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In this study, innovative Lightweight Self-compacting Geopolymer concrete made of industrial and agricultural wastes is developed and used as the in-fill material in Fiber Reinforced Polymer (FRP) composite columns. The axial compressive performance of the columns is investigated with critical parameter variations such as the effect of the Diameter to thickness ( D/ t) ratio and fiber orientation of the FRP tube. Two types of D/ t ratios, i.e., 30 and 50, and three fiber orientations ±0°, ±30°, and ±45° were used for the key parameter variations. An increased D/ t ratio from 30 to 50 reduces the performance in terms of load despite increasing the deformation. The columns containing the fiber orientation of ±0° exhibit greater performance compared to other types of fiber orientation (±30° and ±45°). The experimental results and failure patterns were compared and validated against the numerical and theoretical studies. A Finite Element model is developed and validated with the experimental results with errors ranging from 0.84% to 4.57%. The experimental results were validated against various existing theoretical prediction models with a percentage error of 7% to 14% An improved theoretical model is proposed for predicting the axial load of concrete-filled FRP composite columns.

Existing studies have demonstrated that insufficient horizontal deformation capacity of columns under high axial compression ratios constitutes a key factor leading to seismic damage in ordinary concrete frame structures. This paper proposes a novel framed structure incorporating composite columns by combining ultra-high performance concrete (UHPC), which exhibits excellent mechanical properties, with normal concrete (NC). The design concept maintains the overall mechanical performance of the composite column frame structure while significantly reducing the lateral stiffness when the composite columns are configured in a “split-column form.” For instance, the lateral stiffness of ZH-5 in the “split-column form” is only one-tenth of that of ZT-1 in its initial state, leading to a substantial enhancement in horizontal deformation capacity. This design approach maintains the overall mechanical performance of the composite column frame structure while significantly enhancing its horizontal deformation capacity by reducing lateral stiffness through the “split-column” configuration. Using the ABAQUS finite element software 2021, a finite element model of a multi-story frame column structure was developed. Research findings indicate that the frame structure utilizing UHPC-NC composite columns exhibits reduced tensile damage, lower peak and plastic displacements, and a relatively smaller inter-story drift angle. Specifically, the plastic drift angle of the UHPC-NC composite column frame structure from the first to the fourth story is 5% to 31% smaller than that of the conventional reinforced concrete column frame structure. The novel UHPC-NC composite column frame structure demonstrates superior seismic performance.

This paper conducts an experimental study on the axial compressive performance of FRP-steel-concrete composite columns. Nine short columns were produced and evaluated in the study, comprising of three concrete-filled steel tube reference columns and six FRP-steel-concrete composite columns, respectively denoted as “reference columns” and “composite columns”. Two categories of failure modes, including shear failure and waist drum, were observed from the experiments. The failure mode may trend toward waist drum from shear failure as more FRP layers were used. The number of FRP layers had a direct effect on the level of compressive strength attained, with a greater number of layers resulting in a greater increase in compressive strength. Moreover, a greater tensile strength and higher elastic modulus of CFRP sheets are more effective at improving the compressive stiffness of the columns. Finally, a four-stage confinement mechanism for FRP-wrapped steel tube concrete composite columns is proposed and discussed, through which the damage mechanisms of the composite structures are more rationally characterized.

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.

Modular structural systems have been used increasingly for low- and mid-rise structures such as schools and apartment buildings, and applications are extending to high-rise buildings. To provide sufficient resistance and economical construction of the high-rise modular structural system, the steel-concrete composite unit modular structure was proposed. The proposed composite unit modular system consists of the composite beam and the partially encased nonsymmetrical composite column. The outside steel member of the composite column has an open section, and is manufactured using a pressed forming procedure so that easy joining connecting work and manufacturing cost reductions are possible. However, the design methods are complicated due to the inherent nonsymmetrical properties of the section. Therefore, in this study, the focus was made on the strength evaluation and development of design methods for the partially encased nonsymmetrical steel-concrete composite column. Four full-scale specimens were constructed and tested. The experimental study focused on the effect of the slenderness ratio of the column, eccentricity, and the through bars on the strength of such columns. Additionally, the P–M interaction curve to estimate the strength of the proposed composite column under general combined loading was developed based on the plastic stress distribution method. The results indicate that the through bars are needed to delay the local buckling and distribute the loading uniformly throughout the composite column. Finally, the proposed design methods provide a conservative strength prediction of the proposed composite column.

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.

