Concrete filled steel tubular (CFT) columns have become increasingly popular in structural application. The increased popularity comes from their excellent structural properties such as high strength, high ductility and large energy absorption capacity. However, a disadvantage feature of CFT-column is its time dependent characteristic by means of creep and shrinkage of inner concrete. The time dependent behavior of CFT-column can cause serious serviceability problems. Therefore, it is necessary to investigate the long-term behavior of CFT-column.
A few researches of long-term behavior of CFT-columns have been studied, but they have not been considered practical load state. In CFT-columns, shear connector or diaphragm are practically used for transferring load to inner concrete. This thesis presents analytical and experimental studies on long-term behavior of rectangular CFT columns with various sizes of diaphragm and various length of columns. Ten CFT column specimens were tested to investigate the influence of loading methods and sizes of diaphragm on the behavior and eight CFT column specimens were tested to investigate the influence of length of CFT-columns. Analysis methods of long-term behavior of CFT-columns with various types of diaphragm are proposed based on experiment results performed for five loading cases.
