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This paper presents experimental and numerical investigations into the web crippling behaviour and load-carrying capacity of stainless steel built-up I-section members under End-Two-Flange (ETF) concentrated transverse loading. An experimental programme was conducted on 23 austenitic and duplex stainless steel built-up I-section specimens, with each consisting of two identical press-braked channel sections assembled back-to-back by means of self-tapping screws. Following the experimental programme, a numerical modelling programme was performed, where finite element models were firstly developed to replicate the tests and then used to conduct parametric studies. Based on the test and numerical data, the existing design rules for stainless steel built-up I-section members failing by web crippling, as set out in the current European, American and Australian/New Zealand design standards, were assessed. The comparisons indicated that the European and Australian/New Zealand design standards resulted in overly conservative and rather scattered failure load predictions, while the American design standard led to less scattered failure load predictions, but with many predictions on the unsafe side. Therefore, an improved design approach was proposed and shown to provide substantially improved failure load predictions for stainless steel built-up I-section members under End-Two-Flange loading. • The web crippling behaviour of stainless steel built-up I-sections under ETF loading was studied. • Tests were conducted on 23 stainless steel built-up I-section specimens. • FE models were developed and validated against test results and then used for parametric studies. • The existing codified design rules were assessed and a new design approach was proposed. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions. • The compressive behaviour of circular RACFSST stub columns after exposure to fire is investigated. • Post-fire compression tests on twelve circular RACFSST stub column specimens are conducted. • The influences of heating durations and RCA replacement ratios are analysed. • Thermal and mechanical FE models are validated against test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. [ABSTRACT FROM AUTHOR]

This paper reports experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled stainless steel tube (HCFSST) beam-columns under combined compression and bending. An experimental investigation was conducted on sixteen HCFSST beam-columns specimens fabricated from stainless steel tubes with two cross-section sizes and high strength concretes with four material grades, and included concrete cylinder tests, tensile coupon tests, initial global geometric imperfection measurements and eccentric compression tests. The test setups and procedures were fully reported and the experimental observations were discussed and analysed in detail. It was found that the plane cross-section assumption was valid for eccentrically loaded HCFSST sections and the lateral deflection distribution patterns for HCFSST beam-columns were approximately half-sine wave shapes. The test results were used in a subsequent numerical investigation for the validation of finite element models, which were then employed to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. Based on the experimental and numerical results, the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to HCFSST beam-columns. The evaluation results revealed that the European code provided accurate but scattered failure load predictions when used for HCFSST beam-columns, while the American specification and Australian/New Zealand standard resulted in conservative and scattered failure load predictions. • The behaviour of high strength concrete-filled stainless steel tube (HCFSST) beam-columns is investigated. • Eccentric compression tests on sixteen HCFSST beam-column specimens are conducted. • The ductility, strength, longitudinal strain development and lateral deflection distribution are analysed. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The applicability of relevant design codes is assessed against test and FE data. [ABSTRACT FROM AUTHOR]

The flexural buckling behaviour and resistances of press-braked stainless steel Z-section columns are investigated in this paper, based on experiments and numerical modelling. An experimental investigation was conducted on two press-braked stainless steel Z-sections and included material testing, initial geometric imperfection measurements and twelve fixed-ended column tests. Minor-axis flexural buckling was observed for all press-braked stainless steel Z-section column specimens upon testing. The key obtained fixed-ended column test results, including failure loads, load–deformation histories and failure modes, were fully reported. Following the experimental investigation, a numerical investigation was performed, with finite element models developed to validate against the fixed-ended column test results and then used to conduct parametric studies to generate additional numerical data. On the basis of the test and numerical data, the relevant buckling curves, as specified in the European code, American specification and Australian/New Zealand standard, were evaluated and shown to provide accurate and consistent flexural buckling resistance predictions for press-braked stainless steel Z-section columns. • The flexural buckling behaviour of press-braked stainless steel Z-section columns was studied. • Twelve fixed-ended column tests were conducted. • FE models were developed to validate against the test results and then used to perform parametric studies. • The codified buckling curves were assessed, showing good design accuracy and consistency. [ABSTRACT FROM AUTHOR]

• The web crippling behaviour of cold-formed steel channel section having elongated edge-stiffened web holes under interior-two-flange loading condition was studied numerically. • The results of a total of 1,227 new finite element analysis were reported. • Design formulae for the web crippling strength reduction factor were suggested. • A direct strength method (DSM) equation was also presented to evaluate web crippling strength. In the past decade, cold-formed steel (CFS) channel sections having circular edge-stiffened web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened holes, while still allowing full service integration. In the case of web crippling, previous research has found that use of edge-stiffened holes almost results in the same strength of an equivalent channel-section having a plain web. Such circular edge-stiffened web holes can now be extended to elongated edge-stiffened web holes. However, for such elongated holes, no experimental tests have been reported in the literature. In this paper, a numerical investigation was carried out, and non-linear finite element (FE) analyses were used to investigate the web crippling behaviour of CFS channel sections having edge-stiffened web holes under the interior-two-flange (ITF) loading condition. The cases of both flange fastened and flange unfastened were considered. The FE models were validated against test results of sections having circular edge-stiffened web holes; good agreement in terms of the load–displacement curves and deformed shapes was shown. Using the validated FE models, a parametric study was carried out on CFS channel sections having elongated un-stiffened and edge-stiffened web holes, comprising 1,227 finite element analyses (FEA) results. Compared to sections having a plain web, for the case of an elongated opening, without any edge-stiffener, having an aspect ratio of two and three, the average reduction in web crippling strength was 39% and 49%, respectively. However, for an edge-stiffened hole, the reduction in the web crippling strength was reduced to only 2% and 16%, respectively. Finally, the design equations in the form of the web crippling reduction factor (R p) and the equations based on the direct strength method (DSM) for CFS sections with elongated web holes were proposed. [ABSTRACT FROM AUTHOR]

