Abstract Membrane structures made from technical textiles or foils have been part of the built environment for decades. They appear in a wide range of applications, from private homes to public buildings and open spaces. Because membrane materials are exposed to climatic conditions, they are subject to aging and are therefore not supposed to last indefinitely. In contrast, most supporting elements age in a way similar to conventional building materials. As a result, it is often only the membrane skin that requires treatment or replacement after a number of years, enabling the entire structure to begin a “second life.” Membrane structures can be preserved through various approaches, and regular maintenance plays a crucial role in achieving long‐term durability.
In recent years, considerable steps have been made in the field of membrane structures. After many years of development, the first European design standard for tensioned membrane structures has been published. This work was accompanied by numerous advancements in testing and modelling of structural membranes. This contribution provides an overview over the contributions of the Institute for Metal and Lightweight Structures at the University of Duisburg-Essen, Germany, in this context. Additionally, it displays developments since the publication of the design standard and provides an outlook on the planned work for the coming years. The goal of the efforts is the transformation of the first design standard into a Eurocode for membrane structures and a set of accompanying product and testing standards.
Flame straightening corrects deviations in steel structures but induces residual stresses and microstructural alterations, potentially affecting safety. This study evaluates its impact on preset beam ends for a steel corridor connection. Deviations resulted from differential building settlement and thermal torsional deformation. A cyclic vein heating process (up to 800 degrees C) was simulated on a Q355B steel beam end using Abaqus coupled temperature-displacement analysis to generate the residual stress field, which was then used as an initial condition in mechanical analysis. The bearing capacity, energy dissipation under cyclic loading, and fatigue life under wind loads were compared before and after straightening. Results indicate that flame straightening has negligible effects on ultimate bearing capacity and displacement ability. It may slightly enhance energy dissipation at small displacements due to earlier localized yielding. Importantly, while fatigue life remains adequate for designed wind loads, it degrades significantly under high-stress fatigue conditions. Thus, flame straightening is a viable correction method under moderate service loads but is not recommended for members experiencing high-stress dynamic or fatigue loading.
Welded box columns made of high-strength steels (HSS) are characterized by high buckling resistance and low self-weight. The residual stresses introduced by the welding process are of particular importance. In the area of the weld seams, the cooling process creates residual tensile stresses that are in equilibrium with the compression stresses distributed across the cross section. In Europe, the buckling resistance is insufficiently covered by the rules of EN 1993-1-1 and -1-12. The present rules were validated for steel grades up to S355, so the application is quite conservative for columns made of HSS, especially in the medium slenderness range. As part of the IGF-FOSTA research project P1588, residual stress distributions of welded box sections were determined for the steel grades S460-S960. The buckling resistance was investigated experimentally and by structural-mechanical calculations. The results led to recommendations for a revision of the buckling curve assignment and residual stress distributions of compression members with welded HSS box sections.
Recently, the content of the technical report CEN/TR 1993-1-102 on elastic critical buckling of members was established by the Eurocode 3 committee CEN/TC250/SC3. This report contains elastic critical buckling solutions for members, frames and bridge components to be used in conjunction with the design rules of Eurocode 3 EN 1993: Design of steel structures. In the various parts of Eurocode 3 EN 1993, limited information is given on elastic critical buckling solutions, though the design rules presented in Eurocode 3 EN 1993 rely on these solutions. Users of this code therefore, in many cases, use elastic critical buckling solutions from the literature. However, using literature information may cause discussion between parties involved in the design of steel structures. Therefore, it was felt that a compilation of generally accepted, simple and correct elastic critical buckling solutions for members, frames and bridge components would be useful. This report pays attention to the determination of elastic critical buckling forces and moments and the associated buckling lengths where relevant. Also, special attention is paid to boundary conditions and the stiffness of springs and beddings. The elastic critical buckling solutions may be used also for structures made of other materials than steel. The purpose and the content of the technical report are described in this article. Eurocode 3 - Technischer Bericht 102 & uuml;ber das elastische kritische Knicken von BauteilenK & uuml;rzlich wurde der Inhalt des technischen Berichts CEN/TR 1993-1-102 & uuml;ber das elastische kritische Knicken von Bauteilen vom Eurocode-3-Ausschuss CEN/TC250/SC3 verabschiedet. Dieser Bericht enth & auml;lt L & ouml;sungen f & uuml;r das elastische kritische Knicken von Bauteilen, Rahmentragwerken