In-plane cyclic performance of damaged confined masonry walls retrofitted with steel elements and polymer-modified mortar

The increasing use of electric arc furnace (EAF) in steelmaking inevitably elevates nitrogen (N) levels, which are traditionally regarded as a detrimental element to the formability of ultra-low carbon (ULC) steels due to the formation of Lüders band. Here, we demonstrate that N could act as a beneficial microalloying element in strip casting ULC steels by promoting V(C, N) precipitation and grain refinement of ferrite. Thermodynamic calculations reveal that N significantly increases both the equilibrium volume fraction and equilibrium precipitation temperature of V(C, N), enabling copious interphase nanoprecipitation during ferrite transformation. Microstructural characterization confirms the enhanced formation of V(C, N) within interphase rows in the N-containing steels, leading to greater Zener pinning effect and smaller ferrite grain size (from 7.50 μm of 0N to 4.67 μm of 96 ppm N and 3.84 μm of 139 ppm N). As a result, owing to the enhanced nanoprecipitation and grain refinement, the N-containing ULC strip casting steels exhibit a superior strength–ductility synergy, with tensile strength increased from 666 MPa (0N) to 805 MPa (96 ppm N) and 825 MPa (139 ppm N), and a slight decrease in total elongation from 29.8% (0N) to 27.3% (96 ppm N) and 22.0% (139 ppm N). In addition, no Lüders plateau was observed in the tensile stress-strain curves as the extensive formation of V(C, N) consumed the N atoms in solid solution. These findings highlight that microalloying V in the steels produced by EAF can effectively leverage the high N content for achieving superior strength–ductility synergy.

Seismic Performance of Steel Elements With and Without FRP Strengthening: A Review

In the scope of the Dissipate&Recentre project, which was granted access to the ELSA Reaction Wall of the Joint Research Centre physical research infrastructure of the European Commission, large scale composite frame structures were tested under lateral loading. The test specimens, comprising pultruded glass fibre reinforced polymer (GFRP) profiles, connected with stainless steel elements, had two longitudinal (test direction) bays, two storeys and a shorter transverse bay. Concrete slabs were provided as flooring system, simulating a quasi-permanent load level - as that used in seismic design. A total of 4 full-scale specimens were tested, two including a bracing system, also comprising pultruded GFRP profiles, and two without bracings. For each configuration, one specimen was tested under monotonic loading and the other under cyclic loading. The aim of this paper is to disseminate the experimental data obtained in these tests. To that end, the experimental campaign is thoroughly described, including all the relevant details of the test specimens, the construction process, the setup and instrumentation, and the test programme. Additionally, a brief description of the test observations is also provided. The test results showed that the structural integrity of these GFRP frames was maintained up to 2% inter-storey drifts, for both braced and unbraced configurations, presenting very limited damage. These results indicate that GFRP frame structures may be designed to withstand significant seismic actions.

The integration of web openings in reinforced concrete (RC) beams for building services severely compromises shear capacity by disrupting load paths and creating critical stress concentrations. While previous research has focused on external strengthening of traditional RC beams, a significant gap exists regarding the performance of composite beams with embedded steel sections near openings. This study introduces a novel strengthening strategy using internally built-up I-section and T-section steel elements as shear reinforcement. The methodology integrated experimental testing with a validated nonlinear 3D finite element model in ABAQUS to conduct an extensive parametric study. Key investigated parameters included I-section web thickness (0.1-2.5mm) and flange width (16-64mm), and T-section compression and tension flange widths (0-64mm). The key findings were substantial: web openings caused a 14% reduction in strength but a 41% increase in ductility, indicating a brittle failure mode. The incorporation of steel sections effectively reversed this; the I-section (176 × 2mm web, 40 × 2mm flanges) in beam BI-W2.0 yielded a remarkable 53.4% increase in ultimate load capacity, outperforming the original solid beam. An optimal I-section web thickness of 2.0 mm was identified, with diminishing returns beyond this point. For T-sections, the tension flange width was far more influential than the compression flange on strength recovery. A fundamental finding was that even a simple steel web alone provided a 43% strength gain, highlighting the critical role of bridging the opening. The reinforcement trade-off was a controlled 16-22% reduction in deflection, enhancing stiffness while maintaining structural safety. The research provides optimized, practical design guidelines for utilizing built-up steel sections to ensure structural integrity in perforated beams, effectively bridging architectural functionality and engineering safety.