• The structural behaviour of cold-formed steel T -stub connections with HRC and screws was studied experimentally and numerically. • The results of a total of 15 new experimental tests were reported. • Finite element analysis was conducted and validated against the test results. • The prediction accuracy of current design standards was evaluated. Cold-formed steel (CFS) T -Stub connections are widely used in single-story buildings, and their use is increasing in multi-story and long-span buildings. Recently, an innovative CFS T -Stub connection was developed using self-drilling screws and the Howick Rivet Connector (HRC), and such a newly-developed connection demonstrated excellent structural performance in the building industry. In this paper, a comprehensive experimental and numerical investigation was conducted to investigate the failure mechanism and structural behaviour of CFS T -Stub connections with a combination of HRC and screws under tension force, considering the effects of screw numbers. Firstly, a total of 15 new experimental tests were conducted on the CFS T -Stub connections with various numbers of screws. From the experiments, it was observed that the HRC was subjected to shear failures, while screws failed primarily due to tilting and bearing failures in all investigated specimens. Then, a non-linear elasto-plastic finite element (FE) model was developed and validated against the experimental results in terms of connection strength and failure modes. Finally, the design strengths obtained from the American Iron and Steel Institute (AISI 2016) & Australia/New Zealand standards (AS/NZS 2018) and Ahmadi et al. (2016) were compared with the test and FEA results, showing that the ultimate design strength of CFS T -Stub connections was overestimated by 16% and 14%, respectively. However, for T -Stub connections with HRC alone and with HRC and one screw, these design guidelines were unconservative by 5%. [ABSTRACT FROM AUTHOR]

• Structural performance of cold-formed steel built-up section members under synchronous non-uniform bending and compression was investigated. • Thirty-five beam-column tests under unequal end moments were conducted to examine the effect of moment gradients. • Failure modes involving local, distortional and flexural buckling were found in the experiments. • Comparisons of experimental loading capacities with nominal strengths were performed to evaluate existing design rules. • Reliability analysis was performed to examine the appropriateness of current design codes. The experimental study presented in this paper aimed to examine the performance of cold-formed steel built-up section beam-columns experiencing non-uniform bending. The test program was performed on built-up open and closed sections that were manufactured from steel grades G500 and G550 zinc-coated sheets. The test specimens were assembled by connecting two identical channels with discrete connectors along the longitudinal direction. Two member lengths and two plate thicknesses were considered for the test specimens to investigate the stability of the newly designed thin-walled section beam-columns. In total, thirty-five beam-column tests were carried out under pinned supports. The test results including loading capacity, failure mode and axial load-lateral deflection response were obtained and are fully reported in this paper. Moreover, the comparison of experimental loading capacities with nominal strengths was conducted to evaluate the applicability of the interaction curves specified in the North American Specification AISI S100, the Australian/New Zealand Standard AS/NZS 4600, the European Code EN 1993–1-1 and the American Specification ANSI/AISC 360 with nominal bending and compression resistances calculated by direct strength method for the thin-walled section beam-column members under moment gradients. Overall, these design methods were conservative for strength predictions of the built-up open section beam-column members under unequal end moments. For the built-up closed section members experiencing synchronous non-uniform bending and compression, the aforementioned design methods generally offered slightly conservative strength predictions, except for the interactive formula in the European Code with bending and compression resistances determined by direct strength method. [ABSTRACT FROM AUTHOR]

• The structural behaviour of press-braked austenitic stainless steel slender channel section beam-columns was studied. • Ten beam-column tests were performed. • FE models were developed to simulate the test results and then adopted to conduct parametric studies. • The codified design interaction curves were assessed, indicating conservatism. • A new improved design interaction curve was proposed. The present paper reports experimental and numerical studies of the structural behaviour and resistances of press-braked austenitic stainless steel slender channel section beam-columns under combined compression and minor-axis bending. An experimental programme, including initial geometric imperfection measurements and ten beam-column tests, was firstly performed. The test procedures, setups and results were fully reported. The experimental programme was accompanied by a numerical modelling programme, including a validation study, where finite element models were developed and validated against the test results, and a series of parametric studies, where the validated finite element models were used to generate further numerical data. The obtained test and numerical data were adopted to assess the current design interaction curves for press-braked austenitic stainless steel slender channel section beam-columns, as provided in the European code, American specification and Australian/New Zealand standard. The assessment results revealed that all the three codified design interaction curves led to conservative and scattered resistance predictions, due to the conservative compression and bending end points and inappropriate shapes. To address these shortcomings, a new design interaction curve has been proposed and shown to yield a higher level of design accuracy and consistency for press-braked austenitic stainless steel slender channel section beam-columns than the codified design interaction curves. [ABSTRACT FROM AUTHOR]

