Search Results (259)

Variations in damper configuration strategies have a direct impact on the seismic damage patterns of long-span deck-type concrete-filled steel tube (CFST) arch bridges. This study developed an analysis and evaluation framework to identify the damage category, state, and progression sequence of structural components. The framework aims to investigate the influence of viscous dampers on the seismic response and damage patterns of long-span deck-type CFST arch bridges under near-fault pulse-like ground motions. The effects of different viscous damper configuration strategies and design parameters on seismic responses of long-span deck-type CFST arch bridges were systematically investigated, and the preferred configuration and parameter set were identified. The influence of preferred viscous damper configurations on seismic damage patterns of long-span deck-type CFST arch bridges was systematically analyzed through the established analysis and evaluation frameworks. The results indicate that a relatively optimal reduction in bridge response can be achieved when viscous dampers are simultaneously installed at both the abutments and the approach piers. Minimum seismic responses were attained at a damping exponent α = 0.2 and damping coefficient C = 6000 kN/(m/s), demonstrating stability in mitigating vibration effects on arch rings and bearings. In the absence of damper implementation, the lower chord arch foot section is most likely to experience in-plane bending failure. The piers, influenced by the coupling effect between the spandrel construction and the main arch ring, are more susceptible to damage as their height decreases. Additionally, the end bearings are more prone to failure compared to the central-span bearings. Implementation of the preferred damper configuration strategy maintains essentially consistent sequences in seismic-induced damage patterns of the bridge, but the peak ground motion intensity causing damage to the main arch and spandrel structure is significantly increased. This strategy enhances the damage-initiation peak ground acceleration (PGA) for critical sections of the main arch, while concurrently reducing transverse and longitudinal bending moments in pier column sections. The proposed integrated analysis and evaluation framework has been validated for its applicability in capturing the seismic damage patterns of long-span deck-type CFST arch bridges. Full article

To reduce the carbon footprint of the concrete industry and promote a circular economy, this study explores the reuse of waste materials such as glass powder (GP) and nitrile rubber (NR) fibres in concrete. However, the inclusion of these waste materials results in lower compressive strength compared to conventional concrete, limiting their application to non-structural elements. To overcome this limitation, this study adopts the concept of confined concrete by developing concrete-filled steel tube (CFST) stub columns. In total, twelve concrete mix variations were developed, with and without steel tube confinement. GP was utilised at replacement levels of 10–30% by weight of cement, while NR fibres were introduced at 0.5% and 1% by volume of concrete. The findings demonstrate that the incorporation of GP and NR fibres leads to a reduction in compressive strength, with a compounded effect observed when both materials are combined. Steel confinement within CFST columns effectively mitigated the strength reductions, restoring up to 17% of the lost capacity and significantly improving ductility and energy absorption capacity. All CFST columns exhibited consistent local outward buckling failure mode, irrespective of the concrete mix variations. A comparison with predictions from existing design codes and empirical models revealed discrepancies, underscoring the need for refined design approaches for CFST columns incorporating sustainable concrete infill. This study contributes valuable insights into the development of eco-friendly, high-performance structural systems, highlighting the potential of CFST technology in facilitating the adoption of waste materials in the construction sector. Full article

To enhance the environmental sustainability and structural performance of concrete-filled steel tubes (CFSTs), this study experimentally investigates the eccentric compression behavior of short CFST columns incorporating alkali-activated concrete (AAC) and internal stiffeners. Fifteen specimens were tested, varying in steel tube thickness, stiffener thickness, and eccentricity. The results show that increasing eccentricity reduces load-bearing capacity and stiffness, while stiffeners delay local buckling and improve stability. Based on the experimental findings, the applicability of the GB 50936-2014, Design of Steel and Composite Structures Specification, and the American AISC-LRFD specification to the design of ACFST columns is further evaluated. Corresponding design recommendations are proposed, and a regression-based predictive model for eccentric bearing capacity is developed, showing good agreement with the test results, with prediction errors within 10%.providing technical references for the development of low-carbon, high-performance CFST members. Full article

