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The performance of concrete-filled steel tubular (CFST) column joints with a group of extended hollo-bolts has been experimentally investigated under the influence of shear loading. The primary focus was to understand the performance of extended hollo-bolts in enhancing the transfer of shear load to the concrete core of the column by bolt bearing. The joint assembly was fabricated with a rigid end-plate, thereby overcoming the influence of endplates in the joint global behavior. A series of full-scale group hollo-bolted CFST column joint tests was carried out, where eight specimens were fabricated with a group of two hollo-bolts, arranged in one row and two rows in the assembly; another five specimens were fabricated with a group of four hollo-bolts, arranged in two rows. Apart from bolt arrangement, the other parameters studied included the use of standard and extended hollo-bolts, the embedment length of the hollo-bolt, and the bolt pitch distance. From the investigation, it is observed that all the joints failed in pure shear signifying utilization of the full capacity of the hollo-bolt, and no prominent bearing failure of concrete was observed. Enhanced composite behavior was achieved using the extended hollo-bolts as the shear load was transferred to the concrete core effectively. A group of two extended hollo-bolts in a single row transmits equal forces to the concrete core, whereas, when two or four extended hollo-bolts are in two rows, the upper row transmits more forces as compared to the bolts in the lower row. Lastly, with pitch distance of 2.5 times bolt hole diameter and beyond, the total strength of the joint is equal to the sum of strength of individual bolts, which confirms that the group action did not deteriorate the joint capacity. Subsequently, an analytical model for the global force-displacement behavior and joint shear strength is proposed by calibrating the test data obtained through this study. [ABSTRACT FROM AUTHOR]

Construction industry as a whole should transform into designs that enable demountability and direct reuse of structural elements to achieve the circularity in construction. Currently, structural connections enabling direct reuse of components in construction are limited. Column base connections are one of the main load transfer units of a steel structure for the magnitude of the forces being transferred from the superstructure. This paper presents an interlocking type of column base connection that enables direct reuse of all associated structural components. The proposed interlocking connection transfers the force through the plate bearing and holding mechanisms and requires minimal number of bolts. In addition to the direct reuse and better load transfer approach, the new interlocking connection enhances and simplifies the mounting procedure that leads to increased productivity in construction. This article discusses the overall concept of the proposed interlocking connection, design philosophy and compares the failure modes with existing conventional bolted column base connections for various loading cases through finite element analyses. Main parameters investigated are the effects of bearing length of connector element and connector element thickness under uniaxial loading. A finite element model of the proposed interlocking connection is built through which the influential parameters are analysed. [ABSTRACT FROM AUTHOR]

Cross-section behaviour for cold-formed high strength steel (HSS) irregular hexagonal hollow section (IHexHS) stub columns under combined compression and bending is studied and presented in this paper. Finite element models were developed and validated using the existing experimental data collated from the previous research. Upon the validated finite element models, extensive parametric studies were subsequently carried out to generate more numerical data covering a wider range of cross-section dimensions, steel grades and load combinations from pure compression to pure bending. The obtained numerical results were utilised to assess the accuracy and the applicability of the current design codes, such as Eurocode of EN 1993-1-12 (EC3) and the North American code of ANSI/AISC 360-16 (AISC) for cold-formed HSS IHexHS stub columns under combined loading. It was demonstrated that the existing design codes can be safely applied and can be extended for cold-formed HSS IHexHS stub columns design under combined loading. In cross-sectional resistance predictions, conservative results were provided from the existing design codes. The over-predictions were primarily due to the neglect of the strain hardening and plate element interaction. The end points used in the interaction curves of EC3 and AISC adopt an idealised elastic-plastic material model to derive the corresponding resistance in cross-sectional level. The employment of Continuous Strength Method (CSM) leads to improved accuracy in cross-sectional resistance prediction with updated end points in the interaction curve. More consistent and reliable predictions were revealed by carrying out reliability analysis in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