• 1. The local–flexural interactive buckling of press-braked stainless steel slender channel section columns is studied. • 2. Ten pin-ended column tests are conducted. • 3. FE models are developed and validated against the test results and then adopted to conduct parametric studies. • 4. The codified design rules are assessed and shown to yield inaccurate interactive buckling resistance predictions. • 5. A new design method is proposed, showing improved design accuracy. The present paper reports experimental and numerical studies of the local–flexural interactive buckling behaviour and resistance of press-braked stainless steel slender channel section columns. A testing programme was firstly performed, including tensile coupon tests, initial geometric imperfection measurements and ten pin-ended column tests. The pin-ended column test setup, procedures and results were fully reported and analysed. The progression of local buckling and flexural buckling was discussed in detail. Following the testing programme, a numerical modelling programme was conducted, where finite element models were developed to replicate the test responses and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were employed to assess the accuracy of the relevant design rules for press-braked stainless steel slender channel section columns, as set out in the European code, American specification and Australian/New Zealand standard. The assessment results revealed that the European code leads to conservative and scattered interactive buckling resistance predictions, while the American specification and Australian/New Zealand standard result in many unsafe and scattered interactive buckling resistance predictions. A new design approach was then developed, based on the Eurocode column buckling curve and the continuous strength method, and shown to lead to accurate, consistent and safe interactive buckling resistance predictions for press-braked stainless steel slender channel section columns. The reliability of the new design approach was confirmed by means of statical analyses. Besides, the relevant design rules for press-braked carbon steel slender channel section columns, as given in the North American specification, were assessed, and shown to result in unsafe though consistent interactive buckling resistance predictions, when used for their stainless steel counterparts. [ABSTRACT FROM AUTHOR]

• The structural behavior and capacity of RACFSST stub columns under combined loading are studied. • Twelve eccentric compression tests on RACFSST stub columns are conducted. • The evolution of neutral axis in RACFSST composite section as well as the confinement effect are discussed. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The relevant design codes are assessed against the test and FE data. This paper reports experimental and numerical investigations into the behaviour and resistance of recycled aggregate concrete-filled stainless steel tube stub columns under combined compression and bending. Eccentric compression tests were conducted on twelve stub column specimens fabricated from austenitic stainless steel tubes with two cross-section sizes and concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%). The test results, including the failure loads, load–mid-height lateral deflection curves, evolution of neutral axis and confinement effect, were discussed in detail. The testing programme was followed by a numerical modelling programme, where finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and loading combinations. Given that there are no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for natural aggregate concrete filled-carbon steel tube stub columns under combined compression and bending, as set out in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to recycled aggregate concrete filled-stainless steel tube stub columns, based on the test and numerical data. The evaluation results revealed that the European code and Australian/New Zealand standard generally provide an acceptable level of design accuracy, while the American specification yields unduly conservative failure load predictions. [ABSTRACT FROM AUTHOR]

• The local–flexural interactive buckling of S690 high strength steel slender channel section columns was studied. • Twelve pin-ended compression tests were conducted. • FE models were developed and validated and then adopted to perform parametric studies. • The accuracy of the codified design rules was assessed, revealing inaccuracy. • A new design approach was proposed, showing a high level of accuracy. This paper reports an experimental and numerical investigation into the local–flexural interactive buckling behaviour and resistance of press-braked S690 high strength steel slender channel section columns. An experimental programme was firstly conducted and included initial geometric imperfection measurements and twelve pin-ended column tests. Interaction between local buckling and flexural buckling was observed for all specimens upon testing and discussed in detail. The experimental programme was accompanied by a numerical modelling programme, where finite element models were developed and validated against the test results and then employed to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member effective lengths. The obtained test and numerical data were used to assess the accuracy of the codified design rules for press-braked S690 high strength steel slender channel section columns failing by local–flexural interactive buckling, as set out in the European code, North American specification and Australian/New Zealand standard. The assessment results revealed that the European code leads to excessively conservative and scattered resistance predictions, while the North American specification and Australian/New Zealand standard result in a higher level of design accuracy and consistency, but still with many conservative resistance predictions for columns with short to intermediate lengths. Finally, a new design approach was proposed and shown to yield substantially more accurate and consistent resistance predictions for press-braked S690 high strength steel slender channel section columns over the design codes. [ABSTRACT FROM AUTHOR]

