Seismic Performance of Concrete Filled Steel Tubular (CFST) Columns with Variously Axial Compressive Loads

Abstract

This paper presents a study on the seismic performance of square concrete filled steel tubular (CFST) columns under different axial compressive loads. A total of four full-scale specimens using the steel tube with a width-to-thickness ratio (B/t) of 42 was tested by combined axial compression and cyclic lateral loading. In which, three specimens were subjected to constant axial compression, P = 0.15, 0.35, and 0.55P0, respectively, and one specimen was applied varied axial compression varying from 0.15 to 0.55P0 (P0 is nominal axial compression strength of the column) that is an assumption for designing exterior columns in a typical moment resistance frame (MRF) system. An identical loading protocol according to the AISC 341–16 code was adopted as the basis of cyclic lateral displacement loading for all four specimens. Test results reveal that there were significant differences in yielding and local buckling process in the steel tube, lateral (shear) strength, deformation capacity, and lateral stiffness degradation of the columns. For three CFST specimens with constant axial compression, the higher the axial compression was, the smaller the lateral strength and deformation capacity were. Another important finding in the specimen with varied axial compression, CFST42–15/55C, was a discrepancy in lateral strength and deformation capacity in positive and negative directions of cyclic lateral displacement. It was found that Specimen CFST42-55C possesses the lowest lateral strength and deformation capacity with the average ultimate interstory drift ratio (IDRu) of only 1.29% radian. The study results also show that these square CFST columns satisfy the highly seismic requirement when the axial compression has not exceeded 0.35P0 with their average IDRu of more than 3% radian. To improve the seismic performance of these composite columns, reducing the B/t limit is one of the most effective ways.