Steel Design Research Articles

Design of high-strength martensitic steels by novel mixed-metal nanoprecipitates for high toughness and suppressed hydrogen embrittlement

To obtain a fundamental understanding of mechanisms of hydrogen embrittlement (HE) and its prevention in advanced high-strength steels containing novel nanoscale mixed-metal precipitates, it is necessary to study local microstructure, H trapping, and crack path with new multiscale experimental and simulation approach. Spatially resolved hydrogen mapping via SKPFM is used together with investigation of the crack path using high-resolution EBSD and HMPT, and global trapping behavior of the alloys by TDS. These results are combined with newly introduced method to elucidate real-time distribution of hydrogen in the alloy using high-energy synchrotron X-ray diffraction (HES-XRD). Mixed-metal precipitates improves HE resistance of the alloy, due to nature of the trapping sites, e.g. irreversible H-trapping by carbon vacancies inside novel nanoprecipitates and high total length of PAGBs. This is because of lower possibility of build-up of critical local hydrogen content at PAGBs for intergranular hydrogen-assisted cracking due to hydrogen-enhanced decohesion mechanism. Less weakly trapped hydrogen also reduces frequency of dislocation activation and enhanced dislocation slip in {011} slip plane due to hydrogen-enhanced localized plasticity in regions with affinity for transgranular hydrogen-assisted cracking at lower local hydrogen content. Direct evidence of carbon vacancies in novel nanoprecipitates is observed for the first time via HAADF-STEM.

Structural assessment of stainless steel stiffened panels

Stiffened plate panels present several applications in Engineering, for instance, in naval/offshore structures, where they are employed as primary elements of ships and vessels. An essential aspect of the failure mechanisms of stiffened plated panels is the initial geometrical imperfections and residual stresses embedded in such structures due to the fabrication processes. Some technical design guides present rules to be applied to the design of carbon steel stiffened plated panels. However, with the technological evolution of the materials and their more strict demands on corrosion and mechanical resistance, it is necessary to utilise special steel whose design is not covered in the codes, as mentioned earlier. This work aims to assess the ultimate resistance of stainless steel stiffened plated panels and verify the influence of different initial imperfections on their capacity. In order to achieve this objective, experimental tests were carried out at the laboratory of stainless steel stiffened panels with an aspect ratio between the panel length and the stiffener spacing of 2.7 and 4.35 to cover the practical values used in the naval/offshore structures. Afterwards, a FE model was developed and calibrated against experimental results. A parametric analysis was performed to enlarge the database to check if the current rules applied to carbon steel structures can be applied to stainless steel stiffened plated panels. The results showed that some design rules could provide conservative and non-conservative designs for low and high slenderness, respectively. Finally, a new equation based on the calibration of the Cx parameter (ratio of the ultimate strength concerning uniaxial stress to the specified minimum yielding point of the plate in the longitudinal direction) was proposed providing improved results.

Experimental study on residual monotonic mechanical properties of high-performance Q690 steel with pre-fatigue damage

In this paper, we conduct an experimental study of the fatigue performance and monotonic tensile properties with pre-fatigue damage of seismic and corrosion resistant Q690 structural steel (abbreviation high-performance Q690 steel). Based on fatigue cumulative damage theory, S-N curves and fatigue cumulative damage curves of high performance Q690 steel were obtained. According to the static mechanical properties with different degree of fatigue damage, the related curves between fatigue damage degree and residual mechanical properties were proposed. Finally, based on the Rambeger-Osgood constitutive relationship, a constitutive model for high performance Q690 steel considering fatigue damage is proposed. The results indicated that the high performance Q690 steel showed good fatigue performance. Its limit fatigue strength is 630 MPa (0.86fy) approximately, which is higher than fatigue limit values specified in steel design standards. In addition, the fatigue crack propagation stage and transient fracture stage accounted for a relatively small proportion of fatigue life. The static mechanical properties with pre-fatigue damage of high performance Q690 steel is similar to the AISI 1045 steel. As the fatigue damage degree increases, the elasticity modulus of high performance Q690 steel decreases and yield strength increases. Whereas, pre-fatigue damage has little effect on ultimate strength and elongation. Finally, a new constitutive model considering fatigue damage was proposed, which was found better simulating tensile curves with different fatigue damage.

