Search

• Dimensionality reduction using a convolutional neural network autoencoder. • Application to highly nonlinear brittle fracture mechanics problems. • Nonlinear reduced order model to predict crack initiation and propagation. • Predictions performed 250 times faster as compared to the finite element method. Dimensionality reduction methods construct a low dimensional or reduced space. Complex structural mechanics problems can be approximated on a low dimensional space with a Reduced-Order Model or surrogate model. For instance, Principal Components Analysis can compute a reduced basis from a database of full-order snapshots. Principal Components Analysis, however, does not reconstruct low dimensional spaces efficiently for highly nonlinear problems, mainly because it is a linear dimensionality reduction method. In this paper, an original approach based on an autoencoder neural network is developed to construct a nonlinear Reduced-Order Model for a highly nonlinear brittle fracture problem. We show on a set of simulations how the autoencoder can be efficient for dimensionality reduction or compression of highly nonlinear data. A complete deep learning framework is proposed to predict crack propagation patterns directly from the loading conditions. Finally, we validate our nonlinear Reduced-Order Model with data sets generated for two problems using proportional and non-proportional loading conditions. In the first problem, the crack always initiates at the same location but propagates in various directions, which may even vary during the simulation if loading conditions are non-proportional. In the second problem, the crack may additionally initiate at various locations. Results for the two problems evaluate the capabilities of the proposed approach. [ABSTRACT FROM AUTHOR]

An implantable capacitive pressure sensor enables continuous and long-term intraocular pressure mon- itoring (IOP) for glaucoma patients. In this paper, a new stretchable conductive film-based capacitive sensor was designed as a proof of concept to show how this technology could be used for IOP measure- ments. This capacitive sensor used a planar structure and could be miniaturised further. A mathemat- ical model of the structural mechanics and capacitance of the proposed capacitive sensor was presented. Simulations are carried out to verify the mechanical and electrical properties of the proposed capacitive sensor. The paper also detailed the novel fabrication process that was used to develop prototypes of the proposed sensor. After the prototype had been built, the viability of the proposed design and the accuracy of simulation results were verified experimentally. Moreover, the reproducibility, repeatability and fabrication consistency of the sensor was also experimentally analysed. [Display omitted] • Using conductive polymer instead of copper. • Using planar structure. • Improved fabrication process to avoid using of photolithography. [ABSTRACT FROM AUTHOR]

In the realm of nonlinear structural mechanics, tracing load-displacement curves becomes complex when approaching the limit points caused by instability. Multiple ideas have addressed this challenge, dating back to the late 1960s. Despite the integration of various algorithms into commercial finite element software, no single algorithm generally solves all nonlinear structural problems. Moreover, many existing methods are sensitive to initial parameters, e.g. step-length and might have problem with large values. This paper introduces a family of minimum residual displacement methods for tracing equilibrium paths. Our approach can be seen as a generalized framework that provides new methods and encompasses some existing ones as specific instances. We develop and apply straightforward techniques to control residual displacement in nodes, elements, or specific deformation components. We present a comprehensive library of methods implemented in OpenSees, enabling a comparison between our presented methods and the minimum residual displacement method, as well as four well-established techniques. We apply these methods to solve complex geometrically nonlinear problems involving truss, frame, and shell structures. The results highlight the enhanced ability to converge with larger step-length even in highly complex behavioral scenarios and the capacity to reduce the required iterations to converge. • Novel nonlinear solution schemes for structural mechanics are offered. • The framework provides control of residual displacement on nodes or elements. • Control of residual of rotational or translational deformation separately is granted. • The methods provide enhancement in efficiency and robustness in path-following. • Library of methods and examples are provided in OpenSees with source code on GitHub. [ABSTRACT FROM AUTHOR]

This paper presents a novel deep learning approach for reconstruction of local through-the-thickness fiber orientation distribution (FOD) in discontinuous long-fiber, prepreg-platelet molded composites (PPMC). The thermal-residual strains on composite surfaces are used as inputs to train a fully convolutional neural network, named U-Net, to predict spatially varying, local FOD. High fidelity synthetic data was generated via computational simulation of PPMC with stochastic material orientation state and was used for training the deep learning model. The proposed U-Net model allowed for rapid recognition of PPMC morphology by solving the inverse structural mechanics problem of determining the average fiber orientation through the composite thickness based on the provided surface strain measurements. Upon training and validation, the U-Net deep learning model was deployed to rapidly predict complex distributions of the local through-the-thickness FOD in PPMC. [ABSTRACT FROM AUTHOR]

Guided wave propagation (GWP) is commonly employed for the design of SHM systems. However, GWP is sensitive to variations in the material properties, often leading to false alarms. To address this issue, uncertainty quantification (UQ) is employed to improve the reliability of the predictions. Computational structural mechanics is a useful tool for the simulation of GWP. Even so, the application of UQ methods requires numerous solutions, while large-scale, transient GWP simulations increase the computational cost. In this paper, we propose a machine learning (ML)-based reduced order model (ROM), annotated as BO-ML-ROM , to decrease the computational time of the GWP simulation. The ROM is integrated with a Bayesian optimization (BO) framework to adaptively sample the data for the ROM training. The results showed that BO outperforms one-shot sampling methods, both in terms of accuracy and speed. The developed ROM, which is orders of magnitude faster than the original solver, is then applied for forward uncertainty quantification of the GWP in an aluminum plate and a composite panel under varying material properties. The UQ analysis reveals the higher impact of the uncertainties in the wave reflections. Furthermore, to compute the influence of the material properties on the predictions, a sensitivity analysis (SA) is performed using the variance-based Sobol' indices and the Shapley additive explanations, where it is shown that the uncertainties in the elastic properties have a varying influence across time. The predicted results reveal the efficiency of BO-ML-ROM for the simulation of the GWP and demonstrate its utility for UQ and SA. [ABSTRACT FROM AUTHOR]

Abstract The number of heavy vehicles and their weight have been increasing over time, implying that many bridges are experiencing traffic loads with higher magnitude and frequency than they were originally designed for. In some cases, it will be necessary to either replace or strengthen the structures to keep the bridges in service. For existing non-composite steel girder bridges, post-installation of shear connectors can often be used to increase the traffic load capacity significantly. One type of shear connector that is suitable for post-installation, even though not commonly used, is the Coiled Spring Pin. These interference fit connectors can be installed from below the bridge deck during traffic, in order to minimize the impact on road users. This paper describes an experimental study on the fatigue strength of Coiled Spring Pins and a compilation of previously performed fatigue tests on this type of connector. The new test series, with nine specimens, are evaluated statistically and a fatigue strength design equation is proposed. The results show that there are large variations between different test series, while tests within the same series show good agreement. The reasons for this are discussed in the paper along with recommendations for future testing. Highlights • Post-installed shear connectors can be used to strengthen non-composite bridges. • Coiled Spring Pins enable an effective post-installation in existing bridges. • A fatigue design criterion has been developed from push-out test results. • For shear, the detail category is slightly lower in comparison to headed studs. • The fatigue strength curve has a different slope in comparison to headed studs. [ABSTRACT FROM AUTHOR]

