(A) study on the improvement for efficiency of structures using circular concrete filled steel tube

Abstract

This dissertation presents a numerical analysis model for economical and efficient structure design using circular concrete filled steel pipe (CFT) columns. The creep effect, which is a major nonlinear effect on concrete, was modified by considering the morphological characteristics of CFT. Through the modified CFT creep prediction model, the P-M interaction diagram of the column reduced according to the time effect was predicted. To confirm the effect of ductility of the CFT column, plastic analysis was introduced and compared with the RC column. At this time, in order to reduce the excessive analysis cost, a direct search method based on the section database was introduced. The plastic analysis was performed by introducing a plastic hinge, which was inserted into the stiffness matrix based on the spring element. Differential axial shortening, one of the effects of columns on structures, was identified by comparing CFT and RC columns. In this process, the influence of each influencing factor on the differential axial shortening was identified by considering the time stage, construction stage, and layer flattening stage. In this dissertation, in order to confirm the cost and performance advantages of CFT columns, they were compared with RC columns with differences in time-dependent behavior and ductility of concrete.