Steel Structural Members Research Articles

Revision of ASCE 8 - Design of cold-formed stainless steel structural members

The American Society of Civil Engineers (ASCE) Specification for the Design of Cold-Formed Stainless Steel Structural Members was last updated in 2002 and significant advancements in research knowledge and companion design standards have occurred in the intervening 20 years. A dedicated group of volunteers re-formed the ASCE 8 specification committee and over the course of four years completely revamped the standard. The new version, ASCE 8–22, still parallels the cold-formed carbon steel standard AISI S100, and has improved and simplified design expressions for members and connections. Both the Continuous Strength Method and the Direct Strength Method are provided in ASCE 8–22, along with traditional effective width design approaches. The standard provides a robust set of provisions for slender austenitic, ferritic, and duplex cold-formed stainless steel structural members and their connections. This paper overviews major changes in the ASCE 8–22 standard highlighting areas of divergence from carbon cold-formed steel (AISI S100) and from stainless structural steel (AISC 370–21).

Influence of cyclic hardening characteristic on seismic performance of welded austenitic stainless steel H-section beam-column

Previous studies have revealed that the cyclic hardening feature of austenitic stainless steel depended on the applied strain amplitude and exhibited unsaturation prior to failure, which greatly affected the seismic response of austenitic stainless steel structures. In view of the limited research on the seismic performance and design of structural stainless steel members, this study investigates the influence of cyclic hardening characteristic on the performance of welded austenitic stainless steel H-section beam-column under combined uniaxial cyclic bending and constant compression. The finite element (FE) models of unsaturated cyclic hardening austenitic stainless steel grade S30408 beam-columns with H-section were initially created and validated with the available test data. The effects of loading history in conjunction with the axial compressive load level and the cross-section slenderness on the seismic performance of specimens were then studied through extensive parameter analysis. Results show that the capacities of load-carrying and deformation for the austenitic stainless steel member are discrete under different loading histories. Apparently, the unsaturated cyclic hardening property of stainless steel S30408 influences the performance of the member under seismic loading. Moreover, current codified design methods and the Continuous Strength Method (CSM) underestimated the ultimate strengths of stainless steel beam-columns under seismic loading. The over-strength factor and seismic deformation capacity design formulae of welded austenitic stainless steel H-section beam-columns were finally proposed.

Enhancement of recovery stress by annealing and prestraining of NiTiNb wires

NiTiNb shape memory alloy has attracted much attention for its use in prestressing and remedying structural steel and concrete members due to its unique shape memory effect. However, the recovery stress values reported in the literature vary significantly, as the interplay between recovery stress and treatment parameters is not fully understood. In this study, we carefully investigated the effects of annealing and prestraining on the martensitic transformation behavior and mechanical properties of NiTiNb alloy and clarified their correlations to the recovery stress. Our results showed that the yield strength and superelasticity decreased while the ductility and retained stress-induced martensite increased with increasing annealing temperature. We found that high recovery stress can be achieved by annealing the sample above the recrystallization temperature while keeping the annealing temperature as low as possible to maintain high strength. Prestraining the sample to beyond the stress plateau but before yielding was found to be most effective for enhancing the recovery stress. By using these criteria, we were able to obtain large recovery stresses of greater than 550 MPa from 20°C to 200°C through a simple one-step annealing at 700°C and a 10% prestrain using commercial superelastic NiTiNb wire products.

Geometric imperfections in CFS structural members: Part I: A review of the basics and some modeling strategies

Unavoidable geometric imperfections complicate the load–displacement response of thin-walled cold-formed steel (CFS) structural members. While the inclusion of geometric imperfections in shell finite element (FE) collapse simulations has long been the subject of research, no consensus exits on modeling their full three-dimensional spatial pattern. This paper is the first part in a two-part series and provides a review of the basics and a summary of some efforts geared towards modeling geometric imperfections. We discuss the necessary ingredients for systematic characterization of elastic buckling mode shapes, due to their frequent use in approximating geometric imperfections, and make a conscious effort to express some of the existing geometric imperfection models through three components: imperfection shape, magnitude, and combination coefficient. Different choices and selections of these components, pertaining to either the inherent buckling behavior of the members and/or physical measurements are critically examined. The details required to develop high fidelity nonlinear FE models of CFS members seeded with geometric imperfections are presented. We then perform a comparative study of collapse analysis results obtained from adopting different imperfection modeling strategies. The noticeable variability in the load carrying capacity and the stability behavior highlights an urgent need for reliable probabilistic frameworks for this class of problems. A stochastic framework to generate samples of imperfect shell FE models from limited available data and validate the prescribed or practice-oriented geometric imperfection models is presented in a companion paper (see Part II Farzanian et al., (2023)).