Abstract Recently, CIDECT (International Committee for the Development and Study of Tubular Structures) has proposed the component method as a unified approach for the design of many types of connections, including welded tubular joints. Although CIDECT provides clear and simple equations for the resistance of welded tubular joints, the design of initial stiffness remains complicated and includes a number of uncertainties. This paper analyzes the theoretical approach for the initial axial stiffness of rectangular hollow section T joints. The validation against experimental data has shown that the component method considerably overestimates the stiffness of T joints. The paper develops new equations for the stiffness of the components "chord face in bending" and "chord side walls in compression". The equations are based on simplified mechanical models, employing finite element analyses to calculate the parameters for which analytical solutions are found extremely complicated. In addition, the article numerically investigates the effect of chord axial stresses on the axial stiffness of joints and proposes a corresponding chord stress function. Highlights • The paper analyses the initial axial stiffness of welded rectangular hollow section (RHS) T joints • Validation with experimental results showed that the CIDECT equations provides inaccurate prediction of initial stiffness • The paper developed and validated stiffnesses of the components "chord face in bending" and "chord side walls in compression" • Numerical simulations showed that chord axial stresses considerably affect the initial axial stiffness of RHS T joints • A chord stress function is proposed for initial axial stresses of RHS T joints [ABSTRACT FROM AUTHOR]

With the increase in computational power and capacity, and the advancements being made in numerical modeling, it has become possible to model the various physical phenomena that take place in nuclear reactors with more and more detail and accuracy. This includes phenomena related to structural mechanics, fluid dynamics and reactor physics amongst others. Additionally, there has been an increased interest to simulate these combined, interacting phenomena simultaneously by coupling various numerical tools. This coupling of different codes is currently a topic high on the research and development agenda of the international nuclear community. It is also a focus point within the research done at NRG in the national PIONEER research program funded by the Dutch ministry of economic affairs. This focus has resulted in two branches of research at NRG: multi-scale modeling of the complete primary system of a nuclear reactor by coupling a 3D Computational Fluid Dynamics (CFD) code with a 1D System Thermal Hydraulics (STH) code, and multi-physics modelling through the coupling of dedicated and advanced thermal-dynamics, structural mechanics and reactor physics solvers. The paper presents simulation results of both branches applied to fast reactors. As both fields of research require the coupling of codes, it has led to the creation of an independent, external, Fortran-based coupling tool named myMUSCLE (MultiphYsics MUltiscale Simulation CoupLing Environment) that arranges the efficient and robust coupling of the different codes. The paper presents the proof-of-principle and first validation of the myMUSCLE tool under development. Additionally, results obtained with MUSCLE-Foam will be presented, which is a new multi-physics code being developed at NRG that includes several reactor physics as well as structural mechanics solvers. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) has often been employed for numerical analysis of fluid dynamics problems and is described as an algorithm based on a simple fully explicit method. When LBM can be applied to structural mechanics problems, there is a possibility that topology optimization can be performed efficiently for non-linear elastic fields and the topology optimization of fluid-structure interaction problems can be performed easily with the single calculation method. We propose a topology optimization method for isotropic linear elastic body problems using LBM in this paper, as a first step to realize this. First, the analysis approach of the isotropic linear elastic field using LBM is constructed with incorporating the expansion technique of the governing equations for applying to a topology optimization framework. Next, based on the density approach, the optimization problem is formulated, and by using the adjoint lattice Boltzmann method (ALBM), the design sensitivity is derived. Finally, the validity of the proposed method is demonstrated with several numerical examples. [ABSTRACT FROM AUTHOR]

The bifurcation problem of a circular Euler–Bernoulli rod subject to a uniform radial force distribution is investigated under three distinct loading conditions: (i.) hydrostatic pressure, (ii.) centrally-directed, and (iii.) dead load. Previous studies on this apparently 'familiar' structural problem have yielded controversial results, necessitating a comprehensive clarification. This study shows that results previously labelled as 'correct' or 'wrong' simply refer to different external constraints, whose presence becomes necessary only for the two latter loads, (ii.) and (iii.). Moreover, the paper presents the first experimental realization of a circular rod subjected to centrally-directed loads. The experimental findings align with the theoretical predictions and show the exploitation of a new type of load acting on a continuous structural element. The feasibility of this load is demonstrated through the use of inextensible cables and opens the way to applications in flexible robotics when cables are used for actuation. • Ring buckling analysed for hydrostatic pressure, centrally-directed and dead loads. • Buckling depends on the external constraints for centrally-directed and dead loads. • New experimental setup designed and tested to generate centrally-directed loads. [ABSTRACT FROM AUTHOR]

The brittleness of ceramic increases the risk of damage or collapse when the ceramic cylindrical pressure hull is directly connected with a rigid part, especially under high hydrostatic pressure. To solve the above problem, this paper systematically explores the design, modeling and optimization of an adhesively bonded ring joint with U-section (ABRJ-U) to avoid the direct connection of the ceramic hull of a small hadal glider, Petrel, with the hemispherical metal end caps. The ABRJ-U is comprised of a U-shaped metal ring, a gasket, and epoxy adhesive layer. To optimize the design parameters, a mechanical model of ABRJ-U is established. The stress tests prove that the model has better efficiency in optimization, but lowered accuracy compared with regular finite element method. Considering the difficulty of obtaining a more accurate theoretical model, the optimization efficiency of regular finite element method is selected for further improvement by integrating the response surface methodology and multi-objective genetic algorithm. According to the optimization results, our optimization method considers the stress calibration of both the adhesive and gasket, simultaneously achieving a 20.8% reduction in the mass of ABRJ-U. The proposed methods also provide valuable reference for the design, modeling, and optimization of other bonded joints. • The mechanical model of the ABRJ-U is constructed based on structural mechanics, and the deformation coordination equation of the adhesive layer and gasket is introduced to solve the underdetermined systems of equations. • Stress tests are carried out, which validates the mechanical model and FEM simulations, and the effect of variables on the stresses of the adhesive and gasket is quantitatively analyzed. • An optimization method is described for the bonded joints with complex structures, involving a parametric model, a response surface model, and multi-objective optimization. [ABSTRACT FROM AUTHOR]

This paper focuses on inspecting the structural buildability of layered objects. Simulating extrusion method process was used to investigate three geopolymer mixes, three-time gaps, and two layering patterns through 18 layered samples. This paper also evaluates effects of the layering process on hardened properties of build-up materials through 9 standard specimens. The used materials were Gladstone fly ash, sand, 8 M sodium hydroxide solution, and D-grade sodium silicate. The weight ratio of sodium silicate to sodium hydroxide was 1, and activators to fly ash was 0.26. Mix 1, mix 2, and mix 3 contained 0%, 1% steel fibers, and 0.5% polypropylene fibers respectively. The structural buildability of layered samples and the influence of the layering process were assessed in terms of flexural strength through 3-point bending tests. Flexural strength results indicated that the layering process has negative impact on the mechanical strength of build-up materials. Also, mix 2 resulted in the highest flexural strength values in standard specimens and layered samples. However, the most bond separation issues between additive layers were achieved with layered samples produced with mix 2. Most layered samples produced with minimum time gaps recorded the highest flexural strength results. [ABSTRACT FROM AUTHOR]

