Abstract
Constructive solutions for tensioned concrete-filled steel tubular (CFST) elements can be applied in bar systems (trusses, arches, frames, structural and cable-stayed structures, radio and television towers, as well as other similar applications) and can be significantly more cost-effective compared to concrete-filled tubes, reinforced concrete, and steel structures. Tensioned CFST elements, in cross-section, consist of a steel shell tube filled with concrete, which is reinforced with either high-strength conventional or high-strength prestressed reinforcement. The load-bearing capacity of a CFST element is determined by the combined strength of the steel tube, the concrete, and the high-strength steel reinforcement bars, all working together as a unified cross-section. It is known that mild steel in the tube, when subjected to tension, is characterized by its yield strength and ultimate strength, while high-strength reinforcement bars are defined by their conditional yield strength and ultimate strength. In experimental tensioned CFST elements, the interaction between the mild steel tube and the high-strength reinforcement steel proves beneficial. This combination allows the mild steel tube to effectively operate beyond its yield limit. When the tube steel reaches its yield point, it temporarily ceases to absorb additional load. At this moment, the increasing load is transferred to the high-strength reinforcement bars, which have not yet reached their conditional yield strength. Regarding the mild steel tube of the tensioned CFST element, it undergoes strain hardening during this phase. Its longitudinal deformations develop in accordance with the deformations of the high-strength reinforcement bars. With further loading, the mild steel tube can bear a portion of the load within the limits of its ultimate strength, which enhances the element’s load-bearing capacity and, consequently, improves the economic efficiency of the structural solution. The aim of this scientific study is to develop a practical algorithm for calculating the load-bearing capacity of tensioned CFST elements.