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• Structure design and DOF analysis of deployable unit. • Selection of actuation and identification of deployment continuity. • Surface fitting based on the hexagonal frustum unit. • Dividing analysis of antenna surface and verification of networking feasibility. • Prototype and deployment experiment were conducted to verify the mobility. With the development of space technology, deployable mechanism has been widely applied in large aperture space antennas. In this paper, a hexagonal frustum deployable antenna unit and an innovative modular assembling concept are proposed for large parabolic truss antenna. Screw topology diagram and screw constraint matrix are established to solve degree of freedom (DOF) of the antenna mechanism. By separating column vectors of screw constraint matrix, whole actuations of antenna mechanism are obtained according to unique solution condition. A new hexagon antenna network method based on hexagon frustum units and rotation transformation matrix is proposed, and correctness and efficiency of the modeling principle are proved by simulation. Finally, a prototype of the proposed hexagonal frustum truss deployable antenna mechanism is constructed, and a deployment experiment is conducted, which demonstrate the mobility and deployment performance of the mechanism. The mechanism proposed in this paper provides a theoretical reference for the parabolic truss deployable antenna mechanism, which is potentially valuable in the application of large aperture deployable antennas. [ABSTRACT FROM AUTHOR]

• A kind of laminated acoustic metamaterials for low-frequency broadband ultra-strong sound insulation is proposed. • The parallel coupling of in-plane gradient parameters and the series laminated in the thickness direction achieve bandwidth widening and amplitude improvement. • The working mechanisms of non-uniform mass distribution and non-consistent frame coupling are studied. • The efficient semi-analytical method based on dynamic surface mass density is successfully extended from periodic plate phonon crystal structures to frame-plate-mass type structures. In this paper, a kind of laminated acoustic metamaterials (LAMS), which can realize the bandwidth widening and amplitude improvement through the parallel coupling of in-plane gradient parameters and the series laminated design in the thickness direction of the local resonance units, is proposed. The designed LAMS consists of two different layers of single-layer acoustic metamaterials (SLAMs) laminated in series in the thickness direction. During the design process of the two layers of SLAMs, non-uniform mass distribution and non-consistent frame coupling layouts are respectively introduced to broaden the sound insulation frequency band of the acoustic metamaterials. Through careful design, the two layers of SLAMs have distinct working frequency bands, effectively preventing the occurrence of sound insulation valleys with low amplitude. Based on numerical analysis of two layers of SLAMs, this study discusses the results of transmission loss (TL) and the working mechanism of interlayer superposition coupling sound insulation. The analysis of TL for LAMS reveals its capability to achieve ultra-strong sound insulation effects across a low-frequency broadband range. The accuracy of the numerical analysis in this study is verified through semi-analytical methods and small-scale impedance tube experiments. The LAMS proposed in this paper holds significant potential for wide-band noise reduction control in various high-noise mechanical equipment or workplaces. [ABSTRACT FROM AUTHOR]

• The results of reference literature tests on tubular joints are summarized. • FE models are built and validated against the experiments. • Parametric studies examining a wide range of geometrical properties are performed. • A novel stiffness formulation for T-joints with CHS chord and branch-plate is provided. • A component model for stiffness and plastic strength of joints with CHS column and double-tee beam is suggested and verified. This paper focuses on predicting the flexural stiffness and strength of beam-to-column joints with Circular-Hollow-Section (CHS) columns and externally welded double-tee beams using the Component Method approach. Currently, Eurocode 3 Part 1.8 lacks guidelines for assessing the stiffness of these joints, resulting in their practical modelling using extreme assumptions like pin or full restraint. Nevertheless, the literature demonstrates that these joints can exhibit semi-rigid behaviour due to the relatively high local deformability of the tube in the joint area. Another concern relates to the strength of these joints. In fact, recent studies have shown that Eurocode 3 Part 1.8 formula for predicting the yield resistance of these joints is over-conservative. Within this framework, the purpose of this study is to fill the current knowledge gaps (over-conservative strength prediction and lack of rules for determining the stiffness) by undertaking a thorough investigation involving numerical and analytical activities. Specifically, the research presents a component-based modelling approach for predicting stiffness and strength of CHS to double-tee beam connections. In this regard, the work presented in this paper has involved the selection of experimental tests from literature to validate a Finite Element (FE) model, specifically focusing on X- and T-joints and internal and external beam-to-column joints. The validated numerical models have been then employed to simulate the response under monotonic loading conditions of additional sets comprising forty T-joints and thirty external beam-to-column joints, respectively. The currently available formulations for predicting the resistance of T-joints were applied to the forty cases simulated, evaluating their accuracy. This allowed the individuation of the most accurate literature formula for the strength prediction of T-joints, showing that the recent proposal of Voth and Packer (2012) yields sufficiently accurate results. Instead, analytical formulations for predicting the stiffness of T-joints were properly derived in a closed-form solution and were validated against the results of the parametric study. Finally, drawing upon knowledge regarding the stiffness and strength of T-joints, the flexural response of external beam-to-columns connections was evaluated proposing a component model, whose accuracy was verified against the cases simulated in the parametric analysis. [ABSTRACT FROM AUTHOR]

