Current Design Rules Research Articles

Geometric analysis and local buckling behavior of wire arc additively manufactured ER110S cruciform section stub columns

The recent prominence and potential of wire arc additive manufacturing (WAAM) in the civil engineering industry have gained significant attention due to its ability to produce complex geometric shapes in a cost-effective and flexible manner. This paper presents the geometric analysis and local buckling behavior of WAAM ER110S cruciform section stub columns. A total of eight specimens with a broad range of width-to-thickness ratios were manufactured. 3D laser-scanning was conducted to capture the geometric characteristics of all the WAAM ER110S cruciform section stub column specimens. Material testing with coupons cut from various orientations of WAAM ER110S plates was performed and this is followed by the stub column testing where digital image correlation (DIC) was employed to monitor the full-field deformations of the specimens. The obtained test data were then employed to assess the applicability of current design rules specified in European, American and Australian standards to WAAM ER110S cruciform section stub columns. The assessment results revealed that (i) the current Class 3 slenderness limits (i.e. slender/non-slender slenderness limits) can be safely used for the classification of outstand plate elements of cruciform sections in compression and (ii) all the three specifications can lead to safe though marginally scattered failure load predictions of WAAM ER110S cruciform section stub columns.

Extreme Convective Gusts in the Contiguous USA

Most damage to buildings across the contiguous United States of America (USA) is caused by gusts in convective events associated with thunderstorms. Design rules for structures to resist these events rely on the integrity of meteorological observations and the methods of assessment. These issues were addressed for the US Automated Surface Observation System (ASOS) in six preliminary studies published in 2022 and 2023, allowing this present study to focus on the analysis and reporting of gust events observed between 2000 and 2023 at 642 well-exposed ASOS stations distributed across the contiguous USA. It has been recently recognized that the response of buildings to convective gusts, which are non-stationary transient events, differs in character from the response to the locally stationary atmospheric boundary gusts, requiring gust events to be classified and assessed by type. This study sorts the mixture of all observed gust events exceeding 20 kn, but excluding contributions from hurricanes and tropical storms, into five classes of valid meteorological types and two classes of invalid artefacts. The valid classes are individually fitted to optimal sub-asymptotic models through extreme value analysis. Classes are recombined into a joint mixture model and compared with current design rules.

Web crippling design of cold‐formed ultra‐high strength steel lipped channels under ITF loading: A numerical parametric investigation

AbstractIn recent years, there has been a compelling need to adopt cold‐formed ultra‐high‐strength steel (CFUSS) in the construction industry owing to its numerous advantages, such as a higher strength‐to‐weight ratio, flexibility in achieving desired shapes, and adaptability over longer spans. Among the various applications, CFUSS lipped channel sections are commonly used as purlins and joists in steel structural systems. However, these sections are susceptible to different failure modes, particularly web crippling, which presents significant challenges. Currently, the current design rules lack specific guidelines for estimating the web crippling capacity of CFUSS sections. To address this crucial gap, the present study focuses on a comprehensive numerical investigation of the web crippling response of CFUSS lipped channel sections under interior‐two‐flange (ITF) loading conditions. Finite element (FE) models were developed using the ABAQUS package, verified against published test data, and subsequently used in an extensive parametric study. The ultimate web crippling capacity obtained from the parametric study was used to evaluate the accuracy of the current design equations in various design standards. The findings revealed that the existing design equations inadequately predicted the ultimate web crippling capacity of CFUSS lipped channel sections subjected to the ITF loading condition. Consequently, a modified design equation is proposed, utilizing the same approach as the current design standards, and a new direct strength method (DSM) approach is developed and verified through reliability analysis. The proposed modified design equations offer promising solutions to ensure safer and more reliable design practices for CFUSS structures in the construction industry.

A General Approach to Activate Second-Scale Room Temperature Photoluminescence in Organic Small Molecules.