Microstructure characterization and formation mechanism of lanthanum phosphide in FeCrAlRE alloy with ultra-low oxygen

Rare earth (RE) could be added to steels to improve their properties, but there is still controversy on its presence form. Taking 0Cr20Al6RE as the research object, the morphology, distribution, chemical composition and phase structure of RE precipitated phases were characterized by SEM, EPMA and TEM. It is found that with ultra-low oxygen (3 ppm) and RE/(O + S) = 37.1, the main existence form of rare-earth is RE-P-As in which the La-P phase is lanthanum monophosphide with a rock-salt structure, while the structure of complex inclusion is mainly RE-Al-O/RE-P-As/(Ti,Nb)(C,N). According to Gibbs free energy, precipitated phase distribution and solidification segregation calculation, it is confirmed that La-P-As is formed at the solidification front. This finding provides a technology idea for the composition design and process improvement of RE steels by avoiding the emergence of large-size RE-O-S inclusions.

Robustness evaluation and design of steel and steel‐concrete buildings according to current standards and recent research results

AbstractIn terms of mitigation of progressive collapse, structural robustness is a specific safety consideration, which requires particular attention from all professionals involved in the construction industry, including architects, designers and constructors. The design of buildings considering robustness has evolved considerably over the last two decades, during which different research activities have been developed, leading to new methods and design processes. These practice‐oriented methods and concepts have been recently summarized in a design manual prepared in the framework of the FAILNOMORE RFCS project (grant No 899371), providing to the designer a general design strategy for robustness based on these methods as well as easy to follow worked examples. The proposed design strategy allows to ensure the global stability and the mitigation of progressive collapse of steel and composite structures when subjected to exceptional events, such as vehicle impact, explosion, cascading events involving localized fire or events which are not explicitly specified in the typical structural design process. In this paper, the application of these recommendations is demonstrated by means of realistic worked examples. Typical steel and steel‐concrete composite office buildings, designed according to the current European standards, are evaluated for robustness against identified and unidentified threats. The results obtained with simple and more advanced verification approaches are compared, and possible solutions to improve the robustness of the structures are provided.

Resistance and behaviour of carbon steel and stainless steel columns with axial and rotational end‐restraints in fire

AbstractDue to the presence of neighbouring structural elements, carbon steel and stainless steel columns are typically axially and/or rotationally restrained at their ends in fire. Despite the significant influence of the axial and rotational end‐restraints on the behaviour, the fire design rules for steel columns provided in the European structural steel fire design standard EN 1993‐1‐2 were originally developed considering the structural response of axially unrestrained steel columns with pin‐ended support conditions. Thus, EN 1993‐1‐2 may provide inaccurate ultimate resistance predictions for axially and/or rotationally restrained steel and stainless steel columns in fire. Considering this, this paper investigates the behaviour and design of carbon steel and stainless steel columns with axial and/or rotational end‐restraints at elevated temperatures. A number of carbon steel and stainless steel I‐section columns are considered, taking into account different axial and rotational end‐restraint stiffnesses, room temperature loading ratios, member and cross‐section slendernesses. A new design method for the fire design of axially and/or rotationally restrained steel and stainless steel columns is put forward. The accuracy of the proposed new design method is extensively verified against the results from nonlinear shell finite element modelling.

Design of Stainless Steel Cross‐Sections by Inelastic Stability Analysis

AbstractWhile carbon steel cross‐sections are traditionally categorized as Class 1, 2, 3 or 4, depending on when local instability occurs relative to the key stages of yielding, for stainless steel the lack of a well‐defined yield point and the presence of continual strain‐hardening render this approach artificial and superfluous. A new design methodology is therefore needed, which accounts for the effects of both strain‐hardening and local buckling.The proposed method is based on a modified finite strip method, which accounts for the effects of gradual loss of stiffness due to yielding on the stability of thin‐walled members. Extensive verification of the new method against experimental data showed that cross‐sectional capacities are generally well predicted, with average ratios of the measured to the predicted capacity of 1.18 and 1.19 in compression and bending, respectively, and a standard deviation of 0.10 in both cases. This is a significant improvement over the EN 1993‐1‐4 design rules, where the averages over the same dataset were 1.27 and 1.40, respectively, with standard deviations of 0.14 and 0.17. The rotational capacity of stainless steel cross‐sections in bending was also reasonably well predicted, with an average ratio of measured to predicted curvature of 1.79.