This research paper introduces a novel, yet simple, column base connection that is reusable for moment resisting frames (MRFs). The performance of this connection was evaluated through a comprehensive experimental investigation. The proposed design incorporates a pinned energy dissipator (ED) that effectively absorbs seismic energy. Moreover, the connection utilises the weight of the column itself to provide a recentring force. Unlike existing self-centring column base connections, the ED in this innovative design is equipped with pins to prevent resistance to recentring caused by inelastic deformation after earthquakes. This unique feature ensures that the connection possesses self-centring capability, energy dissipation ability, and reusability. The analytical simplified models developed in this study effectively illustrate the monotonic and cyclic behaviours of the proposed connection. To validate the design concepts and simplified models, tests were conducted on specimens of the ED and the complete column base connection. • A novel column base connection to achieve self-centering has been developed. • Pinned energy dissipators can reduce the residual lateral drifts after earthquakes. • Reusability of the column has been verified by quasi-static cyclic tests. • Self-centering of the column can be achieved by self-weight. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on axially loaded polygonal-shaped steel-tube columns filled with high-strength concrete. The tubes had triangular, hexagonal and octagonal cross-sections, the concrete had a nominal concrete compressive cylinder strength of 100 MPa and the steel had a nominal yield strength of 285 MPa. For each tube cross-section, two identical specimens of concrete-filled tubes and one specimen of a hollow tube were examined. Load shortening, strain histories and failure modes were recorded and compared. Finite-element analysis with three different existing constitutive models of concrete were also developed and validated against the experimental results. The load-carrying capacities of the concrete-filled tubes were compared with the derived values from BS EN 1994-1-1:2004, ACI 318-11/AISC 360-16 and GB 50936-2014. The feasibility of current design standards for concrete-filled steel-tube columns of different cross-sections is discussed. [ABSTRACT FROM AUTHOR]

• Database of concrete-filled steel tubes under eccentric loading was created. • Machine learning models were used to predict the ultimate strength of CFSTs. • Support Vector Machine, Random Forest, Neural Network were adopted. • Machine learning models are more accurate than methods in design codes. • Hyperparameters were optimized through random and grid search using cross-validation. Concrete-filled steel tubes (CFSTs) are popularly used in structural applications. The accurate prediction of their ultimate strength is a key for the safety of the structure. Extensive studies have been conducted on the strength prediction of CFSTs under concentric loading. However, in real situation CFSTs are usually subjected to eccentric loading. The combined compression and bending will result in more complex failure mechanisms at the ultimate strength. The accuracy of methods in design codes is usually limited due to their simplicity. In this study, three machine learning (ML) methods, namely, Support Vector Regression (SVR), Random Forest Regression (RFR), and Neural Networks (NN), are adopted to develop models to predict the ultimate strength of CFSTs under eccentric loading. A database consisting of information of 403 experimental tests from literature is created and statistically analyzed. The database was then split to a training set which was used to optimize and train the ML models, and a test set which was used to evaluate performance of trained ML models. Compared with the methods in two typical design codes, the ML models achieved notable improvement in prediction accuracy. The parametric study revealed that the trained ML models could generally capture the effect of each primary input feature, which was verified by the relevant experimental test results. [ABSTRACT FROM AUTHOR]

Structures in modular buildings typically have some unique characteristics as compared with conventional structures, e.g., discrete connection of modules through inter-module connections, discontinuous floor diaphragms. The behavior of steel modular structures under earthquake excitations has not been fully understood, and no seismic design method specifically tailored for modular building structures is available. Moreover, although various inter-module connections with different rotational connectivity have been proposed, their suitability for seismic application is questionable. In this paper, the distributed seismic design method, which makes use of the lateral resistance inherent in all modules, was proposed for modular buildings with steel frames. A numerical parametric study was conducted on a 9-story prototype building. The effect of three parameters, i.e., the rotational stiffness of inter-module connections, the seismic design force level, and the height-wise distribution of the design base shear, were studied. The results show that the rotational stiffness of inter-module connections has limited impact on the elastic lateral stiffness and the fundamental period of modular steel frames. However, in the inelastic range, the increase in the rotational stiffness will lead to less plastic drift concentration and better collapse prevention performance. Increasing the seismic design force may not result in enhanced collapse prevention performance, as it is also dependent on the height-wise distribution of the design base shear and if significant higher-mode response is involved in the total response of the structure. • Seismic design using resistance of all modules was proposed for modular buildings. • First period is not affected by rotational stiffness of inter-module connections. • Soft story can be avoided by increasing rotational connectivity between columns. • Level and distribution of seismic design force were varied in the parametric study. • Higher-mode effect affects inter-story drifts under strong earthquakes. [ABSTRACT FROM AUTHOR]

