Axial Compressive Behavior of Concrete-Encased CFST Stub Columns with High-Level Two-Stage Initial Stresses

Abstract

Concrete-encased concrete-filled steel tube (CFST) is an innovative composite member that consists of the inner CFST components and an outer reinforcement concrete encasement. One increasing application scenario of concrete-encased CFST is acting as the arch rib in large-span arch bridges that are generally constructed through a three-stage procedure. Consequently, significant two-stage initial stresses in the steel tube and inner CFST are commonly generated, which might influence the structural behavior of the arch ribs. This paper aimed to study the effect of the high-level two-stage initial stresses on the sectional performance of concrete-encased CFST arch subject to axial compression. Accordingly, six concrete-encased CFST stub column specimens with two-stage initial stresses, as well as 12 reference specimens with preload on steel tube or CFST only, were tested and analyzed through a refined finite-element model. The simplified prediction formula for ultimate compressive strength of concrete-encased CFST stub column with different initial stress scenarios were also established. The results show that the column specimens with two-stage initial stresses generally failed due to the premature crushing of outer concrete caused by the pronounced outward swelling effect from the yielded and locally buckled inner steel tube. The yielding and local buckling of steel tube were fairly hastened by its initial stress. Therefore, it is recommended that the initial stress ratio of steel tube should be limited within a reasonable value in the design. The specific value is around 0.6 within the scope of the structural parameters of this study.