Steel Circular Hollow Section Research Articles

Buckling behaviour of high-strength retrofitted steel sections manufactured through post heat-treatment processes

High-strength steel is increasingly popular in construction for its strength-to-weight ratio, which lowers the self-weight of structures and reduces transportation, erection, and foundation costs. Induction hardening (IH) process which involves rapid heating and cooling of the material leads to microstructural changes which enhance the hardness and strength of conventional steel, elevating it to the level of High Strength (HS) steel. This study reports an extensive investigation on the buckling response and design of IH post-treated structural steel Circular Hollow Sections (CHS). It includes tensile coupon tests, microstructural analyses, initial geometric imperfection measurements, and residual stress evaluations to determine the effects of IH treatment on CHS. Column buckling tests were conducted, and a numerical model was developed and validated against the experimental results which was utilised to study systematically the effect of imperfections. The findings suggest that the magnitude of the imperfections in IH steel sections doubled compared to the non-treated condition, whilst there was a minimal impact on the residual stresses. A comprehensive parametric study was performed using finite element models to study the structural response of IH steel CHS columns over a large range of global slendernesses and allow the assessment of the buckling curves specified in EN 1993–1–1. It was concluded that the buckling curve a (imperfection factor, α=0.21) specified in EN 1993–1–1 provides the best buckling load predictions for the IH steel CHS columns, the response of which is superior to that of their virgin counterparts, despite the increased imperfections caused by the heat-treating process.

Interpretable machine learning models for predicting probabilistic axial buckling strength of steel circular hollow section members considering discreteness of geometries and material

Steel circular hollow section (CHS) members are widely utilized as axial force-resisting structural members in civil engineering structures. The buckling strength under axial loads is one of the critical parameters to determine the performance of the steel CHS members, which is significantly affected by the discreteness introduced by geometries, material, and initial imperfections. However, the reduction factor employed in the modern design codes (i.e. Chinese codes and EC3) only accounts for the reduction caused by all kinds of discreteness and does not reflect the impacts of every single discreteness and imperfection. To fill the gap, this paper proposed an interpretable machine-learning method to provide the probabilistic axial buckling strength of steel CHS members prediction result in a distribution form with the consideration of detailed discreteness. The model to predict the nominal axial buckling strength of steel CHS members was first developed utilizing ten machine learning algorithms after sufficient numerical simulations, where the numerical model was verified using test results. The artificial neural network (ANN) was selected for developing the prediction model due to its highly reliable performance in testing. The developed ANN models were further interpreted utilizing Shapley Additive exPlanations (SHAP) to determine the interrelationship of different parameters. Then, the probabilistic axial bucking strength prediction model was established based on the developed ANN models, where the Latin hypercube sampling method was applied to address the discreteness of geometries, material, and initial imperfections. The generated probabilistic axial bucking strength prediction model’s effectiveness was verified by the evidence that the machine learning prediction results can highly match the numerical results' probability density function and the result from codes while significantly reducing the computation time. Finally, the design parameters’ impact on the axial buckling strength’s discreteness was evaluated using the global sensitivity analysis (GSA) method. The result shows that the discreteness of design parameters substantially influences the distribution of the axial buckling strength of the steel CHS members and the proposed prediction model can provide an accurate probabilistic distribution prediction.

Parametric analysis of innovative corrugated profile of soil‐steel composite bridge

AbstractComposite soil‐steel corrugated structures are well recognized and widely used for construction of culverts and pedestrian or animal crossings. Moreover, for the past decade corrugated soil‐steel structures because of their large span are also recognized and chosen for bridges and tunnels engineering. Record holder composite corrugated structure of 32.40 m span encourages new research in the development of innovations. This paper investigates innovative the deepest corrugation cross‐section strengthened with circular hollow section steel pipes influence on plate utilization of large span soil‐steel composite bridge. The numerical 2D model of 17.5 m span structure was developed for investigation. Parametric analysis indicated that introduction of circular pipes will reduce corrugated profile steel thickness because of reduction of buckling length of straight region of corrugation. Moreover, 3D numerical analysis of buckling shapes allowed to conclude that local buckling of the deepest corrugation of 500 × 237 mm could be controlled strengthening the plates with circular steel pipes.