und Br & uuml;ckenbauteilen die in Verbindung mit den Bemessungsregeln der Eurocode 3 EN 1993 "Bemessung von Stahlkonstruktionen" zu verwenden sind. In den unterschiedenen Teilen der Eurocode 3 EN 1993 werden nur wenig Informationen zur Bestimmung der elastischen Knicklasten gegeben, obwohl die Bemessungsregeln auf diesen L & ouml;sungen beruhen. Daher verwenden die Anwender des Eurocode 3 in vielen F & auml;llen L & ouml;sungen f & uuml;r das elastische Knicken aus der Literatur. Da es keine autorisierten L & ouml;sungen gibt kann dies jedoch zu Diskussionen zwischen den am Entwurf von Stahlkonstruktionen beteiligten Parteien f & uuml;hren. Daher wurde es als sinnvoll erachtet, eine Zusammenstellung allgemein anerkannter, einfacher und korrekter L & ouml;sungen f & uuml;r das elastische kritische Knicken von Bauteilen, Rahmentragwerken und Br & uuml;ckenbauteile zu erstellen. Dieser Bericht befasst sich mit der Bestimmung der elastischen kritischen Knickkr & auml;fte und Biegedrillknickmomente sowie der damit verbundenen Knickl & auml;ngen, sofern relevant. Besonderes Augenmerk wird auch auf die Randbedingungen und die Steifigkeit von Federn und Auflagern gelegt. Die elastischen kritischen Knickl & ouml;sungen k & ouml;nnen auch f & uuml;r Strukturen aus anderen Materialien als Stahl verwendet werden. Der Zweck und der Inhalt des technischen Berichts werden in diesem Artikel beschrieben.
The Ayrton-Perry approach is the basis of Eurocode 3 rules for buckling resistance, with distinct curves and imperfection factors depending on section type, steel grade, and other parameters. For generic members - built-up or not, uniform or not, with complex supports or not - the code allows either the general method (clause 8.3.4 of Eurocode 3) or advanced numerical simulations. Yet, the general method shows wide scatter and often underestimates resistance, while numerical analyses are time-consuming and strongly user-dependent. To overcome these limitations, the general formulation was introduced by Tankova et al. (2018) for members with variable geometry, loads, and supports and recently extended to mono-symmetric I-beams. However, it has only been validated for Class 1 and 2 sections, not for Class 4. This paper extends the general formulation to uniform and non-uniform slender I-section beams subjected to arbitrary loads, boundary conditions, and partial lateral restraints. An advanced numerical model, calibrated against experimental data, was employed to conduct a comprehensive parametric study considering different cross-sections, a range of normalized slenderness values, S460 and S690 steel grades, and different load applications. The proposal was compared with the numerical results, demonstrating a safe-sided and well-calibrated solution for the buckling resistance of high-strength steel slender I-section beams.
The challenges the construction industry is facing to reduce its environmental impact and to efficiently use the available resources lead to an extensive search for sustainable construction alternatives. In the last decades, competitive engineered wood products (EWPs) appeared in the market. The synergy between EWPs and steel, in the so-called steel-timber composite (STC) form, can be an efficient and sustainable solution for the execution of building floors and decks. Various shear connections for STC have been developed. However, the majority relies in the dowel-type connectors, with limited mechanical performance strongly affected by the flexibility of the EWPs. Furthermore, the nonlinear and permanent deformations often developing in a low range of loading may hinder reuse of the materials and strongly limit the nondestructive disassembly at end of life. Thus, this paper presents the development of a new reversible shear connector for efficient STC floor beams meeting the needs of an optimize use of construction materials through reuse. First, a brief overview of existing shear connections for STC is given, identifying their potential and limitations. Then, the concept of the new proposed connection is exposed. Finally, a preliminary assessment through analytical calculations and numerical simulations is done, demonstrating the efficiency of the proposed shear connection towards a designed for disassembly STC composite beam.
In the structural stability design of steel structures, the effects of imperfections arising from steel members' fabrication must be adequately accounted for. In the case of welded members, residual stresses have a substantial impact on the structural performance due to the high thermal energy input during production and subsequent non-uniform cooling. In simplified design methods for steel beams, these imperfections are taken into account by assigning the members to buckling curves and the associated imperfection factors. A review of simplified design methods and their structural efficiency for welded members is timely, given the latest results on residual stresses. This paper presents a study on the lateral torsional buckling behaviour of welded steel beams and the subsequent consequences of the findings for simplified design methods. A comprehensive numerical study analysed the load-bearing behaviour of steel beams made of S235 to S690. Residual stresses were taken into account using the residual stress approach according to current standards, as well as a state-of-the-art approach. The numerical study confirmed that residual stresses have a lesser influence on the structural performance of members made from higher steel grades. To take the identified effects into account for structural designs, an adjustment of the imperfection factors is proposed in this paper.
