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Erection of modularised shell structures with prestressed dry joints The exponential growth of concrete production in recent decades has led to a high raw material consumption and a large amount of CO2 emissions. To minimise the use of resources, material‐efficient structures such as shell structures, which are adapted to the distribution of forces, can be used as a basis. However, due to their curved geometry, these structures involve a complex construction process. Modular construction with industrially prefabricated concrete components can contribute to more efficient production and construction processes, combining the advantages of prefabrication with the benefits of material‐efficient load‐bearing structures. This article presents a concept for the modularisation of simply curved shell structures and demonstrates a method for the rapid erection of curved structures with prefabricated individual precast elements and prestressed dry joints. The feasibility is demonstrated by experimental investigations. [ABSTRACT FROM AUTHOR]

Self‐supporting concrete shell structures are highly efficient in distributing loads, which can result in very reduced thicknesses (ultra‐thin), giving them remarkable slenderness. Due to their geometric complexity, it is difficult to predict how they interact with wind action. The main aim of the present study is to assess the mean surface pressure coefficient distribution in a shell with a triangular plan shape and three supports for different angles of wind incidence. To determine the distribution of surface pressure coefficients and lift and drag force coefficients, an experimental study was carried out in a wind tunnel, and a numerical simulation study was performed through computational fluid dynamics. The experimental and numerical results were analyzed and compared, and making it possible to identify the most critical surface zones and wind incidences when the shell is under the wind action. [ABSTRACT FROM AUTHOR]

This paper proposes a level set-based method for optimizing shell structures with large design changes in shape and topology. Conventional shell optimization methods, whether parametric or nonparametric, often only allow limited design changes in shape. In the proposed method, the shell structure is defined as the isosurface of a level set function. The level set function is iteratively updated based on the shape sensitivity on the surface mesh. Therefore, the proposed method can represent an arbitrary manifold surface while dealing with topological changes, for example, from a spherical surface to a toroidal surface. We applied the proposed method to the mean compliance minimization problems of 3D shell structural designs for dome, bending plate and cantilever beam examples to demonstrate its efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

In a global context, where the construction industry is a major source of CO2 emissions and resource use, is dependent on concrete and its risks, and lags behind in digitalization, a clear need arises to direct architecture towards more practical, efficient, and sustainable practices. This research introduces an alternative technique for building timber space structures, aiming to expand its applications in areas with limited access to advanced technologies such as CNCs with more than five axes and industrial robotic arms. This involves reconfiguring economic and ecological constraints to maximize the structural and architectural advantages of these systems. The method develops a parametric tool that integrates computational design and manufacturing based on two-axis laser cutting for shells with segmented hexagonal plywood plates. It uses a modified 'half-lap joint' mechanical joint, also made of plywood and without additional fasteners, ensuring a precise and robust connection. The results demonstrate the compatibility of the geometry with two-axis CNC machines, which simplifies manufacturing and reduces the cuts required, thus increasing economic efficiency. The prototype, with a span of 1.5 m and composed of 63 plywood panels and 163 connectors, each 6 mm thick, supported a point load of 0.8 kN with a maximum displacement of 5 mm, weighing 15.1 kg. Assembly and disassembly, carried out by two students, took 5 h and 1.45 h, respectively, highlighting the practicality and accessibility of the method. In conclusion, the technique for building timber shells based on two-axis CNC is feasible and effective, proven by practical experimentation and finite element analysis. [ABSTRACT FROM AUTHOR]

In the case of solid slabs made of reinforced concrete that are usually subjected to bending, large areas of the structure are stressed well below their load-bearing capacity. Contrary to this are shell structures, which can bridge large spans with little material if designed according to the force flow. To improve the efficiency of ceiling slabs, we want to utilize the shell load-bearing behavior on a smaller scale by resolving the solid interior accordingly. In order to study a wide range of such constructions virtually, a parametric multi-objective simulation environment is being developed in an ongoing research project. The basic analysis approaches that were implemented are presented in this paper. The basic workflow, the used programs and material models, and their calibration on the tests on textile-reinforced concrete (TRC) samples are described.