• The proposed model only places the PD subdomain in the crack initiation region of porous material, which greatly improves the computational efficiency while ensuring the calculation accuracy. • The displacement vector and mass matrix are reconfigured to ensure the calculation consistency in the process of adaptive expansion of the PD subdomains. • The fracture phenomenon of porous materials based on this model is well reproduced and interesting results are obtained. Predicting the dynamic failure process of porous materials is a challenging task due to their complex structure. To minimize the use of time-consuming peridynamic (PD) models and to avoid surface effect issues in the dynamic failure of complex porous materials, this paper proposes a strength-induced PD model. The paper first presents the dynamic formula and relevant finite element discrete equation of the coupled PD and classical continuum mechanics (PD-CCM) model based on the Morphing method. The Morphing function is implemented to control the material parameters and enable the free transformation of PD and CCM models. Based on the coupled PD-CCM model, the strength-induced PD model is established to adaptively expand the PD subdomain in porous materials by controlling the Morphing function value through the strength state of the structure. This model enables the PD subdomain to appear automatically when the porous materials reach the critical stress state. The proposed model accurately predicts the location of crack initiation and path while minimizing computational costs and improving efficiency. Three two-dimensional numerical examples are used to verify the effectiveness, efficiency, and accuracy of the model. The results of the simulation suggest that the location where the crack initiates in the porous materials is strongly influenced by the amplitude of the dynamic load. Cracking is dependent on the pores and typically occurs through them. [ABSTRACT FROM AUTHOR]

• Compressive failure behaviors of stepped-scarf repaired composite honeycomb sandwich panels are analyzed experimentally and numerically. • Progressive failure analysis model, cohesive zone model and sandwich plate theory are utilized in the numerical models. • Failure modes of composite facesheets, adhesive film and honeycomb core are revealed. • Influence of repair parameters on the repair performance of composite honeycomb sandwich panels is investigated. Composite honeycomb sandwich panels (CHSPs) have been widely used in the aerospace industry owing to their lightweight and superior mechanical properties. However, these CHSPs are susceptible to impact damage, leading to a significant reduction in compressive strength and potentially jeopardize aircraft safety. It is crucial to investigate repair methods for CHSPs with impact damage. This paper aims to evaluate the repair performance of CHSPs with impact damage through an analysis of their compressive failure behaviors. To accomplish this, both experimental tests and advanced numerical models are employed. The numerical models for the intact, damaged and stepped-scarf repaired CHSPs are established using the progressive failure analysis model, cohesive zone model and sandwich plate theory. A good agreement is observed between the experimental results and numerical predictions of compressive failure behaviors. Moreover, the validated numerical models are successfully utilized for determining optimum repair parameters by parametric analysis of the repaired CHSPs. The establishment of these numerical models offers an accurate and cost-effective evaluation of repair performance for CHSPs with impact damage, highlighting the novelty and main contribution of this paper. [ABSTRACT FROM AUTHOR]

• CEL approach is employed to simulate the fluid-structure interaction. • CDP model considering the strain rate effect is adopted to this paper. • Damage evolution of prestressed thin-walled aqueducts to UNDEX. • The influence of the prestress on the dynamic response of aqueducts to UNDEX. To solve the problem of regional water resource shortage, water diversion projects have been built around the world. As an essential lifeline project, the prestressed aqueduct is commonly used in cross-regional water transfer and diversion projects. However, the prestressed aqueduct is inclined to damage and collapse under explosion loading due to its thin structure. The main purpose of this paper is to investigate the nonlinear dynamic performance and failure modes of the large prestressed U-shaped thin shell aqueduct to underwater contact explosion. The prestress application approach is validated by theoretical calculations. The reliability of the analysis method of underwater contact explosion for reinforced concrete structures is verified by the underwater contact explosion test. Damage cracking process and nonlinear dynamic response characteristics of prestressed aqueducts to the underwater contact explosion with different explosive weights are performed. Blast resistance performances of prestressed aqueducts are discussed in terms of the crack length, residual displacement, and prestressing force loss. The influence of prestress level on the damage modes of the prestressed aqueduct under the blast loading is discussed. The results indicate that thin-walled U-shaped structures are extremely vulnerable to localized damage from underwater contact explosions. The blast-resistance performance of the U-shaped thin shell aqueduct can be significantly improved by applying prestress. [ABSTRACT FROM AUTHOR]