Porous materials have numerous applications in industry. Elements such as gears, pins, filters, bearings, and connecting rods, among others, are examples of parts that can be manufactured from these materials, where the presence of varying loads may cause a catastrophic failure. The shakedown analysis is a useful tool to establish the safe conditions for the operation of a structural or mechanical component subjected to varying loads. However, the shakedown analysis of porous materials has received little attention and a general formulation for this problem is not available. This paper presents a static and a mixed variational principle for the shakedown analysis of porous materials and the corresponding numerical solution via the finite element method. A yield function for porous material is obtained from the specific strain energy combined with a relationship between the relative density and the applied hydrostatic pressure. The shakedown analysis performed in this paper is based on a mixed variational principle which gives rise to an optimization problem. The solution provides, not only the largest amplification factor for the domain of load variation, but also the residual stresses and velocities fields. The discretization of the mixed variational principle is performed by the finite element method and uses a triangle with six nodes which permits a quadratic interpolation of velocities together with a linear interpolation of stresses. The validation of the numerical procedure is accomplished by comparing the present simulation with previously published results and analytical solutions for the residual stresses and amplification factor. The finite element method provided good solutions for all the presented examples. The presented variational formulation may be used to obtain the safe condition for mechanical parts made of porous materials and subjected to variable loads. Moreover, it can be used to estimate the relative density distribution in the parts. [ABSTRACT FROM AUTHOR]

The paper considers a method of geometric interpolation of basic solutions for two-dimensional problems in the theory of elasticity and structural mechanics, particularly as applied to mechanical engineering. The scope of the study is the vibrations of thin elastic parallelogram plates of constant thickness. To determine the fundamental frequency of vibration it is suggested to use an interpolation method with a newly introduced geometric characteristic of plates which is a ratio of inner conformal radius to outer conformal radius. Taken from the theory of conformal mapping, the conformal radii of domains are obtained by mapping the plates onto the interior and exterior of a unit circle. The studies have shown that the use of the suggested ratio ​​gives up to twice more accurate results of the geometric interpolation. The paper presents the basic terms and formulas of the method with comparative analysis of the curve diagrams using a shape factor and a conformal radii ratio. [ABSTRACT FROM AUTHOR]

This paper reviews the types of bacteria used in concrete and the ways it can be applied as a healing agents. This paper also gives a brief description of the various properties of concrete which vary with the addition of bacteria. Micro-cracks are inherently present in concrete. This causes degradation of concrete leading to ingress of deleterious substances into concrete, resulting in deterioration of structures. Due to this concrete needs to be rehabilitated. To surmount these situations self-healing techniques are adopted. By the addition of urease engendering bacteria along with calcium source results in calcite precipitation in concrete. Bio-mineralization techniques give promising results in sealing the micro-cracks in concrete. The freshly composed micro-cracks can be sealed up by perpetual hydration process in concrete. The ureolytic bacteria which include Bacillus Pasteurii, Bacillus Subtilis which can engender urea are integrated along with the calcium source to seal the freshly composed micro cracks by CaCO 3 precipitation. For the amelioration of pore structure in concrete, the bacterial concentrations were optimized for better results. The literature shows that Encapsulation method will give better results than direct application method and also shows that the use of bacteria can increase the strength and durability properties of concrete. [ABSTRACT FROM AUTHOR]

The Information-Theoretic Interpretation of Quantum Mechanics from (Bub & Pitowsky, 2010) has been criticized in two ways related to the ontological picture it supplies. This paper explores whether Ontic Structural Realism can supplement the metaphysics of ITIQM in a way that would satisfy its critics. The many similarities between the two views are detailed. And it is argued that the ITIQM view ca. 2010 does seem to be compatible with OSR, but as the view evolved in Bub's Bananaworld (2016), its fundamental metaphysical commitments shifted, making it a less clean fit with OSR. • Bub and Pitowsky's ITIQM from (2010) has many of the same features of Ladyman and Ross's Ontic Structural Realism. • This view was criticized in two ways that parallel criticisms of OSR. • OSR has answers to these two criticisms, which offer a view of how ITIQM could be viewed as an OSRist view. • Bub's later development of ITIQM posits a basic ontology of a mosaic of events, which is less in line with Ladyman and Ross. • Bub's view is, on the OSR analysis, a higher-level science, and not a 'final' interpretation of a fundamental theory. [ABSTRACT FROM AUTHOR]

Motivated by the fact that the tool cutting point (TCP) receptance demonstrates significant variation between the idle and in-motion conditions of a machine tool, this paper studies the relationship between guideway friction and TCP dynamics. The fundamental effect is modelled and demonstrated on a laboratory testbench considering structural mechanics, servo dynamics, and guideway friction. The findings are then extended to an industrial-scale machine, for which improved measurement of the TCP receptance is obtained using a dedicated inertial linear actuator. Finally, practical in-motion impact hammer testing guidelines are proposed for more accurate characterization of the TCP receptance and chatter stability predictions. [ABSTRACT FROM AUTHOR]

This paper uses Weibull stress analysis to investigate whether the effective notch toughness K m a t ρ for cleavage fracture measured using Compact Tension (CT) specimens containing a U-notch is dependent on the size and geometry of the CT specimen. Notched CT specimens are typically used to measure a material's effective notch toughness K m a t ρ and to assess failure of a structure containing a non-sharp defect using the Notch Failure Assessment Diagram (NFAD). The paper concludes that K m a t ρ is dependent on specimen thickness B over and above the microstructural weakest link effect arising from differences in the volume of the plastic zone; K m a t ρ is a function of not only the in-plane effect of the notch radius but also an out-of-plane constraint loss which itself is enhanced by the presence of the notch radius. This out-of-plane constraint loss can be more significant than the in-plane effect of the notch radius. The use of experimentally measured K m a t ρ values in an NFAD assessment of a notched structure may therefore be non-conservative if the out-of-plane constraint loss in the CT specimen is more significant than in the structure. For the material considered in this paper, doubling the thickness B of the CT specimen resulted in plane strain conditions being sufficiently dominant to eliminate out-of-plane constraint loss in the CT specimen. [ABSTRACT FROM AUTHOR]

The Carrera Unified Formulation (CUF) was recently extended to deal with the geometric nonlinear analysis of solid cross-section and thin-walled metallic beams (Pagani and Carrera, 2017). The promising results provided enough confidence for exploring the capabilities of that methodology when dealing with large displacements and post-buckling response of composite laminated beams, which is the subject of the present work. Accordingly, by employing CUF, governing nonlinear equations of low- to higher-order beam theories for laminated beams are expressed in this paper as degenerated cases of the three-dimensional elasticity equilibrium via an appropriate index notation. In detail, although the provided equations are valid for any one-dimensional structural theory in a unified sense, layer-wise kinematics are employed in this paper through the use of Lagrange polynomial expansions of the primary mechanical variables. The principle of virtual work and a finite element approximation are used to formulate the governing equations in a total Lagrangian manner, whereas a Newton–Raphson linearization scheme along with a path-following method based on the arc-length constraint is employed to solve the geometrically nonlinear problem. Several numerical assessments are proposed, including post-buckling of symmetric cross-ply beams and large displacement analysis of asymmetric laminates under flexural and compression loadings. [ABSTRACT FROM AUTHOR]

