement stress is obtained by stripping analysis. Finally, fivemethods are adopted to analyze the size effect of CFST members.