Ensuring high quality, specific structures, and defined mechanical properties of materials requires the widespread application of non-destructive methods for control and investigation of the structural elements of materials, in particular ultrasonic methods. The subject of this study is samples of low-carbon steel, in which equilibrium ferrite-pearlite structures with different grain sizes have been obtained through targeted heat treatments. Through quantitative metallographic analysis, the average grain size, the percentages of ferrite and pearlite, and the grain size distribution have been determined. The aim of this study is to investigate the structural elements of carbon steels using an ultrasonic method. Ultrasonic spectral analysis is employed, which is based on the changes in the frequency spectrum of ultrasonic waves after their interaction with the material. The way ultrasonic waves scatter and attenuate in a polycrystalline material provides information about the size, shape, and distribution of the structural elements that make up the material. This work analyzes the influence of grain size distribution and the quantitative assessment of different phases on the attenuation of ultrasonic wave

Global annual production of niobium is only around 100,000 tonnes; however, it is a critical metal for modern industry and is mined in only a limited number of regions. This study reviews the current status of niobium smelting and recycling technologies. Approximately 90% of niobium is produced as ferroniobium (FeNb) for use in steel alloys, although niobium is also utilized in superalloys, superconductors, capacitors, semiconductors, and other applications. Niobium coexists with tantalum in columbite and tantalite ores. These ores are decomposed by hydrofluoric acid digestion or alkali fusion, followed by solvent extraction to separate Nb2O5 and Ta2O5. Niobium metal and FeNb are produced from Nb2O5 primarily via aluminothermic reduction, although metallic niobium can also be manufactured by thermal reduction using Mg, Ca, or C, as well as by molten salt electrolysis. Crude niobium is subsequently refined into high-purity niobium through molten salt electrolytic refining, high-temperature vacuum treatment, and electron beam melting. Because most niobium is used as an alloying element in stainless steel and high-strength low-alloy steel, recycling practices for niobium remain poorly documented.

This work investigates the full cycle of heat treatment (carburizing and quenching) of steel elements of metal molds used in the production of concrete products manufactured by the semi-dry vibrocompression method.Severe abrasive wear of the working surfaces of metal molds necessitates the optimization of chemical–heat treatment. Traditional methods do not allow accurate prediction of the final phase composition or hardness profile, particularly considering the complex influence of carbon concentration on quenching kinetics. Therefore, a numerical model for process prediction and quality control is required.A coupled multiphysics 2D model (diffusion, heat transfer, and phase transformations) was developed and implemented for a steel specimen with dimensions 100 × 100 × 20 mm. Carburizing simulations were performed for two initial carbon concentrations (0.08 and 0.2 wt.%) achieving a final surface concentration of up to 0.9 wt.%. After water quenching (typical heat-transfer coefficient h ≈ 5000 W/(m²·K)), the simulations demonstrated the formation of 80–85% martensite in the carburized layer. However, an increased content of retained austenite (15–20 %) was observed in the near-surface region.The presence of retained austenite in the carburized layer is explained by the significant reduction of the martensite-start temperature (MS) due to high local carbon enrichment. This confirms that even at high cooling rates (h ≈ 5000 W/(m²·K)), complete martensitic transformation does not occur, indicating the need for additional heat-treatment operations.The use of the Koistinen–Marburger model with concentration-dependent MS(c) and a locally refined mesh enabled accurate determination of the boundaries of the carburized and quenched layers. This provided a quantitative evaluation of the final phase composition profile, which is essential for hardness prediction.The simulation results can be applied by process engineers to optimize carburizing parameters (temperature and duration) and quenching conditions (cooling rate) to increase the service life of steel metal molds, as well as to justify the necessity of low-temperature tempering.