Concrete is quasi-brittle material susceptible to cracking under tensile or shear stress. In case of continuous network of crack is formed, concrete structure becomes permeable and embedded rebar may be exposed to ambient air, hence escalating the risk of material degradation. On the other side, concrete infrastructures industry is facing pressing sustainability issues. Concrete production consumes high amount of energy and produces large amount of CO2 emission. The scale of the problem is even greater in the event of many concrete structure premature failure which consumes more raw material for rebuilding. Designing new infrastructures for longer service life by improving concrete (materials and structure) durability is one solution to overcome the dilemma. One promising concept is by incorporating self-healing mechanism found in nature into cement-based materials / concrete structural element. This paper presents inherent autogeneous healing which occur due to its heterogeneous nature of concrete. This contribution also demonstrates some laboratory proven bio-inspired techniques that makes concrete materials and/or structural element self-healing autonomously. It involved diverse methods across several categories. The methods designed have demonstrated to have a good prospect in making concrete structural element self-healing. Finally the paper concludes with the claim that If unavoidable cracks due to inherent brittleness in concrete could be self- sealed/healed/repaired, concrete structure will certainly serve longer service life, making it more durable, therefore sustainable. [ABSTRACT FROM AUTHOR]

Soot particles are formed through combustion processes and have fractal-like shapes. They influence our climate by absorption and scattering of the solar radiation directly, and indirectly by their influence on cloud (liquid or glaciated) formation and their deposition on snow and ice surfaces. An Instrument, which we would like to introduce in this paper was developed and built at the University of Applied Sciences Northwestern Switzerland to measure light scattering properties of combustion type aerosols. A closed chamber was designed where the scattered light can be detected at 7 fixed, predefined angles simultaneously. Two lasers at 405 nm and 852 nm serve as light sources, and with that almost simultaneous measurements at the two different wavelengths can be carried out. The instrument is calibrated with aerosol particles of known scattering properties and concentration. We used nebulized, size selected ammonium sulphate particles for this purpose. The angular light scattering is influenced by the shape of the particles. In the case of fractals information on the fractal dimension and characteristic size can be derived from the angle dependence of the scattered light. In this paper we demonstrate and test the performance of this new light scattering instrument through the measurement of different soot or soot–containing aerosols. These examples include the measurement of artificial soot particles generated by two different soot generators (Cast soot and Palas soot generators) and different kind of combustion produced aerosols like: flaming ethanol, smouldering wood and mixed smouldering/flaming wood smokes. [ABSTRACT FROM AUTHOR]

The thermal conduction properties of 2.5D angle-interlock woven composites (2.5DAWC) were investigated along warp, weft and thickness directions both from experimental measurement and finite element analyses (FEA). A self-designed apparatus was established to measure the thermal conductivity of 2.5DAWC. The multi-scale FEA models were selected from representative volume elements (RVE) of matrix, yarns and composites by detailed geometrical structural analyses. The micro-scale models including the matrix-voids RVE and the fiber-matrix RVE were used to calculate the thermal properties of resin matrix and yarns, respectively. The meso-scale model was created to analyze the overall thermal conduction behaviors of 2.5DAWC, including the temperature and heat flux distributions. The effects of voids and interface thermal contact resistance on the thermal conductivity were also considered and analyzed in this paper. The results from FEA showed reasonable agreement with the experimental with an error of less than 5%. The methodology of this paper could be applied to understand the thermal conduction behaviors of complicated structural composites, and also can be used to predict the coupled thermal-mechanical properties of composites. [ABSTRACT FROM AUTHOR]

Modeling and analysis of masonry continuum through mechanical models that embed some low tensile skill of the masonry and account for its decay process during time is rarely treated in literature. More sophisticated models are to be considered able to produce results in major agreement with real data. The development of theoretical formulations aimed at a priori producing evaluations about the overall performance of these models have a central importance, since they allow to make reasoned computational choices about the mechanical models to be referred to for computations. In this paper one focuses on a special mechanical model for masonry bodies, which is referred to as Elastic Brittle tension (EB) model. Actually the EB model is evolutionary since the non-null tensile stress yield value is assumed to decay during time and converge towards the No-Tension behavior. This involves the need of investigating the relationships of the solution with other solutions related to more known mechanical models, which requires for the EB model the development of a proper theoretical formulation that is presented in the paper. One starts from the consideration that in this case, since the failure in tension is brittle, the theorems of Limit Analysis (LA) are not justified. Thereafter one sets up an approach to the problem aimed at investigating how far the collapse behavior of EB structures can be analyzed through the usual LA tools; some bounding thresholds for their ultimate load-carrying capacity with some original stability statements are then formalized. The proposed approach is here referred to masonry arches modeled under the EB hypothesis but it may be easily generalized to different structural typologies. [ABSTRACT FROM AUTHOR]

This paper considers the problem of parametric, nonlinear, projection-based model order reduction (PMOR) and makes three contributions to advance its state of the art. First, it presents a computational strategy for reducing the total offline cost of nonlinear PMOR by enabling hyperreduction to be performed adaptively within the typical greedy sampling procedure, rather than uniformly at each of its iteration. Then, it presents a more accurate and computationally efficient approach for training hyperreduction based on residual Jacobians rather than residuals. Finally, it demonstrates for a large-scale, industrial-grade, parametric, nonlinear application, that the two aforementioned contributions make both offline and online stages of nonlinear PMOR practical in today's engineering environments. The paper also shows that despite the so-called Kolmogorov n -width barrier for the model reduction of convection-dominated transport problems, the current state of the art of nonlinear, Petrov–Galerkin PMOR equipped with the advances proposed in this paper is capable of accelerating by orders of magnitude the accurate solution of shape-parametric, high Reynolds number, viscous flow problems represented by the Reynolds-averaged Navier–Stokes equations augmented with turbulence modeling. All three contributions are presented and discussed in the contexts of steady-state CFD problems; however, they are equally applicable to unsteady CFD problems as well as problems in solid mechanics and structural dynamics. [ABSTRACT FROM AUTHOR]

• The method of multi-threaded parallelization of the assembly and numerical factoring of the symmetrical sparse matrices, realized in the super-nodal finite element solver PARFES and oriented on multi-core computers of NUMA architecture, is proposed. • An algorithm for binding RAM to NUMA nodes is presented, which allows minimizing the access of the cores of each NUMA node to the memory of other NUMA nodes (to a distant memory). • Parallelization of the sparse matrix assembling uses atomic operations to avoid the collision between threads. It ensures a stable speed-up even in the case of a large number of threads. • Parallelization of the sparse matrix factorization is based on the use of a dependency vector that controls the mapping of computational tasks to threads. This approach proved its efficiency on numerous real-life examples of the finite element problems of structural and solid mechanics. This paper considers the implementation of PARFES – the direct supernodal method for solving systems of linear equations with symmetric matrices resulting from the finite element method applied to problems of structural and solid mechanics. Unlike previous publications describing the implementation of PARFES for multicore SMP computers, this paper focuses on the implementation of the solver on NUMA computers, where storing data in near memory of the corresponding processor is crucial for achieving high performance, which leads to significant changes in the basic solver algorithms. [ABSTRACT FROM AUTHOR]

