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This research proposed the modular prefabricated permanent formwork system made of ultra-high-performance concrete (UHPC). Two kinds of modular formwork shapes were designed: the flat formwork and the ribbed. The experimental investigation on the axial compression performance of the composite columns that consist of the normal strength concrete (NSC) core and the modular UHPC permanent formwork was demonstrated. Compared with the flat formwork, the ribbed formwork exhibited better bonding with the NSC core. As observed from the test results, the composite column with the ribbed formwork presented a similar axial behavior as the NSC column with a slight improvement in ultimate loads. Therefore, the modular UHPC ribbed permanent formwork could be regarded as the additional cover to the conventional NSC column. In addition, the finite element analysis (FEA) model was also developed to simulate the composite columns numerically. The predicted capacities agreed with the experimental results, which validated the numerical models. The crack pattern estimated by the FEA model revealed that the interaction between the permanent formwork and the inner concrete introduced many tiny cracks to the concrete core. However, as protected by the UHPC permanent formwork, the overall durability of the composite columns can still be enhanced.

CFRP possesses the advantages of lightweight and high strength, but its cost is relatively high, and its ductility is insufficient; aluminum alloys have a relatively low cost and good ductility. This paper develops a CFRP-aluminum alloy laminated tube (CFRP-AL tube), which combines the advantages of CFRP and aluminum alloy. Such composite components have broad application prospects in the field of spatial structures. The CFRP-AL tubes were studied by experimental, numerical, and theoretical research on their axial compression performance in this paper. Firstly, the standard tensile test was carried out on 6061-T6 aluminum alloy. Combining the test results and references, the Johnson–Cook hardening model parameters of aluminum alloy were determined. The tensile test of CFRP was conducted to determine its material parameters. Based on composite material mechanics and fracture mechanics, a composite progressive damage model for the CFRP-AL tube was established. Secondly, axial compression tests were carried out on 27 CFRP-AL tubes and 3 aluminum alloy tubes with a small slenderness ratio. The test results show that the typical failure mode of CFRP-AL tubes with small slenderness ratios is strength failure, and the ultimate bearing capacity rises by 11~31% compared to aluminum alloy tubes. Thirdly, a user material subroutine capable of simulating CFRP failure was developed. Based on the user material subroutine, the effect of the initial imperfection, the fiber layer angle, the fiber layer thickness, the slenderness ratio, the diameter-thickness ratio and the CFRP volume ratio were discussed. And the failure mechanism and response of the CFRP-AL tubes under the axial compression were obtained. Finally, based on the strength theory, the formula predicting the bearing capacity of the strength failure was established, and the results of the formula were in a good agreement with the experimental and numerical results.

In order to investigate the change in the axial compression performance of circular recycled concrete-filled steel tubular short columns under chloride ion corrosion, 24 circular recycled concrete-filled steel tubular (RCFST) short columns and 12 circular natural concrete-filled steel tubular (NCFST) short columns for axial compression tests after being subjected to different corrosion degrees were designed. The experimental parameters include the corrosion degree (0, 2, 4, 6, 8, 10, 12, 14%) and the recycled concrete replacement rate (0, 100%). The experimental results show that the damage mode of the specimen after corrosion is localized buckling deformation of the steel tube. Due to the good confinement effect of the steel tube, the internal concrete was crushed only at the localized buckling part of the steel tube. The stiffness and ductility decreased significantly with increasing corrosion degree. As the corrosion degree increased from 0 to 14%, the stiffness of the circular RCFST short columns decreased by approximately 36.3%, and the ductility dropped by around 23.3%. And the corrosion resistance of the circular RCFST short column was worse than that of the circular NCFST short column. Based on the experimental results, the ultimate load capacity calculation model of the circular concrete-filled steel tubular short column is proposed.

To solve the problem of a large amount of fly ash accumulation and study the axial compression and bearing capacity prediction of the self-compacting fly ash concrete filled circle steel tube (SCCFST) columns, eight specimens are designed to explore the impact of concrete strength grade, internal structural measures, and additional parameters. The stress, progression of deformation, and failure mode of each specimen are observed during the loading process. The load–displacement curves, load-strain curves, characteristic load and displacement, ductility, and stiffness degradation are analyzed. The findings revealed that shear deformation occurred predominantly in the middle and upper portions of the steel tubes. Enhancing the strength of the concrete or adopting internal structural measures could increase the bearing capacity and ductility of the specimens. The peak load and ductility could be increased by up to 17.6 and 53.6%, respectively. The proposed unified calculation equation for the axial compression bearing capacity of SCCFST columns demonstrates notable reliability and precision. Furthermore, these tests offer valuable references for the engineering application of various forms of SCCFST columns, which are of significant importance in practical engineering.

In order to improve the physical and mechanical properties and the ability to perform in practical applications of prefabricated monolithic composite columns, high-performance fiber-reinforced cementitious composites (HPFRCC) material was prefabricated into mold shells to form HPFRCC precast monolithic composite columns. Through the axial compression test, the axial compression failure form, failure mechanism, bearing capacity, deformation ability, and influencing factors were studied. The results showed that compared with RC precast monolithic composite column, the HPFRCC specimens showed better deformation performance. HPFRCC prefabricated shells provided additional restraint beyond stirrups. The HPFRCC composite columns’ yield compressive strain increased by 11.59% on average compared with the RC composite column, and the peak compressive strain increased by 10.92%. The larger the ρv of stirrups was, the larger the compressive strain of the key point of the columns was. Compared with the FC-P-01 (ρv was 1.05%), the yield compressive strain of FC-P-02 (ρv was 1.48%) increased by 21.63%, and the yield compressive strain of FC-P-03 (ρv was 0.74%) decreased by 11.20%. The calculation model of the axial bearing capacity of the HPFRCC composite column was established through theoretical mechanical analysis, and the calculated values of the model fit with the experimental values.