Behaviour, finite element modelling and design of high strength steel homogeneous and hybrid welded I‐section beams

AbstractThe behaviour and design of homogeneous and hybrid high strength steel (HSS) beams are addressed in the present study. Six in‐plane three‐point bending tests on three different welded I‐sections were first conducted. Following the experimental investigation, a finite element (FE) modelling programme was performed, which included a validation study confirming the accuracy of the developed FE models in replicating the flexural behaviour of HSS welded I‐section beams, and a parametric study generating additional FE data on HSS welded I‐section beams over a broader range of cross‐sectional slendernesses, steel grades and loading configurations. Then, the suitability of the current Eurocode 3 cross‐section slenderness limits for HSS homogeneous and hybrid welded I‐sections in bending were evaluated. It is shown that the current Eurocode Class 2 and Class 3 slenderness limits are suitable for the classification of the outstand flange (in compression) and internal web (in bending) elements of both HSS homogeneous and hybrid welded I‐sections subjected to major axis bending, while stricter Class 1 slenderness limits are considered necessary to achieve sufficient rotation capacity for plastic design. The findings indicate that plastic design can be used for HSS structures, provided the proposed stricter Class 1 slenderness limits are employed. Further work is underway to develop advanced design approaches using second‐order inelastic analysis with strain limits for HSS welded I‐section members.

The FAILNOMORE project – Practice‐oriented design recommendations against progressive collapse in steel and steel‐concrete buildings

AbstractStructural robustness is a specific safety consideration which is currently addressed in modern codes and standards, including the Eurocodes. It requires particular care from all professionals involved in the construction industry. The need for practical guidelines to mitigate the risk of progressive collapse has been emphasised by recent catastrophic events such as the 9/11 terrorist attack in New‐York. The lack of consistent design rules for practitioners is however clearly identified in existing normative documents and literature. Accordingly, various research projects were launched, particularly in Europe through RFCS research projects. Thanks to these research activities, significant scientific background has been developed, with the aim of understanding and characterising the behaviour of steel and composite structures subjected to exceptional events such as impact, explosion, or loss of a bearing member. Nevertheless, there was a need to consolidate the available scientific knowledge and to transform it into a consistent set of practical recommendations in order to facilitate the design of steel and composite structures for robustness. This was the purpose of a recent RFCS project “FAILNOMORE” (grant No 899371) which was concluded in June 2022. A brief summary and discussion of the main outcomes of this project are provided in the present paper.

Design assisted by finite element analysis – Introduction to prEN 1993‐1‐14 and Technical Report

AbstractThe application of design by finite element analysis (FEA) is becoming increasingly prevalent in applied engineering; however, codified provisions remain scarce. The vision of CEN/TC 250/SC 3 was to develop a new comprehensive document based on the existing provisions currently distributed throughout the different Eurocode 3 parts, and with extension where necessary to cover all fields of structural steel design. Within the development process, two documents are being prepared: (i) the code, prEN 1993‐1‐14 and (ii) a Technical Report. The new code aims to provide rules on the use of finite element analysis and other numerical methods for verifying ultimate limit states, serviceability limit states and fatigue. In parallel, the Technical Report will provide background information and explanations of all aspects of the code, as well as benchmark cases and design examples to support the correct application of the prEN1993‐1‐14 design rules and the necessary benchmarking required for model validation. The assumed stakeholders are mainly designers who can find direct guidance for design by finite element analysis in daily engineering practice. This current paper gives an overview of the new code and accompanying Technical Report, as well as the development process and harmonisation within the current Eurocode 3 framework.

Ontological Description of Design Rationale of Steel Design Knowledge and Its Use

Ontological Description of Design Rationale of Steel Design Knowledge and Its Use

General method for I‐section stainless steel beam‐columns

AbstractA significant progress in the development of stainless steel design procedures which were implemented also in new design standards proposals, prEN 1993‐1‐4:2021 and AISI 370‐21, has been going on in the last 15 years. For compressed members, buckling curves were revised and beam‐column interaction formulas were published for hollow and open sections. Buckling curve was significantly improved for double‐symmetrical I section beams. The Continuous Strength Method was introduced in the code. Also, a verification procedure using a plastic global analysis was developed and implemented in design procedures very recently. However, clear design rules for geometrically non‐linear analysis with equivalent member and structural imperfections need further research. This approach, known also as the general method, became a very popular method for carbon steel structures, but cannot be used for slender stainless steel structures without modification. The stainless steel nonlinear stress strain diagram leads to a reduction of the bending stiffness and thus higher second‐order effect, which needs to be covered in the procedure. In this research, a comparison is made on numerical parametric studies. Limits will be set for the applicability of the carbon steel design procedures and a preliminary recommendation for general method of stainless steel members will be presented.