Geometric imperfections in CFS structural members, Part II: Data-driven modeling and probabilistic validation

This paper is the second part in a two-part series that examines the role of geometric imperfections in load–displacement response and collapse behavior of cold-formed steel (CFS) structural members. In part I (Farzanian et al., 2023) a review of the basics and a summary of efforts geared towards modeling geometric imperfections was provided. This included the ingredients needed for systematic identification of elastic buckling mode shapes, due to their frequent use in approximating geometric imperfections, and the development of high fidelity shell finite element (FE) nonlinear collapse analysis of CFS members seeded with different geometric imperfection models. Part II is the companion to the analysis in part I that revealed a noticeable variability in the collapse behavior and load carrying capacity of CFS members as a result of adopting different imperfection modeling strategies. In this part we provide the necessary steps to build a probabilistic framework that rests on machine learning, polynomial approximation, and parametric and non-parametric statistical inference and uses imperfection data to build a consistent stochastic field model of geometric imperfections. This data-driven model is then used to generate the much needed realizations of geometric imperfections that are faithful to the underlying statistics of measured data and therefore can be seeded, directly, in nonlinear collapse analysis of CFS members. Nonlinear shell FE analysis, within a stochastic simulation framework, is finally used to (statistically) quantify the impact of geometric imperfections and to enable probabilistic validation of geometric imperfection models.

The overall imperfection method for fire design situation

In this paper the Overall Imperfection Method, which is a well validated method for the assessment of the global stability resistance of thin-walled steel structural members with any load and supporting conditions, is used for fire design situation. The method uses equivalent initial geometrical imperfection in the shape of relevant elastic global buckling mode. The assessment of the global stability resistance is performed by geometrically nonlinear analysis and by checking of cross-sectional resistance using reduced elastic moduli in the analysis and reduced design strength for the cross-section checking. The validation of the method is carried out through the analysis of more thousands different structural members with hot-rolled I cross-sections. The reference values for the safety study are calculated by geometrically and materially nonlinear analysis with imperfections.

Norm and interpolation based absolute stress evaluation in steel members using the Lcr wave

The uniaxial absolute stress in steel members is a vital indicator for evaluating the performance of steel structures. Non-destructive ultrasonic detection is widely applied in the absolute stress measurement of steel members with the advantages of easy implementation, no limits on materials and high precision. The acquisition algorithm of time-of-flight (TOF), the sampling rate of ultrasonic signal and the processing of outliers determine the accuracy of the stress measurement. In this study, we proposed a norm and interpolation based algorithm for absolute stress measurement using the longitudinal critically refracted (Lcr) waves, which improves the accuracy and velocity of the absolute stress measurement. Firstly, the norm was designed to obtain the TOF of the ultrasonic signal. When only the Lcr wave arose in the ultrasonic signal, the two-norm similarity algorithm was found to be consistent with the cross-correlation-based algorithm and the corresponding theoretical expressions were derived. With the non-Lcr wave in the ultrasonic echo, the two-norm similarity algorithm has stronger anti-interference ability. Secondly, the pchipslopes, spline and linear interpolation algorithms were introduced via which the TOF of ultrasound with low sampling rate reaches the same accuracy as that of high sampling rate signal. Finally, a special class of outliers in TOF was explored, and a threshold based on the number of shift points and the stress feature was proposed to calibrate these outliers to normal values. Experiments demonstrate the proposed algorithm improves the accuracy and velocity of uniaxial absolute stress measurement in structural steel members.