Splitter plates attached to a cylinder looking like hair (SPCH) is one of the self-adaptive devices used to control actual flow conditions, which in turn interact with Aeolian tones constituting a typical case of study in engineering industries. The direct numerical simulation of the sound waves stimulated by such devices is a complicated task due to the small levels of sound pressure and the time-consuming existing solvers. However, the Cumulant Lattice Boltzmann Method (LBM) provides stability and robustness at high Reynolds numbers and carries out these simulations satisfactorily. First, the fundamental acoustical properties of the Cumulant LBM are studied in this paper. Propagation of point and planar acoustic waves is considered including the temporal decay of a standing plane wave, the spatial decay of a planar acoustic pulse, and the propagation of spherical waves. Then, the Cumulant LBM as a fluid flow solver is coupled with a Finite Element structural mechanics solver to predict the effects of SPCH on the noise generated by cylinders at high Reynolds numbers as a practical fluid structure interaction (FSI) application. The spectral modification and possible acoustic damping impact of such flaps, plus the sound propagation from one and two circular cylinders are studied. A comparison of the theoretical and numerical results shows a reasonable capability of the Cumulant LBM to predict acoustical events with small errors in dissipation and dispersion. Furthermore, the results show that SPCH alter the phase of the vortex shedding cycle and decrease the transversal distance from the center line of the shed vortices. Flaps, thus, control the wake generated past a cylinder and have an effective impact on decreasing sound generation. [ABSTRACT FROM AUTHOR]

As loose sediment transported and deposited by wind, changes in the grain size of loess is the main source of changes in its macromechanical properties, mesostructural characteristics and microparticle effects. However, at present, there is almost no relevant research on the relationship between grain size and structural mechanics of wind-sorted loess, which significantly restricts the in-depth understanding of the mechanism and evolution of geological disasters and resulting engineering damage. In this paper, grain size optimization is performed by a wind sorting device developed in this laboratory to reveal the intrinsic mechanism associated with sorting, structural mechanics and particle interactions. The results show that the average grain size is positively correlated with the wind speed and negatively correlated with the transport distance. Further study finds that the grain size of aeolian loess consists of superimposed medium and fine particle fractions with good distribution sorting and coarse particle fractions with poor distribution sorting. Under the same conditions of water content and dry density, cohesion increases with increasing transport distance and wind speed. However, the internal friction angle first decreases and then slowly increases during the whole wind transport process. Fine particle content is the decisive factor for the change in shear parameters. Microscopic analysis shows that the contact mode, pore characteristics, azimuth of particles and variations in coarse, medium and fine ternary particle accumulations are closely related to the grain size distribution caused by wind sorting. The negative (loosening, wall, wedge) and positive (filling, adsorption) effects in these microstructures correspond to the structural characteristics of soil at different transport distances, and different structural characteristics correspond to different mechanical properties. This correspondence fully reveals the close relationship between the grain size characteristics produced by wind sorting and structural mechanics. This study helps to elucidate the relationship between grain size variation and mechanical characteristics of aeolian loess and provides theoretical references for relevant applications in the fields of geological and geotechnical engineering. • A new method for restoring the natural accumulation of aeolian loess is proposed. • Effectively inverts the paleoclimate change information in the Loess Plateau. • The mechanical response of wind-sorted loess is explored. • Innovatively proposes the positive and negative stacking effects with ternary particles. [ABSTRACT FROM AUTHOR]

This paper considers the problem of parametric, nonlinear, projection-based model order reduction (PMOR) and makes three contributions to advance its state of the art. First, it presents a computational strategy for reducing the total offline cost of nonlinear PMOR by enabling hyperreduction to be performed adaptively within the typical greedy sampling procedure, rather than uniformly at each of its iteration. Then, it presents a more accurate and computationally efficient approach for training hyperreduction based on residual Jacobians rather than residuals. Finally, it demonstrates for a large-scale, industrial-grade, parametric, nonlinear application, that the two aforementioned contributions make both offline and online stages of nonlinear PMOR practical in today's engineering environments. The paper also shows that despite the so-called Kolmogorov n -width barrier for the model reduction of convection-dominated transport problems, the current state of the art of nonlinear, Petrov–Galerkin PMOR equipped with the advances proposed in this paper is capable of accelerating by orders of magnitude the accurate solution of shape-parametric, high Reynolds number, viscous flow problems represented by the Reynolds-averaged Navier–Stokes equations augmented with turbulence modeling. All three contributions are presented and discussed in the contexts of steady-state CFD problems; however, they are equally applicable to unsteady CFD problems as well as problems in solid mechanics and structural dynamics. [ABSTRACT FROM AUTHOR]

This paper investigates the structural performance of hybrid members consisting of reinforced concrete flat slabs, with and without shear reinforcement, connected to steel columns by means of fully integrated shear-heads. A detailed account of the results from a series of six large scale tests on this form of hybrid structural system is provided. The test results offer a direct evaluation of the full load–deformation behaviour of the specimens as well as the ultimate punching shear strength attained prior to failure at the critical slab perimeter outside the shear-head region. The experimental findings enable the development of analytical models that depict the rotational response and flexural strength as a function of the shear-head embedment length, layout and section size. Additionally, the test results support the definition of a shear-head dependent control perimeter which is used in conjunction with the analytical slab models for full assessment of punching shear strength. The adequacy of strength predictions incorporated in current design methods for conventional reinforced concrete members are also examined in the paper. It is shown that existing design procedures either lack direct guidance for members provided with shear-heads, or lead to overly conservative strength predictions. Finally, in order to provide a reliable evaluation of the ultimate punching shear strength of hybrid elements, analytical design expressions which account for the characteristics of the shear-head system, are proposed. In comparison with conventional reinforced concrete design provisions, the suggested approach captures in a more realistic manner the influence of the embedded length of the shear-heads for such hybrid members with or without shear reinforcement. [ABSTRACT FROM AUTHOR]

This paper represents the first public exhibition of Thermadapt™ building coverings which were invented more than eight years ago. The paper starts with a brief overview of the field of adaptive materials and their applications in various industries. Thermally adaptive building covering sheet fundamentals are explained by laying out the basic structural mechanics of thermally induced gross shape changes in lamina. As a truncated paper, the driving theory, coupon, test chamber and subscale building data could not be included due to length constraints, but will be delivered during oral presentation. Nonetheless, data from outdoor range testing on three independent buildings is presented. These three buildings measuring 1.8m (6 ft) deep x 2.4m (8 ft) wide x 2.1m (7 ft) high showed excellent results. The first was outfitted with Thermadapt™ siding and roofing. The second was outfitted with a variety of different amounts of insulation. The third was used as a control. The configuration of the full-scale test range buildings is shown along with performance data in all midwestern seasons. The data demonstrated that thin thermally adaptive building coverings are as effective as 27 cm (10.5”) of fiberglass insulation, indicating an equivalent R-value of more than 40/cm (100/in). The paper concludes with an overview of the economics of Thermadapt™ building coverings and the intellectual property landscape. [ABSTRACT FROM AUTHOR]