Bracing requirements for a semi‐rigidly connected column considering column lateral stiffness and initial curvature

AbstractThis paper theoretically assesses the required brace stiffness and strength for a semi‐rigidly connected column with a lateral brace at the mid‐height, by introducing a half‐length column model and adopting the concept of storey‐based buckling. Unlike that in Winter's model, column lateral stiffness and initial curvature associated with column initial out‐of‐straightness are accounted for. A coefficient, which is a function of applied load and column end connection stiffness, is introduced to characterize the effect of column initial curvature on bracing requirements. By comparing the results obtained from the analytical method and current structural steel and cold‐formed steel design standards, it has been found that the required brace strength stipulated in these standards are generally conservative in various degrees for design loads; however, the required brace stiffness should be increased if the effect of column initial curvature is considered. The results obtained from the proposed approach are verified against the finite element analysis, indicating that the proposed approach provides an accurate evaluation of required brace strengths for semi‐rigid columns and is recommended to be adopted for engineering practice.

Uncertainties in the structural design of the high‐bay cold storage warehouses

AbstractThe paper presents the structural analysis and critical evaluation of the modelling process of a high‐bay cold storage warehouse structure, which is a clad rack structure, composed of cold‐formed steel members, with different profile shapes and thicknesses. A major issue of the global structural analyses of these types of steel structures is the mixed application of design rules since the design is governed by racking structural rules, seismic design rules and cold‐formed steel design rules. To manage this problem, the structure's spatial model was divided into characteristic partial models, and spring supports were used to make the behavior of the partial models more realistic. The influence of the gravity loads (self‐weight, show), horizontal loads (wind and seismic action), geometrical imperfections, and loads induced by the temperature variation on the structure was investigated in the structural design. Even the wind actions resulted as dominant, some uncertainties related to the seismic analysis of these structures are presented in the paper.

GMNIA‐based design of stainless steel structural systems

AbstractDesign by GMNIA (Geometrically and Materially Nonlinear Analysis with Imperfections) allows the key behavioural features of structures to be directly captured in the analysis, dramatically reducing the need for subsequent design checks. Since the analysis of frames typically employs beam finite elements, which do not explicitly account for local buckling, cross‐section classification and capacity checks remain necessary. To resolve the step‐wise and overly conservative nature of traditional checks, the alternative use of strain limits, defined using the Continuous Strength Method, has been proposed. The framework allows cross‐sections of all classes to be treated in a consistent manner, and results in an accurate and consistent representation of the true behaviour of structures. To date, the accuracy of the design approach for stainless steel has been comprehensively demonstrated for isolated stainless steel members; the design method is extended to indeterminate stainless steel structural systems herein. The method is included in AISC 370 and prEN 1993‐1‐14; inclusion of this design framework in international codes of practice presents a step change for the future direction of efficient structural stainless steel design.

Axial compressive behavior and design of semi-precast steel reinforced concrete composite columns with permanent ECC formwork

This paper proposes an innovative semi-precast steel reinforced concrete (SRC) hybrid composite column, which incorporates a precast engineered cementitious composite (ECC) jacket as the permanent formwork for the infilled concrete. The ECC jacket enhances the column compressive resistance and provides superior post-peak ductility. To evaluate the compressive performance of the ECC-SRC composite column, an experimental program of six axially-loaded stub column specimens was conducted by varying the thickness of the ECC jacket, section size of structural steel and spacing of transverse reinforcing bars. The axial performance of the ECC-SRC column is evaluated in terms of failure characteristics, initial stiffness, load-carrying capacity, post-peak resistance and ductility, and the full range load-deformation response. The test results show that the ECC-SRC column exhibits improved compression capacity and ductility compared to conventional SRC columns. The assessment of compiled database also reveals the applicability of current design codes EN 1994-1-1 and JGJ 138-2016 in predicting the load-carrying capacity of ECC-SRC columns. Finally, based on the parametric study of the database, design suggestions are proposed to maximize the merits of ECC when employed in ECC-SRC columns.

Automated clash resolution for reinforcement steel design in precast concrete wall panels via generative adversarial network and reinforcement learning

