Steel Structural Members Research Articles

Experimental and finite element analysis of batten-reinforced high-strength steel built-up compression members with web perforations

Assembling two or more channel sections is a common method to enhance the load-bearing capacities of thin-walled compression members in light gauge steel structures. However, perforations in these members redistribute stress across the section, reducing load-bearing capacity and increasing calculation complexity. This study combines experimental and finite element analysis to quantitatively examine: (1) the relationship between web perforations and the load-bearing capacities of built-up sections, and (2) the effectiveness of batten plates in compensating for the reduction in load-bearing capacities of perforated built-up sections. Specimens were categorized into three types: flat-web, V-shaped web-stiffened, and bow-shaped web-stiffened built-up sections. The analysis included specimens without holes, with web holes, and with web holes but reinforced with batten plates. Results indicate that flat-web built-up sections experience the least reduction in load-bearing capacity (average reduction of 5.4 % to 8.3 %) after perforations, while V-shaped web stiffener sections suffer the greatest loss (average reduction of 11.2 % to 15.6 %). Batten plates can compensate for the loss in flat-web built-up sections, resulting in a more uniform stress distribution. Notably, bow-shaped web-stiffened built-up sections can achieve load-bearing capacities with average increase up to 18 % after batten reinforcement, significantly exceeding those of unperforated built-up columns. Reliability analysis showed that the current direct strength method has low reliability and high variability. Therefore, this study proposes strength reduction factors for calculating the load-bearing capacities of perforated built-up sections, which are reliable and have low variability. Correspondingly, strength enhancement factors for batten-reinforced built-up sections are proposed, ensuring reliable and precise calculations with low variability.

Metal additive manufacturing of damage-controlled elements for structural protection of steel members

This paper develops hybrid steel members by integrating additively manufactured, ultra-lightweight, damage-controlled elements (DCEs) into hot-rolled structural steel members. This approach relies on segmenting a structural member into distinct sections; one or two segments are enlarged to be capacity protected; however, anotherend or middle DCE segment is optimized to emulate theconventional member’s strength and stiffness. A small-scale DCE was topologically optimized and then additively manufactured using apowder bed fusion technique through adirect metal laser sintering process of 17-4PH stainless steel andthen was experimentally tested to study the buckling behavior under compression. The experimental testing of the optimized DCE shows acompressive strength of 81,000 times the specimen’s weight with stable post-peak buckling behavior. Numerical simulation confirms experimental results, showing agood correlation in fracture energy. A parametric study on four DCE specimens, scaled up by three, four, five, and six times, was performed and compared to hollow structural sections (HSS) of A500 Gr. C in tensile and compression strengths. The numerical simulation shows a linear relation between the weight ratio and HSS length. Additionally, numerical simulation of conventional member, DCE (scaled by three), and three hybrid members revealed that failure occurred in DCE as intended.

Localized loading behavior of cold-formed stainless steel RHS under interior-one-flange load case at elevated temperatures

The localized loading behavior of cold-formed stainless steel (CFSS) rectangular hollow section (RHS) members at elevated temperatures is investigated in this paper. Fifteen localized loading tests conducted at various temperatures up to 800 °C were reported. The tests were carried out under the Interior-One-Flange (IOF) load case as specified in American Specification for the design of cold-formed stainless steel structural members. Tensile coupon tests were performed to obtain the material properties of the CFSS RHS at various temperatures. Detailed information on dimensions, temperature histories, failure modes, load-deformation curves, localized loading capacities of specimens at various temperatures were presented. In addition, a numerical investigation was supplemented, where a total of 192 finite element (FE) analyses were undertaken after validation of developed FE model against the elevated-temperature test results. The influence of various parameters on the localized loading capacities of CFSS RHS at different temperatures under IOF load case was revealed. The obtained results were utilized to assess the applicability of the localized loading design provision for CFSS RHS under IOF load case codified in the American Specification to elevated temperature conditions. Moreover, the results were also compared with predictions based on existing design rules in literatures for cold-formed RHS at elevated temperatures. Furthermore, reliability analyses were carried out to assess the reliability levels of the assessed design methods. It is shown that the existing design rules can generally provide conservative and reliable predictions of the localized loading capacities for the CFSS RHS under IOF load case at elevated temperatures.