To investigate the axial compressive behavior of double C-section partially encased composite (DCPEC) columns, 10 DCPEC specimens and two back-to-back bare steel C-section specimens were designed and tested under axial compression. The effects of key parameters, including steel wall thickness, member slenderness ratio, connection type of the built-up double C-sections and connection density, on the failure mode, load–displacement response and ultimate load-carrying capacity were examined. The test results showed that, under otherwise identical conditions, the ultimate load of the bolted stub column was 8.4% higher than that of the welded stub column. When the steel wall thickness increased from 2.0 mm to 3.0 mm, the ultimate load increased by approximately 16%. In contrast, when the slenderness ratio increased from 25.98 to 41.57, the ultimate load decreased by approximately 30%. A finite element model was then established in ABAQUS and validated against the experimental results. The numerical analysis further confirmed that increasing the slenderness ratio reduced the axial load-carrying capacity, whereas increasing the steel wall thickness improved the resistance of the member. The results indicate that the proposed DCPEC column can effectively develop the composite action between cold-formed thin-walled steel and lightweight aggregate concrete, thereby improving axial resistance and showing promising potential for engineering applications.

Glass-reinforced composite columns (GRCCs) may provide an economical alternative to conventional construction materials due to the superior cost to strength provided by bulk glass. Prior to this study, no GRCCs had been physically tested, having previously relied on simulation to predict the behavior of the columns. This study utilizes polyurethane resin bonds in place of sizing agents for adherence between materials, a key requirement for the development of the structural system of the columns. The unreinforced control column failed at a load of 11.2 kN while the maximum GRCC load was 30.8 kN. This indicates that glass can be loaded to 123 MPa before the onset of delamination failure of the GRCCs. Maximum shear stress of 53 MPa was reached, exceeding the 11 MPa required for practical GRCCs. Buckling of the columns occurred at 30.8 kN, below the theoretical maximum of 64.4 kN. Through gradual delamination, the column slowly transferred to an unbonded condition, causing buckling failure. Delamination is unlikely to occur in practical GRCCs due to the lower required shear strengths.

The square steel tube–timber–concrete composite L-shaped columns are lighter in weight due to the inclusion of wood and exhibit superior seismic performance. This combination not only reduces transportation and labor costs but also enhances earthquake resistance. The wood contributes lightness and flexibility, the steel provides strength, and the concrete offers excellent compressive performance, thereby achieving an optimized design for performance. To investigate the axial compression performance of square steel tube–timber–concrete composite L-shaped short columns, axial compression tests were conducted on eight groups of L-shaped columns. The study examined ultimate load, failure modes, load–displacement relationships, initial stiffness, ductility, and bearing capacity improvement factors under different slenderness ratios, steel tube wall thicknesses, and wood content rates. The results show that the mechanical performance of the composite columns is excellent. Local buckling of the steel tube is the primary failure mode, with ‘bulging bands’ forming at the middle and ends. When the wood content reaches 25%, the synergy between the steel tube, concrete, and wood is optimal, significantly enhancing ductility and bearing capacity. The ductility of the specimen increased by 31.1%, and the bearing capacity increased by 4.14%. The bearing capacity increases with the steel tube wall thickness but decreases with increasing slenderness ratio. Additionally, based on the Mander principle and considering the partitioned constraint effects of concrete, a simplified calculation method for the axial compressive bearing capacity was proposed using the superposition principle. This method was validated to match well with the test results and can provide a reference for the design and application of these composite L-shaped columns.

Special-shaped partially encased steel–concrete composite (PEC) columns could not only improve the aesthetic effect and room space use efficiency, but also exhibit good mechanical performance under static load when used in multi-story residential and office buildings. However, research on the seismic performance of special-shaped PEC columns is insufficient and urgently needed. To investigate the seismic performance of cross-shaped partially encased steel–concrete composite (CPEC) columns, three CPEC columns were designed and tested under combined constant axial load and lateral cyclic load. The test results show that the CPEC columns had good load capacity and ductility, and that the columns failed because of concrete crushing and steel flange buckling after the yielding of the steel flange. The plump hysteresis loops indicated that the CPEC column also had good energy dissipation capacity. Due to the constraint of hydraulic jacks, increasing the load ratio would decrease the effective length, thereby increasing the load capacity of the CPEC column and decreasing the ductility. A finite element model was also established to simulate the response of the CPEC columns, and the simulated results agree well with the experimental results. Thereafter, an extensive parametric analysis was performed to study the influences of different parameters on the seismic performance of CPEC columns. For the CPEC column with an ideal hinged boundary condition at the top, its lateral load capacity gradually decreases with the growth of the load ratio and link spacing and increases with the rise of the steel yield strength, concrete compressive strength, flange and web thickness, and sectional aspect ratio. This research could provide a basis for future theoretical analyses and engineering application.