Organic small molecules that exhibit second-scale phosphorescence at room temperature are of interest for potential applications in sensing, anticounterfeiting, and bioimaging. However, such materials systems are uncommon-requiring millisecond to second-scale triplet lifetimes, efficient intersystem crossing, and slow rates of nonradiative recombination. Here, a simple and scalable approach is demonstrated to activate long-lived phosphorescence in a wide variety of molecules by suspending them in rigid polymer hosts and annealing them above the polymer's glass transition temperature. This process produces submicron aggregates of the chromophore, which suppresses intramolecular motion that leads to nonradiative recombination and minimizes triplet-triplet annihilation that quenches phosphorescence in larger aggregates. In some cases, evidence of excimer-mediated intersystem crossing that enhances triplet generation in aggregated chromophores is found. In short, this approach circumvents the current design rules for long-lived phosphors, which will streamline their discovery and development.

A new analytical tool for the elastic/plastic buckling design of pressure vessels subjected to external pressure

This paper deals with the elastic/plastic buckling design of pressure vessels under external pressure loading. The objective is to build a simple analytical tool devoted to the elastic and elastoplastic buckling analysis of pressure equipments. This tool is aimed to provide the critical external pressure of cylindrical pressure vessels with ellipsoidal (or possibly hemispherical) heads. Depending on the geometry of the equipment and material parameters, the first buckling pressure may involve either the cylindrical shell or the closure ends, in the elastic or plastic range. The calculation tool will be thus based on a series of exact or approximate analytical solutions of the critical pressure of each part of the considered equipment. In this paper, the elementary shell structures involved in such pressure equipments are first individually examined. The fundamental critical pressures for each of them are recalled or introduced, both in elasticity and plasticity. The new solutions are validated against reference numerical results obtained through finite element computations. Then, approximate solutions of the critical pressure are derived for the same shells, taking account of specific boundary conditions (and not idealized ones, as before) due to the presence of the remaining part of the equipment. In the end, a VBA Excel software is developed. It is able to provide the mappings of the buckling mode type and the corresponding critical pressures for large ranges of geometric and material parameters in a very efficient way. These analytical solutions are finally confronted to numerical calculations performed on complete pressure equipments and they are shown to give quite reliable results. A discussion is also initiated on the use of such a program to update the current design rules in this scope of application.

Contact-angle hysteresis provides resistance to drainage of liquid-infused surfaces in turbulent flows

Lubricated textured surfaces immersed in liquid flows offer tremendous potential for reducing fluid drag, enhancing heat and mass transfer, and preventing fouling. According to current design rules, the lubricant must chemically match the surface to remain robustly trapped within the texture. However, achieving such chemical compatibility poses a significant challenge for large-scale flow systems, as it demands advanced surface treatments or severely limits the range of viable lubricants. In addition, chemically tuned surfaces often degrade over time in harsh environments. Here, we demonstrate that a lubricant-infused surface (LIS) can resist drainage in the presence of external shear flow without requiring chemical compatibility. Surfaces featuring longitudinal grooves can retain up to 50% of partially wetting lubricants in fully developed turbulent flows. The retention relies on contact-angle hysteresis, where triple-phase contact lines are pinned to substrate heterogeneities, creating capillary resistance that prevents lubricant depletion. We develop an analytical model to predict the maximum length of pinned lubricant droplets in microgrooves. This model, validated through a combination of experiments and numerical simulations, can be used to design chemistry-free LISs for applications where the external environment is continuously flowing. Our findings open up new possibilities for using functional surfaces to control transport processes in large systems. Published by the American Physical Society 2024

Simulation of interlayer coupling for electroactive covalent organic framework design.

Porous, stacked two-dimensional covalent organic frameworks (2D COFs) bearing semiconducting linkers can support directional charge transfer across adjacent layers of the COF. To better inform the current and possible future design rules for enhancing electron and hole transport in such materials, an understanding of how linker selection and functionalization affects interlayer electronic couplings is essential. We report electronic structure simulation and analysis of electronic couplings across adjacent linker units and to encapsulated species in functionalized electroactive 2D COFs. The detailed dependence of these electronic couplings on interlayer interactions is examined through scans along key interlayer degrees of freedom and through configurational sampling from equilibrium molecular dynamics on semiempirical potential energy surfaces. Beyond affirming the sensitivity of the electronic coupling to interlayer distance and orientation, these studies offer guidance toward linker functionalization strategies for enhancing charge carrier transport in electroactive 2D COFs.