A novel composite column, consisting of an outer fiber reinforced polymer (FRP) tube, an engineered cementitious composite (ECC) ring and an inner high strength concrete (HSC) core, has been proposed and experimentally investigated in this study. Due to the high brittleness of HSC, localized cracks may occur and lead to premature failure for conventional FRP-confined HSC columns. With the excellent tensile and cracking behavior, ECC ring is used to redistribute the hoop stress and strain from HSC core to FRP tube in the proposed novel FRP-ECC-HSC composite column. A total of 12 stub columns with different HSC core strengths and ECC ring thicknesses were tested under axial compression. It is found that FRP-ECC-HSC composite columns can develop larger FRP confining efficiency with more uniform hoop strain distribution in comparison to the corresponding normal FRP-confined HSC columns. The ultimate axial strain is obviously enhanced as well for this composite column, leading to an improved ductile compressive behavior. Based on the test results obtained from this study, design equations are proposed to predict the ultimate loading capacity and ultimate axial strain for the FRP-ECC-HSC composite column. [ABSTRACT FROM AUTHOR]

The behaviour of cold-formed normal- and high-strength steel columns with square and rectangular hollow sections (SHSs and RHSs) at elevated temperatures was investigated numerically in this paper. A finite element model was developed and validated against experimental results for the cold-formed steel SHS and RHS stub and long columns tested at ambient and elevated temperatures. Parametric studies were subsequently conduced on cold-formed normal- and high-strength steel SHS and RHS columns with various cross-section slenderness and member slenderness at elevated temperatures ranging from ambient to 800 °C. Based on the numerical results and experimental results reported in literature, the applicability of existing design approaches in European and North American standards to the columns at elevated temperatures was evaluated. The evaluation shows that the approaches in standards provide quite conservative strength predictions for the cold-formed normal- and high-strength steel SHS and RHS columns at elevated temperatures except for the overestimation of cross-sectional resistance obtained based on the North American standard. Modified design approaches were proposed to improve the accuracy of strength predictions and can be safely applied to generate designs for the columns under various elevated temperatures. • Cold-formed SHS and RHS columns under elevated temperatures were investigated. • A FE model was validated for accurately predicting the structural behaviour. • Results of FE parametric studies and experiments were used to assess design methods. • Accuracy of design methods was discussed. • Modified design methods for more accurate strength predictions are developed. [ABSTRACT FROM AUTHOR]

• Eighteen FRP-confined ECC columns were tested under monotonic and cyclic loadings. • Compressive behavior of FRP-confined ECC columns was presented and analyzed. • Existing models for FRP-confined normal concrete were evaluated for FRP-confined ECC. • Design equations on ultimate conditions were developed for FRP-confined ECC columns. • Analysis-oriented model was proposed for FRP-confined ECC and exhibited good performance. A total of 18 specimens of fiber-reinforced polymer (FRP) confined engineered cementitious composite (ECC) were tested under axial compression in this study. Both monotonic loading and cyclic loading were considered. Effects of different FRP materials, glass FRP (GFRP) tube and carbon FRP (CFRP) jacket, as well as different FRP thicknesses were investigated. All the specimens exhibited the typical strain hardening behavior, indicating the effective enhancement of compressive strength and strain of ECC under FRP confinement. Failure modes, stress–strain behavior and dilation behavior were presented and analyzed. The FRP-confined ECC showed large ultimate axial strains, demonstrating the superior deformability and ductility performance. Design equations were developed to predict the ultimate compressive strength and strain. Based on the test results obtained from this study and other test results collected in the literature, an analysis-oriented model was proposed to predict the overall compressive stress–strain behavior of FRP-confined ECC columns. [ABSTRACT FROM AUTHOR]

