This paper presents an experimental and numerical study on the eccentric compression behavior of cold-formed thin-walled steel C-shaped members with localized corrosion. A total of eight specimens with artificial defects simulating localized corrosion were tested under eccentric load, with four intact specimens for comparison. The main test parameters included the corrosion length, width, and eccentric loading angle. The failure modes, loaddeflection curves, and load-strain relationship curves of corroded specimens were determined through experiments. The experiments indicated that the local defect significantly contributed to the degradation of the performance of specimens, and the loading angle had a considerable effect on the ultimate strength. Test results revealed that localized corrosion can decrease the ultimate strength by 24.1% when the loading angle is 0 degrees, while the influence of corrosion can be ignored when the angle is 180 degrees. Based on the experimental results, finite element models were established and validated. Subsequently, the randomness of localized corrosion, including irregular corrosion profiles and uneven surface morphology, was simulated and analyzed in the numerical study. A parametric study was then conducted to examine the effect of corrosion dimensions, corrosion locations, and eccentricity on the ultimate strength. To determine the eccentric compressive strength of cold-formed thinwalled steel C-shaped members, a calculation method based on the direct strength method was developed. For loading angles of 0 degrees, the predicted mean value of the method is 0.869, and for 180 degrees, it is 0.975.

Localized corrosion can occur on multiple areas of the outer surface of square concrete-filled steel tubes (CFSTs), which can significantly compromise structural safety during service. The nature of localized corrosion is characterized by significant stochasticity, manifesting as spatial dispersion in both location and extent, coupled with irregular morphology. To evaluate the influence of multi-region localized corrosion in terms of area, position, and degree, an experimental program was conducted involving seven square CFST columns containing simulated local corrosion defects, alongside two uncorroded reference specimens subjected to axial compression. The experimental phenomenon, ultimate strength, and lateral deflection profiles of tested specimens were obtained. Numerical models were developed and validated against experimental results, then extended to incorporate the irregular profile and uneven surface of corrosion morphology. Finite element analysis indicated that single random corrosion damage can be considered a regular defect region with an even surface for axially loaded square CFSTs. The influence of corrosion dimensions and the position of single and multiple corrosion regions on axial compression performance was probed through a parametric investigation. It was indicated that the controlled section of the square CFST was significantly influenced by the corrosion locations. If the controlled section remains intact, the corrosion effect can be negligible, and if the controlled section is corroded, the ultimate strength can decrease by 28 %. A controlled section-based method was proposed to predict the ultimate strength, demonstrating reasonable accuracy.

Through a series of tests and numerical analyses, this study examines the axial compression behaviour of stub cold-formed steel (CFS) lipped channels subjected to simulated local web corrosion. In the tests, the random nature of local corrosion is simplified as a circumscribed rectangular defect with a constant corrosion depth. Corrosion degradation alters the load transfer path, causing stress concentration in the plate and promoting the early onset of local buckling, thereby reducing the ultimate resistance. As corrosion spreads increase, the ultimate resistance decreases significantly. A numerical study was conducted to assess the randomness of corrosion spread and location for subsequent parametric analysis. Finally, an equivalent thickness was introduced to account for the impact of local corrosion on the local buckling stress. The modified calculation method, validated by both experimental and numerical results, provides a practical, adaptable tool for predicting the ultimate resistance of stub CFS-lipped channels with simulated local web corrosion. This approach offers engineering implications by enabling corrosion-aware design and assessment of CFS members under service-degradation conditions.

To address the issues of local buckling of the steel tube and insufficient confinement of the core concrete in T-shaped concrete-filled steel tubular (CFST) stub under axial compression, a new stiffening form using angle steel stiffeners was proposed. The stiffeners transform the confinement mechanism in the reentrant corner region from an ineffective passive state to a more effective rigid stiffening system, thereby improving the confinement and enabling reliable prediction of the capacity gain. Axial compression tests were conducted on 16 T-shaped CFST stub, and ABAQUS finite element models were validated and used for parametric analysis. Furthermore, a capacity calculation method incorporating the angle steel stiffeners’ contribution was proposed based on Mander's confined concrete theory. Test results show that setting angle steel stiffeners effectively restricts local buckling in the reentrant corners, enhances the confinement, and changes the concrete failure mode from shear failure to localized crushing. After stiffening, the bearing capacity of the specimens increased by up to 18.3%, and the ductility by up to 19.9%. The finite element parametric analysis showed that smaller angle steel spacing, higher steel strength, higher concrete strength, and thicker tubes improve performance, while angle steel and vertical rib size, and vertical rib angle have a limited effect. In addition, the calculation formula proposed in this study agrees well with test and finite element results. Considering both economy and mechanical performance, it is recommended to prioritize the combined stiffening form of angle steel and vertical rib, with an angle steel spacing not exceeding 200 mm in practical engineering.