Thin-walled galvanized helical corrugated steel tubes (HCSTs) filled with concrete are promising composite members, consisting of concrete, an anti-corrosion shell, and a multifunctional exterior corrugated steel tube. To investigate the synergistic working mechanism of concrete-filled HCSTs (CFHCSTs), six specimens were designed for axial compression tests, with the inner diameter of the column and the volumetric steel ratios of the longitudinal reinforcement as the variation parameters. The results show that HCSTs can better confine the concrete core and increase its strength. The failure mode of HCSTs is significantly influenced by the column’s diameter, and those with a smaller diameter are prone to slide failure and lock seam tearing. The strains and stresses on HCSTs are discussed in detail to elucidate the confinement effect. This paper proposes a suitable design method to predict the ultimate axial compression load capacity of CFHCST columns based on early studies on steel tube-confined concrete.

Axial compression performance and bearing capacity of reinforced concrete column is crucial to concrete structure. Lateral Impact load could pose severe danger to the security and service life of reinforced concrete column. Impact dynamic response, axial compression performance and residual bearing capacity of reinforced concrete columns after lateral impact load were investigated in this paper. Investigation results indicated that with the increase of impact energy, residual displacement and crack width on column increased, impact damage on column exacerbated. It was proved that impact resistance performance of reinforced concrete column could be enhanced by preload axial force. Residual bearing capacity of reinforced concrete column degenerated obviously after subjected to lateral impact load. And RC column would be under elastic stage when impact energy was low. According to analysis results on the correlation between residual displacement and residual bearing capacity, prediction model on residual bearing capacity of reinforced concrete column after lateral impact load was proposed.

In this paper, a new type of bamboo scrimber column embedded with steel bars (rebars) was proposed, and the compression performance was improved by pre-embedding rebars during the preparation of the columns. The effects of the slenderness ratio and the reinforcement ratio on the axial compression performance of reinforced bamboo scrimber columns were studied by axial compression tests on 28 specimens. The results showed that the increase in the slenderness ratio had a significant negative effect on the axial compression performance of the columns. When the slenderness ratio increased from 19.63 to 51.96, the failure mode changed from strength failure to buckling failure, and the maximum bearing capacity decreased by 43.03%. The axial compression performance of the reinforced bamboo scrimber columns did not significantly improve at a slenderness ratio of 19.63, but the opposite was true at slenderness ratios of 36.95 and 51.96. When the reinforcement ratio increased from 0% to 4.52%, the bearing capacity of those with a slenderness ratio of 51.96 increased by up to 16.99%, and the stiffness and ductility were also improved. Finally, based on existing specifications, two modification parameters, the overall elastic modulus Ec and the combined strength fcc, were introduced to establish a calculation method for the bearing capacity of the reinforced bamboo scrimber columns. The calculation results were compared with the test results, and the results showed that the proposed calculation models can more accurately predict the bearing capacity.

To enhance the mechanical properties of a precast monolithic column, the ECC material was made into a prefabricated shell with reinforced bars. Post-cast concrete was poured into the precast parts to form the reinforced ECC precast monolithic composite columns. An axial compression test was conducted to investigate the failure pattern, load-bearing capacity, and deformation performance. The results showed that the R/ECC composite columns had good integrity. The R/ECC prefabricated shell exerted an extra confinement effect on the column and enhanced deformability. At the yield stage, the displacement of the reinforced ECC prefabricated columns was 16.19% greater than that of RC composite columns on average. Additionally, the maximum load point displacement exhibited 15.30% growth. The ECC material delayed the yield time of longitudinal bars and stirrups. Before reaching the maximum load, the strains in the R/ECC composite column rebars were smaller than those in the RC column rebars. At the maximum loading point, the longitudinal reinforcement exhibited a 9.36% greater strain than that of the RC composite column.

In order to explore the axial compression performance of external steel rib ring restraint waste-steel-fiber-reinforced concrete-filled steel tubes (ERWCFSTs), 18 short-column axial compression tests were conducted. The effects of the number of rib rings, rib ring spacing, rib ring setting position, and waste steel fiber (WSF) content on the axial compression performance of the columns were analyzed. The results show that the concrete-filled steel tube (CFST) short columns with rib rings were strengthened, the specimens were mainly characterized by drum-shaped failure, and the buckling was concentrated between the rib rings. Without rib ring specimens, the steel tube is unable to resist the rapid increase in lateral expansion, leading to buckling initiation near the bottom of the specimens. The columns with rib rings exhibited a minimum increase of 32.5% and a maximum increase of 53.17% in load-bearing capacity compared to those without rib rings, with an average improvement of 37.78%. The columns achieved the best ductility when the rib ring spacing was 50 mm. When the rib ring spacing remained constant, columns with a number of rib rings no less than the height-to-diameter ratio (H/D) demonstrated more uniform stress distribution and optimal confinement effects. For a fixed number of rib rings, specimens with rib ring spacing between H/8 and H/4 showed significant improvements in both load-bearing capacity and ductility. The confinement effect was better when the rib rings were positioned in the middle of the column height rather than near the ends. The incorporation of WSF resulted in a minimum increase of 2.86% and a maximum increase of 10.49% in column load-bearing capacity, indicating limited enhancement. However, WSF improved the ductility performance of the columns by at least 10%. Combined with theoretical analysis and experimental data, a formula for calculating the bearing capacity of ERWCFSTs was established.