Recycled concrete is widely recognized as favorable for environmental protection and sustainable development. However, recycled concrete, especially containing abandoned brick aggregate, is rarely used in main structural members due to its inherent defects. Concrete-filled double steel tube columns (CFDSTCs), consisting of an outer and an inner steel tube with concrete filling the entire section, are effective in load bearing and deformation resistance. The structural application of abandoned brick aggregate, resulting from urbanization renewal, might be widened through CFDSTCs. This paper presents an experimental and analytical study aiming to investigate the axial compressive behavior of recycled-brick-aggregate-concrete-filled double steel tube columns (RBCDSTs). A total of six specimens were tested under concentric compression, including five RBCDSTs and one concrete-filled single steel tube column. The varied parameters included the replacement ratios (0% and 25%) of brick aggregate and the thickness ratio of the inner and outer steel tubes (0.75, 1, and 1.25). Theoretical analysis was also carried out. A new constitutive model of RBCDST was proposed and used in finite element analysis. The investigation indicated that, under the current conditions, the presence of the inner steel tube only increased the strength by 0.14%. When the inner and outer diameter ratio is 0.73, using a 25% replacement rate of bricks in the entire cross-section or only in the ring area of the cross-section will result in 21.1% and 10.1% strength decreases, respectively. For every 0.6% increase in the diameter-to-thickness ratio of the outer tube, the strength of RBCDST increases 16.3% on average. Full article

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. Full article

A novel endplate bolted rigid joint is proposed in this study for connecting circular concrete-filled steel tube (CCFT) columns to wide-flange (WF) steel beams. The seismic performance and potential failure mechanisms of the proposed joint were investigated through quasi-static cyclic tests and finite element (FE) simulations. This study aims to address several engineering challenges commonly observed in existing joint configurations, including an irrational force-resisting mechanism, complicated detailing and installation, on-site construction difficulties, constraints on beam size, and limited repairability. By optimizing the force transfer path, the new joint effectively reduces the number of critical tension welds, thereby enhancing the ductility and reliability. The experimental results indicate that the joint exhibits adequate flexural strength, stiffness, and ductility, with stable moment–rotation hysteresis loops under cyclic loading. Moreover, full restoration of the joint can be achieved by replacing only the steel beam and endplate, facilitating post-earthquake repair. FE analysis reveals that, under the ultimate bending moment at the beam end, multiple through cracks develop in the high-strength grout—which serves as a key load-transferring component—and significant debonding occurs between the grout and the surrounding steel members. However, due to confinement from adjacent components, these internal cracks do not compromise the overall strength and stiffness of the joint. This research provides an efficient and practical connection solution, along with valuable experimental insights, for the application of CCFT columns in moment-resisting frames located in high seismic zones. Full article

Based on the research on concrete-filled circular steel tubular columns, the influence of carbon-fiber-reinforced polymers (CFRPs) on the ultimate bearing capacity of concrete-filled steel tubes (CFSTs) was further explored in this paper. Ten different concrete-filled circular CFRP–steel middle long columns were made for an axial compression test, and the influence of the CFRP layers, the concrete strength grades, the steel tube wall thickness, and the slenderness ratio on the ultimate bearing capacity was discussed. Combined with theoretical analysis, the calculation method of ultimate bearing capacity of it was found. The load midspan deflection diagram was obtained by numerical simulation with finite element analysis software ANSYS2021R1, and the test results were compared. The results demonstrate that CFRP layers significantly enhance the ultimate bearing capacity of circular steel tube–CFRP confined concrete columns, with one to three layers increasing the capacity by 42.5%, 69.4%, and 88.4%, respectively, under identical conditions. In comparison, the concrete strength, the steel tube thickness, and the slenderness ratio showed lesser effects (<20% improvement), providing critical support for engineering applications of CFRP-confined circular steel tubular columns. Moreover, the error of ANSYS calculation results is small, which is in line with the test. This is of great significance to verify the correctness of the test of concrete-filled circular CFRP–steel middle long columns. Full article

Concrete-filled steel columns are increasingly recognised for their enhanced structural performance. This study investigates an innovative shear connector design with screw connectors as an alternative to conventional connection types. From push-out testing, the shear capacity of screw connectors in composite columns comprising cold-formed steel sigma sections and concrete infill was evaluated. Experimental push-out testing demonstrated the effectiveness of theoretical equations in estimating the shear strength of screw connections. The comparison indicates that established design methods provide reasonable predictions, supporting their applicability in practical scenarios. Theoretical equations in the literature for estimating shear strength were tested for suitability and gave comparable results. Disassembling of tested specimens showed that a concrete failure was the prominent mode of ultimate condition. Shear screws offer a novel design alternative to conventional shear connection methods. They demonstrate significant potential for structural applications when integrated with advanced composite column sections, such as the four-sigma built-up CFS sections. The study highlights screw connectors as a cost-effective, sustainable, and practical solution for innovative composite column designs, offering significant potential for construction and maintenance efficiency. Full article