• A total of 41 cold-formed steel built-up I-sections were tested under ETF, ITF, EOF and IOF loading conditions. • Finite element models were developed to replicate the experiments. • Parametric study of 258 specimens was performed. • The existing codified web crippling design provisions were assessed. • Design rules were proposed based on the unified equation and direct strength method. This paper reports the experiments, numerical modelling and design of cold-formed steel built-up I-sections subjected to localised loadings. The built-up I-sections were made up of two equal-sized plain channels fastened back-to-back in the web. The web crippling tests were undertaken on 41 built-up I-section members under Interior-Two-Flange (ITF), End-Two-Flange (ETF), Interior-One-Flange (IOF) and End-One-Flange (EOF) loading conditions. The effects of the arrangement of screws along the web height were investigated. After the experiments, finite element (FE) analyses considering the initial local imperfections of the web of the specimens were performed and the validity of the FE models was assessed using the test results. A parametric investigation including 258 numerical simulations was conducted to expand the database and evaluate the influences of the screw arrangements in the web height. The test and numerical results indicated that the failure modes of the specimens with different screw arrangements were generally similar in each loading condition, and the screws located close to the flange-web junctions of the sections could generally provide maximum web crippling resistances of the built-up I-sections. The design recommendations on the arrangements of screws along the web height were proposed. The experimentally and numerically generated web crippling resistances were utilized to assess the current North American specification (AISI S100), Australian and New Zealand standard (AS/NZS 4600) and European code (EN1993-1-3). The results show that the existing codified design formulas lead to either conservative or highly unsafe results. Therefore, two sets of design formulas were derived on the basis of unified equation and direct strength method. [ABSTRACT FROM AUTHOR]

• Eccentric compression tests on high strength concrete-filled high strength steel tube (HCFHST) stub columns were conducted. • The structural behaviour and resistances of HCFHST stub columns under combined loading were studied. • The eccentric compression test results for HCFHST stub columns were discussed. • FE models were developed to validate against the test results and then used to conduct parametric studies. • The applicability of the existing design codes to HCFHST stub columns under combined loading was evaluated. This paper presents comprehensive experimental and numerical investigations into the structural behaviour and resistances of high strength concrete-filled high strength steel tube (HCFHST) stub columns under combined compression and bending. The combined loading tests were conducted on twelve stub column specimens fabricated from S700 high strength steel square hollow section tubes with two cross-section dimensions and concretes with three grades (C40, C80 and C110). The combined loading test setup, procedures and results, including the failure loads, load–mid-height lateral deflection curves and failure modes, were reported in detail. The failure loads and the evolution of the neutral axis of the HCFHST stub column specimens under combined loading were analysed. The development and distribution of the transverse and longitudinal strains of the outer S700 high strength steel tubes were discussed. The experimental programme was followed by a numerical modelling programme, where finite element models were initially developed and validated against the test results and then used to conduct parametric studies to generate further numerical data. The test and numerical data were used to evaluate the applicability of the relevant design rules, as set out in the European code, American specification and Australian/New Zealand standard, to HCFHST stub columns under combined loading. The evaluation results generally indicated that the European code and Australian/New Zealand standard slightly overestimate the failure loads for HCFHST stub columns under combined loading, while the American specification offers accurate, consistent and safe failure load predictions when applied to eccentrically loaded HCFHST stub columns. [ABSTRACT FROM AUTHOR]

• A novel controlled-rocking concentrically braced frame (CR-CBF) system is developed. • Seismic performance of the (CR-CBF) system is evaluated by using incremental dynamic procedure (IDA). • The developed CR-CBF shows an efficient safety margin against collapse under different hazard intensities. • The new CR-CBF can be used as an alternative earthquake resisting system. Recent earthquakes in New Zealand and Japan showed that structures designed according to modern building codes might suffer significant damages with hefty financial and social losses. The primary reason lies in the seismic design approach, where most seismic force resisting systems (SFRS) were designed to prevent structures from collapse during strong earthquake shaking, without considering the damage and the usability of the structure after an earthquake. In this paper, a controlled rocking-concentrically braced frame (CR-CBF) is proposed. CR-CBF is a fused structural system that uses a combination of post-tensioned tendons (PTs) and energy dissipation devices (EDs) to create a controlled-rocking mechanism to minimize structural repair costs and down time after a strong earthquake. PTs are placed in the structure to provide the restoring forces and to minimize any residual deformation in the structure, while EDs are placed at the base of a structure to dissipate the earthquake energy. To ensure the CR-CBF can achieve high performance, two (CR-CBF) prototypes with different heights are designed using the novel equivalent energy design procedure (EEDP). The EEDP procedure allows designers to select different performance objectives at different shaking intensities. The results of nonlinear dynamic analyses of the CR-CBFs show that CR-CBFs have superior seismic performances as intended and can be efficiently designed using EEDP. Finally, the seismic performance of CR-CBF against collapse is assessed using incremental dynamic analysis (IDA) outlined in the FEMA-P695 methodology. The results show that the CR-CBFs designed by EEDP have sufficient safety against collapse, hence it can be used as an efficient seismic force resisting system. [ABSTRACT FROM AUTHOR]