Seismic collapse fragility analysis of steel moment-resisting frames (MRFs) with stiffness and strength deterioration considering the spectral shape of ground motion records

In this paper, the seismic collapse fragility analysis of special steel moment-resisting frame (MRF) buildings with strength and stiffness deterioration is comprehensively evaluated, taking into account the effect of record selection based on the spectral shape parameters. For this purpose, three special steel moment-resisting frame buildings, including 3, 10, and 20-story structures as representatives of low-rise, mid-rise, and high-rise buildings, are investigated. The modified bilinear Ibarra-Medina-Krawinkler (IMK) relation is used for modeling the concentrated plasticity and considering cyclic degradation in beams and columns under earthquake effects in Incremental Dynamic Analysis (IDA). The ground motion records are selected and categorized based on the three parameters, including the epsilon, SaRatio, and Np from a large database consisting of 2000 earthquake records. The records are divided into 7 groups using the epsilon parameter. The SaRatio and Np parameters further divide the records into 5 categories. Additionally, a randomly selected set of 200 earthquake records is used. The effects of hysteretic deterioration and spectral shape parameters of earthquake records on the median IDA curves, collapse fragility curves, and collapse capacity of the steel MRF structures are investigated. In addition to the hysteretic deterioration of steel structural members based on the results of the previous experiments, different values of the deterioration parameter (λ) are used in the nonlinear time history analyses to parametrically study the effect of deterioration on the collapse capacity. Finally, the effect of various parameters on the seismic collapse capacity of the structures in the form of Tornado diagrams is illustrated. The results demonstrate that the randomly selected records yield results close to the records sets with Np = 1, SaRatio = 1, and ε = 0. Furthermore, for a constant deterioration level, increasing epsilon and SaRatio, and decreasing Np lead to an increase in the collapse capacity of the structures. The results also show that the effect of deterioration on the collapse capacity of the buildings, especially the low-rise 3-story building, is significant.

Progressive Collapse Analysis of Single-Layer Latticed Domes Under Seismic Loading Using Enhanced Fiber-Based Approach

This paper presents a novel computational framework based on the Finite Particle Method (FPM) for the progressive collapse analysis of single-layer latticed domes subjected to seismic loading. The framework integrates a fiber-based approach to simulate the nonlinear behavior of steel structural members, including yielding, cyclic buckling, and fracture. For structural seismic analysis, the fiber-based approach is enhanced by incorporating a dynamic increase factor, which accounts for the impact of high strain rates during seismic events. Furthermore, the framework extends the pseudo-dynamical stiffness of the particle to consider Rayleigh damping, surpassing the limitations of the original mass damping model. The computational efficiency of the proposed framework is optimized by implementing it on a generic parallelized GPU platform. The computational framework has the advantage of elaborately simulating the response of individual structural members while efficiently capturing the complex behavior of the overall structure. Subsequently, the effectiveness of the enhanced framework is demonstrated through the analysis of the collapse behavior of a representative single-layer latticed dome under seismic loading. The study conducts a parametric analysis to evaluate the influence of two key factors, namely, rise-to-span ratios and imperfections, on the collapse behaviors. The findings contribute to a better understanding of the complex behaviors of single-layer latticed domes during seismic events, providing knowledge for improving structural safety and resilience in public buildings.

A Model generation method and iteration algorithm for optimising fire protection thickness

With temperatures rising above 1000 °C within 5 min, hydrocarbon fire causes rapid strength degradation of structural steel members. It is among the most dangerous hazards, such as boiling liquid expanding vapour explosion (BLEVE) in the oil and gas industry. Intumescent coating as passive protection is widely adopted to prevent the steel structure from material property reduction. However, when optimising fire protection with heat transfer simulation, repetitive modelling work and lacking recalculation principle hinder productivity improvement. This method is developed to generate steel beam models and provides an effective algorithm to optimise coating thickness considering the temperature of a specific region. The main functions of the method include:•Providing section dimensions, initial insulation thickness, target temperature and heating time, temperature allowance and mesh size as variables.•Automatically generating the Abaqus steel beam model under 3-side heating conditions.•Effective iteration algorithm to modify fire protection thickness: test containing 38 Universal beam sections with a 5 °C allowance below target shows that 55.2% were completed within five iterations and 76.3% were completed within eight iterations.