This paper presents experimental findings of ten full-scale blind-bolted concrete-filled steel tubular (CFST) connection tests under predominant shear loading. Previous works show that, the performance of blind-bolts with extended shank and headed nut performed significantly well under tensile loads, but research on such connections under shear loading is at scarce. In this testing programme, the performance of individual blind-bolted CFST column connection is assessed where various parameters including presence of infill concrete, bolt embedment length, tube wall thickness and concrete strength are considered. Material tests for all the elements in the connection assembly have also been conducted. The study is accompanied by assessment of international codes. It is observed that, with higher bolt embedment length, the concrete contribution can be enhanced up to 58% of the total load applied, where the load is transmitted to the concrete core by bearing, and the tube wall yielding could also be delayed. Test results also shows that, ultimate capacity of the bolts can be achieved with CFST connections under shear load. For all the connections, the failure mode was consistent to shear fracture of bolt. At the end, a modified prediction equation for blind-bolt shear resistance is proposed. The test results presented in the investigation provides scientific data for further numerical investigations and can also provide insights towards load-introduction mechanism in bolted CFST column connections. • Conducted ten full-scale experimental investigation of blind-bolted CFST connections. • Tests were carried out under predominant shear loading on single bolted connections. • Influence of extended hollo-bolt in shear load transfer to CFST columns studied. • Higher bolt embedment length led to enhanced concrete contribution under shear loads. • Full ultimate strength of single hollo-bolt can be achieved with CFST connections. [ABSTRACT FROM AUTHOR]

This paper presents experimental numerical investigations on the structural behaviour of cold-formed high strength steel irregular octagonal hollow section (OctHS) columns with both non-slender and slender cross-sections. An experimental programme, including material tests, measurements of initial global geometric imperfection, and pin-ended column tests, was first conducted. The key findings from the experimental programme are presented and discussed. Following the validation against the experimental results, the proposed finite element modelling methodology was established to replicate the test observations, and then was adopted to generate a boarder range of numerical results through parametric studies. The collected experimental and numerical data were used to evaluate the applicability of current structural steel design methods on the column buckling strength for irregular OctHS columns. Assessment results demonstrate that the design method adopted in Chinese code can provide accurate prediction, whilst modified design method adopted in Eurocode 3, considering the effect of steel grade on the column strength, has been proposed and shown to greatly enhance the prediction accuracy with improved consistency. The corresponding assessments on the design approaches adopted in American and Australian codes were also discussed. • Cold-formed steel irregular octagonal hollow section columns were fabricated through press-braking and subsequent welding. • Variations of material properties within the cross-section and initial global imperfection were measured and presented. • A total of 12 irregular octagonal hollow section long columns were tested. • FEM for irregular octagonal hollow section columns was developed and a total of 539 numerical models were generated. • The applicability of current design methods was assessed and modified against the experimental and numerical results. [ABSTRACT FROM AUTHOR]