This paper presents the lateral load behavior of a 1/10th scale model of a pressurized water reactor (PWR) containment internal structure (CIS). The entire CIS including the steam generator compartments, pressurizer, reactor cavity walls, etc. are made of steel–concrete composite (SC) walls. The lateral load behavior of the 1/10th scale model of the CIS was investigated experimentally by researchers in Japan, and presented at the 10th Structural Mechanics in Reactor Technology (SMiRT) Conference in 1989. Recent advancements in finite element modeling techniques, and computer-based analysis approaches have enabled the numerical simulation of the lateral load behavior of the 1/10th scale CIS tested earlier. This paper presents: (i) the development of 3D nonlinear inelastic finite element (NIFE) models of the 1/10th scale CIS, (ii) the comparison and benchmarking of numerical results with experimental results and observations, and (iii) the overall lateral load-deformation behavior of the CIS including the formation of ductile energy dissipating mechanisms in the SC walls. The results and findings are used to provide recommendations for modeling CIS structures consisting of SC walls while conducting nonlinear analysis to evaluate their seismic performance for design and beyond design basis events. [ABSTRACT FROM AUTHOR]

Rheology is a high quality tool to evaluate the effect of variations in constituent materials and mixture proportions on fresh properties of cement-based materials. However, interpreting rheological measurements is relatively complicated, and some pitfalls can lead to wrong conclusions. This paper offers a review of measuring devices and transformation equations used to express rheological parameters in fundamental units. The paper also discusses some of the major issues that can lead to errors during the interpretation of rheological measurements. Although the Bingham model is mostly used for cement-based materials, some non-linearity has been observed, necessitating the selection of an alternative rheological model, which could influence the rheological parameters. Other measurement errors related to thixotropic and structural breakdown, plug flow and particle migration are also demonstrated. The paper also discusses the challenges of using numerical simulations to derive rheological parameters for complicated rheometers or industrial devices, such as a concrete truck. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures affected by corrosion of steel bars are often repaired and rehabilitated by wrapping fibre reinforced polymer (FRP) sheets. Most commonly available FRP materials are glass and carbon fibre composites. This paper uses ultrasonic guided waves as a non-destructive tool to monitor the initiation and progression of corrosion in reinforcing bars in concrete after repairing with bonded FRP sheets. Concrete cylinders embedded with reinforcing bars are subjected to accelerated impressed current corrosion in chloride environment. After specific days of exposure to corrosive environment the cylinders are repaired by wrapping with GFRP and CFRP sheets. Anodic current was further continued for specified times. Specific core and surface seeking guided wave modes were used to ultrasonically measure the resistance offered by FRP wraps to corrosion. The ultrasonic measurements were correlated with destructive parameters of pull-out strength and mass loss. This paper demonstrates that guided waves were able to discern the corrosion protection offered by the FRP. It is observed that Glass FRP gives better protection than Carbon FRP. [ABSTRACT FROM AUTHOR]

Pultruded glass fibre reinforced polymer (GFRP) profiles are finding increasing applications in civil engineering structures, owing to the several advantages they offer over traditional materials. However, due to the combustible nature of their polymer matrix, there are well-founded concerns about their behaviour at elevated temperature and under exposure to fire. These concerns are hindering the widespread acceptance of GFRP profiles, particularly in buildings, which need to comply with relatively strict requirements in terms of fire reaction and fire resistance behaviour. This paper presents a review about the fire performance of pultruded GFRP profiles. It first addresses the effect of elevated temperature on the thermophysical and thermomechanical properties of the pultruded GFRP material. Then the fire reaction properties of pultruded GFRP profiles and the effects of different fire protection measures on those properties are discussed. Next comes a section reviewing previous experimental and modelling studies about the fire resistance behaviour of different types of GFRP structural members. The final part of the paper provides a summary of the design guidance set out in the most relevant guidelines and codes applicable to pultruded GFRP structures. The most pertinent research needs for the various fire behaviour aspects addressed are also identified. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the capability of numerical approaches such as finite difference methods and finite element methods, in approximating exact one-dimensional continuous eigenvalue problems (such as lateral vibrations of a string, the axial or the torsional vibrations of a bar, and the buckling of elastic columns). The numerical methods analysed in this paper are converted into difference equations. Following a continualization procedure or the method of differential approximation, the difference operators are then expanded in differential operators via Taylor expansion or Padé approximants. Analogies between the finite numerical approaches and some equivalent enriched continuum are shown, using this continualization procedure. The finite difference methods (first-order or higher-order finite difference methods) are shown to behave as integral-based nonlocal media (or stress gradient media), while the finite element method is found to behave as gradient elasticity media (or strain gradient media). The length scale identification of each equivalent enriched continuum strongly depends on the order of the numerical method considered. For the finite difference methods, the length scale identification of the equivalent nonlocal medium depends on the static versus dynamic analysis, whereas this length scale appears to be independent of inertia effects for the finite element method. Some comparisons between the exact discrete eigenvalue problems and the approximated continuous ones show the efficiency of the continualization procedure. An equivalent enriched Rayleigh quotient can be defined for each numerical method: the integral-based nonlocal method gives a lower bound solution to the exact eigenvalue multiplier, whereas the gradient elasticity method furnishes an upper bound solution. [ABSTRACT FROM AUTHOR]

The evolution of essentially periodic crack patterns appears in many natural and technical processes. For example, typical cases of periodic crack patterns are known from drying soils, from the formation of basalt columns, from high temperature loaded ceramics, from fissure formation in coke, and from drying protein solution drops. The appearance of more or less periodic crack patterns is the result of cascades of bifurcation-instabilities of the propagation process. There exist established, mathematically rigorous criteria for the bifurcation of the crack growth process of two initially equally long parallel cracks (Nemat-Nasser et al., 1978; Bazant et al., 1979). These criteria require the determination of the mutual influence of the neighboring cracks on their growth by calculation of partial derivatives. If discretization methods are used for simulating such a growth process, the calculation of these partial derivatives may become very sensitive with respect to the density of the spatial discretization. This is especially true if strong gradients of a crack driving eigenstress field appear as, for instance, in chemical diffusion processes. In the present paper, an alternative approach is introduced, which circumvents estimations of partial derivatives and, in addition, provides a more realistic picture of the generation of crack patterns. This approach is inspired by a computationally efficient method for investigating the buckling and post-buckling behavior in structural mechanics by introducing small imperfections. As a typical example, in which the approach introduced here is especially beneficial, the simulation of self-organized crack pattern evolution in alkali feldspar, a very common brittle crystal, is presented. There, the cracks are driven by eigenstrains caused by cation exchange between the crystal and a salt melt. Comparisons between the character of the pattern formation in the simulation and in experiments show excellent agreement. Furthermore, by combining simulations and experiments the J c -value can be determined at considerably high accuracy. [ABSTRACT FROM AUTHOR]