The article investigates the impact of a parametric fire on the temperature distribution in a steel beam, which is a critical factor in assessing its fire resistance. Numerical modeling of thermal processes was conducted using the Transient Thermal computational module in ANSYS WB, employing the finite element method. In solving the heat transfer problem, the properties of steel were adopted in accordance with the recommendations of Eurocode 3. The boundary conditions were applied based on a three-sided heating scenario, taking into account convective and radiative heat transfer. This approach enabled the determination of temperature fields in the beam under various fire exposure scenarios. A comparative analysis of the structural behavior under both standard and parametric fire conditions revealed significant differences in the heating dynamics. The study showed that the maximum temperature in the standard fire scenario reaches 943.09°C, which is 18.3% higher than the corresponding value for the parametric fire (770°C). This indicates that under the standard fire regime, the beam undergoes more intense heating, potentially leading to a faster loss of load-bearing capacity. Based on the obtained results, a polynomial dependency for temperature variations in the steel beam was formulated, demonstrating a high level of accuracy (R² = 0.9978) compared to the calculated data. These dependencies can be utilized to enhance methods for assessing the fire resistance of steel structures and for calculating their thermal state under fire conditions. The findings of this study are particularly relevant for the development of modern regulatory guidelines and the improvement of design strategies for steel structures, considering the impact of parametric fires. This research highlights the importance of accounting for realistic fire scenarios in structural fire engineering to ensure more accurate predictions of thermal performance and fire resistance of load-bearing steel elements in building design.

The paper presents the results of numerical simulation of the dynamic behaviour of the post-tensioned beams subjected to a constant force impulse load over time and a short-term force impulse load varying over time. Abaqus programme was used for numerical analysis, introducing necessary and detailed modifications to the modelling and calibration parameters. The numerical dynamics models were calibrated using results previously obtained from our own experimental and numerical static analysis. To estimate the dynamic strength of structural materials, the dynamic strength coefficient was applied in the concrete damage plasticity model, and the Johnson–Cook model was used to describe the evolution of the dynamic yield strength of steel elements. An explicit procedure was used to solve the dynamic equilibrium equations. The selection of the Rayleigh damping parameter and the methodology for determining the external load in a dynamic problem are discussed. The study presents new results on the influence of the type of force impulse loading and variable prestressing eccentricity in numerical simulations of post-tensioned beams. The results of the simulation show that the post-tensioned beams achieved a lower dynamic load capacity under a constant force impulse load of approximately 5% compared to the static load capacity achieved in the experimental static tests, regardless of the assumed prestressing eccentricity. A dynamic load capacity significantly exceeded the static load capacity under short-term time-varying force impulse loading. The beam with the larger prestressing eccentricity achieved a dynamic load capacity of 211% of the static load capacity, while the beam with the smaller prestressing eccentricity achieved a dynamic load capacity of 198% of the static load capacity.

Abstract Cold‐formed steel profiles are increasingly in demand in the construction market because of their speed of assembly and low material consumption. Thus, it is necessary to investigate their behaviour in depth, since in recent years they have been used as the main structural components of buildings. The paper presents an experimental program where several types of built‐up section configurations were tested made of lipped or plain channels, such as simple built‐up back‐to‐back and back‐to‐back with spacers cross‐sections and two types of discrete connections, i.e. bolts and spot welding. The static scheme of the beams used the 4‐point bending setup so that the central area is subject only to the bending moment. The length between the loading points was monitored to capture the behaviour of the beams from local to distortional and interactive local‐global buckling. A total of thirty beams subjected to pure bending with built‐up sections were tested. Additionally, out‐of‐plane displacements were restricted at the loading points to control the failure area. Before the tests were performed, the sectional dimensions and imperfections of the elements were measured, as this represents a critical issue in the behaviour of thin‐walled cold‐formed steel elements. A 3D laser scanner was used to determine the initial imperfections. The records allowed measurement of the initial imperfections in relation to the nominal cross‐section. Force‐displacement curves of the tests highlight the good performance of spot‐welds to reach similar resistance as for the bolted elements. The gapped built‐up elements showed a higher resisting force when compared to the direct contact back‐to back elements prone to global buckling.

Abstract In typical light steel framed (LSF) buildings, floor joists are connected to studs through web connections assuming pinned behaviour. This often results in deeper joist sections, as the design is primarily governed by mid‐span deflections. Consequently, the full load‐bearing capacity of cold‐formed steel (CFS) elements is underutilized, leading to heavier structures and increased environmental impact. This paper investigates the behaviour of a novel semi‐rigid joist‐to‐stud connection, where the joist and stud webs are screwed together. The semi‐rigid nature of this connection allows for the development of rotational stiffness and bending resistance, enabling the use of smaller joist sections and more efficient utilisation of structural capacity. To this end, detailed experimentally validated Finite Element (FE) models are developed in ABAQUS software to assess the influence of key design parameters, including connecting element sizes, screw arrangements, construction methods and gravity loads, on the structural performance of joist‐to‐stud connections. The performance of the connections is compared in terms of initial stiffness and flexural strength. Depending on the screw configurations and the section sizes, two main failure mechanisms are anticipated: (i) shear failure in the screwed connection; (ii) local buckling of the stud or joist flanges near the connection zone. The results indicate that implementing a semi‐rigid connection led to an average 25% reduction in the steel weight of the structure of six storey case study buildings compared to its conventionally designed counterpart with simple connections.

