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A joint system was proposed to connect square thin‐walled concrete‐filled steel tube (CFST) columns and reinforced concrete (RC) beams. In the system, longitudinal beam reinforcing bars are continuous through the joint zone by passing the rectangular holes in the steel tube, aiming to achieve direct load‐transfer of the beam and joint integrity; and the square thin‐walled steel tube with holes is strengthened by internal diaphragms. Previous cyclic tests showed that the proposed joint system satisfied the requirements of strong‐joint weak‐component, namely the shear capacity of the joint zone was larger than that provided by CFST columns and RC beams. However, further research was necessary to evaluate the behavior under axial compression, as the discontinuous diagonal ribs and holes in the joint steel tube weakened the load capacity. In this investigation, the effect of internal diaphragms was first evaluated based on the axial compression tests on six square CFST stub columns. The test results showed that the internal diaphragms effectively improved the strength and ductility. The finite element analyses (FEA) on square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were then carried out based on the verified FEA models. The analysis results showed that thicker internal diaphragms increased the strength, and changed the failure mode from the column‐center failure to column‐end failure for columns and from the joint failure to column failure for joints, respectively. Finally, the mechanics‐based models and axial strength equations of square CFST columns and RC beam to CFST column joints stiffened by internal diaphragms were proposed, and the predictions agreed well with the test and analysis results. [ABSTRACT FROM AUTHOR]

This paper investigates the static performance of jacket joints to promote the application of CFST jacket foundations for offshore wind power. An experimental and numerical study of the influence of loading patterns, concrete filling in the chord, geometric parameters, and material strength is examined. In total, five 1:6 scale tests and twenty-eight FEAs are described. The novelty is that a limit device is introduced to consider the interaction among the braces by connecting four braces. The experimental results indicate that, compared to symmetrical loading joints, the bearing capacity of CHS-KK joints decreased by 14% under anti-symmetric loading. Concrete filling in the chord alters the failure mode, enhancing the ultimate bearing capacity of the KK joint. However, its effect on the punching shear failure strength of the joint is limited. An FEA model incorporating the modified Mohr-Coulomb criterion (MMC) was established to explore the ultimate strength of CFST-KK joints, following validation through experiments. Through parameter analysis, it was found that the punching shear capacity of CFST-KK joints is significantly influenced by the diameter ratio of the brace to chord (β), the chord diameter to thickness ratio (2 γ), the angle between the brace and chord axis (θ), and the chord steel strength. In addition, the recommended formula in GB50017–2017 for CHS-KK joint punching shear capacity conservatively predicted CFST-KK joint performance. • An experimental and numerical study of the impact of loading patterns, concrete filling in the chord, geometric parameters, and material strength is examined. In total, five 1:6 scale tests and twenty-eight FEAs are described. • This experiment introduces, for the first time, a constraint set that considers the interaction among the braces. • An FEA model incorporating the modified Mohr-Coulomb criterion (MMC) was established to explore the ultimate strength of CFST-KK joints, following validation through experiments. • The recommended formula in GB50017‐2017 for CHS-KK joint punching shear capacity was found to conservatively predict CFST-KK joint performance. [ABSTRACT FROM AUTHOR]