The local buckling behaviour of cold-formed high strength steel (HSS) irregular hexagonal hollow section (IHexHS) stub columns under concentric compression is studied numerically in this paper. Finite-element (FE) models were developed and validated against the experimental data. The validated FE models were employed to conduct extensive parametric studies. The obtained numerical results together with the experimental data were used to evaluate the applicability of the existing design codes and design approaches to the cold-formed HSS IHexHS under concentric compression. The evaluation shows that the current slenderness yield limit values codified in design codes cannot be applied to cold-formed HSS IHexHS stub columns. The Eurocode 3 (EC3) and the North American code AISC 360-16 provide slightly over-estimated predictions for slender sections whereas the Australian code AS 4100 yields conservative predictions. For stocky sections, all the design codes show high degree of conservatism due to the lack of consideration for strain hardening. Furthermore, design approaches of Continuous Strength Method (CSM) and Generalised Slenderness Resistance Method (GSRM) have been found to provide more accurate predictions than the Direct Strength Method (DSM). Modified design approaches are also proposed to improve the accuracy of the strength predictions. • Numerical models for HSS cold-formed IHexHS stub columns were developed. • Extensive parametric studies were carried out. • The current design codes were assessed. • The existing design approaches of DSM, CSM, and GSRM were assessed. • Modified design codes and design approaches are proposed. [ABSTRACT FROM AUTHOR]

A systematic experimental and numerical investigation on the behaviour of octagonal concrete-filled steel tube short columns fabricated with S690 high-strength steel and C90 high-strength concrete, and subjected to combined compression and bending is reported in this paper. Experiments were firstly performed on twelve short column specimens with different plate width-to-thickness ratios. The experimental results and observations including the ultimate loads, load versus displacement responses and failure modes of the specimens were discussed. In supplementary to the experimental investigation, numerical investigation using a validated finite element model was performed to examine the behaviour of the structures with a wide range of plate width-to-thickness ratios, yield strength of high-strength steel and compressive strength of high-strength concrete that subjected to various combinations of compression and bending. Based on the experimental and numerical results, the applicability of existing design approaches in standards was also evaluated. The assessment shows that the design approaches provide conservative strength predictions for the high-strength octagonal concrete-filled steel tube short columns under combined compression and bending and can be applied to provide safe designs for the structures. • High-strength octagonal CFST short columns under combined loading were investigated. • Both experiments and numerical modelling were performed for the investigation. • The variation of compressive resistance with increasing moment was observed. • The suitability of existing design methods was assessed using the research results. • The design methods in standards can be safely applied for the structures. [ABSTRACT FROM AUTHOR]

• 15 hybrid welded T-section stub columns were tested under axial compression. • Material properties and residual stresses were measured. • Numerical models were developed. • Extensive parametric studies were carried out. • Design codes and design approaches of DSM and CSM were evaluated and compared. Comprehensive experimental and numerical investigations on hybrid T-section stub columns under compressive load were performed and are presented in this paper. The hybrid welded T-section stub columns comprise high strength steel Q690 flange and normal strength steel Q355 web. Material property studies were implemented through tensile coupon tests. Residual stress in membrane type was measured and recorded and its impact on structural performance was also assessed. Initial local geometric imperfection measurements were conducted for all the specimens. In conjunction with experimental studies, numerical investigation was performed to generate more test specimens extending the range of cross-section dimensions by which test data pool can be supplemented. The Eurocode of EN 1993-1-1, EN 1993-1-5 and EN 1993-1-12, the North American code of ANSI/AISC 360-16 and the Australian code of AS 4100 together with design approaches of Direct Strength Method and Continuous Strength Method were examined for its applicability for cross-section classification and compression resistance predictions of hybrid T-sections. Overall, the current specified limits were applicable for hybrid welded T-section and strength predictions from design codes were comparatively consistent and reliable. Strength predictions from Direct Strength Method and Continuous Strength Method were relatively appropriate though overly conservative predictions were provided for cross-section with large slenderness. In this study, modifications on the Direct Strength Method and Continuous Strength Method are proposed, which is shown to provide accurate predictions at cross-sectional level in a reliable manner. [ABSTRACT FROM AUTHOR]