Filler beam decks are a traditional steel-concrete typology widely used in bridge construction and covered by the normative framework. The cross section is characterised by a deep-lying neutral axis which calls for a restriction on the concrete cover thickness and eventually the application of an adjustment factor when applying plastic moment resistance. The present study assesses the use of the plastic resistance for conventional reinforced concrete with respect to the current limitations on the maximum concrete cover and steel grade. The application of steel fibre reinforced concrete is also assessed, an option which permits improvement of this typology at the serviceability and ultimate limit state. The superior concrete ductility in compression conferred by the fibres permits to eliminate the risk of concrete crushing in the concrete cover. This study conducts therefore some practical proposals for extending the current design method for filler beam decks concerning the material range and geometrical boundaries.
Usually, pinned ends are assumed to calculate the compression capacity of closely spaced double-angle members. In reality, the joints used in practice provide additional rotational restraint at the member's ends, which significantly influence the compression member capacity of such built-up sections. The current study systematically investigates this effect. This is realized through a numerical parametric study using finite element models. The varied parameters are: i) member length, ii) type and dimension of the individual angle sections, iii) number of interconnections, and iv) dimensions of the gusset plates at the member's ends (i.e., thickness width and depth). Finally, a design model is introduced that is based on the second-order theory calculation of an eccentrically loaded column with rotational end restraints. Furthermore, appropriate stiffness functions for these rotational end restraints are presented, also including cases with plastic hinges in the gusset plate. It is shown that this new design model can accurately predict the ultimate compression capacity of closely spaced double-angle members.
This study develops a simplified analytical formulation for evaluating the minimum rigidity of discrete braces in relation to the lateral-torsional buckling of steel beams. The main contribution lies in deriving closed-form expressions that incorporate key dimensionless parameters, offering a practical alternative to fully numerical approaches. The formulation is validated against finite element simulations performed with LTBeamN, demonstrating good agreement. The analysis is carried out under the assumptions of linear elastic behaviour, idealised support and bracing conditions, and doubly symmetric I-sections, while residual stresses, imperfections and plasticity are not considered. Within these boundaries, the results provide valuable guidance for both the design and assessment of brace rigidity in steel structures.
Accurate design rules are crucial for the safety, sustainability and economy of steel structures. To predict the load-bearing capacity of sway structures, Eurocode 3, Part 1-1, uses individual member unity checks, which are assumed to include the interaction between members, related to their stability and plastic behaviour. To verify this assumption, basic (one-bay single-storey) 2D and 3D sway structures, and building-size 3D structures are simulated by nonlinear finite element simulations, and predictions are compared to those according to Eurocode 3. The results show that as long as basic 2D and 3D structures are loaded such that all their members fail due to instability, the load-bearing capacity is predicted accurately by Eurocode 3. If, however, they are loaded to have members failing due to stability and plasticity, Eurocode 3 predicts the load-bearing capacity to be too low, i.e., conservatively. For building-size 3D structures, it is shown that system eigenvalues, which may range from single-member buckling, via coupled multi-member instabilities, to overall buckling, are important for ultimate load predictions; however, they are not taken into account in all Eurocode 3 methods. In conclusion, for the investigated cases, the design rules of Eurocode 3 are able to capture stability and plasticity interaction effects safely. However, for more economic design, design rules should take system stability into account, e.g., by predicting column buckling via system eigenvalues, and by considering plastic redistribution and formation of subsequent plastic mechanisms. Finally, for the assessment of a building structure in general, also for other materials than steel, it is advised to perform a linear buckling analysis on the complete building, and to study all relevant local, intermediate and system eigenmodes for their impact on the stability, strength and safety of the building structure.
The stability behaviour of steel structures is important when performing design. Standards (such as EN 1993‐1‐1 – Eurocode 3 Part 1‐1) take the stability of steel members into account and allow for verifications using reduction factors or by second‐order theory analysis considering equivalent geometric imperfections. Eurocode 3 is well‐suited for I‐profiles as the reduction factors and equivalent geometric imperfections have been calibrated using experimental and numerical data for this profile type. However, when it comes to U‐profiles, the standard lacks clear specifications. In literature, some authors have studied the stability behaviour of U‐profiles. For example, the imperfections required for performing a detailed geometrically and materially nonlinear analysis with imperfections included (GMNIA), as well as the residual stresses for U‐profiles, have been studied. Nevertheless, there are still gaps to be addressed, such as the equivalent geometric imperfections for second‐order theory analysis (GNIA). In this paper, the lateral torsional buckling capacity of U‐profiles is determined by GMNIA, with explicit residual stresses definition, and subsequently, corresponding equivalent GNIA are calibrated and proposed.