A series of fire tests on eight circular tubed steel reinforced concrete (CTSRC) stub columns subjected to axial loading are presented in this paper. The influences of load level and steel tube thickness on the fire resistance of the CTSRC stub columns were investigated. Two similar specimens were tested with the same test scenario to obtain more reasonable data. The temperatures in steel and concrete, axial displacement, fire resistance, and failure mode were recorded and discussed. The test results show that the load level has a great influence on the fire resistance of CTSRC stub columns. The steel tube thickness has a significant influence on the fire resistance of CTSRC stub columns when subjected to a higher load level. Thermal and structural finite element (FE) models were developed to analyze the temperature distributions and fire responses of CTSRC stub columns by employing the program ABAQUS. These developed models were validated by the test data. Extensive parametric studies were carried out by using the FE method to investigate the influences of key factors on the temperature distributions and fire resistances of CTSRC stub columns. The factors considered for thermal analysis include cross-sectional dimension, steel tube thickness, and concrete type, while the factors considered for structural analysis include load ratio, cross-sectional dimension, steel tube thickness, concrete strength, and steel strength. The parametric studies indicate that the cross-sectional dimension has a more significant influence than the steel tube thickness on the temperature magnitudes of CTSRC stub columns. The load ratio, cross-sectional dimension, and steel tube thickness have more significant influence than concrete strength on the fire resistance of CTSRC stub columns. Based on the results of the parametric studies, a simplified method to predict the steel temperatures and the compressive load bearing capacities of CTSRC stub columns exposed to fire is proposed. • Full-scale fire tests on circular tubed steel reinforced concrete (CTSRC) stub columns were presented. • A finite element model was established to predict the fire response of CTSRC stub columns subjected to axial compression. • Parametric studies were carried out to investigate the factors effecting fire behavior of CTSRC stub columns. • Simplified methods to predict the temperatures and load capacities of CTSRC stub columns in fire is proposed. [ABSTRACT FROM AUTHOR]

A stiffened rectangular concrete-filled steel tubular (CFST) member offers improved composite action over the unstiffened counterpart in terms of delaying local buckling of the rectangular steel tube and enhancing confinement to the infilled concrete, and thus various stiffening forms were proposed. Choosing an appropriate stiffener in practical design needs comprehensive understanding and comparison on the efficiency of various stiffeners. However, most studies focused on a single type of stiffener only, no guidance was provided on how to account for the benefits of stiffened rectangular CFST members in mainstream design specifications, and no unified calculation method for load capacity was formed. In this work, finite element models for stiffened rectangular CFST members were established and verified by test results. Then parametric analyses were conducted to compare the axial compressive and flexural behavior of rectangular CFST members with various types of stiffeners. The appropriate arrangement and detailing of stiffeners were proposed, and the diagonal ribs showed the best performance under the same material strength and steel consumption. Finally, mechanics-based models and unified calculation methods were proposed to calculate the axial compression and interaction strength, and were found to well predict the strength of stiffened and unstiffened CFST members. These results will further facilitate the use of stiffened rectangular CFST members in practical engineering projects. • The appropriate arrangement and detailing of stiffeners were proposed. • The comparison on efficiency of different types of stiffeners was carried out, and the diagonal ribs showed the best performance under the same material strength and steel consumption. • Mechanics-based models and unified calculation methods were proposed to calculate the axial compression and interaction strength of stiffened rectangular CFST members. [ABSTRACT FROM AUTHOR]

The steel jacketing approach is effective and economic for retrofitting reinforced concrete short column. Steel jacketed concrete columns are referred as steel tubed-reinforced-concrete columns when applying in new building structures. To investigate the cyclic shear behavior and shear strength of tubed-reinforced-concrete short columns with a large diameter-to-thickness/width-to-thickness ratio (D/t), four specimens were designed and tested under a constant axial compression combined with quasi-static cyclic lateral loading. Three main system parameters were considered in the test: (1) type of column cross section (circular and square), (2) D/t (106–150), and (3) axial load ratio (0.4 and 0.6). All the columns showed shear-failure mode during the tests, and the sheared plates of steel tubes yielded when the peak load had reached. The circular columns showed good ductility, while the square ones were just in opposite. Based on the analysis results, a simplified shear strength model for both circular and square columns is proposed, in which the relationship between cyclic shear strength and lateral drift ratio of the columns and the shear-resisting mechanisms for both shear and hoop stresses of the tube are considered. [ABSTRACT FROM AUTHOR]