• Flat-ended circular hollow sections were tested in tension. • Three bolt configurations were established in flattened ends. • Bearing failure and net-section fracture were observed. • The test load increased with increase in the number of bolts. • An adjusted bearing coefficient is suggested for bearing. Experiments were performed to investigate the behaviour of 28 circular hollow sections (CHSs) in tension, with flat ends and three bolt configurations (2, 3 and 4 bolts). The length of the members between the flat ends was kept constant at 1500 mm for all CHSs, and the sizes of the sections ranged from 60.3x2.0 to 101.6x4.5. Two modes of failure were observed, viz; bearing failure (BF) and net-section fracture (NSF). CHSs connected with 2 bolts failed in bearing, whilst net-section fracture was dominant in sections with 3 and 4 bolts. The notion that the change in the number of bolts can lead to different behaviours of the connections is a significant contribution to knowledge, particularly if flat-ended CHSs are used as structural truss elements. This paper demonstrates that the sections are capable of supporting large loads, however, the capacity of the tested specimen did not reach the full yield strength. It is apparent from the tensile strengths that a larger increase in strength was accomplished when the number of bolts was increased from 2 to 3 bolts than from 3 to 4 bolts. A comparison of the tensile strength with the strengths predicted by the North American standard (AISI S100-16w/S1-18), Australia/New Zealand standard (AS/NZS-4600:2018) and European standard (EN 1993–1-3) confirm that both standards provides a reasonable assessment of the strength of the 3 and 4 bolt configuration, which failed purely by net-section fracture. However, for the 2-bolted connections, which failed in bearing, it is proposed to use AS/NZS 4600:2018, with a bearing coefficient of C = 2.85, instead of C = 3.0, to increase the accuracy of the bearing strength expression for these specimens. [ABSTRACT FROM AUTHOR]

• The net section failure behaviour and capacity of stainless steel staggered botled connections are studied. • Tension tests on 31 stainless steel staggered bolted connections are conducted. • The influences of the staggered bolt hole pattern and pitches on the failure loads and modes are disscussed. • The accuracy of the codified design rules is assessed, indicating conservatism. • A new design approach based on the continuous strength method is proposed and results in substantially improved predictions. The present paper reports a thorough experimental investigation into the net section failure behaviour and capacity of stainless steel staggered bolted connections in tension. The testing programme was carried out on 31 stainless steel staggered bolted connection specimens, with 18 made of austenitic stainless steel (grade EN 1.4301), 7 made of duplex stainless steel (grade EN 1.4462) and 6 made of ferritic stainless steel (grade EN 1.4016). The geometric parameters, including the transverse and staggered pitches, and the staggered bolt hole patterns of the connection specimens, were varied. The test setup and procedures, as well as the key experimentally observed results, including the net section failure modes and loads, are reported in detail. The experimentally obtained net section failure loads and modes are analysed and discussed, and then utilised to assess the accuracy of the established design rules for stainless steel staggered bolted connections, given in the European, American and Australian/New Zealand standards. All three examined standards consider (i) net section fracture and (ii) gross section yielding in the design of stainless steel staggered bolted connections, and specify that the design failure load shall be taken as the minimum value calculated from all potential failure modes. It was found that the current design standards lead to overly conservative and scattered failure load predictions as well as inaccurate failure mode predictions. A new design approach based on the continuous strength method (CSM) is proposed, and shown to result in substantially improved predictions of both failure loads and failure modes. [ABSTRACT FROM AUTHOR]

• The flexural buckling of press-braked S960 ultra-high strength steel angle section columns have been studied. • Initial geometric imperfection measurements and 12 pin-ended column tests have been conducted. • Flexural buckling in both the 'C' orientation and 'reverse C' orientation has been investigated. • FE models have been developed and validated against the test results, and then used to conduct parametric studies. • The applicability of the relevant codified design provisions has been evaluated, based on test and FE results. The structural performance and compression resistances of pin-ended press-braked S960 ultra-high strength steel (UHSS) angle section columns have been studied based on experiments and numerical modelling, and are reported in the present paper. An experimental programme was firstly performed on two series of press-braked S960 UHSS angle section column specimens, with each series containing six specimens of the same cross-section dimension but different member lengths, and included initial torsional and global geometric imperfection measurements and pin-ended column tests. The detailed pin-ended column test setup, procedures and results, including the failure loads, deformations at the failure loads, load–mid-height lateral deflection curves and failure modes, were fully reported. It is worth noting that two distinct flexural buckling orientations about the minor principle axis were observed from the tests, namely 'C' orientation (indicating that the failed column specimens buckled towards the angle corners) and 'reverse C' orientation (signifying that the failed column specimens buckled towards the angle tips). A numerical modelling programme was then followed; finite element (FE) models were firstly developed to replicate the test responses, and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that the current design codes for steel structures, as used in Europe, Australia/New Zealand and North America, are only applicable to members and joints with material grades up to S700 (or S690), the relevant codified design provisions for press-braked S700 (or S690) high strength steel angle section columns were evaluated for their applicability to press-braked S960 UHSS angle section columns, based on the obtained test and numerical data. The evaluation results revealed that the European code yields unduly conservative and scattered compression resistance predictions when applied to press-braked S960 UHSS angle section columns, while the Australian/New Zealand standard and North American specification lead to a higher degree of design accuracy and consistency, on average, when used for press-braked S960 UHSS angle section columns, though some of the compression resistance predictions are unsafe for those failing by flexural buckling in the 'C' orientation. [ABSTRACT FROM AUTHOR]