The increasing adoption of precast concrete elements (PCEs) is evident in civil infrastructure projects. The structural integrity of prefabricated structures relies on the quality of connections between adjacent components, necessitating the design of reinforcing steel bars (rebars) in PCEs. Dealing with PCEsand the complex design codes for rebars' arrangement can be labor-intensive, impractical, and error-prone when using traditional computer software due to their irregular shapes. This often results in frequent rebar clashes on construction sites. On the other hand, Building Information Modeling (BIM) technology, which is widely employed for structural design in the industry, offers potential solutions to these challenges. Several studies have proposed clash resolution strategies for moving components using optimization algorithms; these strategies are only suitable for regular reinforced concrete (RC) structures. The optimized path of rebars cannot be adjusted to avoid obstacles in PCEs. Due to strict design codes and large dimensions, existing studies do not possess the learning knowledge from design codes or drawings needed to generate clash-free rebar arrangements for real-world PCEs automatically. To overcome this limitation, we present a BIM-based framework that utilizes Generative Adversarial Network (GAN) and Deep Reinforcement Learning (DRL) to automatically generate clash-free rebar designs in prefabricated concrete wall panels (PCWPs). Our method employs GAN to learn from designers’ experiences from existing design drawings and generate 2D preliminary rebar designs, which are then transformed into mesh environments for DRL. The DRL engine incorporates state, action, and rewards designed according to buildability constraints and design codes. We conduct extensive experiments on real-world PCWPs to assess the efficacy of the proposed method. The results indicate that our framework can reduce engineering time for rebar designs by up to 80% compared to manual design, while achieving clash-free designs that adhere to design codes.

Grey Relational Analysis-based Interactions of Machining Parameters for Optimal Process Response: An Experimental Initiative

This study, investigated the optimal combining of tool nose radius and cutting variables for the overall performance for both AISI 4140 steel and IS-2062 steel. The both materials were machined on a centre lathe and measurements were taken. The data collected was analysed through grey relational analysis. Results showed that grey relational optimal interactions of machining parameters for the overall performance were: N R (0.35mm), U o (0.5mm), V w (65m/min), R f (0.2mm/rev) for both materials. Also, grey relational grade improved by 1.2767 (24.69%) for the expected optimal design for AISI-4140 steel, and improved by 1.7417 (33.68%) for the expected optimal design for IS-2062 steel. The expected responses were: cutting power 11.157 kW, specific metal removal rate 9.710 mm3/min.kW, cutting force 173.110 N, thrust force 77.207 N, shear force 124.838 N, surface roughness 5.00 , and Shear work 7945.9kNm/min for AISI-4140 steel; and cutting power 5.544 kW, specific metal removal rate 19.541 mm3/min.kW, cutting force 86.074 N, thrust force 39.440 N, shear force 65.688 N, surface roughness 6.165 , and shear work 4158.67 KNm/min for IS-2062 steel. Grey relational analysis reduced the factors affecting on the dependent variables to feed rate and depth of cut.

Performance Analysis of Multiple Steel Corrugated Pipe Arch Culvert under Construction and Periodic Vehicle Load

The arrangement of multiple culverts has gradually increased in road engineering. However, the arrangement will face a series of risks in both the construction and operation stages. A numerical model was established to analyze the construction and operation safety of multiple steel corrugated pipe arch culverts by using a fully fluid–solid coupling two-dimensional (2D) model of a highway project. The sensitivity of factors affecting the settlement of the composite foundation such as modulus and depth of ground reinforcement was discussed. Based on the results of the 2D model, a fully fluid–solid coupling three-dimensional (3D) model was established to study the influence of dynamic cyclic vehicle load on the mechanical properties of multiple steel corrugated pipe arch culverts. The ground deformation, soil stress and pore pressure, structure stress, and deformation were analyzed. The results show that the maximum settlement of the soil in the arch culvert area is at the junction of the two different arch culverts after construction. The maximum vertical deformation of the structure appears at the vault, and the arch waist is prone to stress concentration. Under cyclic vehicle dynamic load, the ground deformation, structural stress, and arch culvert subgrade deformation showed a rapid growth stage, and then tended to be stable. The weak points in the structure during the construction and operation stages were revealed, which can provide a useful reference for the design and construction of multiple steel corrugated pipe arch culverts.

Design and Optimization of the Bi-Directional U-Ribbed Stiffening Plate–Concrete Composite Bridge Deck Structure

The steel–concrete composite structure is widely used in civil engineering for large-span bridges. Orthotropic steel bridge decks (OSDs) have particularly gained popularity due to their excellent mechanical performance. To address cracking issues in OSDs and concrete in negative moment regions, a novel bi-directional U-ribbed stiffening plate (BUSP)–concrete composite bridge deck is proposed. By using finite element analysis, the mechanical performance is evaluated based on maximum tensile stress and vertical displacement of concrete overlays. Results show that the BUSP–concrete deck outperformed conventional flat decks. It is also found that increasing the height, thickness, and opening width of U-ribs reduced tensile stress and maximum displacement. Adjusting height had the most significant effect on displacement while opening width affected tensile stress the most. Considering material usage, optimizing height is proved to be more effective than adjusting thickness and opening width. Decreasing spacing parameters improved performance but added complexity and reduced construction convenience. These findings will guide the design and optimization of steel–concrete composite bridge deck structures.