Classification criteria for austenitic stainless steel H-section under cyclic loading about major-axis

Stainless steel exhibits strain hardening characteristics under cyclic loading, hence presenting significant potential for application in seismic design. However, the current stainless steel structural design code fails to account for this beneficial effect in the cross-section classification. Given the scarcity of research about the behavior of structural stainless steel members under cyclic stress, this paper establishes the preliminary finite element model for the austenitic stainless steel (EN 1.4301) H-section. Firstly, finite element model validation of the existing cyclic tests on stainless steel members from literature was performed, followed by numerical analyses of a total of 370 beam and beam-columns members with different axial compression ratios and plate width-thickness ratios, and subsequently evaluated the cross-section classifications specified in prEN 1993-1-4, AISC 370 and CECS 410 through extensive parametric studies. The results indicate that the current design codes are conservative in the provisions for cross-section classification because they neglect the influence of plate interactions and material strengthening effects during cyclic loading. In this paper, limit and generalized expressions for austenitic stainless steel H-section with different axial compression ratios and cross-section classes under cyclic loading about major-axis are proposed. Additionally, the effect of material strengthening on cross-section classification under cyclic loading is examined.

Experimental programme on austenitic stainless steel RHS members subjected to monotonic and cyclic bending

Stainless steel is a corrosion resistant iron alloy with great potential in structural engineering due to its excellent mechanical features, durability and aesthetic properties. Since most of the existing research has concerned the behaviour of the material, the response of individual structural members, or the performance of simple structural systems under monotonic loading, one of the challenges that remains is the evaluation of the cyclic performance of members to promote its use in seismic design and exploit the excellent ductility and strain hardening properties of this material. For this reason, an experimental programme on austenitic stainless steel Rectangular Hollow Section (RHS) specimens was carried out at the Department of Civil Engineering of the Università degli Studi di Salerno in collaboration with the Universitat Politècnica de Catalunya. A total of eight RHS specimens were tested around the minor axis under both monotonic (three specimens) and cyclic (five specimens) loading, in an experimental set-up that followed a cantilever scheme. The main purpose of this study was to acquire information on the cyclic performance of austenitic steel structural members, focusing on the comparison between monotonic and cyclic behaviours. The outcomes of the tests included the load–displacement and the moment–rotation curves, the energy dissipation capacity, and the evaluation of the key rotation capacities of the members. The reported data are essential to enhance the still scarce research on the seismic behaviour of stainless steel structures.

Seismic Retrofitting of a 7-storey Hospital Building

In this work, two main structural solutions have been proposed to retrofit an existing Italian hospital building located within the National Cancer Institute “G. Pascale Foundation” in Naples. The structure under consideration is composed by nine reinforced concrete cores connected by means of steel structural members. Preliminarily, the seismic vulnerability has been evaluated according to the linear dynamic analysis with reference to both for the Life Safety (SLV) limit state and the Operational (SLO) limit state according to the current Italian code. The analyses have been performed using the SAP2000 program, post-processor VIS15 and plugin SPF. Subsequently, in order to improve the structural performance of the building, two solutions have been developed both based on the reinforcement of the RC cores but by adopting two different approaches: the first one characterized by the use of the added RC walls; the second one based on the using of steel plates. Then, the attention is focused on the pile foundation. In particular, the structural vulnerability has been evaluated by adopting a static linear analysis and, consequently, a retrofitting intervention has been provided. Finally, the proposed interventions have been evaluated from the economic and environmental points of view.

A Proposal of a Heat Input Model, for Heating Correction, on Welded Steel Structural Members

A Proposal of a Heat Input Model, for Heating Correction, on Welded Steel Structural Members

Influence of surface roughness on the mode II fracture toughness and fatigue resistance of bonded composite-to-steel joints

Hybrid bi-material concepts in engineering structures where fibre-polymer composites are used together with steel structural members have potential to reduce material usage, extend fatigue life and improve structural reliability. The bond performance of the bi-material composite-to-steel interface is of crucial importance and highly relies on the surface preparation quality of the steel element. This paper investigates the influence of steel surface roughness on the mode II fracture toughness and fatigue crack growth behaviour of the bonded composite-to-steel joints. Glass fibre composite and mild structural steel material is considered directly bonded in a wet lay-up process. 4-point end notch flexure (4ENF) tests are conducted on specimens with the steel plates prepared with low, medium and high roughness, respectively. In addition, morphology of the fracture surfaces are characterised by a 3D profilemeter and the friction coefficient is measured by a tribometer for each roughness level. Results show that in quasi-static fracture, fibre bridging is dependent on the surface roughness. A roughness level with Sq ≥ 22 µm of the steel surface can promote significant fibre bridging thus improved fracture toughness due to enlarged effective bonding area. Under cyclic loading, no fiber bridging is observed across all roughness levels tested. However, the Paris curve parameter C is significantly affected by the roughness level, which decreases by approximately 100 times as the steel surface roughness increases from the low level of Sq = 5 µm to high level of Sq = 22 µm. The m parameter of the Paris curve remains fairly constant across all the roughness levels tested.