Compression test results of CFS structural members

The subject of the study is the stress-strain state of a cold-formed steel structural members under axial compression. The aim is to experimentally study the behavior of a sample from a cold-formed thin-walled profile in axial compression with stress control. A mechanical method was used to test compression samples on a universal testing machine, a strain gauge method for measuring relative deformations by strain gauges with data collection in the registration unit. The processing of the test results was carried out using the methods of the theory of elasticity. As a result of the tests carried out, a qualitative picture of the deformation of the sample was obtained, the values of relative deformations at specific points of the cross sections of the sample; as a result of processing the data obtained, the main normal stresses at the points of the cross sections of the element were determined. As conclusions, an assessment of the reliability of the results obtained based on the nonlinear theory of plates is given; a conclusion is made about the inapplicability of the strain gauge method to the analysis of the behavior of thin-walled steel profiles. A promising study is the study of fields of relative deformations by non-contact optical methods.

Strength of bolted steel structural members under eccentric tension

AbstractThe effective cross‐sectional area method for the outstanding leg is utilized as an ineffective area to evaluate the strength in the present Japanese design standard. Given that this evaluation method is fundamentally premised on experimental outcomes derived from relatively thick plates, it must be extended to brace members composed of thin plates. In this study, we conduct bolt joint experiments and numerical analyses on thin‐plate angles and channel members, with the aim to elucidate the elements influencing the efficiency of the joint. We propose a unified bolt joint strength evaluation formula that also considers thin‐plate members.

Searching for a compromise solution in cross-section size optimization problems of cold-formed steel structural members

A parametric optimization problem of cross-sectional sizes for cold-formed steel lipped channel structural members subjected to axial compression has been considered by the paper. An optimization problem is formulated as to define optimum cross-sectional sizes of cold-formed structural member taking into account post-buckling behavior (web and flange local and distortional buckling) of the member as well as structural requirements when the profile perimeter (strip width), profile thickness, design lengths of the structural member as well as material properties are constant and specified in advance. Maximization of the load-carrying capacity of the cold-formed structural member has been assumed as purpose function. The formulated parametric optimization problem has been solved by exhaustive search method using the software written in Python. As optimization results the cold-formed steel lipped channels with optimum cross-sectional dimensions have been obtained depending on the profile thickness and design lengths of the structural member. In order to obtain optimum solutions for cross-sectional dimensions of the CFS lipped channel structural members which are independent from the design flexural lengths and profile thickness, searching for a compromise solution has been performed by exhaustive search method. The obtained cold-formed steel lipped channel structural members with optimum cross-sectional sizes have higher design buckling resistance under the axial compression at the same material consumption (stripe width) comparing with the cold-formed steel lipped channels proposed by the manufacturer. Web local buckling phenomenon has been occurred in all obtained CFS lipped channel cross-sections with optimum sizes.

Behavior of Steel Beams Subjected to Bending and Shear Loading Under Localized Fire Conditions

Civil structures were designed to carry a variety of loading during their service life, including fire hazards. As a result, providing fire safety to structural members is one of the most important tasks in civil infrastructure design. Steel structural members are subject to fire-induced damage or collapse due to their high heat conductivity and quick loss of strength and stiffness qualities. Furthermore, the failure in steel beams under the combined effects of bending, shear, and fire loading is poorly understood in the literature. A present study consists of experimental investigations on the fire response of steel beams under bending and shear dominant loading. The specimens have a constant length of 1250 mm. The total depth of the specimens was changed according to the section chosen: 4 in, 6 in, and 8 in (10 cm, 15 cm, and 20 cm). The results of tests show that beams can fail suddenly due to a high drop in yield and ultimate strength of the steel beam. the increase in temperature degree reduced greatly the yield and ultimate flexural strength of the steel beams with different sizes (for all groups). This reduction reached at some times to 50% for the ultimate strength capacity of the specimen. Shear strength is also affected greatly by fire exposure and the reduction reached to about 38%. Furthermore, the design strength capacity can only tolerate loads at low temperatures. This reduction in strength was noted under flexural and shear dominant loading. Moreover, the design strength capacity can withstand against loading at low-temperature degrees only.

Fatigue strength of cold-formed structural steel details: Numerical modelling and experimental results

Cold-formed structural steel members are more and more adopted in the logistic industry. This makes them particularly susceptible to cyclic loads during their service life, while recommendations related to fatigue design of cold-formed structural steel details are completely missing at European level. This paper will discuss the experimental and numerical procedures adopted to investigate the fatigue strength of cold-formed structural steel details typically used in logistic industry. The results of the research are part of a wider project aimed at defining and providing guidelines for the implementation of fatigue design rules for cold-formed steel details in current European Recommendations.