Among various proposed stiffening forms, the diagonal binding ribs, made of thin-walled steel plates with circular holes and welded to the steel tube, were found to particularly effective in improve the cyclic-bending and cyclic-shear behavior of square thin-walled concrete-filled steel tubular (CFST) columns. Although the mechanical behavior can be obtained from the experiments, numerical models are still needed to expand the range of investigation beyond what was tested physically and to facilitate the practical design. A 3D model using shell and solid elements is able to explicitly show the influence of different parameters, and simulate the details including the holes in diagonal ribs and the contact interaction between different parts. However, such analyses are relatively complicated, time-consuming, and are susceptible to numerical issues that cause lack of convergence. By contrast, a 2D model using fiber-based beam–column elements is far more efficient thus allowing for a wider range of investigation. In this work, the fiber models of flexure-dominated diagonal ribs stiffened square thin-walled concrete-filled steel tubular (DSCFST) columns were firstly developed in OpenSees and validated based on the effective stress–strain relationships of steel tubes and moment–rotation curves of RC bases. The fiber models of shear-dominated DSCFST columns were further developed by defining the nonlinear shear force–deformation relationships at the section level. These models were verified by the test results, and then the effect of the deformable RC base, tube local buckling, shear effect, and types of beam–column elements was analyzed in detail. Based on extensive parametric analyses, the effective stress–strain relationships applicable to various square thin-walled steel tubes stiffened by diagonal ribs and infilled concrete were derived, and the simplified shear force–deformation relationships were proposed. These results facilitate understanding of the behavior of DSCFST columns and lay a foundation for further system-level analysis. • The deformation of the RC base was simulated by the zero-length element with linear elastic rotational spring. • The effective stress–strain relationships for square steel tubes stiffened by diagonal ribs were derived to capture the effect of local buckling. • The nonlinear shear effect was modeled by force-based beam–column element through defining the shear force–deformation relationships at the section level. [ABSTRACT FROM AUTHOR]

• Square CFST columns up to 1000 mm in width were tested under axial compression. • The difference in strength between the different thicknesses of steel tube used in the tests was only 18 MPa. • The effects of size and width-to-thickness ratio on the steel tube stresses were discussed. • A axial bearing capacity model considering the size effect was proposed for square CFST columns. In this study, eight specimens with the sectional widths (B) of 200–1000 mm and the width-to-steel tube thickness ratios (B / t) of 40 and 50 were tested to failure under axial compression to investigate the size effects of square concrete-filled steel tubular (CFST) short columns, specifically those on the failure mode, composite elastic modulus, peak axial strain, peak axial stress, ductility index, strength index, and stress development. The test results indicate that the peak axial stress, ductility index, and strength index decrease with the increasing specimen size, while the failure mode and composite elastic modulus maintain relatively steady. Under the peak axial load, the longitudinal to yield stress ratio of steel tubes increases with the increasing specimen size, while the trend of transverse to yield stress ratio is opposite. The size effect on the transverse stress in the steel tube reduces the tube confinement effect, thus degrades the compressive strength of the core concrete. Compared to the test results, both the EC4 and the GB50936 codes are unconservative in predicting the strength of large square CFST columns. Therefore, a model considering the ratio of width to thickness (B / t) and specimen size is proposed to evaluate the axial bearing capacity of square CFST short columns. [ABSTRACT FROM AUTHOR]

Abstract: Reinforced concrete (RC) short columns are vulnerable to brittle shear failure during an earthquake. The objective of this research is to evaluate the performance enhancement of RC short columns tubed with circular or square tubes. Eight short columns were tested under combined constant axial load and cyclic lateral load. The tested specimens included three circular tubed RC (CTRC) columns and three square tubed RC (STRC) columns. Two common RC short columns including one circular RC column and one square RC column were also tested as control specimens. The test results indicated that common RC short columns suffered brittle shear failure with little ductility, while the ductility of tubed RC short columns was excellent due to the effective confinement of the outer thin tube to the core concrete. The lateral load strength of CTRC short columns increases with the increasing of axial load ratio, while the axial load ratio has little effect on the plastic deformation capacity of CTRC short columns. The shear strength increases with increasing of axial load ratio, while the plastic deformation capacity decreases with increasing of axial load ratio for STRC short columns. A circular tube prevents the core concrete from shear failure more effectively than a square tube for the tubed RC short columns. A modified ACI design method is adopted to calculate the nominal shear strength of STRC columns as well as CTRC columns based on the test and analysis results. [Copyright &y& Elsevier]