Experimental investigations into stocky composite columns of concrete-filled circular S690 steel tubes under compression

Composite columns of concrete-filled steel tubes (CFSTs) are very efficient in providing large structural resistances and rigidities. However, high strength S690 steel tubes are not covered in current design codes. Therefore, a series of experimental investigations into stocky composite columns with circular CFSTs under compression were conducted. A total of 21 stocky composite columns with different tube diameters and thicknesses made of Grades S355, S460 and S690 steel and Grade C60/75 concrete were tested under different loading conditions. Moreover, extensive measurements on the surface strains of the steel tubes were made during tests. Data analyses on the test results reveal that all composite columns exhibit enhanced section resistances and ductility at large deformations, indicating that the use of S690 steel and C60/75 concrete in these composite columns are highly efficient. A simple method for determining confining pressures provided by the steel tubes to the concrete cores in these composite columns is proposed, which involves a systematic analysis on the measured data and the use of von Mises yielding criterion without any complicated plasticity formulation. Based on the proposed method, the resistance contributions of both the steel tubes and the concrete cores are successfully quantified. Comparison between the measured and the predicted resistances using EN 1994–1-1 of these composite columns reveals that while the section resistances of these composite columns are safely predicted, the resistances of the steel tubes are underpredicted while those of the concrete cores are overpredicted correspondingly. The findings highlight the need to improve the predictability of the current design rules, and to give increased resistances of the steel tubes when high strength S690 steel tubes are used.

FEATURES OF BEHAVIOR AND CALCULATION OF DOWEL TIMBER JOINTS WITH SLOTTED-IN PLATES ACCORDING TO EC5

The paper presents an overview of theoretical and experimental studies of connections of timber structures with steel dowel with steel slitted-in plates. The correct choice of the type of connections allows you to significantly influence the total cost of the structure due to the formation of thestructural and assembly scheme of the structure (minimization of the number of nodal and assembly connections), optimal unification of connections isan additional argument for creating an economical and competitive solution. For the analysis of the dowel connection, it is taken into account that theforce is transmitted due to the bending and shear resistance of the fastening element, as well as crumpling in the connected timber elements. The limitstates of the dowel joint are considered loss of strength due to crumpling and splitting of the wood of the hole wall, as well as due to bending of the nailin the nail socket. The works considered in the review provide extensive factual material on the strength of connections depending on the geometricand physical parameters of its components, as well as the stiffness of the connection, which is currently the subject of active attention of researchers. Attention is paid to the need to study the operation of nodes under the action of a moment during group operation of the connection. The analysis of numerous experiments makes it possible to check the reliability of the current design rules and norms of EC5 and the design norms of DBN В.2.6-161:2017 implemented to them, and also revealed the shortcomings and limits of the application of the design rules for this type. connections The results of numerical and experimental studies are the basis for improvingthe structural solutions of the joints of wooden elements and allowed to accumulate significant factual material for the verification of numerical simulation models.

Cyclic Deterioration of High‐performance Concrete – Findings of the Priority Programme SPP 2020

AbstractModern high‐performance concretes with ever‐higher compressive strengths allow the construction of slender structures which are exposed to higher fatigue‐relevant loads. Current fatigue design rules include a high reduction of the fatigue resistance, which increases with increasing concrete strength. Thus, the fatigue verification becomes crucial for the realisation of such concrete structures. However, there is still a lack of knowledge regarding the damage mechanisms which hinders a substantial improvement of the fatigue design rules. The objective of the priority programme SPP 2020 is to gain more knowledge concerning the fatigue behaviour of high‐performance concretes and damage mechanisms in a strong network of different research institutions. The investigation of the concrete fatigue behaviour is challenging because of the multiple interdependence of influences on the concrete fatigue behaviour, and the damage effects occurring on different scales. Highly instrumented experiments combined with the latest microstructural investigation techniques and numerical modelling on different scales are used to explore the fatigue damage mechanisms. The scope of the priority programme SPP 2020 is outlined and selected results from the projects involved are presented in this paper.

