Abstract: Hollow concrete filled steel tube is a composite material with excellent performance, widely used in engineering structures such as buildings, bridges, and tunnels. Compared with circular concrete filled steel tube columns, rectangular concrete filled steel tube columns have advantages such as convenient construction and simple node structure. However, research has shown that compared with circular hollow concrete filled steel tube, rectangular members have lower composite strength and poorer ductility. Reinforcement and reinforcement measures can effectively enhance the strength and ductility of composite columns. PHC tubular pile is a hollow circular reinforced concrete prefabricated member made by pre tensioning and centrifugal molding technology and steam curing. The built-in longitudinal bars can improve the bending performance of the tubular pile, and the spiral hoop bars can improve the ductility of the structure. Its single pile bearing capacity is high, the cost is low, and its application range is very wide. This article proposes a new type of composite member-ribbed reinforced hollow square concrete filled steel tube-by placing PHC pile into ribbed steel tube and pouring sandwich concrete afterwards. Previous studies have shown that the wall thickness and width to thickness ratio of the steel tube have the most significant impact on the axial compressive bearing capacity of such composite members.
To study the axial compression performance of reinforced hollow square steel tube high-strength concrete short columns with ribs, this paper conducted finite element simulations on 18 reinforced concrete filled steel tube members with ribs and steel tube wall thickness as variable parameters including the number of stiffeners and the thickness of steel tube. The results were compared with existing experimental results, and the load displacement curves were well fitted. The finite element analysis results indicate that the stress process of the member can be divided into elastic stage, elastic-plastic stage, plastic strengthening stage, and descending stage. The influence of stiffeners on the axial compressive mechanical properties of the member is manifested in all four stages. Stiffening ribs can effectively suppress local buckling of steel tubes, allowing them to share more axial loads and fully utilize the axial compression performance of the steel. Research has shown that compared to non stiffener members, the ultimate bearing capacity of single-stiffener members has significantly improved. Continuing to increase the number of stiffeners will further enhance the ultimate bearing capacity of the member, but the increase is relatively small. The steel tubes in members with stiffeners will share the internal force and reach the peak earlier, and the share internal force displacement curve will enter the descending stage, while the steel tubes in members without stiffeners will share the internal force and reach the peak later, and the share internal force displacement curve will not have a significant descending segment, indicating that the steel tubes in members with stiffeners can bear more axial loads in the later stage of loading, thereby improving the ductility of the members. Compared to increasing the wall thickness of steel tubes, adopting reasonable reinforcement measures can more effectively enhance the bearing capacity of composite members and save more steel. At the end of this article, a formula for the axial compressive bearing capacity of reinforced hollow square concrete filled steel tube short columns with ribs is provided, and the calculation results have errors within 5% and tend to be conservative.