Mechanical Behavior of Concrete-filled Steel Box Columns in Fire
|關鍵字:||火害試驗;填充型箱型鋼柱;軸向變形;力學分析;Fire test;concrete-filled steel box column;axial deformation;mechanical analysis|
This study aims to investigate experimentally and analytically the fire resistance of concrete-filled steel box columns under axial compression and at elevated temperatures. Three specimens were tested to study the effects of the variables such as load ratio, size of the cross section, and presence of the longitudinal bars on their fire behavior. Test results demonstrated that the specimens expanded axially while the specimens were subjected to temperature increase in the early stages of fire exposure. However, the axial deformation changed from expansion to contraction while the specimens’ axial capacities gradually decreased because of further temperature increase. The magnitude of the applied axial compressive force highly affected the axial elongation and fire resistance. The size of the cross section of the specimens influenced the elongation magnitude, but had little effects on the fire resistance. Specimen with longitudinal bars had larger fire resistance than those without the longitudinal bars. The results of the analytical approach indicated that the load share of the steel section and concrete related to their material properties and cross-sectional areas before the fire test. When the specimens exposed to fire, the load share of the steel section gradually increased because the steel section expanded faster than the concrete. Next, the load share of the steel section progressively shifted back to the concrete since the steel section further lost its load-carrying capacity caused by the elevated temperatures. The specimens finally failed when both steel section and concrete reached their capacities at elevated temperatures. Analytical approach reasonably predicted the axial deformation-time relations of the specimens. The fire behavior of concrete-filled steel box columns was established experimentally and analytically in this study.