Interaction of flutter and forced response in a low pressure turbine rotor with friction damping and mistuning effects

In modern LPT designs, which typically can assume a tolerable level of flutter, the simultaneous presence of forced response and flutter in different operation regimes becomes unavoidable. Current design rules rely on the linear superposition of vibration levels from the isolated problems. However, recent evidence from reduced order model calculations and from experiments suggests that this may be an over conservative approach. In order to check this finding, this study examines the flutter and forced response interaction in a realistic low pressure turbine rotor. A high fidelity model is used, and an efficient numerical method is implemented for the computation of the aeroelastic vibrations of the rotor with nonlinear friction effects at the blade-disk contact interfaces. A hybrid approach is used that combines a traveling wave description for the linear modes with a physical space representation for the displacement of the nonlinear contacts. The resulting equations are integrated in the time domain in order to account for the unknown flutter frequencies present in the response. Both tuned and mistuned configurations are considered, and it is confirmed that the actual response of the system is much smaller than that coming from the linear superposition of the separated effects.

Cold-formed stainless steel beams with single web hole at elevated temperatures

Steel structures are often used in buildings due to their advantage in weight-to-strength ratio. However, their structural capacity deteriorates in fire as the temperature of the structures rises. Investigation of cold-formed stainless steel (CFSS) structures at elevated temperatures is still limited, especially for rectangular hollow section (RHS) beams having a single web hole in the mid-span (perforated web). Therefore, a numerical investigation was conducted to evaluate the current design provisions to calculate the strength of such beams at elevated temperatures ranging from 22 - 900 °C. A total of 400 specimens of stainless steel grades austenitic (EN 1.4301) and lean duplex (EN 1.4162) were considered. The investigation used finite element analysis (FEA) to simulate the behaviour of RHS beams with perforated web under pure bending. The finite element (FE) model was validated against a series of experimental results available in literature. The comparison between flexural strengths obtained from FEA with design values calculated from the current design rules showed that the design rules are conservative. However, they are not always reliable and safe for RHS beams without and with a perforated web for the two material grades at elevated temperatures. In this study, only the design rules specified by Eurocode 3 are shown to be reliable and safe.

Stainless steel I-section beams subjected to combined torsion and bending: Experimental results

In this paper, the details of an experimental program, during which fabricated stainless steel I-section beams subjected to combined bending and torsion are tested, are presented. The test specimens consisted of 10 laser welded austenitic (EN 1.4307 and EN 1.4404) and traditionally welded duplex (EN 1.4162) beams of different cross-sectional dimensions and lengths. The experimental boundary conditions idealized a simply supported beam loaded at mid span with a transverse force applied away from the shear centre, leading to combined torsion and bending to model civil engineering applications. During the tests, the rotations were measured using inclinometers as well as Digital Image Correlation, while strains were measured using strain gauges. Mid span rotations of up to 35° were reached leading to plasticity spreading across the cross-section. Firstly, the test results were compared against the elastic theory, including theoretical evaluations of the initial stiffness. Secondly, the ultimate capacities were compared to elastic and plastic verifications, showing the extent to which the current design rules are overconservative.

