Code For Design Of Steel Structures Research Articles

Numerical and experimental verification of column web in transverse compression

This paper focuses on the problem of steel members of open double symmetrical cross-sections in transverse compression. First, the problem is introduced with examples of its application in steel structures of buildings and followed by the overview of selected substantial literature resources and current design codes provisions. The essential part of the paper is a presentation of results of experimental tests and advanced numerical analysis of members subjected to selected cases of transverse compression. Where possible, the results are compared with resistances obtained using provisions in currently valid design codes for steel structures. The influence of selected parameters on the resistance in transverse compression is quantified within the evaluation with specific attention paid to plate buckling of the web. Based on data obtained from the experimental and numerical investigations, the most notable findings are summarized.

Unified machine-learning-based design method for normal and high strength steel I-section beam–columns

High strength steel is regarded as a promising construction material due to its superior mechanical properties. However, the codified failure load predictions for high strength steel welded I-section beam–columns are not accurate in some cases owing to the lack of relevant design codes for high strength steel structures. In addition, current design codes ignore the interaction effect of the cross-section plate elements, leading to the inaccuracy of codified predictive ultimate resistances for both normal and high strength steel beam–columns. In this paper, a unified and accurate design method was proposed based on machine learning for both normal and high strength steel welded I-section beam–columns failing by different failure modes. Firstly, a total of 812 experimental and numerical data on welded I-section beam–columns with various steel grades, geometric dimensions, including cross-section dimensions and member lengths, and failure modes, including global buckling, local buckling and local–global interactive buckling were collected to establish a database. Seven machine learning algorithms, including Decision Tree, Random Forest, Support Vector Machine, K-Nearest Neighbour, Adaptive Boosting, Extreme Gradient Boosting and Categorical Boosting were applied to develop regression models to predict failure loads. Based on the established database, each machine learning model was then trained and key hyperparameters were optimised. The model performance was evaluated through a series of statistical indicators and the feature importance analysis, and the evaluated results indicated that the XG-trained regression model had the highest level of accuracy. Finally, the predictions given by the XG-trained regression model were compared with those of the existing codified design provisions, as given in Eurocode and American codes. The evaluation results indicated that the codified predictive bearing capacities of I-section beam–columns were scattered and inaccurate, while the XG-trained regression model provided substantially improved failure load predictions.

Probabilistic fatigue strength modelling based on various statistical approaches for a double-side welded connection

S355 steel is currently used in the fabrication of most wind turbine monopile support structures and offshore structures. In these types of structures, most fatigue failures occur in the welded connections where cyclic loading is the main responsible for this phenomenon. For the high-cycle fatigue analysis, the stress life method utilizing S-N curves can be used to determine the strength of a welded joint under fatigue loading. In this research, the evaluation of design S-N curves for a double-side welded connection made of S355 steel is proposed. This study concludes with a comparison between the experimental fatigue curves obtained and the design S-N curves at 5% and 2.3% probability of failure proposed in design codes (EN1993-1-9, DNVGL-RP-C203 standards and IIW recommendations) for offshore structures and general steel structures. For the specimens under investigation, the hot-spot and nominal stress approaches are taken into consideration. The characteristic fatigue curves of the double-side welded connection are obtained using statistical analyses based on the ASTM E739, ISO 12107, Bayesian inference, and Weibull distribution. The hot-spot and nominal stress approaches yield very similar S-N results considering the specimens under study.

In-plane buckling strength of high strength steel I-section arches

This paper investigates the in-plane inelastic buckling of high strength steel (HSS) circular arches with pinned or fixed end supports. A finite element (FE) model is developed to analyse in plane behaviour and buckling loads of HSS circular arches under general loading conditions which considers geometric non-linearity, material inelasticity, initial imperfection and residual stresses of welded HSS I-sections. The FE model is validated by comparison to analytical elastic buckling loads for arches in uniform compression, and experimental results reported in the literature on the out-of-plane elastic-plastic buckling of steel arches. It is found that current design codes for normal strength steel (NSS) structures require modification before application to HSS arches. Based on the results of the FE analysis, design equations are proposed which are in-line with existing provisions for NSS structures for both fixed and pin-ended arches under uniform compression and combined compressive and bending actions. The presented design rules give good lower-bound predictions for in-plane buckling strength of fixed and pinned HSS arches. Additionally, the influence of residual stresses and size of initial geometric imperfections on in-plane buckling strength are explored.