Post-fire behavior and residual resistances of S890 ultra-high strength steel circular hollow sections under combined compression and bending

This paper presents experimental and numerical investigations into the post-fire local buckling behavior and residual resistances of S890 ultra-high strength steel (UHSS) circular hollow section (CHS) under combined compression and bending. The physical testing was firstly conducted and encompassed heating, soaking and cooling of specimens, as well as post-fire tensile coupon tests, measurements of initial local geometric imperfections and eccentrically loaded stub column tests. Then, finite element models were developed and validated with reference to the experimental observations and then adopted for parametric analyses to derive additional numerical data, considering various cross-section dimensions and loading combinations. As a result of the lack of design provisions for ultra-high strength steel structures after exposure to elevated temperatures, the applicability of the relevant ambient temperature design interactive curves given in the current European, American and Australian standards to post-fire S890 UHSS CHS under combined compression and bending was assessed, with post-fire material properties used. The assessment results showed that all design standards exhibited conservative and scattered predictions of residual resistances for S890 UHSS CHS under combined compression and bending at ambient temperature and after exposure to elevated temperatures. The American specification provided more precise predictions of residual failure loads for non-compact and slender (Class 3 and 4) sections than the Eurocode and Australian standard, due to the accurate compression and bending endpoints. In comparison to the American and Australian specifications, the Eurocode resulted in more precise results in predicting residual failure loads of compact (Class 1 and 2) sections, owing to the accurate compression and bending endpoints as well as the nonlinear design interaction curve.

Numerical investigation and design methods of the local buckling of WAAM stainless steel circular hollow section stub columns

3D printing is an advanced technology that has been used in biomedical and automotive engineering, and has raised a significant response in civil engineering. Wire and arc additive manufacturing (WAAM), a metal 3D printing technology, has prospective applications in steel construction because it can fabricate large-scale structural members at an acceptable cost and manufacturing efficiency. Fundamental studies are still urgently needed to realize its engineering application. However, due to the irregular geometric features, limited studies on the structural performance of WAAM components, particularly the numerical studies, have been carried out. To this end, a numerical investigation on the local buckling of WAAM stainless steel circular hollow section (CHS) stub columns under axial compression has been conducted and presented herein. The finite element (FE) models were established and validated against the existing experimental research. Parametric studies were subsequently carried out to broaden the cross-sectional resistance data pool using the developed FE models. The applicability of the cross-section design provisions specified in EN 1993-1-4:2006 + A2:2020, ANSI/AISC 370-21 and the continuous strength method (CSM) for the design of WAAM CHS was evaluated according to the experimental and FE results. Furthermore, a modified design method with improved accuracy was suggested.

Experimental and numerical investigation on short CHS steel columns restrained with HFRP under axial compressive loading

Fiber-reinforced polymer (FRP) is a practical approach to delay or even suppress the deformation of steel structures. However, their application has been constrained by brittle damage and low strengthening efficiency. This paper presents an investigation of the mechanical behavior of short circular hollow section (CHS) steel columns restrained with hybrid fiber-reinforced polymer (HFRP) composed of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) under axial compression. The results show that the restraint effect of HFRP composed of one layer of transverse CFRP as the middle layer and two layers of transverse GFRP as the inner and outer layers is better than two layers of transverse CFRP, with peak load and ductility increased by 7.29 % and 12.36 % over the latter. Then, a simplified method for simulating HFRP and single FRP restrained short CHS steel columns is proposed and verified by experimental results. Moreover, a parametric study is performed to discuss the effect of the diameter-to-thickness ratio on the bearing capacity. Finally, a universal method is proposed to calculate the ultimate bearing capacity of HFRP and single FRP restrained short CHS steel columns, for which the average error and standard deviation from the measured values are 2.27 % and 0.024, respectively.