• The flexural-torsional buckling behaviour of fixed-ended press-braked S690 high strength steel angle columns was studied. • Twelve compression tests of fixed-ended press-braked S690 high strength steel angle columns were carried out. • FE models were developed and validated against the test results, and then adopted for parametric studies. • The accuracy of the codified design rules and a new DSM-based design approach was evaluated. The flexural-torsional buckling behaviour and resistances of fixed-ended press-braked S690 high strength steel angle section columns have been studied based on testing and numerical modelling, and reported in this paper. A testing programme, employing four different equal-leg angle section sizes, was firstly conducted, and comprised material tensile coupon tests, initial global and torsional geometric imperfection measurements and twelve fixed-ended column tests. The column test setup and procedures were thoroughly presented, and the key obtained test results, including the failure loads and deformations at the failure loads, load–end shortening curves, load–mid-height torsional rotation curves and failure modes, were fully reported and discussed. This was followed by a numerical modelling programme, where finite element models were initially developed to simulate the experimental responses and then adopted to perform parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. The obtained test and numerical data were then used to evaluate the accuracy of the relevant codified design rules, given in the European code, North American specification and Australian/New Zealand standard, and a recently proposed DSM-based design approach. The results of the evaluation revealed that all the codified design rules yield excessively conservative and scattered flexural-torsional buckling resistance predictions for fixed-ended press-braked S690 high strength steel angle section columns, while the DSM-based design approach leads to substantially improved resistance predictions, owing to the rational consideration of the length-dependent characteristic of flexural-torsional buckling and the interaction of flexural-torsional buckling with minor-axis flexural buckling. [ABSTRACT FROM AUTHOR]

• Pin-ended tests on circular high strength concrete-filled stainless steel tube (HCFSST) columns were conducted. • The flexural buckling behaviour and resistances of circular HCFSST columns were discussed. • FE models were developed to validate against the test results and then used to conduct parametric studies. • The applicability of the existing design codes to circular HCFSST columns was assessed. The flexural buckling behaviour and resistances of circular high strength concrete-filled stainless steel tube (HCFSST) columns were examined based on experiments and numerical modelling, and reported in the present paper. The experimental programme was conducted on 12 circular HCFSST columns with various member relative slendernesses, and included material tests, initial global geometric imperfection measurements and pin-ended column tests, with their procedures and setups fully described. The experimentally observed results, including the failure loads and modes as well as the load-deformation curves (load-end shortening curves and load-mid-height lateral deflection curves) of the circular HCFSST column specimens and the development of the longitudinal strains of the outer stainless steel tubes, were presented and discussed. The experimental programme was then supplemented by a numerical modelling programme, where finite element models were developed and validated against the test results, and then used for conducting parametric studies to generate further numerical data on circular HCFSST columns over a broad spectrum of cross-section dimensions and member lengths. Owing to the lack of international design codes for stainless steel–high strength concrete composite structures, the relevant codified design rules for circular normal strength concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, America and Australia/New Zealand, were assessed for their applicability to circular HCFSST columns, based on the obtained experimental and numerical data. The assessment results indicated that the design rules, as given in the Australian/New Zealand standard and American specification, lead to many unsafe flexural buckling resistance predictions when used for circular HCFSST columns, while the design rules, as adopted in the European code, result in more safe and reliable design resistances for circular HCFSST columns failing by flexural buckling. [ABSTRACT FROM AUTHOR]

• Flexural buckling of S960 UHSS channel section columns was investigated. • Flexural buckling in both the 'C' and 'reverse C' orientations was examined. • Initial imperfection measurements and ten pin-ended column tests were conducted. • FE models were firstly validated and then used to perform parametric studies. • The applicability of the relevant codified design rules was assessed. Grade S960 ultra-high strength steel is receiving increasing attention owing to its excellent strength-to-weight ratio. However, its application in construction engineering is rather limited due to the lack of adequate design rules, as the current established codes in Europe, North America and Australia/New Zealand only cover the design of steel components with material grades up to S700 (or S690). This prompts investigations into different types of S960 UHSS structural components and development of accurate and efficient design rules for them. The present paper focuses on press-braked S960 UHSS channel section columns prone to flexural buckling about the minor principal axes, with their behaviour and resistances thoroughly examined through experiments and numerical modelling. An experimental programme was firstly performed on two non-slender press-braked channel sections, with five column specimens of varying member lengths employed for each cross-section, and included initial global and local geometric imperfection measurements and pin-ended column tests about the minor principal axes. This was followed by a parallel numerical modelling programme, where finite element (FE) models were developed to simulate the experimental results and afterwards adopted to perform a parametric study to generate additional numerical data over a broader spectrum of cross-section dimensions and member lengths. It is worth noting that there were two orientations associated with minor-axis flexural buckling of press-braked S960 UHSS channel section columns, namely 'C' orientation (indicating that columns buckled towards the webs) and 'reverse C' orientation (indicating that columns buckled towards the flange tips), and both of the two types of failure modes were carefully examined in the present study. It was found that channel section columns failing by flexural buckling in the 'reverse C' orientation generally exhibited superior resistances relative to their counterparts with failure in the 'C' orientation. The experimental and numerical data were also used to assess the applicability of the codified provisions for press-braked S700 (or S690) channel section columns failing by flexural buckling about the minor principal axes to the design of their S960 counterparts. The assessment results indicated that (i) the existing European code leads to overall conservative and scattered design flexural buckling resistances, especially for those relatively short and intermediate press-braked S960 UHSS channel section columns with failure in the 'reverse C' orientation, and (ii) the North American specification and Australian/New Zealand standard result in a higher degree of design accuracy and consistency than the European code, but with many over-predicted flexural buckling resistances for press-braked S960 UHSS channel section short and intermediate columns failing in the 'C' orientation. [ABSTRACT FROM AUTHOR]