Derivation of stainless steel material factors for European and U.S. design standards

Modern structural design standards are based on the Limit State Design (LSD) philosophy, also known as Load and Resistance Factor Design (LRFD), which involves the use of resistance functions with accompanying safety factors that are based on a statistical evaluation of relevant experimental data, carried out within the framework of a probabilistic reliability theory. This paper presents the derivation of material factors for the yield strength and ultimate tensile strength of austenitic, duplex and ferritic stainless steels, and their associated coefficients of variation (COV) for use in evaluating the safety factors for the European design code EN 1993-1-4 and the American design codes Specification for Structural Stainless Steel Buildings (ANSI/AISC 370–21) and Specification for the Design of Cold-Formed Stainless Steel Structural Members (ASCE/SEI 8–22). Separate material factors and associated COV values are required for the U.S. and European design codes due to the different minimum specified strength values that are given in the respective product standards. The material factors were derived by analysing a large amount of material data provided by different stainless steel producers, which encompassed a wide range of stainless steels and material thicknesses.

Reuse of decommissioned offshore steel components for new buildings: A case study

Reuse process of structural steel members, which are extracted from decommissioned offshore platform, for new apartment building is presented in this paper. An index is introduced to assess the technical feasibility of the reuse process of offshore steel components to steel buildings. The applicability and significance of the reuse process is demonstrated by a real case study. Steel columns of a new four-storey apartment building are replaced by selected members from recently decommissioned offshore platform in this case study and hence feasibility, cost benefits and environmental advantages are investigated. Utilization ratios of selected pre-used columns shows that those columns have more than sufficient capacities to withstand the loads. This indicates that considered decommissioned module of offshore topside is applicable for similar size of new buildings. The results indicate significant environmental benefits such as reduction of the CO2 emission, low global worming potentiality, and etc. The reusability index of the considered case study is 51.5%, which shows marginal feasibility of reuse, and this can be increased, if the reuse process is industrialized and streamlined by the offshore decommisioning companies. Three ways are proposed to industrialize and streamline the reuse process in the latter part of this paper.

Numerical assessment of the cyclic behaviour of structural steel members subjected to biaxial bending

AbstractIn recent decades, there has been extensive research on the behaviour of steel structures under seismic actions. While the monotonic behaviour of steel elements subjected to uniaxial bending is well understood, there is still a need to investigate the cyclic behaviour and energy dissipation capacity, especially in relation to metal elements subjected to biaxial bending. This is of paramount interest for seismic analysis and performance assessment of steel buildings. Modelling and damage assessment criteria derived for members subjected to uniaxial bending may not be entirely appropriate for the seismic analysis of buildings composed of structural steel members subjected to biaxial bending. Therefore, this research aims to investigate the behaviour of steel members subjected to biaxial cyclic bending and compare it to behaviour under uniaxial loading conditions. To this end, detailed 3D finite element analyses are conducted to examine the effects of bidirectional lateral cyclic loading on the hysteretic response of steel members under different uniaxial and biaxial lateral displacement‐controlled load paths. The numerical results presented in this paper provide an insight into the influence of biaxial loading on the behaviour of steel members in terms of backbone curves and deformation capacity, and indicate that biaxial cyclic loading paths can significantly affect the rotation capacity of steel elements.

Geometric tolerances of welded connections with inelastic panel zones

AbstractPrequalified beam‐to‐column connections in steel moment resisting frames usually concentrate inelastic deformations in the steel beam ends. As such, nonlinear geometric instabilities (i.e., local buckling) may occur in these regions at modest lateral drift demands, leading to potentially high residual deformations. Previous research has shown that welded connections featuring inelastic panel zones exhibit a stable hysteretic behaviour. In this case, residual deformations in steel beams are often not visually detectable after inelastic cyclic straining. This paper contrasts the residual deformations of steel beams as part of welded connections with elastic and inelastic panel zones through continuum finite element analyses. The employed finite element model is thoroughly validated with available test data. Besides the actual hysteretic response of the connections, the primary focus of the present work is on a number of geometric tolerance indicators, such as the web concavity, flange out‐of‐square and beam axial shortening. These are strongly correlated to the potential for reuse of structural steel members. The results suggest that connection designs featuring inelastic panel zones delay beam local buckling relative to their strong panel zone counterparts, achieving acceptable residual deformations even at lateral drift demands higher than 4% when considering the geometric tolerances of international standards.

Lateral Load Behavior of C-PSW/CFs Using Steel Members as Boundary Elements

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures.