In the case of solid slabs made of reinforced concrete that are usually subjected to bending, large areas of the structure are stressed well below their load-bearing capacity. Contrary to this are shell structures, which can bridge large spans with little material if designed according to the force flow. To improve the efficiency of ceiling slabs, we want to utilize the shell load-bearing behavior on a smaller scale by resolving the solid interior accordingly. In order to study a wide range of such constructions virtually, a parametric multi-objective simulation environment is being developed in an ongoing research project. The basic analysis approaches that were implemented are presented in this paper. The basic workflow, the used programs and material models, and their calibration on the tests on textile-reinforced concrete (TRC) samples are described. [ABSTRACT FROM AUTHOR]

Based on the first-order shear deformation theory (FSDT), the large-amplitude vibration behavior of shallow spherical shells made of functionally graded materials (FGMs) due to the rapid decrease of temperature (cooling shock) is investigated. FGM is assumed to be a mixture of stainless steel and low-carbon steel whose properties are considered temperature dependent and are estimated based on the power-law model. According to FSDT and von Kármán assumptions, the governing equations of motion in conjunction with corresponding boundary conditions are obtained using Hamilton's principle. The temperature distribution is also achieved by means of the 1D Fourier transient heat conduction equation, considering two time-dependent thermal loading scenarios. The considered thermal boundary conditions allow that a temperature difference is created with a time delay for the structure under cooling shock. Also, the results of recent experiments are employed to estimate the temperature-dependent properties of structures. In the solution approach, the generalized differential quadrature method and the Newmark-beta integration scheme are utilized. Selected numerical results are presented to study the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material gradient index on the thermally induced vibrations of spherical shells. Stresses generated in the shell due to the thermally induced vibrations are also investigated. [ABSTRACT FROM AUTHOR]

Studies that optimise both the shape and topology of shell structures typically utilise CAD parametrisations to describe the geometry of the shell and density-based methods to characterise its material layout. Relying on CAD-based approaches has the advantage that only a few design variables, usually the control points of the surface, are included in the shape optimisation problem, thereby resulting in fast optimal shell geometries. This approach, however, requires a CAD description of the shell surface that must be updated continuously and, depending on the number of shape parameters, the set of possible designs is in many cases very small. To combine the optimisation of the shell topology and shape, in this work we integrate a density-based method to find the optimal topology with a node-based method to find the optimal shape. Because of a larger design space, a node-based approach offers much greater freedom in realisable geometries. Further, since both the density-based and node-based methods exclusively rely on information from the finite element models, the proposed approach is easy to integrate into existing finite element software. We find that when comparing sequential workflows—where the shape and topology optimisation problems are performed in independent, consecutive steps—to a concurrent scheme where the shape and the topology are optimised simultaneously, the lowest cost function is generally achieved by the concurrent workflow. Moreover, because node-based shape optimisation involves highly non-convex cost functions, we observe that the different workflows converge to notably different geometries and topologies. [ABSTRACT FROM AUTHOR]

Topology-optimisation strategies for structural design of discrete surface structures result in unstructured patterns that require post-rationalisation to limit the number and complexity of the various structural elements. Fabrication-related objectives still demand further processing. Designers need topology exploration, before topology optimisation, following a generative-design approach that is decoupled from density tuning and shape design, to produce high-quality patterns. Such an approach allows to flexibly embed multiple design constraints, benefit from state-of-the-art form-finding algorithms and explore design trade-offs of the multiple requirements related to architecture, engineering and construction. This research investigates a parameterisation strategy to encode topological exploration of structured patterns based on quad meshes. The focus is set on singular vertices, which connect an irregular number of blocks, cables, or beams. Singularities are independent from pattern density and geometry, and have a fundamental influence on the qualitative and quantitative performance of the structure. We introduce an L-system encoding a quad-mesh grammar into a string that describes topological transformations of these singularities. Design applications to a net and a gridshell demonstrate the influence of singularities on the design of surface structures, and highlight the flexibility and generality of the approach in terms of geometrical processing and performance metrics. Beyond exploration, this parameterisation strategy opens to novel applications of search and optimisation methods for generative design of singularities in structural patterns. [ABSTRACT FROM AUTHOR]