Axial compressive behavior of non-symmetric cold-formed angular column with complex edge

Currently, the assembled-type light steel (ATLS) modular house is increasingly used for apartments, schools, hotels, and other similar buildings with repetitive units, in which the non-symmetric cold-formed angular section is usually served as column in the module unit. However, the compressive behavior and design method of the non-symmetric cold-formed angular column remain unknown due to the complex edge. In this paper, a series of tests were conducted on the axial compressive behavior of the non-symmetric cold-formed angular column. A total of 12 specimens with complex edge were tested under monotonic axial compression. A special support was designed at the end of the column to apply the axial compression along different loading axes of the complex section. The failure mode and axial compressive capacity of the test specimens were revealed and discussed in detail. It indicated that the loading axis significantly influenced the failure mode and axial compressive capacity of the non-symmetric cold-formed angular column. Furthermore, a 3D finite element model was developed and validated against the test results to broaden the research. Lastly, given that the current design codes for steel structures, as used in Europe, Australia/New Zealand and North, the relevant codified design was utilized to evaluate the axial compressive capacity of unequal angular column with a double edge fold stiffener, based on the obtained test data.

Pin-ended press-braked S960 ultra-high strength steel angle section columns: Testing, numerical modelling and design

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.

Flexural buckling behaviour and residual strengths of stainless steel CHS columns after exposure to fire

The flexural buckling behaviour and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were studied, based on a thorough experimental and numerical modelling programme, and reported in this paper. The experimental programme was performed on three series of specimens, and each series contained five geometrically identical specimens, with one unheated and the other four heated to different levels of elevated temperatures (namely 300 °C, 600 °C, 800 °C and 1000 °C). The detailed heating, soaking and cooling processes, material testing and pin-ended column tests were described, with the derived key experimental results fully presented. The testing programme was supplemented by a numerical modelling programme, including a validation study where finite element models were developed and validated against the test results, and a parametric study where the validated finite element models were employed to derive further numerical results over an extended range of cross-section dimensions and member lengths. Due to the absence of existing design codes for stainless steel structures after exposure to fire, the codified design provisions for stainless steel CHS columns at ambient temperature, as established in the Europe, America and Australia/New Zealand, were assessed for their applicability to stainless steel CHS columns after exposure to fire, based on the obtained test and numerical data. The assessment results generally revealed that the design buckling curve, as adopted in the European code, and the tangent modulus method, as employed in the American specification, lead to unsafe and scattered design flexural buckling strengths for stainless steel CHS columns after exposure to fire, while the explicit approach, as used in the Australian/New Zealand standard, yields a high level of accuracy and consistency in predicting the post-fire flexural buckling strengths of stainless steel CHS columns. • The flexural buckling responses and residual strengths of stainless steel circular hollow section (CHS) columns after exposure to fire were investigated. • Three series of stainless steel CHS column specimens were tested, with each series containing one unheated specimen and four specimens heated to different levels of elevated temperatures. • Finite element models were developed and validated against test results, and then utilised to perform parametric studies. • The accuracy of the codified flexural buckling design rules for stainless steel CHS columns at ambient temperature was assessed for their post-fire counterparts.

Flexural behaviour and strengths of press-braked S960 ultra-high strength steel channel section beams

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.

Structural response and continuous strength method design of slender stainless steel cross-sections

In current structural stainless steel design codes, local buckling is accounted for through a cross-section classification framework, which is based on an elastic, perfectly-plastic material model, providing consistency with the corresponding treatment of carbon steel cross-sections. Hence, for non-slender cross-sections, the codified design stress is limited to the 0.2% proof stress without considering the pronounced strain hardening exhibited by stainless steels, while for slender cross-sections, the effective width method is employed without considering the beneficial effect of element interaction. Previous comparisons between test results and codified predictions have generally indicated over-conservatism and scatter. This has prompted the development of more efficient design rules, which can reflect better the actual local buckling behaviour and nonlinear material response of stainless steel cross-sections. A deformation-based design approach called the continuous strength method (CSM) has been proposed for the design of stocky cross-sections, which relates the strength of a cross-section to its deformation capacity and employs a bi-linear (elastic, linear hardening) material model to account for strain hardening. In this paper, the scope of the CSM is extended to cover the design of slender stainless steel cross-sections under compression, bending and combined loading, underpinned by and validated against 794 experimental and numerical results. The proposed approach allows for the beneficial effect of element interaction within the cross-section, and is shown to yield a higher level of accuracy and consistency, as well as design efficiency, in the capacity predictions of slender stainless steel cross-sections, compared to the effective width methods employed in the current international design standards. Non-doubly symmetric sections in bending, which may be slender, but still benefit from strain hardening, are also discussed. The reliability of the CSM proposal has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures.

