Seismic performance of concrete-filled double-skin steel tubes after exposure to fire: Experiments

Structural engineers often face the challenge of assessing the residual structural performance of fire-damaged structures, especially the performance under seismic loading. This study presents investigations on concrete-filled double-skin steel tubes (CFDSTs) after exposure to fire. Physical tests are performed on 12 concrete-filled double-skin steel tubular (CFDST) specimens. The fire tests are conducted first with specimens heated for a specific heating period. After cooling down to ambient temperature, the cyclic tests are carried out with the constant axial load and reverse lateral cyclic load applied on the specimens. Parameters varied include the heating period, the nominal steel ratio, the hollow ratio and the axial load level on the column. Various indexes are used to evaluate the post-fire seismic performance of the CFDST columns, such as the stiffness degradation, the strength degradation and the energy dissipation. Finally, a simplified method is proposed to predict the residual initial flexural stiffness of the CFDST columns exposed to fire. The experimental results provide a basis for the assessment of fire-damaged CFDST structures, and the proposed method provides predictions with reasonable accuracy.