• Numerical models for CFS built-up columns with spacers were developed. • Detailed nonlinear response of CFS built-up columns was investigated. • Predictions as per current Australian/European CFS standards were inconsistent. • Improved design equations were proposed for better/reliable strength predictions. This paper deals with the numerical investigation aimed to study the axial capacity and the nonlinear deformation response of pin ended cold-formed steel (CFS) built-up columns under monotonic axial loading, applied concentrically. The built-up sections were constructed by adequately spaced channel sections in a back-to-back configuration, connected through webs by means of connecting elements (CFS channels) called spacers. Self-driving screws were used as fasteners to assemble together the lipped channels and spacers. Finite element (FE) models were established and verified against the previously published built-up columns with similar configuration. An extensive parametric study was conducted by varying the key parameters like plate slenderness of the lipped channels, unbraced chord slenderness, and global slenderness in order to investigate their variation on the ultimate compression resistance of these built-up columns. The effective width method was used to determine the design strengths for these built-up columns using the AS/NZ Specifications and European Specification on cold-formed steel structures, which were later compared with the results obtained from the numerical parametric study. This study indicated that the provisions that are given in the current AS/NZS and European Specification in predicting the strengths of the built-up column with spacers had shortcomings. Therefore, new design equations for the reliable design strength predictions of the CFS built-up column composed of lipped channels with spacers were proposed. The incorporation of spacers curtailed the local buckling half-wave length, which improved the buckling resistance, predominantly in the columns failing by local buckling. [ABSTRACT FROM AUTHOR]

• Finite element modelling (FEM) of perforated unreinforced masonry walls. • Wall geometry and vertical pre-compression has significant effect on the behaviour. • FEA successfully captured the global in-plane behaviour of the tested walls. • Spandrel effect on the global behaviour of the wall is significant. This paper presents numerical modelling of the in-plane shear behaviour of unreinforced masonry (URM) walls with a semicircular arch opening. To do so, two dimensional finite element (FE) modelling of a series of experimentally tested walls was conducted using the simplified micro-modelling approach. The models successfully captured the load-displacement behaviour and, to a large extent, the failure modes of the piers and spandrels observed in the experimentally tested walls. The exception was that the FE modelling did not show pier diagonal shear cracking which was observed in some of the tested walls. The model was then used to perform parametric studies to investigate the effect of geometric variations of the walls as well as the effect of vertical pre-compression stresses on the lateral in-plane capacity of the walls. The results obtained from the FE analyses were compared to the anticipated maximum shear strength and the predicted failure modes according to the New Zealand Society for Earthquake Engineering (NZSEE, 2017). From this study, it is shown that there is a significant effect of the wall geometry and vertical pre-compression load on the failure modes and the lateral load resistance capacity of the walls. In most of the cases investigated, the NZSEE equations for maximum shear strength and failure modes agree well with the FEM results. The arch opening was remodelled to a rectangular opening and it was found that the effective pier height for an equivalent rectangular pier adjacent to a semi-circular arched opening can be taken up to the half height of the arch radius. [ABSTRACT FROM AUTHOR]

• Stub column tests were conducted on press-braked S960 ultra-high strength steel angle and channel sections. • Numerical models were developed and validated against test results, and then used to perform parametric studies. • The existing codified design rules were assessed against the test and numerical results, indicting inaccuracy. • Revised design rules were proposed and shown to yield improved design accuracy. A comprehensive experimental and numerical study of the cross-sectional compressive behaviour and resistances of press-braked S960 ultra-high strength steel (UHSS) angle and channel section stub columns is reported in this paper. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections, and comprised material testing, initial local geometric imperfection measurements and 18 stub column tests. The experimental setups, procedures and key observations were fully presented. The experimental study was then supplemented by a finite element (FE) simulation programme, in which FE models were firstly developed to replicate the test structural responses and subsequently used to generate further numerical data over a wide variety of cross-section sizes. It is worth noting that the current international standards established in Europe, America and Australia/New Zealand only cover the design of structural members with material grades up to S700, and thus the examined S960 UHSS angle and channel section stub columns are out of the scope of the existing design standards. In this study, the experimentally and numerically acquired data was adopted to assess the applicability of the codified provisions and formulations to the design of S960 UHSS angle and channel section stub columns. The assessment results generally indicated that the current European code leads to overall consistent and accurate predictions of cross-section compression resistances, but with many overestimated predicted resistances for S960 UHSS channel section stub columns, while the American and Australian/New Zealand standards yield unduly scattered design cross-section compression resistances, with unsafe and overly conservative predicted resistances respectively for S960 UHSS channel section stub columns and slender angle section stub columns. Revised codified design rules were also proposed, and shown to yield safe, accurate and consistent design cross-section compression resistances for S960 UHSS angle and channel section stub columns. [ABSTRACT FROM AUTHOR]