Buckling-restrained steel plate shear walls (BRSPSWs) are effective lateral force-resisting systems in which the infilled steel plate is restrained against out-of-plane buckling, allowing it to yield in shear and dissipate energy stably. However, clearances between the steel plate and the restraining panels, resulting from manufacturing and assembly tolerances, adversely affect the seismic performance of the system. This study experimentally and numerically investigates these clearance effects. Cyclic tests were conducted on two 1:3 scale BRSPSW specimens with and without enlarged steel plate-restraining panel clearances. Furthermore, finite element (FE) models incorporating both flat and curved constraint surfaces were developed to evaluate clearance effects. Experimental results revealed that enlarged clearances led to pinched hysteretic curves, reducing the cumulative energy dissipation per cycle by approximately 20 % and causing a significant drop in the constraining force of the restraining panels after a 1.4 % story drift, indicating buckling restraint deterioration. FE analyses revealed that convex constraint surfaces promote higher-order buckling and superior hysteretic performance compared to concave or flat surfaces. Based on these findings, a reduction factor for predicting ultimate shear resistance and an iterative coupled design method for bolt tension, both accounting for clearance effects, were proposed. This research provides practical design methodologies for optimizing the BRSPSWs, enhancing seismic reliability by incorporating clearance effects.

Cruciform concrete-filled steel tube stiffened by steel angles (CCFST-SA) is an innovative special-shaped column that strongly connects steel plates, avoiding local buckling at inner corners. This configuration provides better confinement to core concrete, significantly enhancing ductility and compressive strength. Moreover, its fabrication and installation are convenient for assembling cruciform sections, making it suitable for use as a central column in multi-story buildings. In this study, twelve CCFST-SA and two conventional columns were tested under axial compression, considering key factors such as the vertical spacing, arrangement, and cross-sectional size of the steel angles, as well as the column's length-to-depth ratio. The stub specimens failed in shear mode, while the medium and long specimens failed in flexure mode. The experimental results indicated that increasing the spacing or reducing the size of steel angles decreased compressive strength; however, variations in their arrangement pattern (i.e., double-long, double-short, and long-short configurations) had little to no effect, and a higher length-to-depth ratio led to lower compressive strength. Meanwhile, a finite element model was developed which effectively simulated the axial mechanism of the CCFST-SA columns. Furthermore, a parametric analysis was performed to describe the effect of different parameters, including the width-to-thickness ratio of the steel tube, material strength, spacing, thickness, and yield strength of the steel angles, and the slenderness ratio, on the axial behaviour. Based on design codes, existing formulas tend to underestimate compressive strength and overestimate the stability coefficient. Therefore, simplified formulas have been developed to efficiently predict compressive and stability capacities of CCFST-SA columns.

The aluminium tube-concrete composite columns with concrete infill (including concrete-filled aluminium tube (CFAT) and aluminium tube-confined concrete (ATCC) columns) exhibit significant potential for enhancing structural durability under harsh environmental conditions owing to the excellent corrosion resistance of aluminium alloys. To promote the application of these structures, accurate prediction of their compressive strength is essential. In this study, dedicated databases for the compressive strength of circular CFAT and ATCC stub columns were compiled from existing literature. The CFAT database contains 274 data points, while the ATCC database contains 192 data points. Subsequently, the existing formulas for the compressive strength of the two column types, which are typically based on limited parameter ranges, were reviewed. For CFAT stub columns, a theoretical prediction formula was developed based on the limit equilibrium theory, incorporating a new formula for concrete under triaxial compression; additionally, a regression-based formula was proposed. For ATCC stub columns, a regression-based formula was also proposed. By using the databases with broader parameter coverage, both the existing and newly proposed formulas were evaluated. The proposed theoretical formula demonstrated better accuracy than the existing theoretical ones. Moreover, the proposed regression-based formula for CFAT stub columns achieved the highest prediction accuracy within the database, with a mean prediction error of only 0.4% and a coefficient of variation (COV) of 7.3%. The proposed formula for ATCC stub columns also showed excellent accuracy, with a mean prediction error of −0.1% and a COV of 3.9%. These findings offer valuable guidance for the design and application of CFAT and ATCC stub columns.