Diagonal binding ribs, made of thin-walled steel plates with circular openings and welded to the steel tube of a square concrete-filled steel tubular (CFST) column, can improve the composite effect effectively by co-carrying axial compressive forces and confining the steel tube and concrete. The column with diagonal ribs is referred to as diagonal ribs stiffened CFST column. This paper summarizes the test results of axially loaded diagonal ribs stiffened and longitudinal ribs stiffened CFST columns comprehensively, followed by further tests of stub columns with longitudinal reinforcing bars. A verified finite element analysis (FEA) model was presented to implement parametric studies. The studied parameters included diagonal rib detailing (i.e., opening diameter, opening spacing, and welding position) and material strengths. Finally, based on the test and analysis results, design considerations, involving width-to-thickness ratio limits of tube plates, diagonal rib detailing, thickness matching relationship between diagonal ribs and the steel tube, detailing of composite column with diagonal ribs, and load-carrying capacity prediction, were proposed. • Diagonal binding ribs significantly improved composite response of CFST columns. • Design considerations for the diagonal ribs stiffened square CFST column were proposed. • Test results about stiffened square CFST columns were summarized and analyzed comprehensively. • A verified finite element analysis model was presented to implement parametric studies. [ABSTRACT FROM AUTHOR]

A novel type of composite bridge bent consisting of slender steel tube confined reinforced concrete (STCRC) double-column connected by binding steel plates is proposed. Its main advantage is the convenient construction process that eliminates the embedment of a steel tube into the concrete foundation. Four STCRC double-column bent specimens were tested under the pseudo-static loading considering the key parameters of the axial load ratio and the disconnection mode of circular steel tube. All test specimens showed the mixed failure mode of column bending and binding steel plate buckling. As the axial load ratio increased from 0.12 to 0.24, the lateral load capacity and flexural stiffness of the specimens were improved. Although the disconnection mode of the steel tube changed the layout of plastic hinges, it had a limited influence on the seismic behavior of STCRC double-column bents. The ultimate limit state of the double-column STCRC bridge bent could be simplified as a frame model with plastic hinges, by which the lateral resistances were well predicted. • STCRC double-column bridge bent is proposed due to the convenient construction process. • Binding steel plates between the pier columns are adopted for energy consumption. • Influences of axial load ratio and disconnection mode of steel tube are discussed. • Lateral resistance model for this novel bridge bent is proposed. [ABSTRACT FROM AUTHOR]

• Dumb-bell steel tube improves the seismic behavior of the RC pier. • A model was proposed to predict DSTCRC bearing capacity. To improve the strength and ductility of short reinforced concrete (RC) piers, dumb-bell steel tube confined reinforced concrete (DSTCRC) piers were proposed and studied, in which the dumb-bell steel tube is disconnected at the foundation and cap beam to avoid the difficulty of inserting steel tubes into RC members. In this paper, five DSTCRC piers and one reference dumb-bell RC pier were tested under pseudo-static loading. The test parameters included shear span-depth ratio (1.25 and 1.75), axial load ratio (0.12 and 0.24), and width of the web (75 mm and 100 mm). Because of the confinement and enhancement effect from the dumb-bell steel tube, failure modes of RC piers changed from shear failure to bending failure, and the strength, ductility, and energy dissipation capacity significantly improved. The seismic performance of DSTCRC piers improved slightly with the increasing axial load ratio and width of the web within the scope of this study. Shear failure of the concrete in the web cavity exhibited in DSTCRC specimens with a shear span-depth ratio of 1.25, but the lateral resistance increased by approximately 90% as the shear span-depth ratio decreased from 1.75 to 1.25 despite slight drops of the ductility ratio and ultimate displacement ratio. A simplified model considering the bending of RC cores and shear of steel webs and concrete web was proposed to predict the lateral resistance of DSTCRC piers, and the predicted results showed a good agreement with the test results. [ABSTRACT FROM AUTHOR]

