Research On Mechanical Properties Of Axially Loaded Steel Columns Reinforced By Ousourcing Reinforecd Concrete While Under Load

Steel structure members reinforced by outsourcing reinforced concrete while under load, which is just adding reinforced concrete around the steel members directly. The reinforcement process has any forms of uninstall or loads transfer on the original steel members. Such reinforced method can not only reinforce steel structure members without any influences on the normal productions and lives, but also has some advantages which other reinforced methods can not compare, that is it can effectively solve the two most important problems which the steel structures faced: fire problems and corrosion problems. However, at present, the researches on steel structure members reinforced by outsourcing reinforced concrete while under load are very rare, and the systematic researches even have not been seen. Although the only two domestic reinforcement specifications introduced the design methods of increasing section method, but the design methods are mostly about welding steel or bonding steel reinforcement method, which have shown obviously insufficient on outsourcing reinforced concrete reinforcement method. Based on these situations, the mechanical properties of axially loaded steel columns reinforced by outsourcing reinforced concrete while under load were researched in this paper through the integration of the experimental study, the finite element simulation and the theoretical analysis. The paper mainly covers the following fields:Through the axial compression experiments of the steel columns without reinforcement, the steel columns reinforced under no initial loads and the steel columns reinforced while under loads, the reinforcement performance of axial compression steel structure members reinforced by outsourcing reinforced concrete while under load, the stress development of steel, concrete and steel bars, and the influences of the initial loads, the concrete strength and the steel strength on mechanical properties of the reinforced members were studied. The experimental results showed that the bearing capacity and the rigidity of the steel members could be significantly improved by the reinforcement of outsourcing reinforced concrete. The ultimate bearing capacity of reinforced members decreased with the increase of initial loads, and increased with the increase of concrete strength and steel strength. Meanwhile, according to the comparison between the stress-strain curves of steel columns reinforced under no initial loads and under loads, it can be found that the steel which reinforced under loads appeared pioneered yield phenomenon, and the steel which reinforced under no initial loads was almost simultaneous yield with concrete and steel bars.On the basis of experimental researches, according to the analysis of the stress and strain states of each parts of reinforced members at the reinforcement moment and the failure moment, the bearing capacity calculation formulas of axially loaded steel columns reinforced by outsourcing reinforced concrete while under load which considered the influences of the initial loads, the concrete strength, the steel strength and the confinement of stirrups were deduced. And the calculation results were compared with the experimental results, which verified the accuracy of the calculation methods.The finite element models of axially loaded steel columns reinforced by outsourcing reinforced concrete while under load were established by the finite element software ABAQUS, and the simulation analysis on the specimens of experimental researches was carried out. According to the comparative analysis between the finite element results and the experimental results, the correctness of the finite element models were verified. Then the finite element parameters analysis were carried out in this model, and the influences of the initial loads, the concrete strength and the steel strength on the ultimate bearing capacity of reinforced members were confirmed. At the same time, combined with the experimental data can be found that the strength of the concrete is the greatest influence factors on the ultimate bearing capacity of the specimens after reinforcement. The ultimate bearing capacity of reinforced specimens with C50 concrete was increased by an average of about 19% when compared with that with C30 concrete under all levels of the initial loads. And the ultimate bearing capacity of reinforced specimens with C70 concrete was increased by an average of about 18% when compared with that with C50 concrete under all levels of the initial loads, which was increased by an average of about 33% when compared with that with C30 concrete under all levels of the initial loads.