In a global context, where the construction industry is a major source of CO2 emissions and resource use, is dependent on concrete and its risks, and lags behind in digitalization, a clear need arises to direct architecture towards more practical, efficient, and sustainable practices. This research introduces an alternative technique for building timber space structures, aiming to expand its applications in areas with limited access to advanced technologies such as CNCs with more than five axes and industrial robotic arms. This involves reconfiguring economic and ecological constraints to maximize the structural and architectural advantages of these systems. The method develops a parametric tool that integrates computational design and manufacturing based on two-axis laser cutting for shells with segmented hexagonal plywood plates. It uses a modified ‘half-lap joint’ mechanical joint, also made of plywood and without additional fasteners, ensuring a precise and robust connection. The results demonstrate the compatibility of the geometry with two-axis CNC machines, which simplifies manufacturing and reduces the cuts required, thus increasing economic efficiency. The prototype, with a span of 1.5 m and composed of 63 plywood panels and 163 connectors, each 6 mm thick, supported a point load of 0.8 kN with a maximum displacement of 5 mm, weighing 15.1 kg. Assembly and disassembly, carried out by two students, took 5 h and 1.45 h, respectively, highlighting the practicality and accessibility of the method. In conclusion, the technique for building timber shells based on two-axis CNC is feasible and effective, proven by practical experimentation and finite element analysis.

Constructing resistive layer with novel structure holds great potential in upgrading electromagnetic properties of soft magnetic materials in a wide frequency range. In this work, FeNi@SiO2 composites with controllable core–shell structures, including 2D-type laminar shell and 3D-type raspberry-like shell, were fabricated by modified Stöber method. The structure of SiO2 shell depends highly on the concentration of tetraethyl orthosilicate (TEOS). In detail, a laminar shell can be formed at low TEOS concentration, owing to slow condensation. While at high TEOS concentration, heterogeneous growth on powder surface and homogeneous growth in solution of silica networks are significantly accelerated, resulting in the formation of the raspberry-like shell. Improved electromagnetic performance of FeNi@SiO2 cores at 2 MHz, including high resistivity, low eddy current loss, and low loss factor, should be ascribed to the unique raspberry-like shell structure. Meanwhile, raspberry-like shell also contributes to enhanced attenuation and acceptable impedance matching in GHz range. Consequently, a wide effective absorption bandwidth of 8.92 GHz can be achieved at a thin thickness of 1.85 mm. This work provides deep insights into the growth mechanism of different SiO2 shells and sheds new light on the design of high-performance soft magnetic composites working in different frequency bands.

Abstract This article presents a literature review on the use of flexible formworks for concrete structures, from their earliest conceptions in the late 19th century to recent applications. The challenges faced by builders, engineers, and architects in designing flexible moulds are discussed. A bibliometric analysis on the subject is also presented. Different methodologies for categorization are analyzed, and a consistent classification based on the application technique is proposed. Advantages and disadvantages of the formwork system are discussed and the article concludes with the perspective of future studies on the construction process through computational models.

In the present work, regularities of changes in the frequency dependence of microwave shielding properties of fabricated 2D and 3D metastructures with periodic lattices based on glass microspheres coated with GNPs, GNPs-NiFe, MoS2 and a mixture of MoS2 + 20 % GNP were established. The influence of the size of carbon-based globular structures, the type of globule coating and the type of polymer matrix on the value and balance between the indices of electromagnetic radiation reflection, absorption and transmission in the frequency range of 25-37 GHz is considered. Glass balls with a diameter of 600 µm and 1.8 mm were used as a glass core. It was established that the increase in the size of glass microspheres leads to an increase in the shielding efficiency, and a large amount of GNP or GNPs-NiFe in the 3D structure contributes to the effective attenuation of electromagnetic radiation by increasing the reflection and absorption of microwaves. The presence of NiFe magnetic component on the glass microspheres leads to an increase in the absorption coefficient A, while the reflection coefficient R decreases compared to composites based on glass microspheres covered only with GNPs. [ABSTRACT FROM AUTHOR]

