Behavior and design of eccentrically loaded circular concrete-filled double steel tubular beam-columns under fire exposure

Circular concrete-filled double steel tubular (CFDST) beam-columns have increasingly been used in tall composite structures and must be designed for fire safety. However, there is a lack of appropriate design methods for the fire safety design of such composite beam-columns because research work on their fire performance has been very limited. This paper studies the behavior and design of circular CFDST beam-columns under eccentric loading and fire exposure. The standard fire tests and results are reported on CFDST beam-columns subjected to eccentric loads. A numerical model developed using ABAQUS is described for simulating the fire performance of CFDST beam-columns, which accounts for the concrete transient creep using the user-subroutine UEXPAN. The finite element simulation technique is employed to study the fire behavior of circular CFDST beam-columns having various parameters. A method is proposed for calculating the strength of CFDST beam-columns in a fire condition. The results demonstrate that increasing the column slenderness, eccentricity ratio, and axial load ratio significantly reduces the fire resistance time and capacity of CFDST beam-columns. Increasing the material strength considerably improves the fire resistance of filled composite columns. The developed finite element simulation model predicts well the behavior of CFDST beam-columns exposed to fire. The proposed method can yield satisfactory strength calculations of CFDST beam-columns, suggesting that it can be utilized in practical design of such composite beam-columns for fire safety.