Hot-Rolled Steel and Steel-Concrete Composite Design Incorporating Strain Hardening

Current design codes for steel and steel-concrete composite structures are based on elastic, perfectly plastic material behaviour and can lead to overly conservative strength predictions due to the neglect of the beneficial influence of strain hardening, particularly in the case of stocky, bare steel cross-sections and composite beams under sagging bending moments. The Continuous Strength Method (CSM) is a deformation based design method that enables material strain hardening properties to be exploited, thus resulting in more accurate capacity predictions. In this paper, a strain hardening material model, which can closely represent the stress-strain response of hot-rolled steel, is introduced and incorporated into the CSM design framework. The CSM cross-section resistance functions, incorporating strain hardening, are derived for hot-rolled steel sections in compression and bending, as well as hot-rolled steel-concrete composite sections where their neutral axes lie within the concrete slab in bending. Comparisons of the capacity predictions with a range of experimental data from the literature and finite element data generated herein demonstrate the applicability and benefits of the proposed approach.

Behaviour and design of stainless steel SHS and RHS beam-columns

Previous studies on stainless steel tubular section beam-columns have revealed shortcomings in established codified design methods. These shortcomings stem principally from inaccurate predictions of the bending and column buckling end points of the design interaction curves, where the bending moment end points are tied to the elastic or plastic moment capacities without considering strain hardening, while the column buckling end points are often over-predicted. Inaccuracies also arise due to the adopted interaction factors, which do not fully capture the structural response of the stainless steel members under combined loading. These observations prompted the present research, which is aimed at developing more efficient design rules for stainless steel tubular section beam-columns. In the presented design proposals, the deformation-based continuous strength method (CSM), allowing for strain hardening, was used to determine the bending moment capacities (i.e. the bending end points), while the column buckling strengths (i.e. the column end points) were calculated according to recently proposed buckling curves. Based on these more accurate end points, new interaction factors were derived following a comprehensive numerical simulation programme. The accuracy of the new proposals was assessed through comparisons against over 3000 experimental and numerical results. Compared to the current design standards, the new proposal yields a higher level of accuracy and consistency in the prediction of stainless steel square and rectangular hollow section (SHS and RHS) beam-column strengths. Use of the proposed interaction factors but with the Eurocode bending moment capacities and revised column buckling strengths as the end points was also assessed and shown to result in more accurate and less scattered strength predictions than the current Eurocode provisions. The reliability of the proposals has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures.

Improved shear design rules for lipped channel beams with web openings

Cold-formed steel Lipped Channel Beams (LCB) with web openings are commonly used as floor joists and bearers in building structures. The shear behaviour of these LCBs with web openings is complicated and their shear capacities are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LCBs with web openings. Hence a detailed numerical study was undertaken to investigate the shear behaviour and strength of LCBs with unreinforced circular web openings. Finite element models of simply supported LCBs under a mid-span load with aspect ratios of 1.0 and 1.5 were developed and validated by comparing their results with test results. They were then used in a detailed parametric study to investigate the effects of various influential parameters. Experimental and numerical results showed that the current design rules in cold-formed steel structures design codes are very conservative. Improved design equations were therefore proposed for the shear strength of LCBs with web openings based on both experimental and numerical results. This paper presents the details of finite element modelling of LCBs with unreinforced circular web openings, validation of finite element models, and the development of improved shear design rules. The proposed shear design rules in this paper can be considered for inclusion in the future versions of cold-formed steel design codes.