Concrete is the most widely used building material today. The enormous amount used goes hand in hand with high material consumption and CO2 emissions. Thus, building with concrete must be improved, becoming part of the solution on the way to climate-friendly building. Non-metallic fibres are an alternative to corrosion-sensitive steel reinforcement, and they enable the production of filigree, high-performance, structured components with low concrete cover. This article presents an alternative manufacturing method. Our thesis was that concreting under negative air pressure conditions (APC) allows the easy production of complicated, thin-walled geometries without defects or loss of mechanical properties. We firstly present the principle of the vacuum-assisted method and its technical realization. The proof of concept included the production and laboratory tests of different specimens, casted under normal and negative APC. The fine concrete's properties were determined in flexural and compression tests. Textile-reinforced concrete was analysed in tensile and bond tests as well as in bending trials on 2.7 m long shell elements. To summarize, it can be stated that the mechanical properties achieved were comparable, independent of the manufacturing conditions. The production quality of the shell elements was improved by concreting under negative APC. Finally, an outlook is given to further improve the method. [ABSTRACT FROM AUTHOR]

This study focuses on the development of novel evaluation methods for the analysis of thin carbon reinforced concrete (CRC) structures. CRC allows for the exploration of slender components and innovative construction techniques due to its high tensile strength. In this contribution, the authors have extended the analysis of CRC shells from existing research. The internal structure of CRC specimens was explored using microtomography. The rovings within the samples were segmented from the three-dimensional tomographic reconstructions using a 3D convolutional neural network with enhanced 3D data augmentation strategies and further analyzed using image-based techniques. The main contribution is the evaluation of the manufacturing precision and the simulation of the structural behavior by measuring the carbon grid positions inside the concrete. From the segmentations, surface point clouds were generated and then integrated into a multiscale framework using a parameterized representative volume element that captures the characteristic properties of the textile reinforcement. The procedure is presented using an example covering all necessary design steps from computed tomography to multiscale analysis. The framework is able to effectively evaluate novel construction methods and analyze the linear-elastic behavior of CRC shells. [ABSTRACT FROM AUTHOR]

The genome inside the eukaryotic cells is guarded by a unique shell structure, called the nuclear envelope (NE), made of lipid membranes. This structure has an ultra torus topology with thousands of torus-shaped holes that imparts the structure a high flexural stiffness. Inspired from this biological design, here we present a novel "torene" architecture to design lightweight shell structures with ultra-stiffness for engineering applications. We perform finite element analyses on classic benchmark problems to investigate the mechanics of torene shells. This study reveals that the torene shells can achieve one order of magnitude or higher flexural stiffness than traditional shells with the same amount of material. This novel geometric strategy opens new avenues to exploit additive manufacturing to design lightweight shell structures for extreme mechanical environments. [ABSTRACT FROM AUTHOR]

• Simultaneous shape and topology optimization of shell is achieved under the explicit framework. • Both structural geometry and topology of the shell can be described in an explicit way. • The obtained results can be seamlessly linked with CAD systems. In the present work, an investigation on the simultaneous shape and topology optimization of shell structures based upon the Moving Morphable Component (MMC) approach is performed. Unlike the problem that is often solved under the traditional implicit optimization methods, the proposed method is developed in a pure explicit way, which is helpful for the optimization and design of shell structures with complicated geometry. To achieve purpose, the geometric shape and topological form of general shell structure are respectively modeled by Non-Uniform Rational B-Splines (NURBS) in physical space and a series of components in parametric space. Resorting to the pure explicit description, the topology and shape of the shell can be optimized simultaneously with fewer design variables and the obtained results can also be seamlessly linked with CAD systems. Some numerical examples are provided to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This presents a mathematical model proposed by the author for description of deformation process of a shell structure under the action of a load that depends linearly on time. Material orthotropy, geometric nonlinearity, transverse shifts are taken into account. A distinctive feature of the model is the use of a refined discrete method for taking into account stiffeners, proposed by the author earlier. Prior to this, the method was used only in static or isotropic dynamic problems. It is proposed to add correction normalizing factors, which makes it possible to obtain the most accurate values of critical loads. The methodology of the calculation algorithm under dynamic loading is based on the Kantorovich method and the Rosenbrock method, which allows solving rigid ordinary differential equation (ODE) systems. New numerical results for cylindrical panels are obtained. The influence of the number of stiffening elements on the values of the critical load is shown. A comparison with the classical discrete method of taking into account stiffeners is carried out. For the problems considered in this paper, the phase portraits of the system are shown. [ABSTRACT FROM AUTHOR]