Castellated steel beams, characterised by their unique perforated web design, have gained significant popularity in the construction of medium-span structures, like industrial and office buildings. These beams offer an economical solution due to their increased bending moment capacity about the major axis with relatively low weight and associated high resource efficiency. However, they are particularly susceptible to lateral-torsional buckling as a result of their increased cross-sectional height. Additionally, the regularly spaced openings weaken the web, leading to further local failure modes. For simplified design methods, boundary conditions are usually incorporated through the elastic critical moment, which itself is influenced by possible local failure modes, such as web distortions. This paper investigates the influence of various boundary conditions on the analytical computation of the elastic critical moment according to the draft Technichal Report CEN/TR 1993-1-102:2025 and the lateral-torsional buckling design according to the 2nd Gen EN 1993-1-1:2022 for castellated steel beams in comparison to regular hot-rolled profiles within a comprehensive numerical and analytical study.
Numerical simulations are widely used in structural engineering research, and validated models enable the efficient expansion of datasets without costly additional testing. They allow the investigation of alternative geometries and loading scenarios beyond those covered by experiments. Their reliability, however, depends strongly on the accuracy of the material modelling. In structural steel, elastic behaviour is well captured by Hooke's law, but the plastic range remains challenging to describe realistically. Existing hardening models provide mathematical representations of the plastic portion of the true stress-strain curve, yet numerous studies have shown that these models require extensive calibration to reproduce experimental behaviour satisfactorily. This calibration is typically iterative, time-consuming, and often yields results that still offer potential for refinement. To address this, an automated optimization tool has been developed to fit flow curves directly from uniaxial tensile test data. This article outlines the fundamentals of material modelling for steel in numerical simulations and presents the development and validation of the proposed optimization algorithm, which allows realistic numerical modelling on a scientific level and aligns with the ongoing standardization efforts in prEN 1993-1-14.
Steel beams with corrugated webs are widely used in construction due to their high strength-to-weight ratio and structural efficiency. However, accurately estimating their shear capacity remains a challenge due to the complex interaction of material properties, geometric features, and corrugation effects. While existing design codes, such as the Eurocode, provide methods for shear capacity estimation, their predictions often exhibit significant deviations from experimental results, highlighting the need for more reliable and comprehensive models. This study aims to address this gap by proposing a novel empirical model that incorporates nonlinear interactions among material properties, section geometry, and corrugation characteristics to estimate the shear capacity of sinusoidal web-corrugated steel beams. A dataset comprising 69 full-scale experimental tests is collected and analyzed to validate the proposed model. The model's accuracy is assessed by comparing its performance against five existing approaches, including the Eurocode method. The results demonstrated that the proposed model significantly outperformed existing approaches, reducing normalized root mean square error and normalized mean absolute error by approximately 48% and 49%, respectively. Additionally, it enhanced the coefficient of determination by 9% and the A20 index by 59% on average.
Knowledge of the seismic behavior of load-bearing structures is essential for reliable seismic design. For the first time, it was possible to capture and analyze the behavior of continuous ship unloaders via video observations in two different real once-in-a-century earthquakes. By means of professional video analysis, not only the seismic behavior and damage can be filtered but also decisive dynamic properties that are important for nonlinear seismic analysis. Furthermore, an interesting phenomenon can be unveiled that may be crucial for the seismic damage potential of large mobile equipment. When exposed to seismic action, large mobile material handling equipment without any anchoring to their subsoil are able to uplift and rock before derailment or major damage occurs. The observations of the continuous ship unloaders in the once-in-a-century earthquakes state this fact, which was also found in previous nonlinear time history analysis. In addition to the video analysis in real earthquakes, vibration measurements were performed on real stackers, from which further essential dynamic properties were determined. All these new findings will be another step forward toward safe and economical earthquake-resistant design for large mobile equipment with the ability of uplift.
A multipile-type frame roadway structure made of compact members is considered to be an effective structure for road construction in mountainous areas. When considering construction in areas with narrow spaces, medium-diameter steel pipes are a desirable option for the columns of pier structures. Medium-diameter steel pipes can be mass-produced in factories as manufactured pipes, and if applied to bridge piers, reductions in construction costs can be expected. On the other hand, electric resistance welded (ERW) steel pipes are commonly used as structural members, but research on the toughness of the steel pipes, which is important for use as bridge piers, is still insufficient. Therefore, in this study, the ERW steel pipes were improved to ensure the Charpy absorbed energy of the 27 J or more for SM490B and the 47 J or more for SM490C at the test temperature of 0 degrees C, similar to the steel plates used in general steel bridge piers. Charpy impact tests were conducted using this improved ERW pipes to grasp the Charpy absorbed energy characteristics.
