To explore the influence of microexpansive concrete self‐stress on the performance of steel pipe concrete, the expansion rate test of microexpansive concrete confined by steel tube was carried out with different expansion rates. Then, the mechanical properties of high‐strength steel tube‐confined microexpansive concrete (HSTCMC) short columns were conducted by the uniaxial compression test. The length‐to‐diameter ratio, the expansion rate of the microexpansive concrete, and the steel tube thickness were investigated in the study. Furthermore, the ABAQUS software was employed to analyze the microexpansive mechanism of the concrete, and it was verified by the uniaxial compression test. The test results show that the concrete possesses a remarkable volume expansion phenomenon, which was up to 150 με after four days of maintenance time. The mechanical properties of the HSTCMC short columns were greatly improved compared to the control RC pier. The yield and ultimate strength of the HSTCMC short columns can be enhanced to 8.9% and 14.6%, and with the content of expansive agent that increased from 8% to 12%. The finite element analysis results highlighted that the end constraint at the two ends has the biggest influence on the mechanical performance of the HSTCMC short columns, followed by the thickness of the steel tube and the content of the expansive agent. It should be noted that the self‐stress of microexpansive concrete will be decreased with the increase in the length‐to‐diameter ratio, when the length‐to‐diameter ratio is less than four. Furthermore, the constraint effect of the circular steel tube on the microexpansive concrete is better than that of the rectangular section steel tube.

Circular steel pipe concrete can give full play to the combination of steel pipes and concrete, resulting in an improvement in the steel pipe’s concrete bearing capacity and ductility. In this study, the axial compression load capacities of nine steel pipe concrete columns, including one traditional steel pipe concrete column and eight steel pipe self-stressed concrete columns, were analyzed using an axial pressure test. The damage patterns and stress–strain curves of all the specimens under axial compression load were analyzed, and a comparison analysis was made between the test results of the different specimens. The test results show that the longitudinal expansion displacement of concrete increases with the increase in the expansion agent content. The greater the self-stress, the higher the bearing capacity of steel-tube concrete columns under axial compressive load within a certain range of the expansion agent, indicating that self-stress can increase the bearing capacity of steel-tube concrete columns under axial compressive load, but the effect of the magnitude of the self-stress on the damage pattern of the specimens is limited. The damage patterns of all the specimens were bulging in the center and concave at both ends. In addition, the existing theoretical calculation method of the bearing capacity of steel pipe concrete columns is modified, and a theoretical calculation method applicable to steel pipe self-stressed concrete columns is proposed to simplify the calculation method of the bearing capacity of steel pipe self-stressed concrete columns, which provides a basis for decision-making in practical engineering.

In order to improve the anti-collision capacity of existing reinforced concrete (RC) columns under vehicle impact load, an experimental study on the anti-collision performance of RC columns strengthened with micro-expansive concrete filled steel tube was carried out. By combining an experiment and finite element calculation, the influence of steel tube strength, micro-expansive concrete strength and steel tube wall thickness on the anti-collision performance of strengthened RC columns were studied. The results showed that the peak displacement of an SM-RC column is 25.9% lower than that of an RC column, due to the increased stiffness, the peak impact force increased by 138.2%. The micro-expansive concrete filled steel tube reinforcement method can significantly improve the anti-collision performance of RC columns and reduce the lateral deformation. Increasing the strength grade of steel tube and thickness of steel tube can greatly improve the impact resistance of strengthened RC columns and reduce the lateral deflection deformation of short columns, compared with steel tube strength Q235, the displacement of Q690 is reduced 47.4%. the displacement of the 8-mm thick steel tube is reduced by 48.1% compared with the 4-mm one. while the strength grade of micro-expansive concrete has little effect on the impact resistance and lateral deflection deformation of strengthened RC columns.

In this paper, eleven high-strength steel tube confined self-stressing concrete (HSTCSC) short columns were tested to study their strengthening mechanism and axial compression performance. The effects of different material strengths, cross-section types, and hollow ratios on the axial mechanical properties of the HSTCSC short columns were investigated using the finite element analysis method. Experimental results highlighted that the HSTCSC short columns presented the waist drum-type failure mode significantly, with a higher axial load-bearing capacity and deformation performance, and possess a large safety reserve. It was also found that the axial compression property of the HSTCSC short column could be improved significantly due to the joint action of the micro-expansion of the self-stressing concrete and the hoop constraint of the high-strength steel tube. Moreover, the circular cross-section HSTCSC short columns were found to result in better mechanical performance after yielding of the high-strength steel tubes, especially entering the strengthening section. Under the condition of equal steel content ratio and cross-section area, the single-layer circular HSTCSC short columns were found to have the largest load-bearing capacities after yielding the high-strength steel tubes, followed by the double-layer circular HSTCSC short columns, and then the double-layer square HSTCSC short columns. The hollow rate of the cross-section could also decrease the load-bearing capacity of the HSTCSC short column with both circular and square sections, although increasing the hollow rate could save material and reduce the weight of the structure. The finite element analysis results showed that the proposed finite element model could be employed to simulate the compressive behavior of HSTCSC short columns with high calculation accuracy.