An experimental and numerical study of ultra-high strength concrete filled circular tube column post-fire

Abstract

Extensive experimental research was conducted on 10 ultra-high strength concrete filled tubular (UCFCT) columns to investigate their performance after exposure to the ISO-834 standard fire and external load. Two different diameters of steel tubes (219.1 mm and 273 mm) with concrete strength ranging from 161 MPa to 181 MPa were included in the study. The primary parameter examined was temperature, ranging from 94 °C to 618 °C. The study obtained data on the residual capacity, working mechanism, and ductility of the columns under compressive load after the fire. The compression experiments revealed that the load capacity of the UCFCT columns remained high. As the columns deformed beyond the inflection point, the load capacity increased gradually without decline. This indicates that the UCFCT columns exhibited notable ductility even after the fire and cooling process. The residual capacity of the columns was influenced by the highest temperature experienced during the experiment. The study also observed the splitting of the ultra-high strength concrete (UHSC) inside the specimens and described the failure mode. Local wall buckling did not occur prior to yielding, and the specimens demonstrated strain-hardening after reaching the plastic point. The mechanical properties of the steel and UHSC were investigated and incorporated into a numerical model that satisfactorily described the post-fire behavior of the composite columns compared to the test data. Based on this theoretical model, the influence of changing material strength (steel and concrete), fire duration time, specimen diameter, and steel ratio on the residual capacity ratio and residual rigidity ratio was discussed. It was generally observed that sectional dimensions and fire duration time had a significant impact on the residual capacity ratio. Finally, formulas suitable for calculating the residual strength of ultra-high strength concrete-filled circular tube columns after exposure to the ISO-834 standard fire were developed based on the results of the parametric analysis.