A partially concrete-filled steel tubular (CFST) member is formed by partially filling concrete into a steel hollow section (SHS). Partially CFST members are mainly used as bridge piers and frame columns due to the improved structural performance, since the potential plastic hinge is expected to occur at the composite section when subjected to an earthquake. In practice, the shear transfer between the upper SHS and the lower CFST part of a partially CFST column needs careful consideration, sometimes leading to complex details. In this study, two types of shear connectors, namely bolted shear connectors and diagonal-rib shear connectors were proposed and arranged below the concrete-filling interface. Five square partially CFST specimens and a reference steel tubular column were designed and tested under combined constant axial compression and cyclic lateral loading. The test variables included the concrete-filling ratio, types of shear connectors, and strength of shear connectors. The results demonstrated the effectiveness of the two types of shear connectors, and the specimens with diagonal-rib shear connectors showed excellent performance. The method and corresponding formulas about the full shear connection were proposed to calculate the resistance of square partially CFST columns under combined compression and flexure. • Two types of shear connectors were proposed and equipped in partially CFST columns. • Five specimens on partially CFST columns and a reference steel tubular column were tested and reported. • Failure modes and cyclic performance were investigated. • The design method of partially CFST columns with full shear connection was proposed. [ABSTRACT FROM AUTHOR]

In this study, a demountable connection that connects the upper and lower concrete-filled steel tubular columns with an inner sleeve section and blind bolts (referred to as Hollo-Bolts in this study) is proposed. The utilization of Hollo-Bolts allows them to be installed outside the steel tubes prior to the concrete casting and renders such connection to be readily dismantled after typical service loading. In order to study the seismic performance of the concrete-filled steel tubular column-column connection, six specimens were designed in the present study. The studied parameters included the axial load ratio, length of the inner sleeve, and location of the connection. The results demonstrated that the proposed connection exhibited good ductility performance, and the disassembly and reassembly of the connection after a service loading had no significant effect on their seismic performance. Additionally, the load-transfer mechanism of the concrete-filled steel tubular column-column connection was explored. Simplified formulae of anti-slip flexural bearing capacity of the connection were proposed, and the predicted values agreed well with the test results on the safe side. • Six specimens on demountable composite column connections were tested and reported. • Failure modes and cyclic performance were investigated. • Feasibility of reusing composite components were explored. • Analytical models were proposed for design purposes. [ABSTRACT FROM AUTHOR]

• Strength of short stiffened RCFST evaluated through comparison between previously published experimental results and design standards. • Neglecting stiffeners is unnecessarily conservative since the beneficial effect of the stiffeners in delaying local buckling is not considered. • Plastic stress distribution method is safe for assessing strength of a broad range of stiffened RCFST. • New cross-sectional slenderness ratio limits proposed for stiffened RCFST. Rectangular concrete-filled steel tubes (RCFST) are efficient structural members that exhibit good strength, stiffness, and ductility. The mechanical properties of RCFST can be further enhanced by the addition of internal stiffeners which delay local buckling of the tube, improve load transfer, and can confine the concrete. Numerous experimental and analytical studies have been performed to characterize the behavior of stiffened RCFST. However, most studies focus on a single type of stiffener. Also, most major design standards do not provide guidance on how to account for the beneficial effects of the stiffeners. The objective of this work was to develop strength design recommendations for short stiffened RCFST columns and beam-columns that are applicable to a variety of stiffener types. A database of previously published experimental tests on stiffened RCFST members was compiled and the experimental results were compared to American, European, and Chinese design standards. Each of these standards employs the plastic stress distribution method for filled composite members that are not susceptible to local buckling as identified using cross-sectional slenderness ratio limits. The results indicate that neglecting the stiffeners is unnecessarily conservative. New cross-sectional slenderness ratio limits are proposed for stiffened RCFST, allowing a greater range of members to be assessed using the plastic stress distribution method. These results provide strong justification for changes to design standards to recognize the benefits of highly efficient stiffened RCFST members. [ABSTRACT FROM AUTHOR]