Fiber-based approach for seismic analysis of steel members using finite particle method

This paper presents an enhanced fiber-based approach for the seismic analyses of the behavior of steel structural members. This approach is built based on the framework of the finite particle method. Specifically, a fiber-beam element is developed to model the behaviors of structural members more elaborately. A cyclic constitutive model for fiber is proposed by enhancing a uniaxial steel hysteretic constitutive relationship to consider large strain amplitude and low cyclic fatigue. In addition, a fiber-based fracture model is proposed for modeling the progressive failure process of members. The proposed enhanced approach combines the finite particle method and fiber-beam element with more elaborated constitutive and fracture models, and it has the advantages in evaluating the cross-sectional plastic development and dealing with non-linear and non-continuum problems, which is suitable for analyzing the cyclic fatigue, buckling, and fracture of steel structural members. The analyses of steel plates and steel tube member specimens are performed to verify the effectiveness of the proposed approach. The proposed method is applied to analyze the collapse of a Kiwitt-8 single-layer latticed dome subjected to different seismic loads, which shows the feasibility of the fiber-based approach for seismic collapse analysis.

Development of Composite Ablative Liners for Solid Rocket Motor Flex Nozzles

Solid Rocket Motor generates high thrust by accelerating high pressure gases to supersonic velocities in convergent divergent nozzle, thus converting pressure energy to kinetic energy of propulsion. As exhaust gas from chamber is of high temperature, the structural steel members of nozzle should be protected from hot gases by highly erosion resistant thermal liners. For this purpose, ablative composite liners made up of Phenolic resin matrix based combined with reinforcement material like carbon fabric is extensively used [1]. Divergent being largest component and contributes more to nozzle weight, the thickness of liner should be as least as possible at the same time; it should be more erosion resistant. The erosion resistant due to hot gases can be increased by fabricating the liner in such a way that the flame only touches the edge of the composite ply of liner and liner has more density. This can be achieved by tape winding of composite prepreg tapes at Zero degrees on tapered metal mandrel using tape winding machine followed by Autoclave curing [2]. This paper gives the details of prepreg, Tape winding, Autoclave Curing and NDT of ablative liner.

Numerical modelling of cold-formed steel built-up columns

Built-up cold-formed steel structural members can provide technically and economically advantageous solutions in cold-formed steel construction. However, there is a need for a deeper understanding of their stability behaviour, and this paper demonstrates that detailed, accurate and reliable finite element models provide an excellent means to achieve this. Apart from the typical issues to be considered in the high-fidelity modelling of thin-walled members, which include geometric and material nonlinearity, element type, mesh density, and the modelling of imperfections and boundary conditions, the paper focuses on two additional complications which arise in built-up members: the modelling of connectors, and contact between constituent parts. A number of alternative techniques to model connector behaviour are investigated and their effect on the predictions of the ultimate capacity quantified by benchmarking against experimental data. Various successful strategies to mitigate stubborn convergence problems, which almost inevitable originate when modelling complex contact problems, are also presented. It is demonstrated, however, that the inclusion of contact as a model feature does not have a significant effect on the predicted capacity in the majority of the considered cases, with its influence typically remaining limited below 10%. The validated models were further used in parametric studies which showed that once the connector spacing is short enough to prevent global instabilities of the component sections between connector points, its effect on the ultimate capacity of the built-up column is very small within the practical range of connector spacings. Modelling connector lines as continuous longitudinal constraints tying surfaces together, on the other hand, is bound to significantly overestimate the capacity.

A sub-region-based method for evaluating regularly and irregularly corroded steel tubes under axial compression

Circular steel tubes (CSTs) are one of the most prominent types of members in spatial steel structures, which are commonly facing increasing durability problems. Although the effect of corrosion on the bearing capacity of CSTs has received increased attention by scholars, there is no sound solution regarding the quantitative evaluation of the bearing capacity of corroded CSTs, especially for those with irregular corrosion areas. This study proposes a solution for the evaluation of the bearing capacity of corroded CSTs. First, the accuracy of a finite element model is verified and a method for calculating the bearing capacity of CSTs with a regular corrosion zone is established. Subsequently, the effect of the relationship between the location of two corroded areas on the residual bearing capacity is investigated. Based on this, an evaluation method for irregularly corroded CSTs is proposed, where the impact is evaluated separately for the middle and edge zones of the tube. Finally, the specific process and essential parameters for the evaluation of the tube middle and edge zones are given, formulating a comprehensive method for evaluating the bearing capacity of corroded CSTs. The present research provides reference for the performance evaluation of steel tubes in spatial structures subjected to corrosion.