Assessment of design procedures for the buckling resistance of hot-rolled steel equal leg angles under concentric and eccentric compression

This work presents an extensive advanced numerical study calibrated with recent experimental results available in the literature on the buckling behavior of hot-rolled steel angles under concentric and eccentric compression to support the ongoing revision in Europe of the design rules for angles concentrically and eccentrically loaded in compression. The numerical results were used for the assessment of existing design procedures commonly applied in practice (Eurocodes and AISC), as well as new recently proposed recommendations. In general, the current analytical rules do not present good agreement with the experimental and calibrated numerical results, even showing unsafe results for some slenderness ranges. In case of fixed members in eccentric compression, these design rules are extremely conservative, reaching ratios rN (numerical versus analytical resistances) in excess of 2. The new proposals resulting from the project ANGELHY present an improved agreement with the numerical results, showing that they may efficiently replace the current design rules in the Eurocodes. However, for concentric compression, a reliability assessment shows that the required partial factor is γM1* = 1.1.

Cold-formed stainless steel elliptical hollow sections under combined biaxial bending and axial compression - Numerical modeling and design

This paper aims to investigate the cross-section response of cold-formed stainless steel (CFSS) elliptical hollow sections (EHS) under combined biaxial bending and axial compression. In the present study, an advanced finite element (FE) model was adopted to perform a comprehensive parametric study for CFSS EHS under combined biaxial bending and axial compression, with different stainless steel alloys, as well as a broad range of cross-section sizes, aspect ratios, loading eccentricities and angles. Numerical results obtained from the parametric study were compared with the design strengths calculated by the current design rules in European code EN 1993-1-4, American specification SEI/ASCE 8-02 and Australian/New Zealand standard AS/NZS 4673. In addition, the Continuous Strength Method (CSM) for CFSS circular hollow sections (CHS) under combined actions, was also evaluated for the design of CFSS EHS under combined actions. The comparisons revealed that the current design codes EN 1993-1-4, SEI/ASCE 8-02 and AS/NZS 4673 provided conservative and very scattered predictions for CFSS EHS under combined actions. The existing CSM can provide more accurate predictions than the current design codes (i.e., AS/NZS 4673, EN 1993-1-4 and SEI/ASCE 8-02), but a further improvement is needed. In the present study, a modified CSM is proposed for CFSS EHS under combined actions, which can achieve reliable and accurate design predictions.

Effects of Deposition Rate on Local Stability of Wire Arc Additively Manufactured Outstand Elements

AbstractA great focus is currently being placed on the development of applications of Wire Arc Additive Manufacturing (WAAM) in structural engineering. To facilitate this development, an experimental programme investigating the effects of the deposition rate on WAAM 316LSi stainless steel outstand elements has been conducted. Equal angle section (EAS) stub columns with four different cross‐sectional slendernesses were produced using WAAM. For each slenderness, four different deposition rates were employed; hence, overall, sixteen EAS stub columns were produced, 3D scanned and tested to examine their local stability. To keep the heat input constant between all cases, for each deposition rate, the travel speed was varied accordingly. Alongside the EAS specimens, tensile coupon testing was conducted to determine the material properties corresponding to each deposition rate. The tensile coupons were extracted at three different orientations (0°, 45° and 90°) relative to the deposition direction in order to investigate the degree of material anisotropy. In the present paper, following the description of the EAS stub column test results, the applicability of current Eurocode design rules and the Continuous Strength Method for the prediction of their design strength is assessed.

Reliability Assessment of Eurocode 3 Design Rules for the Minor‐Axis Buckling of HSS I‐section Columns

AbstractSince the main purpose of the codes is to provide satisfactory safety levels, the reassessment of the reliability of the current design rules considering the new structural steels, as high strength steels (HSS), is necessary. As the reliability directly depends on several variables, their influence should also be considered. This paper aims to evaluate the influence of the randomness of the geometry, material, initial geometrical imperfections and residual stresses on the minor‐axis flexural buckling resistance of S690 HSS welded I‐section columns and the reliability of the Eurocode 3 [1,2] stability design rules. Monte Carlo simulations were executed to obtain the ultimate resistance of simply‐supported compressive members with slenderness varying from 0.3 to 2.2. The basic variables were stochastically modeled using existing statistical distributions from the literature and each generated element was numerically analyzed by a general‐purpose finite element software. Finally, the influence of the randomness of the basic variables and the safety provided by FprEN1993‐1‐1 [2] is discussed.