Experimental and numerical investigations of S890 and S960 ultra-high strength steel circular hollow section columns

The experimental and numerical investigations of the buckling behaviour and load-carrying capacities of S890 and S960 ultra-high strength steel (UHSS) circular hollow section (CHS) columns were conducted and reported in this paper. The experimental program encompassed tensile coupon tests, initial global and local geometric imperfection measurements and pin-ended column tests. Parallelly, the numerical modelling program was carried out, where the developed finite element (FE) models were validated with reference to the experimental observations and then employed in parametric studies to result in additional numerical data, considering various cross-sectional dimensions and member lengths. Based on the obtained FE and test data, the applicability of the relevant codified design buckling curves in the current European, Australian and American specifications to S890 and S960 UHSS CHS columns was evaluated, since the aforementioned standards only cover the design rules with steel material yield strength no greater than 700 MPa. The assessment results showed that the European code and Australian standard can generally accurately predict the resistances of S890 and S960 UHSS CHS columns, but result in some unsafe data points, while the American specification yielded accurate and consistent resistance predictions. Finally, a revised Eurocode design buckling curve was proposed, accompanied by the reliability assessment through statistical analyses, with the improved design accuracy and consistency revealed.

A cradle-to-site life cycle analysis of laser-cut passing-through tubular joints under different seismic conditions

Steel circular hollow sections (CHS) offer a number of advantages compared to their open section counterparts such as better resistance under tension, compression, bending in all directions and an overall reduction of structural weight, required material for corrosion and fire protection. Nevertheless, the traditional methods to connect open section beams to CHS columns often demand a significant amount of fabrication work, leading to high expenditure and resource consumption – therefore limiting their use in the current industry. These issues can be solved with an automatized joint fabrication. To that purpose, this article proposes two innovative “passing-through” I-to-CHS joints, achieved via laser cutting technology (LCT). Experimental and numerical studies were conducted to assess the joint fabrication aspects as well as the structural performance of the proposed joints. The results showed that the proposed joints can offer respectively 2.5- and 10-times larger strength and stiffness properties compared to a conventional directly welded I-to-CHS joint having similar section properties for the beam and the column. However, this study focuses on the environmental sustainability and economic feasibility of the proposed joints. A cradle-to-site life cycle analysis is conducted using multi-storey frame structures. The environmental and economic impact of the proposed joints are compared with different types of existing I-to-CHS joints in order to assess their possible benefits and limitations. Thanks to the savings in the raw material, surface treatment and transportation resources, it could be stated that, the passing-through approach with LCT offers approximately 32−42% reduction in the construction and fabrication costs of the multi-storey structures while reducing the CO2 emissions by 24−28%, compared to the directly welded I-to-CHS joints.

Global buckling and resistances of austenitic stainless steel semi-oval hollow section beam-columns

As advanced manufacturing technologies become increasingly mature in civil engineering, novel tubular sections, characterised by appealing architectural appearance and prominent structural efficiency, can be fabricated, with an example being semi-oval hollow section. The present paper reports an experimental and numerical investigation into the global buckling behaviour and resistances of austenitic stainless steel semi-oval hollow section beam-columns under combined compression and bending. An experimental programme was firstly performed on ten austenitic stainless steel semi-oval hollow section beam-column specimens and included initial geometric imperfection measurements and eccentric compression tests. The obtained test failure loads, load–mid-height lateral deflection curves and failure modes were fully reported. Following the experimental programme, a numerical modelling programme was conducted, including validation studies to validate developed finite element models against the test results and parametric studies to generate additional numerical data. Given that the existing European code and American specification do not cover the design of stainless steel semi-oval hollow section components, the applicability of the codified design interaction curves for austenitic stainless steel circular hollow section beam-columns to their semi-oval hollow section counterparts was evaluated based on the obtained test and numerical data. The European code was found to result in relatively accurate and consistent resistance predictions for austenitic stainless steel semi-oval hollow section beam-columns with Class 1 and 2 cross-sections, but the resistance predictions for those with Class 3 cross-sections were conservative and scattered. The American specification was shown to offer overall accurate and consistent resistance predictions, but some resistance predictions were marginally unsafe.