Abstract Corrosion is commonly observed in reclaimed steel elements, often leading to significant challenges for their re‐use. Corrosion potentially might favor failure in the cross‐section, by yielding or local buckling due to the reduction of the plate thickness. The buckling resistance of the member or structure may also be affected for the same reason. This paper examines numerically the effect of corrosion on the cross‐section bending resistance as it represents the reference both for members sensitive to buckling and restrained members. In particular, two cross‐sections are considered hereafter: HEA200 and HEAA260. A finite element model is developed in ANSYS and compared to existing test results obtained for members subjected to uniaxial and biaxial bending moments but without corrosion. Then, a sensitivity study is performed on these two short members varying the shape of the corrosion area as well as the thickness of corrosion. The comparison of the cross‐sectional resistance obtained numerically with the design rules of Eurocode 3 Part 1‐1 highlights that the major‐axis bending moment is the most critical loading situation.

Abstract In addition to axial forces and bending moments, the bimoment can significantly influence both the resistance and stability of steel members, independently of the geometry of their cross‐section. The complex interaction between the bimoment and other internal forces, and its implications for overall frame stability, remains an area of ongoing research. Despite numerous proposals by various Authors for interaction equations that account for these effects, the problem is not yet fully resolved, and current European standards often fail to adequately address this issue. Specifically, the old version of Eurocode 3 (EN1993‐1‐1:2005) did not comprehensively cover the influence of the bimoment on member stability. To cover this gap, the next generation of Eurocode 3 (EN1993‐1‐1:2022) introduces two new stability equations that account for the combined effects of all internal forces, including the bimoment. In the paper, after a recall on the Vlasov theorem, the ultimate load carrying capacity of selected isolated beam elements, experimentally and numerically evaluated has been compared with those derived from the application of the new EC3‐1‐1:2022 interaction equations. The selected cases demonstrated the importance of the new design rules for structural safety.

Abstract The paper presents results of an experimental campaign of the innovative floor system LWT‐FLOOR developed at the University of Zagreb, Faculty of Civil Engineering, Croatia, aiming to address challenges regarding the reuse and recycling of composite structures. The system consists of built‐up steel girders with four cold‐formed C profiles connected by spot welds to the corrugated web, additional shear plates near supports and a lightweight aggregate concrete slab connected with a demountable shear connection realised with structural bolts. This paper summarises experimental findings regarding the system components and detailed results regarding six bending tests of 6 m long steel and composite girders. The key system performance indicators regarding bending capacity and stiffness, failure modes, deformations and concrete slab end slip are investigated. The results show that the failure modes of beams are complex and influenced by the height of the girder cross‐section, the thickness of steel elements and consequently, the characteristics of spot welds. Four specimens (two steel and two composite) show expected results regarding preliminary numerical studies, while two specimens (one steel and one composite) failed due to the premature failure of spot welds.

Abstract This paper presents a novel approach for developing lightweight structural steel elements by integrating algorithm‐aided design with Wire‐and‐Arc Additive Manufacturing (WAAM). A computational design protocol was established, combining WAAM‐specific constraints, Eurocode‐based structural requirements, and topology optimization to generate efficient lattice geometries. Diamond‐shaped lattice prototypes were fabricated using a dot‐by‐dot WAAM strategy and tested under compression. The study highlights how physical deviations, particularly the formation of line‐nodes at bar intersections, significantly reduce the compression capacity compared to ideal point‐node geometries. Finite element simulations of both ideal and printed geometries were conducted, with results closely matching experimental observations. This research demonstrates the potential of WAAM and computational design in producing sustainable, high‐performance steel structures for architectural and engineering applications.