Distortional–global interaction buckling of stainless steel C-beams: Part II — Numerical study and design

The paper presents a detailed finite element (FE) model intended for studying the distortional–global interaction buckling behaviour of thin-walled stainless steel beams. The model incorporated actual measured material properties of three stainless steel alloys (austenitic S30401, ferritic S44330 and lean duplex S32101), as well as measured initial geometric imperfections. The model was verified against the experimental data presented in the companion paper [1]. A parametric study was then carried out using the calibrated model to augment the ultimate strength database The accuracy of the Australian/New Zealand (AS/NZS 4673 [2]), American (SEI/ASCE-8 [3]) and European (Eurocode3, Part1-4 [4]) standards for stainless steel structures was evaluated using the available data. It was found that the current Australian/New Zealand and American design codes do not contain rules for checking distortional buckling strength nor do they account for distortional–global interaction buckling effects. The European standard accounts for distortional buckling effects by reducing the effective area of flange stiffeners using an effective thickness method, and covers the effect of distortional–global interaction by using the effective cross-section for overall buckling strength checks. The European code was therefore more conservative than the other two standards. Following the principles of the Australian and American design codes for cold-formed steel structures, additional provisions for checking distortional buckling strength were suggested to improve the current Australian/New Zealand and American stainless steel design codes. Variants of the proposed provisions to account for distortional–global interaction were also examined which resulted in generally better predictions than those of the European code. However, the distortional–global interaction effect was found to vary with the section slenderness, and none of the design provisions performed consistently better than others.

Experimental studies of the shear behaviour and strength of lipped channel beams with web openings

Cold-formed steel members are increasingly used as primary structural elements in the building industries around the world due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. However, their shear capacities are determined based on conservative design rules. Current practice in flooring systems is to include openings in the web element of floor joists or bearers so that building services can be located within them. Shear behaviour of LCBs with web openings is more complicated while their shear strengths are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LCBs with web openings. Hence a detailed experimental study involving 40 shear tests was undertaken to investigate the shear behaviour and strength of LCBs with web openings. Simply supported test specimens of LCBs with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. This paper presents the details of this experimental study and the results of their shear capacities and behavioural characteristics. Experimental results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LCBs with web openings. Improved design equations have been proposed for the shear strength of LCBs with web openings based on the experimental results from this study.

Concepts and implementation of strain-based criteria in design codes for steel structures

A uniaxial tension test is commonly used to determine the mechanical properties of steel, but it has no meaning for the response of the material in a structure. The test was developed as a consensus solution by producers, fabricators, designers and code writers, to have a standard by which similar materials could be compared to a common base. It does not represent the actual behavior of the steel in a structure, and was never intended to do so. To study the true behavior of the structure and how the material responds it would be better to determine the strains and deformations that will take place during actual service condition. Such characteristics reflect the real behavior, whether in the elastic or inelastic range. If stresses or forces are needed, these are easily determined by the value of the strain and the relevant material modulus, along with the type of cross section, whether elastic or inelastic. The paper addresses the properties of a range of structural steels, how these are incorporated into design standards and how the standards define deformation characteristics and demands for bolted and welded connections.

Shear Behaviour and Strength of LiteSteel Beams with Web Openings

The LiteSteel Beam (LSB) is a new cold-formed steel hollow flange channel beam recently developed in Australia. It is commonly used as a floor joist or bearer in buildings. Current practice in flooring systems is to include openings in the web element of floor joists or bearers so that building services can be located within them. Shear behaviour of LSBs with web openings is more complicated while their shear strengths are considerably reduced by the presence of web openings. However, no research has been undertaken on the shear behaviour and strength of LSBs with web openings. Therefore a detailed experimental study involving 26 shear tests was undertaken on simply supported LSB test specimens with web openings and an aspect ratio of 1.5. This paper presents the details of this experimental study and the results of their shear capacities and behavioural characteristics. Experimental results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LSBs with web openings. Improved design equations have been proposed for the shear strength of LSBs with web openings based on the experimental results from this study.