The duct wall and inter-assembly gap make up ∼5–15% of the volume of a typical fast reactor core and these components have a profound impact on the system neutron economy. In this paper, a methodology for the design of optimum hexagonal fuel assembly geometries was developed. For each nuclear reactor core made up of ducted assemblies there exists a unique optimum solution of duct wall thickness and inter-assembly gap, where these components have the minimum impact on the core neutron balance while adhering to applicable structural constraints. The assembly duct wall must maintain its structural integrity and intended function while being exposed to a harsh environment of pressure, temperature and neutron fluence causing elastic and inelastic deflections and swelling. Analytical expressions, applicable to any internally pressurized hexagonal structure, were defined for the peak stress and elastic wall deflection. Detailed analysis of fuel assembly duct designs requires finite element code analysis, radial bowing analysis codes and the full temperature, flux and stress distribution over the lifetime of the assembly in the core to accurately estimate creep deformation. The simple analytical methodology presented in this paper can provide a good initial guess for an optimal geometry to be iteratively improved and refined using more advanced codes and methods. [ABSTRACT FROM AUTHOR]

The paper shortly presents the history and development of the traditional design in civil engineering. Next, the idea of Building Information Modelling (BIM) and its practical benefits are described. Main part of the paper is devoted to discussion about what kind of difficulties we may encounter during the implementation of the BIM technology and how they are related to the potential benefits. Case study presents the existing design prepared in BIM technology. [ABSTRACT FROM AUTHOR]

Due to their combination of high-temperature coated-particle fuel, molten salt coolant and related materials requirements, fluoride-salt-cooled, high-temperature reactors (FHRs) exhibit different thermal hydraulic, neutronic and structural mechanics phenomena compared to conventional and more extensively studied other advanced nuclear reactor concepts. This paper highlights key phenomena unique to FHRs, and reviews general issues for developing, verifying, and validating evaluation models for FHR technology that may apply to other advanced reactors. System response codes that are appropriate to predict the behavior of FHRs under steady-state operation and licensing basis events are identified, along with experimental data needs to validate these codes. FHR materials requirements are highlighted, and the missions and licensing program for an FHR test reactor, providing ultimate validation data and proof of concept before a commercial prototype is built, are presented. This review draws upon information compiled in a series of four white papers based on FHR experts workshops held in 2012 in the U.S. [ABSTRACT FROM AUTHOR]

This paper considers the preconditioned block conjugate gradient method for solving the algebraic, generalized partial eigenvalue problem, which arises when the finite element method is applied to dynamic analysis in structural and solid mechanics. The focus is on the development of an algorithm that keeps constant the iterable subspace dimension, independently of the number of eigenpairs required. Novelties in this approach include a preconditioning strategy based on block incomplete factorization of the shifted stiffness matrix, and analysis of unremovable errors, which accumulate with increasing numbers of eigenpairs. [ABSTRACT FROM AUTHOR]

The paper deals with the Isogeometric Analysis (IGA) technology, which has received much attention over the last decade due to its increased flexibility, accuracy, and robustness in many engineering simulations compared to classical Finite Element Analysis (FEA). In this context, we present a verification method, based on duality and the concept of Constitutive Relation Error (CRE), that enables to derive fully computable a posteriori error estimates on the numerical solution provided by IGA. Such estimates, which can be used for a wide class of structural mechanics models, thus constitute effective and practical tools to quantitatively control the numerical accuracy and drive adaptive algorithms. The focus is here on the construction of so-called admissible flux fields which is a key ingredient of the CRE concept, and which was until now almost exclusively addressed in the FEA framework alone. We show that this construction can be performed in a similar way for FEA and IGA, provided some technical issues (due to the use of B-Spline/NURBS basis functions instead of Lagrange polynomials) are carefully addressed. We also use the CRE concept along with adjoint techniques and local enrichments in order to derive accurate goal-oriented error estimates. Two- and three-dimensional numerical experiments are presented, for thermal, linear elasticity and nonlinear damage problems, to illustrate the capabilities and versatility of the proposed approach. • A fully computable a posteriori error estimate is defined to certify IGA solutions. • The approach applies for a large range of computational mechanics models. • The estimate permits the control of global error and error on quantities of interest. • The recovery of equilibrated fields, which is the key point of the approach, is detailed. • The methodology is applied and evaluated on several 2D/3D numerical experiments. [ABSTRACT FROM AUTHOR]

The self-centering buckling restrained braces (SC-BRBs) are capable of dissipating energy through BRBs elements during seismic events and restoring to their initial positions after the earthquake, thus reducing residual deformations in structures. The traditional design of the SC-BRBs has a complex structure with dual/three steel load transfer tubes and prestressed tendons anchored by steel end plates as a prestressing system. The complexity of these structures and the possibility of errors in machining dimensions and interactions between components can result in uncertainties of the mechanical behavior of the traditional SC-BRBs. As a consequence, a new design has been developed that uses the brace component as the inner load transfer tube for improved stability and load transfer capabilities in this paper. The structural features and mechanics of the new SC-BRB are first described. Then, to examine the performance of new SC-BRB, a quasi-static cyclic loading test was conducted on one scaled model specimen. The results showed that the new SC-BRB exhibited a consistent flag-shaped hysteretic response, with maximum residual strain of 0.15% within the target design drift of 2%. Nonlinear finite element analyses using ABAQUS were conducted to examine the influence of initial prestress magnitude and properties of prestressing tendon materials on the performance of the new SC-BRBs. The findings indicate that pretension is crucial for full self-centering capabilities of the new SC-BRB. When pretension exceeds the yield bearing capacity of the BRB core, it results in full self-centering and eliminates residual deformations. Additionally, the elastic elongation of the prestressing tendon material determines the deformation capacity of the new SC-BRB, while the elastic modulus of the material affects its post-yield stiffness. • A universal restoring force model for the SC-BRB was developed and validated. • A new type of SC-BRB is designed and manufactured. • Prestressed system plays a crucial role in achieving full self-centering capabilities of the new SC-BRB. [ABSTRACT FROM AUTHOR]

In the field of structural mechanics, the study of elastic stability is a very important stage in the design of slender, thin, and/or shallow elements. The loss of stability can lead to the global collapse of the structural element. This is achieved when the load applied to the structure reaches the critical value. There are two fundamental instabilities in rectilinear beams: the axial buckling, due to the axial force, and the lateral–torsional buckling, due to the bending moment. In general, these two instabilities may interact, when both axial force and bending moments are applied at the same time. The present paper will illustrate a three-dimensional coupled formulation, including Vlasov's Theory for thin-walled open-section beams. The compactness of the final expressions, made even more evident by the matrix formulation, allows us for a very convenient use in the case of automatic computations. [ABSTRACT FROM AUTHOR]