Even though computational design has paved the way for the design of complex forms, construction is still difficult, inefficient, and costly. This paper aims to compile the most recent fabrication techniques for shell structures to create an overview of fabrication methods. This paper reviews existing, recently developed, and previously unexplored techniques for building and fabricating shell structures. The objective of this review is to find trends, patterns, or gaps in the literature that can direct future research. As a result, each fabrication technique is explained and demonstrated with relevant built projects. Moreover, each method's advantages, disadvantages, and limitations are highlighted. These techniques are grouped into four main classes and evaluated. In conclusion, categorizing fabrication techniques reveals the state-of-the-art in fabrication and highlights potential research gaps. Moreover, this research might encourage researchers to explore novel methods and solutions to overcome the current method's limitations. • The state-of-the-art fabrication techniques for shell structures are presented. • A comprehensive, up-to-date literature review of fabrication methods is presented. • The methods of fabrication are classified in an exclusive manner. • The pros and cons of fabrication techniques are discussed. • This review highlights the current gaps in fabrication methods. [ABSTRACT FROM AUTHOR]

Concrete is the most widely used building material today. The enormous amount used goes hand in hand with high material consumption and CO2 emissions. Thus, building with concrete must be improved, becoming part of the solution on the way to climate-friendly building. Non-metallic fibres are an alternative to corrosion-sensitive steel reinforcement, and they enable the production of filigree, high-performance, structured components with low concrete cover. This article presents an alternative manufacturing method. Our thesis was that concreting under negative air pressure conditions (APC) allows the easy production of complicated, thin-walled geometries without defects or loss of mechanical properties. We firstly present the principle of the vacuum-assisted method and its technical realization. The proof of concept included the production and laboratory tests of different specimens, casted under normal and negative APC. The fine concrete’s properties were determined in flexural and compression tests. Textile-reinforced concrete was analysed in tensile and bond tests as well as in bending trials on 2.7 m long shell elements. To summarize, it can be stated that the mechanical properties achieved were comparable, independent of the manufacturing conditions. The production quality of the shell elements was improved by concreting under negative APC. Finally, an outlook is given to further improve the method.

Spline functions are a useful tool for modelling the shape of shell structures. They have curvature continuity that allows good approximation accuracy for various objects, including hyperboloid cooling towers, spherical domes, paraboloid bowls of radio telescopes, or many other types of smooth free surfaces. Spline models can be used to determine the displacement of structures based on point clouds from laser scanning or photogrammetry. The curvature continuity of splines may, however, cause local distortions in models that have edges. Edges may appear in point clouds where surface patches are joined, on surfaces equipped with additional technical infrastructure or with cracks and shifts in the structure. Taking the properties of spline functions into account, several characteristic types of edge configurations can be distinguished, which may, to a different extent, affect the values of modelling errors. The research conducted below was aimed at identifying such configurations based on theoretical considerations and then assessing their effect on the accuracy of modelling shell structures measured by laser scanning. It turned out to be possible to distinguish between edge configurations, based on the deviation values. [ABSTRACT FROM AUTHOR]

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This work presents an accurate and efficient numerical tool for geometrically nonlinear thermoelastic analyses of thin‐walled structures. The structure is discretized by an isogeometric solid‐shell model with an accurate approximation of geometry and kinematics avoiding the parameterization of finite rotations. An efficient modeling of thermal strains, temperature‐dependent materials and general temperature profiles based on a numerical pre‐integration through the shell thickness is proposed. Then, a generalized path‐following method is developed for solving the discrete equations with the temperature amplifier as additional unknown, in order to trace the temperature‐displacement nonlinear curve also in case of limit points and unstable paths. A consistent definition of the tangent operators and a mixed integration point strategy give a robust and efficient analysis. Finally, a reduction technique is derived for a quick estimate of the nonlinear thermal buckling point. The reduced model consists of the initial path tangent, the first linearized buckling modes and their second order corrections. Numerical applications are given. [ABSTRACT FROM AUTHOR]

This paper presents the evolution of and influence that the use of a triangular grid has had on the transformation of layered grid structures during the last two centuries. Historical facts, technological advances, economic and social crises among other factors influence the process of change and evolution of the grid systems in architecture to make construction processes more efficient by reducing the consumption of materials and qualified labor. Geometry and structure innovate styles and processes that are perfected over the years, achieving lighter and more stable structures. For the purpose of this paper historical data will be collected that allows the development of a theory that shows the influence of various periods based on technological advances. This research shows four historical periods in the evolution of layered grid structures. Being the triangular grid a widely used methodology in the construction of a diversity of geometric proposals and innovative construction systems for the solution of a diversity of buildings from the first domes built in the early 19th century to the free-form structures built from the late 20th century to the present day.