Comparing solar inverter design rules to subhourly solar resource simulations

The input of a solar inverter depends on multiple factors: the solar resource, weather conditions, and control strategies. Traditional design calculations specify the maximum current either as 125% of the rated module current or as the maximum 3 h average current from hourly simulations over a typical year, neglecting extreme irradiance conditions: cloud enhancement events that usually last minutes. Inverter power-limiting control strategies usually prevent extreme events to cause strong currents at the inverter, but in some cases, they can fail, leading to high currents. In this study, we aim to report how frequent and strong these high currents could be. We use 10 years of 1 min data from seven stations across the United States to estimate the photovoltaic string output through modeling the short-circuit current Isc, and the maximum-power point current Imp, and compare them to traditional inverter design values. We consider different configurations: minutely to hourly resolution; 5 min to 3 h averaging time intervals; monofacial and bifacial modules (with a case of enhanced albedo); and 3 fixed-tilt angles and horizontal single-axis tracking. The bifacial modules with enhanced albedo lead to the highest currents for 1 min data, exceeding 3 h averages by 53% for Isc and 38% for Imp. The 3 h average maxima surpass the conservative 125% design rule for bifacial modules. Inverter ratings at either a 200% of the rated current or 1.55 times the 3 h maximum could withstand all events regardless of control strategies. In summary, for some locations it is prudent to compare current design rules to subhourly simulations to guarantee the fault-free operation of solar PV plants.

The cross-sectional resistance of square and rectangular hollow steel sections loaded by bending moment and shear force

This paper presents an evaluation of the design rules for the bending moment–shear force (M−V) interaction of cold- and hot-formed square, and rectangular hollow steel sections (SHS & RHS). More specifically, the design rules, as provided by EN1993-1-1 regarding RHS and SHS of section class 1 and 2 are covered for the steel grades S235 up to and including S460. A 4-point bending test was simulated by means of a finite element model, which was validated on the basis of experimental tests from existing literature. A parametric study was performed and numerical M−V interaction results were compared to the provisions in EN1993-1-1. This comparison indicates that the current design rules in EN1993-1-1 regarding M−V interaction are conservative and overestimate the reduction of the bending resistance due to the presence of shear. Alternative design rules for the shear area and M−V interaction of RHS and SHS are proposed and evaluated by means of a statistical assessment procedure based on existing literature and EN1990-1-1. Both newly developed design rules are shown to ensure an adequate reliability level when a partial safety factor equal to 1 is used.

Behaviour and design of cold-formed high strength steel RHS T-joints undergoing compression loads at elevated temperatures

This study presents a comprehensive numerical program aiming to investigate the static resistances of cold-formed high strength steel (CFHSS) T-joints with square and rectangular hollow section (SHS and RHS) braces and chords at elevated temperatures. The included angle between brace and chord members was 90°. The static behaviour of simply supported SHS and RHS T-joints undergoing compression loads through brace members was investigated at four elevated temperatures, including 400°C, 500°C, 600°C and 1000°C. The mechanical properties at elevated temperatures given in the literature for cold-formed S900 steel grade tubular members were used in this study. The numerical investigation was performed using the finite element (FE) models developed and validated by Pandey et al. [1] and Pandey and Young [2] for cold-formed S960 steel grade T-joints at ambient temperature and post-fire conditions. In total, 756 FE T-joint specimens were analysed in this numerical study, including 189 FE T-joint specimens for each elevated temperature. The tubular T-joint specimens were failed by chord face failure, chord side wall failure and a combination of these two failure modes. The resistances of investigated T-joints at elevated temperatures were compared with the nominal resistances predicted from design rules given in European code and CIDECT using the mechanical properties at elevated temperatures. Overall, it is shown that the current design rules given in European code and CIDECT are uneconomical and unreliable. As a result, economical and reliable design rules are proposed in this study through two design approaches for predicting the resistances of cold-formed steel SHS and RHS 90° T-joints of S900 grade at elevated temperatures.