Experimental study on axial compression performance of circular CFST columns considering extreme ambient temperature

To examine CFST short columns' mechanical properties under extreme temps, 14 specimens were designed, focusing on temp's impact on materials. Axial compression tests revealed temp-dependent changes: concrete strength surged at low temps but ductility diminished, while steel's properties stayed stable. Concrete strength gains boosted columns' strength, enhancing steel-concrete synergy. Shear failure dominated at low temps. Ductility improved with thinner diameters or wetter mixes. Calculations underestimated actual capacity, likely due to temperature neglect in design codes, EC4 most notably. Finally, incorporating the experimental results, the bearing capacity calculation formula of CFST based on the unified theory was modified and accounts for ambient temperature.