Comprehensive experimental and numerical investigations into the structural behaviour of cold-formed high-strength steel (HSS) irregular octagonal hollow sections (IOctHS) are presented in this paper. A total of 13 IOctHS stub columns were tested. Material properties measurements were conducted on the tensile coupons taken from both parent plates and within the cross-sections of HSS IOctHS stub columns. Initial local geometric imperfection measurements were also carried out. In conjunction with experimental tests on the stub columns, finite element (FE) models were developed to replicate the test results and failure modes. Afterwards, the validated FE models were employed to conduct parametric studies to supplement the experimental data by generating further structural performance data covering a broader range of cross-section slenderness. Cross-section slenderness limits set out in design codes such as EN 1993-1-1, ANSI/AISC 360-16, AS 4100 as well as ASCE/SEI 48, and design methods of DSM as well as CSM were evaluated against the experimental and numerical data. It was found that the current limits for internal compression plate elements of rectangular hollow sections set out in the design standards are not suitable for the design of cold-formed HSS IOctHS under compression load. Cross-section strength predictions obtained from EN 1993-1-12, ANSI/AISC 360-16, AS 4100, ASCE/SEI 48, DSM, CSM and modified design methods were also compared with the tests and numerical results. Relatively accurate predictions are provided by design codes. Non-conservative results are obtained from DSM and the CSM yields more consistent and precise results than DSM. The modified design approaches were also assessed and discussed. • HSS cold-formed IOctHS stub columns have been tested under axial compression. • Material properties were measured for both parent plates and the sections. • Numerical models for HSS cold-formed IOctHS stub columns were developed. • Extensive parametric studies were carried out. • The applicability of design codes as well as design approaches was evaluated. [ABSTRACT FROM AUTHOR]

The paper presents an investigation on welded stainless steel I-section columns. In total, 22 experiments on welded I-section columns, including members buckling about major and minor axis, for both austenitic and duplex stainless steel columns were carried out. Specimen cross-sections and lengths were carefully selected to cover a wide range of geometries and non-dimensional slenderness. Measurements were taken on geometry, global initial geometric imperfection, residual stresses and material properties. The experimental results have been supplemented by the finite element simulation. The resulting structural performance data have been used to assess the applicability of the current design provisions from EN 1993-1-4, ASCE 8-02 and AS/NZS 4673 for the design of stainless steel welded-I sections. Results showed that the design provisions from EN 1993-1-4 and AS/NZS 4673 can be conservatively adopted while the ASCE 8-02 provision shows scattered predictions. [ABSTRACT FROM AUTHOR]

• Three different fabrication routes were examined. • 18 HSS HexHS stub columns were tested under axial compression. • Material properties within the cross sections were measured. • The slenderness yield limits in design codes were assessed. • Design approaches of DSM and CSM were evaluated and compared. This paper presents a comprehensive experimental investigation into the structural behaviour of the high strength steel (HSS) hexagonal hollow sections (HexHS) stub columns under concentric compression. A total of 18 HSS HexHS stub columns encompassing three fabrication routes were performed. The HSS plates used to fabricate the specimen were delivered in Quenched and Tempered (QT) condition. The material properties within the cross sections of the HSS HexHS were measured. Initial local geometric imperfections for all the examined stub columns were measured. The cross-section slenderness yield limits in the existing design codes of the EN 1993-1-12, ANSI/AISC 360-16, AS 4100 and ASCE/SEI 48-11 were compared and assessed against the experimental results. It was found that the current limits for internal compression plates in HSS rectangular and square sections cannot be extended to cover the cross-section classification for HSS HexHS. In terms of the cross-sectional resistance predictions, all the design codes tend to under-estimate the resistance of HSS HexHS under axial compression. For sections failed by local buckling prior to the attainment of yield load, the AS 4100 yields more accurate predictions compared with those predictions based on the other design codes. Compared with the design approach of Direct Strength Method (DSM), Continuous Strength Method (CSM) provides more consistent and satisfactorily predictions, particularly for stocky sections due to the consideration of strain hardening. [ABSTRACT FROM AUTHOR]

