The fully encased and partially encased columns offer good fire and corrosion resistance properties, owing to the protection offered by concrete;concrete prevents local buckling,more effectively in fully encased sections but also in partially encased ones. Concrete filled columns:the steel tube also serves as form-work for concrete even if adequate additives have to be used for reducing the concrete separation from the steel section due to shrinkage;confinement effect due to steel is high for the rectangular sections and very high for circular sections,resulting in the increasing of strength with a great enhancement of ductility.核心混凝土可增强钢管壁的稳定性；钢管对核心混凝土的约束 作用，混凝土三向受压，提高混凝土的强度和变形能力 The fully encased and partially encased columns offer good fire and corrosion resistance properties, owing to the protection offered by concrete; concrete prevents local buckling, more effectively in fully encased sections but also in partially encased ones.  Concrete filled columns: the steel tube also serves as form-work for concrete even if adequate additives have to be used for reducing the concrete separation from the steel section due to shrinkage; confinement effect due to steel is high for the rectangular sections and very high for circular sections, resulting in the increasing of strength with a great enhancement of ductility. 核心混凝土可增强钢管壁的稳定性; 钢管对核心混凝土的约束 作用，混凝土三向受压，提高混凝土的强度和变形能力