Effect of the CFRP length and beam curvature on the strength gain of CFRP-strengthened vertically curved circular hollow sections: an experimental study

ABSTRACT The effects of CFRP wrapping length and the beam curvature on the ultimate strength of carbon fibre reinforced polymer (CFRP)-strengthened in-plane curved steel circular hollow sections (SCHS) were studied by means of an experimental study. A total of 16 beams having four curvatures 0 mm, 2000 mm, 4000 mm and 6000 mm, which were strengthened with three CFRP lengths 500 mm, 750 mm and 1000 mm, were tested under three-point bending. Failure loads, failure mechanisms, strain variations and load-deflection responses were observed. Four types of failure modes were observed in CFRP-strengthened vertically curved SCHS depending on the CFRP wrapping length. The best performance was noted in strengthened beams when the ratio between CFRP wrapping length and beam span is 0.625.

Numerical simulation of corroded circular hollow section steel columns: A corrosion evolution approach

This study introduces a numerical simulation method for corroded circular hollow section steel columns, utilising a newly developed corrosion evolution model. This model was formulated by characterising the corrosion morphology and calibrating parameters throughout the entire corrosion process. An interpolation method was implemented to estimate the number of corrosion pits, based on experimentally measured corrosion ratios. Consequently, this allowed for the numerical prediction of the time-varying corrosion morphologies. Finite element (FE) models, incorporating this corrosion evolution model, were constructed. These corroded column models underwent validation through comparison with experimental findings. To further establish the effectiveness of the proposed FE models in predicting the structural behaviour of corroded members, FE models were also developed using the traditional uniform thickness reduction approach for comparative analysis. The results revealed that the proposed FE models for corroded structures offer a more accurate prediction of mechanical performance, particularly in instances of severe corrosion damage.

Fire behaviour of stainless steel circular hollow section stub columns: Experimental study and design

Circular hollow sections (CHS) are common in structural engineering owing to their excellent aesthetic appearance and structural behaviour. However, there is no existing experimental study into the cross-sectional behaviour of stainless steel CHS in fire. To fill this gap, an experimental study performed on austenitic stainless steel CHS in fire is presented in this paper. A total of eight CHS stub columns were examined at different temperatures, spanning from 20 °C to 800 °C. The material properties, geometric characteristics and local geometric imperfections of the tested CHS stub columns were also obtained simultaneously. Finally, the accuracy of EN 1993-1-2 design rules and a recent design method proposed by Quan et al. was assessed based on the obtained test data. It is shown that, compared to the design rules of EN 1993-1-2, the ultimate cross-sectional resistances predicted by the design method of Quan et al. can achieve higher accuracy and reliability for stainless steel CHS in fire.

Behaviour and design of high strength steel circular hollow section member under pure torsion

The paper presents a detailed numerical investigation on the performance of high strength steel (HSS) circular hollow section (CHS) member subjected to pure torsion. Three grades of HSS, viz., S700, S900 and S1100, were considered in the study. Finite element (FE) models were initially developed and validated against the available test results. Further, the validated FE models were used for parametric study. Cross-sections of varying thickness and diameters, as well as HSS grades, were considered for the parametric study. The results generated from the parametric study were then utilised to assess the effect of steel grades on the torsional capacities and deformed shapes at ultimate and post-ultimate capacities. The effect of ratio of yield strength to ultimate ratio on the normalised member capacities has also been studied. Furthermore, the applicability of existing design equations for members subjected to pure torsion have been assessed against the FE generated member capacities. Based on the analysis, most of design predictions outlined in European and American Standards, as well as those proposed by various researchers were found unsuitable for design of HSS CHS under torsion. Hence, two modified design equations based on continuous strength method and direct strength method has been proposed. The modified design methods were found to predict more accurate and reliable torsional capacities.