Comprehensive experimental investigations into the material properties and stub column behaviour of cold-formed high strength steel (HSS) irregular hexagonal hollow sections (IHexHS) are presented in this paper. Apart from the tensile coupons taken from the parent plates, tensile coupons extracted from the flat and corner portions from the cross-sections were also tested in order to measure the effect of the fabrication process on material properties. The strength enhancement predictive models proposed by previous studies were compared with the obtained test results from corner coupons with increased strength due to the cold-forming effect. A total of 20 HSS IHexHS stub column specimens were tested under axial compression and the cross-section classification from the existing structural steel design codes of EN 1993-1-12, ANSI/AISC 360–16, AS 4100, AISI S100–16 and design approaches of DSM and CSM were compared and assessed against the obtained results. It was found that the design provisions of cross-section classification in current design codes cannot be extended to the HSS IHexHS stub columns. Based on current codified yield slenderness limits, the strength predictions from design codes exhibit conservatism without the consideration of strain hardening and beneficial effect of element interaction whereas cross-sections with intermediate slenderness values were over-predicted. • 20 HSS cold-formed IHexHS stub columns were tested under axial compression. • A total of 69 tensile coupons were tested to measure the material properties. • Applicability of the design rules for the cross-section classification to IHexHS is assessed. • Cross-section strength predictions based on design methods are compared against test results. [ABSTRACT FROM AUTHOR]

The local buckling behaviour of high strength steel (HSS) hexagonal hollow section (HexHS) stub columns encompassing three different fabrication routes under axial compression is numerically investigated in this study. Finite-element (FE) models were developed and validated against the experimental results. The validated FE models were subsequently employed to carry out parametric studies to expand structural performance data covering a wider range of geometries and cross-section slenderness as well as two different steel grades. The obtained results from FE models in line with the experimental data were used to evaluate the applicability of the existing design codes and the design approaches in literature to HSS HexHS under pure compression. The comparison indicates that the current slenderness yield limiting values in design codes cannot be simply extended to HSS HexHS stub columns. All the design codes exhibit a high degree of conservatism due to the lack of consideration for strain hardening whereas the Continuous Strength Method (CSM) was found to provide more accurate predictions than the Direct Strength Method (DSM). Modified design approaches are proposed to improve the accuracy of the strength predictions for HSS HexHS stub columns. • Numerical models were developed and validated. • Extensive parametric studies were carried out. • The current design codes were evaluated. • The design approaches of DSM and CSM were assessed. • Modifications to design approaches are proposed. [ABSTRACT FROM AUTHOR]

As inspired by the concept of modular integrated construction, component-assembly-structure, it leads to a great opportunity to reassess the basic structural elements made by an uncommon manufacturing process. Rectangular hollow sections (RHS) can be fabricated by tip-to-tip welding two press-braked channels together to form an integrated cross-section. This unique technique gains more flexibilities and economic efficiencies regarding the setup of production equipment as compared to the mainstream manufacturing process. In this paper, a comprehensive investigation into press-braked RHSs comprising material tests, residual stress measurements, stub column tests, and numerical studies is presented. A total of 40 tensile coupons, 108 sectioned residual stress strips, 10 stub columns, and 290 numerical models were combined to investigate various characteristics of press-braked RHSs. Of the results observed, the strength enhancement of corner materials due to the cold-working can be conservatively captured by the predictive model from AISI S100-16. A simplified predictive residual stress pattern is proposed to represent residual stress distributions of press-braked RHSs. The applicability of Eurocode 3, ANSI/AISC 360-16, and the direct strength method (DSM) for the design of press-braked RHS stub columns under compression was evaluated based on the experimental and numerical results. And modified design approaches were also proposed and shown to have a more accurate, consistent, and safe prediction of compressive resistance for press-braked RHSs. [Display omitted] • Cold-formed rectangular hollow sections of Q355 and Q460 steels were fabricated through press-braking. • Material properties and residual stresses of press-braked RHS were measured. • 10 press-braked RHS stub columns were tested under axial compression. • Finite element analyses on press-braked RHS stub columns were carried out. • Design methods in EN 1993-1-1 and direct strength method (DSM) were evaluated. [ABSTRACT FROM AUTHOR]