The eccentrically braced frame (EBF) is a typical structural system used in high-rise buildings. Current related design methods focus on the concrete and steel structures rather than on the complex composite structure. In addition, they tend to overlook the contribution of the energy-dissipation unit and its corresponding additional influence on the structure. In this study, a precast composite EBF structure is selected as a case study, including the partially steel-reinforced concrete (PSRC) beam and the concrete-filled steel tubular (CFST) column. A modified energy-based design method is proposed to leverage the excellent seismic performance of the precast composite EBF structure. The multi-stage energy-dissipation mechanism and the additional influence of the eccentric braces are systematically considered through the energy distribution coefficient and the layout of dampers. A case study of a 12-floor, three-bay precast composite EBF structure is conducted using a series of nonlinear time-history analyses. Critical seismic responses, including the maximum inter-story drift ratio, residual inter-story drift ratio, and peak acceleration, are systematically analyzed to evaluate the effectiveness of the proposed design theory. The distribution coefficient is recommended to range from 0.70 to 0.80 to balance the energy-dissipation contribution between the frame and the eccentric braces. In terms of the damper layout, the energy-dissipation contribution of the eccentric brace should differ among the lower, middle, and upper floors. Full article

The application of recycled concrete in building structures can not only effectively reduce the generation of construction waste and reduce the excessive dependence on natural aggregates but can also promote the sustainable use of resources and meet the national “double carbon” strategic requirements. This study investigates the effect of the recycled aggregate replacement ratio on the seismic performance of concrete-filled steel tube column–composite beam frames. Five finite element models were developed, considering varying recycled aggregate replacement ratios and the presence or absence of column-end stirrup-confined reinforcement. Dynamic response analyses were conducted. The results reveal that replacing natural aggregates with recycled aggregates reduces the stiffness of concrete-filled steel tube columns by weakening the core concrete, negatively impacting seismic performance and increasing structural stiffness damage. Column-end stirrup-confined reinforcement reduces interface slip between the core concrete and the steel tube by directly restraining the core concrete, thereby enhancing the bending stiffness of the concrete-filled steel tube column and improving the seismic performance of the structure. The seismic performance of recycled concrete frames with column-end stirrup-confined reinforcement is superior to that of conventional concrete frames, demonstrating that column-end reinforcement can effectively mitigate the adverse effects of recycled aggregate replacement on the structure’s seismic performance. Full article

This paper presents a numerical simulation and theoretical analysis of the eccentric compressive performance of a novel composite concrete-filled steel tube (CFST) latticed column with corrugated steel plates for industrial buildings. The influence of multiple parameters was systematically examined, encompassing the eccentricity ratio, material strengths (steel tube and concrete), corrugated steel plate waveform, and steel lacing tube strength. The results show that eccentric loading causes typical bending failure, with corrugated steel plates providing significant restraining effects, and diagonal lacing tubes optimizing load distribution and bending resistance. Increased eccentricity reduces the load capacity by up to 41.8% but improves the ductility by 50.6%, with benefits ceasing beyond 350 mm of eccentricity. A higher steel strength enhances the load capacity (28.6%) and ductility (14.5%), while a higher concrete strength improves the capacity but reduces the ductility. Longer waveforms in corrugated steel plates improve the stress redistribution, enhancing both capacity (19.1%) and ductility (9.7%). The eccentric compression modification formulas proposed in this study for the latticed column show a reliable calculation accuracy within 11% of simulations. Full article

Machine learning methods are widely used to predict the bearing capacity of concrete-filled steel tubular (CFST) columns. However, in addition to this task, the engineer often faces the inverse problem: to determine what cross-section dimensions of the CFST column are required for given loads. This paper is devoted to the development of machine learning models for predicting the geometric parameters of a circular cross-section for concrete-filled steel tubular (CFST) columns under the combined action of bending moments and compressive axial forces. This problem has not been solved by machine learning methods before. The main focus is on automating the design process of CFST columns using the CatBoost algorithm and artificial neural networks. Three machine learning models were developed to solve the problem. The first and second models are based on the CatBoost algorithm. They predict the column diameter at minimum and maximum wall thicknesses, respectively. The third model is an artificial neural network, which is designed to determine the wall thickness of a CFST column. The models were trained on synthetic data generated in accordance with Russian design codes. The first and second models demonstrated high accuracy in predicting the column diameter (RMSE = 3.86 mm and 4.12 mm, respectively). The third model showed high efficiency over the entire range of wall thicknesses (correlation coefficient R = 0.99974). Feature importance analysis using SHAP values confirmed the key role of bending moment and axial force in predicting geometric parameters. Full article