• The diagonal ribs significantly improve the cyclic-shear behavior of square thin-walled concrete-filled steel tubular (CFST) columns. • Numerical analyses indicate that the concrete and steel part contribute to the shear strength by 41.3%-57.4% and 42.6%-58.7%, respectively. • The shear strength equations in AISC specification and Eurocode overestimate the shear contribution of steel sections while underestimate that of concrete, as the shear stresses are reduced due to the horizontal stresses confining the concrete and the strength of the concrete compression strut is enhanced due to confining. There is no doubt that stiffeners for square concrete-filled steel tubular (CFST) columns can improve the composite action in terms of delaying local buckling of steel tubes and enhancing the confinement on infilled concrete. Among various proposed stiffening forms, diagonal binding ribs, made of perforated thin-walled steel plates and welded at all the four pairs of adjacent sides of a square tube, are found particularly effective. Recent research has experimentally evaluated the axial compressive and cyclic-bending behavior of square thin-walled CFST columns stiffened by diagonal ribs. However, further investigation is necessary to better understand their cyclic-shear behavior. In this work, four diagonal ribs stiffened square thin-walled CFST columns and one unstiffened counterpart were designed and tested under combined cyclic-shear load and constant axial compression. Main parameters included the shear span to depth ratio, axial load ratio, width-to-thickness ratio of the steel tube, and thickness of diagonal ribs. Test results showed that the diagonal ribs improved the confinement from the steel tube to the infilled concrete. The stiffened specimens exhibited satisfactory cyclic-shear behavior with much higher load capacity, better ductility and larger energy dissipation than the unstiffened counterpart. Numerical modeling of the shear specimens was then conducted, indicating that the concrete and steel part contributed to the shear strength by 41.3%-57.4% and 42.6%-58.7%, respectively. Finally, the test results were compared with current design provisions, the average ratio of the predicted to tested shear strength were 0.60 and 0.66 for the calculation methods in the AISC specification and Eurocode, respectively. [ABSTRACT FROM AUTHOR]

The bond behavior of longitudinal beam bars passing through the joint zone is affected by the column flexural capacity, while there is a paucity of research results; in addition, the bond behavior can be improved by the axial compressive load, while the upper limit of the axial load was still not clear due to lack of experimental researches with high axial load ratios (larger than 0.6). In this investigation, the hysteretic behavior of 8 interior joints with 600 MPa high-strength longitudinal beam reinforcing bars was compared and analyzed in detail. Four joints adopted the concrete-filled steel tubular column with continuous steel tube, namely CFSTJ specimens; and the other four joints, i.e., their counterparts, adopted the concrete-filled steel tubular column with discontinuous steel tube, namely TRCJ specimens. The discontinuous column steel tube led to different column flexural capacities and axial load ratios. The test results showed that all specimens exhibited good hysteretic behavior before 5% drift, and the bond behavior of CFSTJ specimens was better than that of their counterpart TRCJ specimens. Combining these observations with available test data of reinforced concrete (RC) interior joints in the literature, the effect of column flexural capacities and axial loads on the bond behavior was then further analyzed and quantified. Finally, based on provisions in NZS 3101 and EN 1998–1, more accurate design equations were proposed by considering the depth of column compression zone and limiting the axial load ratio. • The reduced column flexural capacities caused by the discontinuous steel tubes led to the reduced depth of the concrete compression zone above the longitudinal beam bars in joint zone, thus resulting in worse bond behavior. • The larger axial load improved the bond behavior, while the excessively large axial load led to higher compressive stresses in the joint concrete and thus weakened the bond behavior. • The modified equations for NZS 3101 and EN 1998–1 were proposed by considering the depth of column compression zone and limiting the axial load ratio. The predicted results were conservative and more accurate. [ABSTRACT FROM AUTHOR]