Experimental Investigation of the Fatigue Life of a Bridge Crane Girder Using S-N Method

Experimental measurement methods used in operational mode provide valuable information about the behavior of mechanical parts of equipment that cannot be determined in advance by analytical calculations or numerical modeling. The strain gauge method, which is often used to investigate the stresses in the load-bearing members of steel structures under operational conditions, was used. The advantage is the fast and accurate acquisition of stress values at critical locations selected based on analytical computations or numerical modeling. In the present paper, the residual operating life of two main girders of a bridge crane was assessed by an analytical-experimental approach. The input parameters for the assessment were obtained from the evaluated stress time records and using the Rainflow Counting method. Experimental measurements identified an almost 50% decrease in the residual life of one of the girders. It was caused by non-compliance with the technological procedures for the regular replacement of the rails, where the rail was welded to the top flange on one of the girders. Considering realistic operating conditions, predicting the effect of welded rail on fatigue damage accumulation, performed by other than experimental procedures, is almost impossible for such complex structures. This paper not only documents the importance of experimental measurements but also highlights the significance of selecting measurement locations with consideration of the current technical state of the structure.

Evaluation of compressive properties of the ship plate after seawater corrosion based on 3D evolution prediction

Stiffened ship plate is one of the most important parts of coasting vessels. Due to long-term immersion in seawater, the mechanical properties of the plates are easily affected by corrosion. This study calculated the long-term corrosion rates of ship plates in 3 typical sea areas around the world by Fick's law and compared them with relevant regional standards. Then, on the basis of randomly setting corrosion parameters (diameters and number of initial exposure areas), a 3D corrosion evolution simulation method for steel was applied to evaluate the compressive capacity degradation rate of a typical size ship plate for different corrosion years. The results showed that the bearing capacity degradation rate of the ship plate was obviously affected by corrosion years (the distribution of corrosion area and depth was determined), distribution of corrosion location and environmental factors (seawater temperature and Cl− content). This study could provide a technical reference for evaluating the safety performance of ship plates and other similar steel structural members of ocean engineering.

Experimental study on stainless steel tubular members under cyclic loading

Stainless steel is an excellent construction material due to its high ductility, strain hardening, durability and aesthetic characteristics. To date, most studies on stainless steel have been devoted to understanding its mechanical properties and the behaviour of individual structural members and simple structures under monotonic loading. As a result, next versions of stainless steel codes, traditionally based on carbon steel codes, will enable efficient structural designs under static forces. However, advances related to the performance of stainless steel structural members under cyclic forces are still scarce, and there are no specific rules for the seismic design of stainless steel structures in Eurocode 8 in spite of the notable differences between this material and other steels. On this basis, an experimental programme on austenitic stainless steel hollow section elements subjected to cyclic loading has been recently conducted. A total of nine specimens with different local and member slenderness values were tested under cyclic bending around their major axis following a cantilever loading scheme. This paper describes the experimental set-up adopted for the tests, including the loading scheme and instrumentation, and discusses the load–displacement, moment–rotation, degradation of stiffness and energy dissipation values obtained in detail. In addition to providing fundamental information on the response of stainless steel members under cyclic loading, the description of the set-up reported in this paper will assist researchers in planning similar experimental programmes, while the results will serve as a reference to validate numerical analyses of stainless steel members and frames subjected to cyclic loading.

Direct Strength Method for Design of Cold-Formed Steel Structural Members

Direct Strength Method for Design of Cold-Formed Steel Structural Members

Design approach against column local–distortional interactive failures based on the Direct Strength Method