In order to investigate the axial compression behavior of four-limb concrete-filled steel tubular latticed columns, experimental and numerical studies were conducted. The varied experimental parameters including height-towidth ratio, lacing member dimensions, and cross-sectional size. The experimental results indicated that all specimens exhibited yielding of limb steel tubes and crushing of concrete cores, while lacing steel tubes remained elastic at the peak load. Significant global bending was observed in the slender column, and the slender column showed a notable reduction in stiffness and a 5% decrease in ultimate load compared to the stub column with identical cross-section. Finite element models were developed and validated against experimental results. A parametric analysis was then conducted to expand the database and quantify the influence of key parameters included height-to-width ratio, steel ratio, material strength of limb, confinement coefficient, and cross-sectional sizes of lacing steel tubes on axial compressive strength and phi-H/h curve, which shows the relationship between stability coefficient (phi) and height-to-width ratio (H/h). The accuracy of existing methods in current design codes for determining the ultimate strength for such members was evaluated. Based on this assessment, an optimized formula for calculating the equivalent slenderness ratio and stability coefficient was proposed.

This paper investigated the hysteretic behavior of circular concrete-filled steel tubes (CFSTs) with local defects. Local defects on the steel tubes simulate localized corrosion encountered in engineering practice. Eight CFST specimens were tested under constant axial load and lateral cyclic load, including six specimens with defects and two intact specimens for comparison. The experimental study investigated the impact of local defects on the failure modes, hysteretic curves, skeleton curves, ductility, and energy dissipation capacity of CFSTs. The experimental results demonstrate that the local defects significantly degrade the hysteretic performance of CFSTs. Compared to intact specimens, CFSTs with defects exhibited reductions in initial stiffness by 6.9%, lateral ultimate strength by 16.5%, and ductility index by 29.8%. Furthermore, the defects induced asymmetry in the hysteretic curves and altered the failure modes. The degree of degradation in the lateral ultimate strength varied with the axial load ratio. At the axial load ratios of 0.35 and 0.5, specimens with defects failed by local buckling, with more pronounced reductions in lateral ultimate strength and ductility in the push loading direction. Finally, a calculation model is proposed to quantify the influence of the defect dimensions and axial load ratio on the degradation and asymmetry of the lateral ultimate strength in different loading directions.

Compared with widely studied steel tube-confined concrete (STCC) columns, aluminium alloy tube-confined concrete (ATCC) columns offer superior corrosion resistance. However, due to the lower elastic modulus of aluminium alloy, the structural behaviour and compressive strength of ATCC columns may differ considerably from those of STCC columns. To date, research on ATCC columns remains limited. This study aims to develop a predictive formula for the compressive strength of ATCC stub columns. Twelve ATCC stub columns were tested under axial compression. Their failure modes, axial load-deformation curves, and strain responses were analyzed. A validated finite element model was then established to investigate key factors influencing compressive strength. Test results show that ATCC stub columns exhibit excellent ductility. Compared with unconfined concrete, the confinement provided by the aluminium alloy tube significantly enhances compressive strength. For example, at confinement factors of 0.58 and 4.14, the compressive strength reaches 1.5 times and 6.61 times the unconfined concrete strength, respectively. Parametric analysis indicates that the diameter-to-thickness ratio, as well as the strengths of aluminium alloy and concrete, markedly affects compressive strength. A comparative analysis indicates that most existing formulas are inaccurate for predicting the compressive strength of ATCC stub columns, regardless of whether they were originally developed for STCC stub columns or previously proposed for ATCC stub columns. Finally, two formulas are recommended for predicting the compressive strength of ATCC stub columns, based on a broader parameter distribution. One is an existing formula originally developed for STCC stub columns, and the other is a new formula proposed.