Investigation of energy-absorbing connections for application in mass timber structures

This study presents the results of an experimental program investigating the use of steel energy-absorbing connections (EAC) for the purpose of improving the energy dissipation capabilities of timber assemblies. The performance of the EACs is investigated both experimentally and numerically. A total of thirty-six specimens, representing nine configurations, including angle and circular hollow-steel sections, were tested under quasi-static and dynamic loading. The results of the study showed that connection configurations with well-defined plateaus were capable of dissipating a significant amount of energy and as such can be used in design for blast mitigation. Scalability of resistance based on the connection's depth was shown to be achievable experimentally. The welding configurations were shown to impact the behaviour significantly, and thus the details used in manufacturing must be identical to those assumed in design. The resistance curves of the EAC configurations investigated were reasonably predicted using Finite Element models. Analysis with single degree of freedom utilizing resistance curves obtained experimentally or from the finite element model mimicked the observed behaviour of the EACs. An example of the application of EACs in a mass timber assembly is demonstrated. This example showed that a 247 % increase in the energy absorption of the system might be obtained when compared to glulam members with idealized simply-supported boundary conditions.

Stability and design of stainless steel hollow section columns at elevated temperatures

This paper investigates the stability and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures. Nonlinear shell finite element models are employed to conduct comprehensive parametric studies whereby extensive benchmark structural performance data on the behaviour and resistance of stainless steel hollow section columns at elevated temperatures is generated. In total, 26,760 cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various member slendernesses, cross-section geometries, cross-section slendernesses and elevated temperature levels. New flexural buckling design rules are put forward for stainless steel hollow section columns in fire, which consistently considers the elevated temperature strength at 2% total strain f2,θ as the reference material strength for all cross-sections classes. The accuracy, safety and reliability of the proposed new design rules are assessed for a wide range of cases. Comparisons are also made against the results obtained through the column fire design rules of the European structural steel fire design standard EN 1993-1-2 [1]. It is demonstrated that the proposed new design rules furnish more accurate, safe-sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the column fire design provisions of EN 1993-1-2 [1].

Numerical Study on Residual Stresses and Plastic Strains in Cold-Formed High-Strength Steel Circular Hollow Sections.

This paper presents a numerical investigation on the residual stresses and co-existent equivalent plastic strains in cold-formed high-strength steel (CFHSS) circular hollow sections (CHS) by using an advanced finite element (FE)-based method. In this method, the entire manufacturing process of the CFHSS CHS was modeled numerically. The accuracy of the numerical predictions of equivalent plastic strains and residual stresses in the CFHSS CHS was verified by comparing the predictions with the existing test results of both the residual stress measurement and load-end shortening response of the stub column. By using the FE-based method, the effects of high-frequency electric resistance welding on the residual stresses and the stub column response were investigated. The through-thickness variations of both the equivalent plastic strains and residual stresses in CFHSS CHS, which are difficult to measure in the laboratory, were explored numerically. Finally, the effect of cold work (which is quantified by the equivalent plastic strains and residual stresses) on the stub column response of CFHSS CHS tubes was evaluated. It can be found that the equivalent plastic strains and longitudinal residual stresses are generally uniform around the cross-section of CFHSS CHS. The transverse and longitudinal residual stresses are generally uniform across each half-thickness, with the inner half-thickness under compression and the outer half-thickness under tension. The results also demonstrate that both the plastic strains and residual stresses may significantly affect the cross-section capacities of CFHSS CHS.

Testing, numerical modelling and design of S890 and S960 ultra-high strength steel circular hollow sections under combined loading

The present paper reports the experimental and numerical investigations into the structural behavior and resistances of S890 and S960 ultra-high strength steel circular hollow sections (CHS) under combined loading. The experimental investigation was performed firstly, comprising the tensile coupon tests on S890 and S960 ultra-high strength steel materials, precise measurements of initial local geometric imperfections and eccentrically loaded tests on 12 stub columns, with each 6 respectively conducted on S890 and S960 ultra-high strength steel CHS. The numerical investigation was subsequently conducted, where numerical models were created and verified against the experimental responses and adopted to conduct parametric studies to produce more numerical data over an extensive variety of loading combinations and cross-section geometries. The design interaction curves, as codified in the European, Australian and American standards, were assessed for their applicability, based on the numerical and test data, to S890 and S960 ultra-high strength steel CHS under combined loading. The evaluation findings demonstrated that (i) the European code leads to the slightly conservative failure load predictions for Class 1 (and 2) S890 and S960 ultra-high strength steel CHS under combined loading, but overly conservative predictions for Class 3 and 4 counterparts, (ii) the predicted failure loads by American specification for non-compact (i.e. Class 3 and 4) are more accurate due to the more precise compression and bending end points and (iii) the resistance predictions by Australian standard for compact (i.e. Class 1 and 2) sections are rather conservative due mainly to its inaccurate design interaction curve.