Lightweight structures made of thin sheet metal For many years, the use of steel in the construction industry was characterized by strict specifications regarding the semi‐finished products that could be used and often gave steel structures the character of "modular systems". The modernization of processing methods changed and improved these conditions. In the digital era, it is now possible to create a process chain not only on the production end, but also on the design, presentation, planning and construction end, with the support of which highly individualized steel components can be produced, which in return form part of individualized structures. With these means, lightweight sheet metal structures with individual design can be created, as impressively demonstrated by two prototypes that were created at RWTH Aachen University in cooperation between the Chair of Structures and Structural Design and the Institute of Metal Forming. The novel construction method using thin sheet metal opens up a canon of shapes that was previously rather inaccessible to steel construction and proves to be extremely material saving, thus being in line with the trend of sustainable construction of our time. [ABSTRACT FROM AUTHOR]

The digital paradigm requires efficient methods of teaching CAAD tools in architecture schools. With the trend of enhancing the design process with parametric methods, linking architecture with other knowledge areas, such as mathematics, is gaining in importance. Equipping future architects with skills in algorithmic thinking is yet another challenge for education. This paper describes the workflow of an early-stage course addressing this challenge, conducted at the Warsaw University of Technology's Faculty of Architecture. The course focuses on the students' ability to construct complex geometric forms in the digital environment by introducing an extensive analytic phase. The students study the geometric foundations of real-world architectural cases and translate them into parametric models. Later, they explore the potential of the generated solutions space. The results compare the course's teaching efficiency with the outcomes of past courses covering similar subjects. [ABSTRACT FROM AUTHOR]

In the field of structural deformation monitoring, the inverse finite element method (iFEM) has significant engineering value as a structural health monitoring technique that provides timely and reliable warnings for shell structures. However, existing inverse finite elements are mainly based on first-order shear deformation theory and kirchhoff–love theory, which are not suitable for deformation reconstruction in plate and shell structures of arbitrary thickness. This study integrates iFEM with the Mixed Interpolation of Tensorial Components (MITC) method to develop a novel four-node quadrilateral inverse curved shell element, named iMICS(inverse Mixed Interpolation Curved Shell)4, aimed at enhancing the accuracy and efficiency of deformation reconstruction in complex plate and shell structures. The method uses the MITC4 shell element as the kinematic framework and applies the least squares variational principle to achieve deformation reconstruction, effectively alleviating shear and membrane locking issues across structures of varying thickness. Numerical examples validate the superior performance of the iMICS4 element, demonstrating its promising application prospects. • Developed a novel iMICS4 method for deformation reconstruction of plate and shell structures. • The iMICS4 element effectively mitigates shear and membrane locking issues in deformation reconstruction. • The iMICS4 method is applicable for deformation reconstruction of plate and shell structures with arbitrary. [ABSTRACT FROM AUTHOR]

• The average displacement state-based hourglass force is adopted to eliminate zero-energy mode. • The convergence of numerical simulation of fracture is improved based on the non-local GTN model. • Crack propagation under penetration loads is accurately simulated by a multi-crack visualization algorithm. A meshfree method is developed based on the peridynamic differential operator (PDDO) for ductile damage and fracture problems in metal shell structures. The kinematic equations coupled to classical continuum mechanics (CCM) are derived with the motion variables discretized by the PDDO. The elastoplastic and fracture behavior of the material are described by applying the Gurson-Tvergaard-Needleman (GTN) model with shear modification, and the non-local form of the model improves the computational convergence for different modeling scales. The zero-energy model in numerical computations is effectively controlled by introducing an hourglass force based on the average displacement state. The particles contact algorithm and multi-crack visualization algorithm are developed to simulate the fracture of shell structures under collision loads. By comparing with experiments, it is verified that the proposed PDDO-based meshfree method can accurately predict the ductile fracture of shell structures subjected to in-plane and out-of-plane loads. [ABSTRACT FROM AUTHOR]