Curved steel-plate composite (SC) walls have been increasingly adopted in nuclear engineering owing to their superior seismic performance and suitability for modular construction. In this study, the out-of-plane flexural behavior of curved SC walls under cyclic lateral loading was experimentally investigated through tests on five curved specimens and two flat specimens, considering the influence of the curvature radius-to-wall thickness ratio (R/T) and the connector spacing-to-steel plate thickness ratio (b/t). The experimental results demonstrate that the curvature effects become significant when R/T < 20. Compared with flat SC walls, curved SC walls exhibit an increase of approximately 4%-8% in out-of-plane flexural capacity. Owing to geometric asymmetry, curved SC walls also exhibit different flexural capacities under opposite loading directions of up to 7%-10%. A finite element model is developed and calibrated against the test results, and the subsequent parametric analyses indicate a coupled influence of R/T and b/t: SC walls with smaller R/T are less sensitive to variations in b/t. Based on theoretical derivations, a calculation method is proposed for predicting the out-of-plane flexural capacity of curved SC walls, explicitly accounting for both curvature effects and steel plate buckling.

L-shaped multi-partition steel-concrete shear walls are commonly used at building corners; however, their seismic behavior under weak-axis loading, especially the torsional response, remains insufficiently understood. In this study, four full-scale specimens were tested under cyclic loading along the weak axis, with the load application not passing through the shear center, resulting in combined bending-torsion responses. The test program was designed to examine the effects of key parameters, including axial compression ratio, section height-to-breadth ratio, and torsion-to-bending ratio. The results indicate that all specimens exhibited flexuredominated failure, accompanied by pronounced energy dissipation behavior. An increase in axial compression ratio enhanced energy dissipation but led to reduced ductility. Increasing the web length significantly improved initial stiffness and lateral load capacity, while effectively limiting out-of-plane displacement. Under the resulting bending-torsion coupling, the specimens demonstrated considerable torsional stiffness, and the maximum torsional angle remained below 0.6 degrees at failure. A full-section plastic stress distribution model was developed to evaluate the lateral resistance of L-shaped multi-partition steel-concrete shear walls. The model explicitly accounts for the combined contribution of both wall limbs, thereby providing a rational basis for design-oriented resistance assessment.

The combination of T-shaped concrete-filled steel tubular (CFST) columns and U-shaped steel-concrete composite beams is widely acknowledged for its superior mechanical properties, efficient prefabricated construction, and optimized building space utilization, presenting broad application prospects in prefabricated structural systems. As the critical load-transferring components and potential seismic vulnerable links of such structures, the beam-column joints between these two members deserve in-depth systematic research. This study innovatively proposes two types of prefabricated corbel connection joints with a fully bolted configuration and a bolt-welded hybrid configuration, respectively. Full-scale quasi-static seismic tests and finite element (FE) simulations were carried out on both joint types, and a theoretical calculation formula for the bearing capacity of the joints was developed. The results indicate that both proposed joints exhibit higher ductility coefficients than conventional reinforced concrete joints, with their positive bearing capacity exceeding the negative counterpart. The fully bolted joint shows superior ductility over the bolt-welded hybrid joint, albeit with a notable reduction in bearing capacity. A plastic hinge forms at the beam end for the fully bolted joint, which maintains favorable deformation capacity after the peak load; by contrast, the bolt-welded hybrid joint develops a plastic hinge at the corbel base, with failure accompanied by tearing along the column wall. The bearing capacity calculation formulas can accurately predict the mechanical performance of the proposed joints.