New Design Rules for the Shear Strength of LiteSteel Beams with Web Openings

A LiteSteel beam (LSB) is a new cold-formed steel hollow flange channel section produced using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. The LSBs are commonly used as floor joists and bearers with web openings in residential, industrial, and commercial buildings. Their shear strengths are considerably reduced when web openings are included for the purpose of locating building services. However, no research has been undertaken on the shear behavior and strength of LSBs with web openings. Therefore, experimental and numerical studies were undertaken to investigate the shear behavior and strength of LSBs with web openings. In this research, finite-element models of LSBs with web openings in shear were developed to simulate the shear behavior and strength of LSBs including their buckling characteristics. They were then validated by comparing their results with available experimental test results and used in a detailed parametric study. The results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LSBs with web openings. Improved design equations have been proposed for the shear capacity of LSBs with web openings based on both experimental and parametric study results. An alternative shear design method based on an equivalent reduced web thickness was also proposed. It was found that the same shear strength design rules developed for LSBs without web openings can be used for LSBs with web openings provided the equivalent reduced web thickness equation developed in this paper is used. This is a significant advancement as it simplifies the shear design methods of LSBs with web openings considerably.

In-plane strength of concrete-filled steel tubular circular arches

More than 400 concrete-filled steel tubular (CFST) arch bridges have been constructed worldwide so far. However, design codes or guidance for the in-plane strength design of CFST arches are yet to be developed. In current design practice, the philosophy for the in-plane strength design of reinforced and prestressed concrete arches is widely adopted for CFST arches. For this, the CFST arches are considered under central or eccentric axial compression and are treated similarly to CFST columns, and the classical buckling load of CFST columns is used as the reference elastic buckling load of CFST arches. However, under transverse loading, the in-plane elastic buckling behaviour of CFST arches, particularly shallow CFST arches, is very different from that of CFST columns under axial compression. In addition, different from CFST columns under central or eccentric axial compression, CFST arches are subjected to significant nonlinear bending actions and transverse deformations prior to buckling and these will influence the strength of CFST arches greatly. Therefore, it is doubtful if the current method for in-plane strength design of CFST arches can provide correct strength predictions. In this paper, a method for the in-plane strength design of CFST circular arches, which is consistent with the current major design codes for steel structures, is developed by considering both geometric and material nonlinearities. A design equation for the in-plane strength capacity of CFST arches under uniform compression, and a lower-bound design equation for the in-plane strength check of CFST arches under combined actions of bending and compression are proposed.

Design Approach of Stiffeners and Model of the Initial Stiffness in Extended End-Plate Connection

End plate stiffener failures occure in a number of tests in recent years. And no relevant rules are given in design codes for steel structures. A design method for angles and thickness of stiffeners in extended end plate connecionts is derived by requiring the eqaul distribution of tensile force among bolts inside and outside of beam flange. And a balance between the force transmitted by the stiffener and by the beam flange is considered too. Comparisons with results of ANSYS show that the stiffeners designed by the proposed method in this paper are able to change the extended portion of endplates from one side clamped to 2 panels fixed on two adjacent sides. Simple formulas for calculating rotational rigidities of the connections with and/or without stiffeners were also proposed with component method, in which the end-plate stiffness, column flange stiffness and bolt stiffness are inclueded. Comparisons with results of ANSYS show that the proposed equations have good precision and can be applied to pratical engineering.

New design rules for the shear strength of LiteSteel beams

The LiteSteel Beam (LSB) is a new cold-formed hollow flange channel section produced using dual electric resistance welding and automated continuous roll-forming technologies. The innovative LSB sections have many beneficial characteristics and are commonly used as flexural members in building construction. However, limited research has been undertaken on the shear behaviour of LSBs. Therefore a detailed investigation, including both numerical and experimental studies, was undertaken to investigate the shear behaviour of LSBs. Finite element models of LSBs in shear were developed to simulate the nonlinear ultimate strength behaviour of LSBs, including their elastic buckling characteristics, and were validated by comparing their results with experimental test results. Validated finite element models were then used in a detailed parametric study into the shear behaviour of LSBs. The parametric study results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LSBs. Significant improvements to web shear buckling occurred due to the presence of torsionally rigid rectangular hollow flanges, while considerable post-buckling strength was also observed. This paper therefore proposes improved shear strength design rules for LSBs within the current cold-formed steel code guidelines. It presents the details of the parametric study and the new shear strength equations. The new equations were also developed based on the direct strength method. The proposed shear strength equations have the potential to be used with other conventional cold-formed steel sections such as lipped channel sections.