• CFST columns up to 1100 mm in diameter were tested under axial compression. • The difference in strength between the different thicknesses of steel tube used in the tests was only 21 MPa. • The effects of size and diameter-to-thickness ratio on the steel tube stresses and the concrete stresses were discussed respectively. • A model considering the influence of D / t and D on the confining effect was established. In this study, eight circular concrete-filled steel tubular (CFST) short columns with diameters (D) of 275–1100 mm and the column diameter-to-steel tube thickness ratios (D /t) of 55 and 69 were tested under axial compression. The bearing capacities of the steel tube and confined concrete were analyzed separately to illustrate the size effect of each component of the composite column. The experimental results show that all test specimens suffered a shear failure. The peak stress, peak strain, ductility index, and strength index decrease with the increasing D , while the composite elastic modules maintain to be relatively constant with the various specimen dimensions. Under the peak load, the vertical stress in the steel tube increases, while the hoop stress decreases with the increasing D. Compared with the specimens with a small D / t ratio, the vertical stress in the steel tube with a larger D / t ratio is lower, while the hoop stress is higher. The confined concrete strength can be divided into the unconfined concrete strength and the increased concrete strength due to lateral confinement, and the reduction of the latter is the main cause of the size effect of the CFST columns. The current design codes such as EC4, AISC, AIJ, and GB50936 overestimate the peak bearing capacity of circular CFST short columns with large diameters, compared to the experimental results. Therefore, a model considering the size effect was established to evaluate the axial bearing capacity of circular CFST short columns. [ABSTRACT FROM AUTHOR]

Thin-walled square concrete filled steel tubular (CFST) members have attracted more attention in practice because of less steel consumption, high construction efficiency, and convenient arrangement for furniture or curtain wall. Compared with circular members, the local buckling of thin-walled square CFST members is a big concern since tube buckling often results rapid strength and ductility degradation. So in this investigation, diagonal ribs were welded on the internal tube corners to improve the performance of square CFST members. Nine diagonal rib-stiffened square CFST specimens, with large width-to-thickness ratio B / t = 100 , were experimentally investigated under eccentric compression. The main test parameters included column slenderness ratios (λ = 13. 9 , 34.6, 55.4) and loading eccentricities (2 e / B = 0 , 0.25, 0.50, 1.00). Detailed finite element models were established and verified. The composite effect of the stiffened column was elaborated through combining test results and the finite element analysis, followed by feasibility of column–column connection details and parametric studies. Finally, design methods for calculating the member resistances subjected to axial and eccentric compression were proposed. • Square CFST specimens with large width-to-thickness ratio were experimentally investigated under eccentric compression. • The composite effect of the diagonal rib-stiffened column was elaborated through combining test results and numerical analysis. • The diagonal rib increased the load-carrying capacities of square CFST columns by 9%–32%. • Construction details for column–column connection and design methods for calculating the member resistances were proposed. [ABSTRACT FROM AUTHOR]

The structural performance of square concrete-filled steel tubular (SCFST) columns can be improved by stiffening the tube. Stiffening delays local buckling and can improve composite action while also facilitates the use of thinner and higher-strength materials. A particularly efficient form of stiffened SCFST column using diagonal binding ribs was proposed recently. Initial studies on the axial behavior of these diagonal ribs stiffened SCFST columns have shown excellent performance. However, further investigation is necessary to better understand their seismic performance under combined loading. In this work, four diagonal ribs stiffened SCFST columns were tested to failure under combined constant axial compression and cyclic lateral load. The main parameters in this study were the presence of holes in the diagonal rib, the width-to-thickness ratio of the steel tube, and the level of axial loading. Detailed analysis demonstrated that the effect of holes was slight, while the width-to-thickness ratio and axial load ratio affected the cyclic behavior significantly. Furthermore, based on the verified ABAQUS model, the use of the plastic stress distribution method for computing the interaction strength of short diagonal ribs stiffened SCFST columns was validated among a range of parameters. These parameters are the hole diameter, axial load ratio, material strength and width-to-thickness ratio, including for columns that would be classified as susceptible to local buckling by current design standards. These results provide new knowledge on the behavior of diagonal ribs stiffened SCFST columns and will support the use of this efficient form of composite construction. [Display omitted] • Seismic behavior of square CFST columns with a particularly efficient stiffening form was experimentally assessed. • The composite effects and mechanisms were analyzed. • Design approach for columns with tube width-to-thickness ratios well beyond current limits in design codes was proposed. [ABSTRACT FROM AUTHOR]