This paper presents experimental and numerical investigations on eccentric compression behavior of four-limb concrete-filled steel tubular latticed columns. Eccentric compression tests were conducted on stub and slender latticed columns with varying eccentricities. The failure modes, load-shortening curves, and ultimate loads of the specimens were obtained through the tests. The experimental results indicate that the steel tubes of the column limbs yielded and the core concrete was crushed at the peak load. As expected, the ultimate load decreased as the eccentricity increased both in stub and slender specimens, with a more significant reduction observed in slender specimens. Subsequently, finite element analysis was carried out. The finite element models were established and validated based on the experimental specimens, followed by a parametric analysis to investigate the influence of slenderness ratio of the member, steel ratio, material strengths, and confinement coefficient of the limb, and cross-sectional area of lacing tubes on N-M curves of the four-limb concrete-filled steel tubular latticed columns. The design methods provided in the current design code for calculating the eccentric compression strength were evaluated based on a data pool from this research and existing experimental research. In order to improve the accuracy for determining the ultimate strength of the four-limb concrete-filled steel tubular latticed columns under combined compression-bending loads, a method was proposed and validated by the established database, with an average error of 3.8%.

The special-shaped concrete filled steel tube (SCFST) column has been widely applied due to its high load capacity, large bending stiffness and excellent architectural effect. However, the researches on the embedded special-shaped CFST column base (SCFST-CB) are quite inadequate, and the shape and initiation position of the shear failure surface of the SCFST-CB are still questionable. To fulfill the gap and obtain the shear principle of the SCFST-CB, five embedded SCFST-CBs were tested with the parameters of the installing of headed studs, the cross-section shapes and the dimension of CFST column. It was shown that installing headed studs would move up the initiation point of the shear failure surface and thereby increase the punching shear capacity and initial stiffness of the embedded SCFST-CBs. The cross-sectional shape of the SCFST column would affect the shape of the shear failure pyramid, while had negligible effect on the shear capacity and initial stiffness of the SCFST-CBs. Increasing the column dimension could significantly increase the punching shear capacity of the SCFST-CB. Bonding and headed studs could help transfer the axial load and the top row of headed studs took a much greater shear force than the bottom rows of headed studs. Neglecting the contributions of bonding and headed studs would make the calculation of the shear resistance by the current specifications too conservative. Finally, a modified method for calculating the punching shear capacity was proposed, taking into account the influence of the bond and headed studs. The predicted results fitted well with the experimental results.

Partially buckling restrained steel plate shear walls (PBRSPSWs) combine effective seismic performance with simplified construction processes. However, their superior mechanical properties depend on the anchoring effect of the existing frame, which leads to inflexibility in the design and application. This paper introduces a partially buckling restrained steel plate shear wall with an intermediate column (PBRSPSW-IC), which offers the advantage of a flexible span. Quasi-static tests on three specimens with different spans were conducted to evaluate their hysteretic behavior and the interaction between the steel plate and boundary elements. All specimens exhibited stable energy dissipation capacity, with equivalent damping ratios ranging from 0.24 to 0.26 at a 2 % inter-story drift angle. Compared to specimens without intermediate columns, the PBRSPSW-IC specimens induced similar additional bending moments in the boundary columns but increased the bending moment in the beam by approximately 10 %-15 %. Finite element analysis and parametric studies revealed that both the subpanel width-to-thickness ratio lambda s and the moment of inertia of the intermediate column significantly affect the load-bearing mechanism. Based on theoretical analysis and numerical simulation results, a shear capacity calculation method for PBRSPSW-IC is proposed, which achieves less than 5 % error compared with test and finite element results. The force patterns of the intermediate column under different conditions are also presented and design recommendations are provided.

Concrete-filled steel tubes (CFSTs) are extensively used in modern construction. Large-scale square CFST columns typically incorporate cross stiffening per construction specifications, yet its structural contribution is not accounted for in current design codes. Cross stiffening improves steel tube boundary conditions, enabling relaxed width-to-thickness ratio limits and reduced steel consumption. It also restrains concrete expansion through tensile resistance, thereby enhancing axial compression performance. Meanwhile, the effect of stiffening discontinuities on column performance remains uninvestigated. This paper examined these gaps through experimental testing of 12 large-scale square CFSTs. Based on experimental results, corresponding finite element models were established and validated. The failure modes, load-longitudinal strain curves, key indicators, and strain/stress distributions were systematically investigated. Research demonstrates that cross-stiffened square CFSTs can accommodate width-to-thickness ratios twice the current code limits when employing stiffening thickness of 0.75 times the tube thickness. For Q355 steel, this approach reduces steel consumption by approximately 29%. Experimental and numerical results indicate that a discontinuity distance of 1/8B (where B is the section width) has negligible influence on the axial compressive behavior of square CFST columns with cross-stiffening. A calculation method for determining the axial bearing capacity of square CFSTs with cross stiffening was proposed based on the Mander confined concrete model, showing good agreement with experimental (within +/- 5%) and numerical results (within +/- 10%).