The static and dynamic behavior of a horizontal cylindrical shell (as used to store fuels in tanks) is investigated in this work by means of computational modeling. Under a distributed pressure commonly used to model effects due to explosions, the geometrically nonlinear behavior is explored to identify bifurcation and limit points along the static equilibrium path, and the associated displacements. Critical load reductions due to imperfections are found in the order of 25%. The dynamic analysis is next presented to identify the possibility of reaching a quasi-bifurcation. It is found that the first peak in the transient response at which the displacement reaches the same value as in the limit static case occurs for a load which is about 3.5 times the static bifurcation load. The velocity is zero at this state and is identified as a quasi-bifurcation, at which the shell is expected to display a static instability. Imperfection-sensitivity of the quasi-bifurcation load is found to be of the same order as the static one. This is the first quasi-bifurcation study of a shell to identify dynamic buckling due to a nearby explosion.

The parametrization of shell structures using the so-called solid shell concept has been widely exploited in the last decades. This trend is mainly attributed to the relatively simple kinematic treatment of solid shells in the corresponding finite element formulation in conjunction with the use of unmodified three-dimensional material laws, among other aspects. In the present investigation, we provide a comprehensive finite element implementation of solid shells incorporating: (i) the use of Enhanced Assumed Strain (EAS) and the Assumed Natural Strain (ANS) methods to prevent locking issues, (ii) the phase-field approach for triggering fracture events, and (iii) some representative inelastic material models. The current modular implementation has been integrated into the FE package ABAQUS via the user-defined routine UEL. Several representative examples demonstrate the applicability of the present formulation. • Application of solid shell theory for parametrization of shell structures for fracture response. • Enhanced Assumed Strain (EAS) and Assumed Natural Strain (ANS) to tackle locking. • Study of three representative inelastic material models for comprehensive analysis. • Innovative implementation of phase-field approach for triggering fracture events. [ABSTRACT FROM AUTHOR]

Metamaterials refer to a class of materials with special properties, whose characteristics mainly come from the microstructures designed artificially. Among them, those metamaterials with tunable shape and mechanical properties under external stimuli provide a new inspiration for the design of the multifunctional structures. This work deals with the three-dimensional (3D) compression-twist lattice metamaterials, studies the surface reconfigurability under external forces, and reveals the torsion-bending coupling (TBC) effect of the special metamaterials. To explain the main characteristics of the TBC effect, the deformation mechanism of the metamaterials is analyzed. Combining the finite element method (FEM) and the spherical fitting algorithm, the relationship between the bending angle and the load of the metamaterials after deformation is analyzed and verified by experiments. Finally, a metamaterial module that could be freely transformed between planar and spherical surfaces is envisaged. A faster and greener solution is proposed for the construction of curved surfaces of engineering structures in the future, which promotes the subsequent applications of metamaterials to engineering practice. [ABSTRACT FROM AUTHOR]

This paper presents a literature compendium about the main studies on the structural behavior, vulnerability, and risk of industrial silos, as one of the most important players of different industrial processes. This study focuses on the main scientific works developed in the last decades, highlighting the more notable issues on circular steel silos as the most widespread typology in practice, such as the content–container complicated interaction, the structural and seismic response, and the several uncertainties in the design and assessment processes. Specifically, this paper proposes a near-full state-of-the-art on (i) the behavior of silos under different kinds of loads, ordinary and extreme, (ii) the effects of imperfections and the interacting structures (e.g., ring beams, supporting structures), (iii) the stored material properties, the relevant uncertainties and the impact on the silo behavior, (iv) the possible failure modes given by the focused structural configuration and the stored materials, and (v) assessment and risk mitigation strategies. Throughout the text, some considerations are provided in order to summarize the more recent research trends about steel silos and to highlight the still open issues on the risk and vulnerability reduction of these kinds of structures. [ABSTRACT FROM AUTHOR]