Abstract Metal Additive Manufacturing (AM), and particularly Wire Arc Additive Manufacturing (WAAM), opens new opportunities for steel structures by enabling efficient, reliable, and material‐saving solutions with reduced environmental impact. The AEC sector is starting to adopt WAAM for full‐scale structural elements, benefiting from its design freedom. However, tailored design approaches are needed to fully harness its potential and realize geometries unachievable with conventional methods. This study evaluates the environmental performance of a novel steel structural element featuring a Tubular Sandwich Section (TSS), fabricated using WAAM. The TSS, which defines the section of the structural element, consists of inner and outer cylinders connected by internal spokes, providing improved radial strength and better alignment with structural requirements. Its performance is compared to that of a conventional Circular Hollow Section (CHS), manufactured through cold forming with equivalent diameter and radial capacity. A cradle‐to‐gate analysis shows that WAAM enables a lighter and more sustainable alternative, highlighting its promise in reducing the carbon footprint of the construction sector.

Abstract Steel plates are integral components of steel members, particularly vulnerable to local buckling when exposed to fire and subjected to compressive loading conditions. These plates, combined with various boundary conditions at different edges, form complete steel sections. This study proposes a behavior and design formulation to determine the ultimate strength of a steel section or member by examining the most vulnerable element with idealized boundary conditions on all edges. Experimental and numerical results from previous studies on whole steel sections were compared and found to align well with this new design approach, proving it simple and effective in determining the behavior and strength of the entire member under elevated temperatures. Using the commercially available finite element software ABAQUS, a numerical investigation was conducted to analyze the compressive and flexural behavior of internal and outstand steel elements, with and without central cutouts, across different plate slenderness and temperature ranges. The reliability and accuracy of the proposed formulation were assessed by comparing it with existing European design standards (EN‐1993‐1‐2) and North American design standards (AISC‐360‐16) for steel structures in fire exposure scenarios.

In accordance with the requirements of regulatory and technical documents on ships, it is necessary to apply protective protection to prevent contact corrosion of ship systems, apparatuses and equipment when using dissimilar materials, as well as selective and pitting corrosion. It is recommended to make protectors from the following materials: zinc Zn, aluminum Al and steel grade ST-3 or South. On many ships of the Kamchatka Fleet, factory-made zinc and steel protectors are used to protect ship structures (steel hulls and elements of the ship's power plant) from corrosion, as well as steel protectors of their own design and manufacture by the shipowner's mechanical service or at the ship repair plant, which are approved and approved for use on ships by classification societies. At the same time, many ship mechanics of the Kamchatka Fleet face the problem of conducting input technical control of the operability of steel treads supplied for replacement, since there is a lack of appropriate monitoring equipment, methods and competencies. The manual control procedure is time-consuming, complex and has a high risk of obtaining unreliable results due to the influence of errors and human factors. The necessity of developing an affordable and reliable method of technical control of shipboard steel protectors of factory and non-factory manufacture, which can be used by the ship's mechanical service, is substantiated. The description of the developed author's technical method of non-destructive testing of the technical condition of steel treads, which can be implemented on ships by ship crews, is given. To monitor the projector protection, an automated measuring system has been developed, the structure and principle of operation of which are discussed in other articles by the authors. The technical condition of three steel protectors (one factory-made, two manufactured by the shipowner's mechanical service) used on the RS-70 vessel to protect the vessel from corrosion was monitored. It has been established that factory-made protectors and protectors manufactured by marine mechanical services can be used on ships, but to increase reliability, it is recommended to use additional input control according to the developed author's methodology.

Lightweight steel structural systems like trusses or built-up beams, made of thin gage steel elements, are highly efficient, with ease of handling and construction. Self-drilling screws are commonly used for connecting thin-walled elements, but the time and manpower required for numerous connections necessitate an improved solution. One possible solution is to use welding technology, but the conventional methods are not suitable for joining thin sheets. Manufacturing defect-free, mechanically sound welding joints remains challenging due to defects like porosity and undesired microstructural phases in the heat-affected (HAZ) and fusion zones (FZ). Conventional welding processes increase heat input, causing difficult challenges. Brazing, a relatively new joining process, offers the advantages of lower heat input for thin and zinc-coated steel sheets. Therefore, the paper aims to present the effect of MIG brazing parameters on the macro-and microstructural properties of Cu-Al-based weld seams manufactured for joining thin sheets with thickens in the range of 0.8-2 mm. The weld seams were manually fabricated using a MEGAPULS FOCUS 330 compact equipped with TBI XP 363S/4m welding torch, focusing on optimal welding regimes. The macro-and microstructures of the joints were evaluated along with the mechanical properties in terms of hardness, confirming that MIG brazing is a promising method for manufacturing lightweight steel structural systems.