Local buckling response and design of stainless steel hollow sections at elevated temperatures

AbstractThe structural behaviour and design of stainless steel hollow sections in fire, including stainless steel (i) circular hollow sections (CHS), (ii) elliptical hollow sections (EHS), (iii) square hollow sections (SHS) and (iv) rectangular hollow sections (RHS), are explored in this paper. Shell finite element models of stainless steel CHS, EHS, SHS and RHS able to replicate their structural response at elevated temperatures are created. Numerical parametric studies are performed on cold‐formed and hot‐rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS subjected to (i) pure compression, (ii) pure bending, (iii) combined axial compression and bending and (iv) combined bending and shear in fire, covering different cross‐section slendernesses and elevated temperature levels. Calibrated against the benchmark structural performance data obtained from the numerical parametric studies, the new design proposals for predicting the ultimate resistances of stainless steel CHS, EHS, SHS and RHS in fire put forward in Quan and Kucukler [1,2] are set out. It is demonstrated that relative to the design recommendations provided in the European structural steel fire design standard EN 1993‐1‐2, the proposed cross‐section design methods provide more accurate and safe‐sided ultimate resistance predictions for stainless steel CHS, EHS, SHS and RHS at elevated temperatures.

Structural response and design of stainless steel hollow section columns at elevated temperatures

AbstractThis paper investigates the flexural buckling behaviour and design of stainless steel circular, elliptical, square and rectangular hollow section (CHS, EHS, SHS and RHS) columns at elevated temperatures through numerical modelling. Shell finite element models are utilised to perform numerical parametric studies whereby benchmark structural performance data are generated. A large number of cold‐formed and hot‐rolled austenitic, duplex and ferritic stainless steel CHS, EHS, SHS and RHS columns at elevated temperatures are taken into account, considering various cross‐section and member slendernesses. Since the fire design provisions provided in the European fire design standard EN 1993‐1‐2 for stainless steel columns are largely based on those originally developed for carbon steel columns, they typically lead to rather inaccurate ultimate resistance predictions for stainless steel columns at elevated temperatures. To address this, in the present study, a new flexural buckling design method for stainless steel hollow section columns at elevated temperatures is put forward. The accuracy, safety and reliability of the proposed design method and the provisions in EN 1993‐1‐2 are assessed. It is observed that the proposed fire design method leads to more accurate, safe‐sided and reliable flexural buckling resistance predictions for stainless steel hollow section columns at elevated temperatures relative to the provisions in EN 1993‐1‐2.

Local buckling of WAAM stainless steel circular columns

AbstractWire and Arc Additive Manufacturing (WAAM) is one of the promising metal 3D printing techniques, with the ability to produce large‐scale structural components with high speed and low cost. However, there is a lack of research on the structural performance of WAAM members. To this end, numerical modeling and design of WAAM stainless steel circular hollow section (CHS) stub columns has been conducted. Finite element (FE) models considering both as‐built material properties and rough geometry were proposed and verified by the existing experimental studies. By using the FE models, parametric studies on the local buckling resistance of WAAM CHS stub columns were conducted to consider a wider range of specimen geometries. Based on the FE results, the applicability of the current column design provisions in EN 1993‐1‐4 and AISC 370 to WAAM stainless steel CHS stub columns was assessed. At last, a new modified method was proposed to predict the local buckling resistance of WAAM stainless steel CHS stub columns. This study provides a novel approach for the FE modelling of WAAM components.