• Presents a new arc-length solution method for structural mechanics problems. • Allows equilibrium paths to be tracked in problems involving snap-back and snap-through. • Method has much wider application to other physical problems involving instability. Tracing load-displacement paths in structural mechanics problems is complicated in the presence of critical points of instability where conventional load- or displacement control fails. To deal with this, arc-length methods have been developed since the 1970s, where control is taken over increments of load at these critical points, to allow full transit of the load-displacement path. However, despite their wide use and incorporation into commercial finite element software, conventional arc-length methods still struggle to cope with non-zero displacement constraints. In this paper we present a new displacement-controlled arc-length method that overcomes these shortcomings through a novel scheme of constraints on displacements and reaction forces. The new method is presented in a variety of serving suggestions, and is validated here on six very challenging problems involving truss and continuum finite elements. Despite this paper's focus on structural mechanics, the new procedure can be applied to any problems that involve nonhomogeneous Dirichlet constraints and challenging equilibrium paths. [ABSTRACT FROM AUTHOR]

Abstract The paper introduces a structural model for bump-type foil bearings based on contact mechanics including gaps and friction. The starting point is a model introduced in [32] were the bump foil is approximated by a specific structure of interacting springs. Following this model, contacts between the top and bump foils and between the bump foil and the sleeve are always closed. Recent analyses [31] showed that this not always verified: contacts can become loose even for very simple loading situations. A new model is then developed for considering these situations. The new model takes into account the elasticity of the top foil and three kind of gaps: between the rotor and the top foil, between the top and the bump foils and between the bump foils and the sleeve. The former model of the bump foil was extended by considering an additional degree of freedom per bump. Friction was modeled with Coulomb law. An efficient numerical procedure borrowed from contact mechanics ([41], [42]) was implemented for solving the structural problem with friction and close/loose gaps. The procedure uses the augmented Lagrangian algorithm for the normal contact forces and the penalty method for the tangential friction force. The procedure is very robust in dealing with stick-slip situations and close/loose contacts. The model was validated by comparisons with results from the literature ([31], [32]). By considering gaps in the foil structure and close/loose contacts, the model is not only closer to reality but can also handle manufacturing errors of the foil structure. This is shown by considering bump foil height manufacturing errors. Highlights • The model takes into account the interactions in a bump-type foil bearing structure. • Coulomb friction forces and close/loose contacts are rigorously taken into account. • Three gap functions are used: bump foil/sleeve, bump/top foil, top foil/rotor. • The model can deal easily with manufacturing errors of the foil structure. [ABSTRACT FROM AUTHOR]

Abstract It is important to account for inherent variability in the material properties in the design and analysis of engineering structures. These properties are typically not homogeneous, but vary across the spatial coordinates within a structure, as well as from specimen to specimen. This form of uncertainty is commonly modelled using random fields within the Stochastic Finite Element Method. Simulation within this framework can be complicated by the dependence of a random field's correlation function upon the geometry of the domain over which it is defined. In this paper, a new method is proposed for simulating random fields over a general two-dimension curved surface, represented as a finite element mesh. The covariance function is parametrised using the geodesic distance, evaluated using the solution to the 'discrete geodesic problem,' and a point discretisation approach is subsequently applied in order to sample the random field at the nodes of the model. The major contribution of the present work is the development of a methodology for simulating random fields over curved surfaces of arbitrary geometry, with a focus upon non-intrusive application to industrial finite element models using 'off the shelf' commercial software. In order to demonstrate the potential impact of the proposed approach, the algorithm is applied in an uncertainty quantification case study concerning vibration and buckling of an industrial composite aircraft wing model. [ABSTRACT FROM AUTHOR]

Abstract Hot-dip galvanizing is widely used for corrosion protection of steel structures. However, there has been a plethora of recent reports on premature cracking in galvanized steel structures, which have resulted in some early decommissions or even hazardous collapses. This research focuses on cold-formed Rectangular Hollow Sections (RHS). A total of 108 tensile coupons were tested to investigate the effects of galvanizing as well as different pre-galvanizing treatments on the material properties around the cross sections of the specimens. For the first time, this paper reports a comprehensive measurement of residual stresses in different directions at the member ends which are directly relevant to the cracking issue. The results were also compared to the residual stresses far away from the member ends, which are relevant to structural stability research. In all, the research provides a better understanding of the characteristics and structural performance of galvanized RHS to facilitate its application. The recommendations can help engineers, fabricators and galvanizers mitigate the risk of cracking in RHS during galvanizing. Highlights • Effects of hot-dip galvanizing on material properties studied. • Effects of different pre-galvanizing treatments on material properties studied. • Measurement of residual stresses at the member ends to study cracking. • Measurement of residual stresses at the middle of the members [ABSTRACT FROM AUTHOR]

Abstract In this paper, the plastic design with mechanism control (PDMC) for steel moment resisting frames (MRFs) is presented. The PDMC method in rigid plastic analysis, by considering the second-order effects, is guaranteed the achievement of global mechanism and prevented undesired mechanisms such as the soft story, which leads to decrease the ductility and energy dissipation capacity of the structures. The concept of PDMC is based on the plastic rotation of columns in developing a mechanism in which for a specified target displacement, the global mechanism has a minimum plastic rotation among all other undesired collapse mechanisms. In the presented method, the design conditions for story mechanisms are derived by using an energy equilibrium equation. For demonstrating the accuracy of the proposed design procedures, both pushover and nonlinear incremental dynamic analyses (IDAs) are applied to evaluate the structural performance. The results show that the designed structures comprise high seismic performance and the design objective that was to obtain a global mechanism is achieved. Highlights • New enhanced plastic design method for seismic designing of the steel structures • Including an optimization formulation to plastic design with mechanism control (PDMC) to prevent undesired collapse mechanisms • Designing frames with minimum weight and best performance during severe earthquakes • Assessing the behavior of the designed structures using nonlinear static and dynamic analyses [ABSTRACT FROM AUTHOR]

Abstract This paper presents an innovative computational approach for fatigue assessment of riveted connections. Such methodology is based on modal superposition principles, submodelling techniques and an elastoplastic post-processing to efficiently evaluate fatigue damaging events considering local geometrical, material and contact nonlinearities. The computational burden, intrinsic to localized detailed numerical analyses, is mitigated implementing a sub-algorithm based on network parallel computing. The developed computational methodology overcomes relevant drawbacks of S–N global approaches suggested in international standards and guidelines and it is an accurate methodology to analyse complex riveted fatigue-critical details, in particular the ones part of large structures, e.g. railway bridges. An idealised riveted beam case-study was investigated and local damage parameters were calculated in reduced computational times. The accuracy of such results proved that the proposed approach allows fully analysing the fatigue life of riveted connections, being applicable to unlimited geometrical configurations submitted to variable loadings. Highlights • An innovative approach to compute fatigue damages in metallic connections is proposed. • The focus is put on riveted connections due to their complex local nonlinear behaviour. • A computational algorithm considering submodelling techniques is developed. • Modal superposition and network parallel computing are considered to increase the computational efficiency. • Such approach allows overcoming relevant drawbacks of the global S–N approaches for fatigue analyses of large structures. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed. Highlights • An innovative double-through plate connection was proposed to connect steel HSS beam and CFST column. • The special characteristic of double-through plates greatly improved the connection performance. • The plates were governing components, which determined the connection behaviors. • In case of oval holes, bolt pretension had a greater influence on both the stiffness at early stage and the whole strength. • The stress level on the steel tube was effectively reduced. [ABSTRACT FROM AUTHOR]