• Material responses and compression capacities of press-braked S690 angle and channel section stub columns were studied. • Thirty-six tensile flat and corner coupon tests on press-braked S690 angle and channel sections were conducted. • A total of twenty-four press-braked S690 angle and channel section stub columns were tested. • Numerical models were developed and validated against test results, and then used to perform parametric studies. • Current design codes and direct strength method were assessed against test and numerical results. This paper reports an experimental and numerical investigation into the cross-section behaviour and compression resistances of press-braked S690 high strength steel angle and channel section stub columns. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections with a range of cross-section sizes (covering both non-slender and slender sections), and included thirty-six material tensile flat and corner coupon tests, initial local geometric imperfection measurements and twenty-four concentrically loaded stub column tests. The experimental study was then supplemented by a numerical modelling programme, where numerical models were firstly developed to simulate the test structural responses and subsequently adopted to derive further numerical data. The experimentally and numerically derived results were utilised to assess the applicability of the Eurocode Class 3 slenderness limits for hot-rolled and welded sections to their cold-formed (press-braked) counterparts. The results of the assessment generally revealed that the Eurocode Class 3 slenderness limits for hot-rolled and welded sections can be safely adopted for the classification of press-braked (cold-formed) S690 high strength steel angle and channel sections subjected to compression. The accuracy of the codified design provisions established in Europe, North America and Australia/New Zealand as well as the direct strength method (DSM) to the design of press-braked S690 high strength steel angle and channel section stub columns was also assessed, based on the test data and numerical results. The North American, Australian and New Zealand standards were found to result in accurate and consistent compression capacity predictions for press-braked S690 high strength steel channel section and non-slender angle section stub columns, but greatly underestimate the compression capacities for those slender angle section stub columns, while the European code and DSM were shown to yield overall precise and consistent design compression capacities. [ABSTRACT FROM AUTHOR]

• Flexural behaviour of press-braked S960 UHSS channel section beams were studied. • 20 beam tests were performed about the minor axes in the u and n orientations. • Numerical simulations and parametric studies were conducted. • The applicability of the design codes was assessed based on test and FE results. A thorough experimental and numerical study of the flexural behaviour and strengths of press-braked S960 ultra-high strength steel (UHSS) channel section beams bent about the minor principal axes is reported in this paper. The experimental study was conducted on eight different UHSS plain channel sections, and included measurements on the material flat and corner properties and initial local geometric imperfections of the beam specimens as well as 20 four-point bending tests performed about the minor principal axes in both the 'u' and 'n' orientations. A complementary numerical investigation was then conducted, where finite element (FE) models were firstly developed and validated against the experimental results, followed by parametric studies carried out to acquire further numerical data over a broader range of cross-section dimensions. It is worth noting that the existing design codes for steel structures, as established in Europe, America and Australia/New Zealand, are only applicable to those with material grades up to S690 (or S700 for Eurocode) and cannot be directly used for S960 UHSS structural members. In the present study, the applicability of the codified design provisions and formulations for flexural members to the examined S960 UHSS channel section beams was evaluated, based on the ultimate moments derived from structural testing and numerical modelling. The quantitative evaluation results generally revealed that the current European code provides overall consistent and precise flexural strength predictions for Class 1 and Class 2 S960 UHSS channel sections in minor-axis bending, but leads to a high level of inaccuracy (scatter and conservatism) for the design of their Class 3 and Class 4 counterparts, whilst the American specification and Australian/New Zealand standard result in scattered and excessively underestimated design flexural strengths, except for the cases of slender S960 UHSS channel section beams in 'u'-orientation bending. [ABSTRACT FROM AUTHOR]

• Quasi-static reversed cyclic testing of slender RC walls. • Effect of bar buckling on the deformation capacity of RC walls. • Effect of boundary zone detailing on buckling tendency of longitudinal reinforcing bars. • Design of transverse reinforcement to restrict bar buckling in slender RC walls. The performance of reinforced concrete (RC) structural walls during the past earthquakes in New Zealand (2010–11) and Chile (2010) have highlighted the susceptibility of these critical structural components to several undesirable modes of failure. One such failure mode is premature buckling of the longitudinal reinforcing bars, which has also been observed in experimental tests of flexurally-dominant structural walls. This paper presents the results of an experimental program investigating the effects of transverse reinforcement detailing on buckling resistance of longitudinal reinforcement located in the boundary regions of RC structural walls. Three large-scale rectangular walls with different boundary zone transverse reinforcement detailing were tested under in-plane cyclic loading. The effects of these three types of detailing are reported in terms of drift capacity, buckling length of the longitudinal bars and cumulative energy dissipation capacity of the specimens. The test results confirm that bar buckling modes depend on transverse reinforcement detailing, which consequently also influences the ultimate flexural deformation capacity of ductile walls. By comparing the responses of the tested wall specimens, the inadequacy of code-compliant transverse reinforcement to restrain bar buckling is discussed and the effect of improved transverse reinforcement detailing (designed using a mechanics-based approach) on deformation capacity of slender walls is scrutinised. [ABSTRACT FROM AUTHOR]