Concrete-filled steel tube (CFST) columns reinforced with latticed steel angles (LSA), referred to as CFST-LSA columns, have been widely adopted in practical engineering. Understanding their mechanical behavior under eccentric loading is crucial for ensuring structural safety and performance in engineering applications. Previous experimental studies have demonstrated that the incorporation of steel angles substantially improves both the axial capacity and ductility of CFST-LSA columns. Existing methods for determining the eccentric bearing capacity of CFST-LSA columns primarily rely on the normalized N/N_u-M/M_u interaction curve. However, this approach involves a complex calculation procedure for evaluating the eccentric bearing capacity. To address this limitation, this study proposes a theoretical model based on the limit equilibrium method to predict the eccentric bearing capacity of CFST-LSA columns. The proposed model explicitly integrates fundamental geometric and material parameters, thereby enabling a more efficient and programmable calculation of the eccentric bearing capacity. Comparisons between the proposed model and experimental results show good agreement, with a tested-to-predicted eccentric resistance ratio of 1.085 and a coefficient of variation (COV) of 0.022. The proposed model can serve as a practical calculation method for eccentric loading of CFST-LSA columns, facilitating their application in high-rise buildings and long-span bridges. Full article

Additional steel supporting joists (ASSJs) can effectively enhance the anti-overturning capacity of the existing solo-column concrete pier (SCP) bridges. Although the interface consists of bolt connections between steel and concrete is the crucial load-transmitting portion, the design of the interface between the ASSJ and SCP still mainly relies on practical experiences. In an actual bridge rehabilitation project with ASSJs in China, a novel connection comprising large-diameter bolts and an epoxy resin layer was adopted to overcome the shortcomings of the initial design. In this study, connections composited with large-diameter bolts and different interfacial treatments were investigated. Four push-out tests on the interfacial shear performance of steel–concrete connections were carried out. The experimental parameters encompassed the interface treatment method (barely roughened surface, smearing epoxy resin, and filling epoxy mortar) and the number of bolts (single row and double rows). The failure modes were unveiled. According to the experimental results, the interfacial treatment method with filling epoxy mortar could uniformly transfer stress between concrete and steel and improve the shear stiffness and shear resistance of the steel–concrete connections. Compared with specimens with barely roughened interfaces, epoxy mortar and epoxy resin employed at the steel–concrete interface can increase the shear-bearing capacity of connections by approximately 47.71% and 43.46%, respectively. However, the interfacial treatment method with smearing epoxy resin resulted in excessive stiffness of the shear members and brittle failure mode. As the number of the bolts increased from a single row to a double row, the shear-bearing capacity of a single bolt in the specimen exhibited approximately an 8% reduction. In addition, by comparing several theoretical formulae with experimental results, the accurate formula for predicting the shear-bearing capacity of bolts was recommended. Furthermore, the load-bearing capacity of an ASSJ in the actual engineering rehabilitation was verified by the recommended formula GB50017-2017, which was found to accurately predict the shear-bearing capacity of large-diameter bolt connectors with an epoxy mortar layer. Full article

A novel concrete-filled corrugated steel tubular (CFCST) column composed of corner steel bars and corrugated steel plates filled with concrete has been proposed recently. Columns with large height-to-width ratios are commonly used in practice, where they are often subjected to eccentric compression. However, there is a lack of research on their stability behavior under such conditions. This study presented a numerical analysis to evaluate the stability performance of CFCST columns under eccentric compression, with eccentricity ratios ranging from 0 to 2.0 and height-to-width ratios between 10 and 30. The numerical results indicated that the N–M interaction curve became less convex as the height-to-width ratio increased. Concrete strength and column width had a greater impact on the stability performance of the CFCST columns at low eccentricity ratios, while steel strength and steel bar width were more influential at high eccentricity ratios. The comparison between numerical and calculation results specified in AISC 360 and GB 50936 showed that both of them were unsuitable to estimate the stability performance of the column under eccentric compression. Finally, a formula was fitted, and the error was basically within 15%, which offered significantly improved accuracy over current design codes. Full article