This paper deals with the development and merit assessment of an efficient and rational design approach intended to handle local–distortional (L–D) interactive failures in cold-formed steel columns (CFS) and based on the Direct Strength Method (DSM). Initially, a brief overview of the mechanical aspects underlying local–distortional interaction is provided, for the benefit of readers not familiar with this coupling phenomenon, and its relevance in CFS column design is addressed. Then, the available experimental failure load data, obtained for columns exhibiting various cross-section shapes (plain, web-stiffened and web-flange-stiffened lipped channels, hats and racks) are collected and used as the basis for the development, calibration and validation of this DSM-based design approach, which relies also on the current DSM local and distortional strength curves and existing numerical failure loads. It covers local–distortional​ interactive failures occurring in columns with several ratios between the distortional and local buckling loads, which are grouped in three families, denoted as “true L–D interaction”, “secondary-distortional bifurcation L–D interaction” and “secondary-local bifurcation L–D interaction”. The failure load prediction quality (accuracy and safety) and reliability of the proposed DSM-based design approach are assessed and compared with those exhibited by the existing methodologies to design CFS columns against L–D interactive failures. The reliability assessments follow the procedure prescribed by the current North American Specification for the Design of Cold-Formed Steel Structural Members and indicate that the design approach proposed in this work should be ready for codification in the near future.

Flexural behavior of delta and bi-delta cold-formed steel beams: experimental investigation and numerical analysis

Cold-formed steel (CFS) structural members retain their positions in the lightweight construction industry. This is due to the significant advantages of CFS. The optimization of these CFS elements will allow the construction of economical buildings with increased load capacities and solutions for stable and economical construction will be obtained. The main aim of this research was to evaluate the effectiveness of these new CFS sections with the estimation of remarkable instabilities and failure modes. This article deals with an experimental study on the behavior of CFS beams of open delta and bi-delta form stressed by four-point bending loads. These cross section shapes are often used in floors as main and secondary beams. The section properties are based on the effective width method designated by the Eurocode 3 standard. A nonlinear finite element (FE) analysis using the ABAQUS program is performed and the comparison between the experimental, numerical and theoretical results is done. Finally, the results showed above all that the breaking loads of the delta and bi-delta beams corresponded to the modes of local buckling and crushing of the web.

Measurement of the stress of steel members using the ultrasonic phase spectrum

The stress state of steel members is an important indicator in evaluating structural safety. The ultrasonic time-of-flight method of measuring the stress of steel members based on acoustoelastic theory has been fully developed. However, the time difference is hard to be measured. The present paper proposes a new method of measuring the uniaxial stress of steel members using the phase spectrum of the ultrasonic transverse wave. The effect of interference of the two wave components generated by shear-wave birefringence under uniaxial stress is investigated. It is found that the derivative curve of the phase spectrum of the pulse-echo comprising the two wave components reaches a maximum periodically, and the frequency corresponding to the maxima is sensitive to stress and relatively easy to be measured. On this basis, a theoretical formula for the measurement of the uniaxial stress of steel members based on the phase spectrum is derived. Results of calibration tests show a good linear relationship between the stress and the reciprocal of the first response frequency corresponding to the maximum of the derivative curve of the phase spectrum. The uniaxial stress can then be measured by obtaining the first response frequency of the phase spectrum of the in-service structural steel member. In addition, the effects of the thickness of steel members and the sampling rate of the oscilloscope on the uniaxial stress measurement are investigated. The present paper also illustrates the correspondence between the amplitude spectrum method and phase spectrum method.

A modified Johnson-Cook constitutive model for structural steel after cooling from high temperature

High temperature has a significant impact on the mechanical properties of steel structural members, which can develop a potential collapse. Currently, various studies have been concentrating on the post-fire mechanical properties of different steels, while few of them considered the corresponding constitutive model. Therefore, in this paper, the classical Johnson-Cook constitutive equation is selected as a benchmark and is modified to fit the conditions in which the effects of heating and cooling on the mechanical properties of fire-affected steel are considered. To this end, three commonly used structural steels, namely Q345B, Q460 and Q690D, are selected in this paper. First, the specimens were heated to different target temperatures, and then naturally cooled down to the ambient temperature in the air. After cooling from the exposure temperatures, the subsequent tensile tests were performed on the fire-affected specimens to capture the failure modes and study the residual mechanical properties. To verify the proposed constitutive model, an Abaqus subroutine (UMAT) program was developed in this study. The experimental data of water-cooled specimens obtained in our previous studies were also selected to further test the feasibility of this new model. The results show that the exposure temperature and steel grade have significant effects on the residual mechanical properties of the structural steel specimens when the target temperature exceeds 700 °C. Meanwhile, the modified Johnson-Cook constitutive is able to predict the stress –strain behavior precisely, regardless of the cooling method. The results obtained in this study are helpful for both further research and engineering application when doing a numerical study of the fire-affected steel structures.