Concrete-filled aluminum alloy tube (CFAT) is an innovative composite member that offers excellent ductility, high bearing capacity, strong corrosion resistance, and lightweight characteristics. However, research on the eccentric compression performance of CFAT columns is still limited. This study focuses on testing nine circular CFAT columns under eccentric compression. The test parameters included slenderness ratio (12, 32, and 56) and eccentricity-to-radius ratio (0.33, 0.67, and 1), both of which led to a reduction in ultimate strength as their values increased. All specimens exhibited overall bending as failure mode. A finite element model was developed to predict the ultimate strength of composite columns, demonstrating good agreement with the test results. The parametric analysis was conducted to evaluate the influence of aluminum alloy grade, concrete strength, tube thickness, and slenderness ratio on the axial load-bending moment responses. The existing design codes of concrete-filled steel tubes (CFSTs) were applied to calculate the ultimate strength of circular CFAT columns. Among them, CECS provided reasonably accurate predictions, while EC4 showed the best agreement with the test results.

Although special-shaped concrete-filled steel tubular (SCFST) columns have gained significant attention for their superior mechanical properties and architectural versatility, research on embedded SCFST column base remains limited. The load-transfer mechanisms and failure modes of embedded SCFST column base under combined vertical and lateral loads are not yet fully understood. To address this knowledge gap, this study experimentally investigated four embedded special-shaped SCFST column bases under combined constant axial load and monotonic lateral loading, examining the effects of embedment ratio and cross-sectional geometry of SCFST columns on monotonic flexural performance. It is indicated that increasing the embedment ratio enhances monotonic flexural capacity and stiffness of the column base. Additionally, it was observed that the failure mode shifted from foundation punching shear to column buckling at an embedment ratio between 0.7 and 1.0 for the T-section. Cross-sectional geometry significantly influences tension-side punching cone configuration and compression zone extent, with T-shaped specimen exhibiting the highest flexural capacity and initial stiffness, while cross-shaped specimen demonstrated the lowest. The experimental study was simulated and validated using ABAQUS, followed by a parametric analysis focusing on the embedment ratio, axial compression ratio, foundation concrete strength, and base plate overhang, with special emphasis on the shear behavior of the studs. Evaluation of current design codes reveals conservative predictions due to neglecting frictional resistance, stud contributions, and base plate effects. Current research on flexural capacity predictions for embedded SCFST column bases remains conservative even when accounting for base plate contributions. Consequently, an improved calculation methodology incorporating compressive bearing, interfacial friction, stud resistance, and base plate action is proposed. The method demonstrates close agreement with experimental and FEA results. This research establishes a theoretical foundation for designing embedded SCFST column bases and informs future investigations.

This study proposes a square concrete-filled steel tubular (CFST) column base with lapped longitudinal reinforcements, and focuses on the investigation of its seismic performance experimentally and analytically. A quasi-static test on five reinforcement-lapped square CFST column bases is first conducted to evaluate the seismic performance, considering the key parameters of reinforcement ratio, lap length of lapped reinforcements, and configuration of the perfobond rib (PBL). The test results of failure modes, bearing capacity, ductility, energy dissipation capacity, and stress distribution, indicating that the proposed column base exhibits good seismic performance. The bearing capacity, ductility, and energy dissipation capacity are comparable to traditional embedded CFST column bases. To further investigate the force transfer path and stress distribution characteristics of the column bases, the software ABAQUS is used to establish a finite element model. Additionally, a calculation method for determining the combined compression-bending capacity is proposed. Validated against the experimental results, the proposed calculation method accurately predicts the bearing capacity of reinforcement-lapped square CFST column bases, making it suitable for practical applications.