• Both the uncertainties in elastic modulus and Poisson's ratio are firstly considered. • Multiple materials can be freely allocated during the optimization. • A non-intrusive method is adopted to quantify material uncertainties. • Multi-material structures possess smooth and clear boundaries. Multi-material structures have attracted more and more attention from scholars and engineers, because they usually have good composite performance. Uncertainty factors are ubiquitous in practice, especially for material uncertainties. Multi-material structures contain many materials with different properties, material uncertainties will affect the allocation of material usage, thereby affecting structural performance. Therefore, it is crucial to consider material uncertainties in the design of multi-material structures. This paper detailedly explores the impacts of elastic modulus uncertainty and Poisson's ratio uncertainty on the design of multi-material structures. The topology optimization is to minimize the compliance subjected to a mass constraint, where multiple materials can be freely allocated during the optimization. Floating projection topology optimization is adopted to search for the structural topologies, and robust sensitivity information is derived. For the quantification of material uncertainties, this paper introduces a non-intrusive polynomial chaos expansion (PCE) method to implicitly quantify them, the computational efficiency and accuracy in PCE is compared with the classical Monte Carlo method. Finally, topology optimization examples are provided to demonstrate the effects of elastic modulus uncertainty, Poisson's ratio uncertainty and hybrid uncertainty on the design of multi-material structures. [ABSTRACT FROM AUTHOR]

• The paper investigates rib-based reinforcement strategies for improving structural integrity of form-found shell structures. • The study introduces diverse stiffening patterns for shell structures, designed with geometric, biomimetic, and optimization-derived methodologies. • The paper demonstrates through mechanical testing and numerical simulations that these patterns significantly improve stiffness and buckling resistance of form-found shells. • The study validates that integrating form-finding with targeted rib-based reinforcements can lead to sustainable and structurally resilient solutions. This paper investigates innovative approaches for enhancing the structural integrity of form-found shell structures with a focus on rib-based reinforcements. It discusses the significance of ribs in enhancing stability and addressing the sensitivity of form-found structures to various loads. Traditional methods such as increasing shell thickness or introducing supports often compromise efficiency and aesthetics. A more intelligent approach involves reinforcing the shell with ribs and advanced materials. Diverse rib patterns are presented, including geometric, biomimetic, and topological optimization-inspired designs, each adhering to a 50 % volume constraint, when compared to the original shell. Physical testing and numerical simulations demonstrate that these rib patterns significantly increase stiffness and buckling resistance. The findings presented in the paper suggest that combining form-finding methodologies with well-designed rib patterns can create sustainable and resilient structures, contributing to a reduction in both the consumption of materials and the environmental impact of these structures. [ABSTRACT FROM AUTHOR]

• Cyclic tests on T-joints with CHS chord and passing-through plate are presented. • A FE model of the connection is built and validated against the experiments. • Parametric studies examining a wide range of geometrical properties are performed. • A GA tool is used to fit the simulated data with a phenomenological model. • A model predicting cyclic response from connection geometry is validated. This paper focuses on modelling the cyclic response of welded T-joints between Circular-Hollow-Section (CHS) chords and passing-through plates. Recent works have highlighted that, in practical applications, this specific joint typology can be regarded either as a standalone connection or as a component representing one of the main sources of deformability and energy dissipation capacity in more complex beam-to-column joints with CHS columns and passing-through I-beams. Currently, research efforts have primarily focused on predicting the strength and stiffness of this type of connection. However, there is a knowledge gap regarding the characterization of the cyclic response of joints with passing-through members, a crucial aspect for modelling steel structures with these connection types in seismic areas. In light of this, the paper aims to characterize the cyclic response of T-joints with CHS members and passing-through plates using a comprehensive approach that incorporates experimental, numerical, and analytical methods. Initially, the results of an experimental study examining the cyclic behaviour of T-joint specimens with passing-through plates are presented. Subsequently, models of the tested joints are implemented in Finite Element software and validated against the experimental outcomes. The validated models are used to conduct a parametric study, considering 44 different configurations to obtain their force-displacement cyclic responses. These responses are mathematically modelled using the hysteretic uniaxial material from the OpenSees library and a Genetic Algorithm based tool previously developed by the authors (MultiCal). Finally, regression analyses are performed to develop formulations for predicting the mathematical parameters of the hysteretic uniaxial material model starting directly from the geometrical and mechanical properties of the connection. This approach enables designers to model the cyclic response in structural analysis with a straightforward approach, without the need for new calibrations or tests, if the modelled joints fall within the proposed range of calibration. From the point of view of the component modelling, the approach presented aligns with the larger research strand devoted to the extension of the component method codified in Eurocode 3 part 1.8 to cyclic loading conditions. [ABSTRACT FROM AUTHOR]

Thin films may experience wrinkling instability when two clamped ends are stretched uniaxially. For a fiber-reinforced anisotropic thin film, the wrinkling distributions and evolutions can be significantly affected by the fiber orientation and the anisotropic parameters. In this paper, we study the stretch-induced wrinkling of anisotropic thin films based on a uniformly-valid asymptotic plate equation for anisotropic materials derived from the three-dimensional field equations. A numerical model is established in COMSOL Multiphysics by virtue of the weak form of plate equations and by employing the Holzapfel–Gasser–Ogden model. The effects of fiber orientations and anisotropic parameters on wrinkling evolutions are unraveled from various case studies. In particular, we find that there exists a critical fiber orientation interval where the usual isola-center bifurcation will give way to the pitchfork bifurcation, and the associated amplitude against strain curve presents an N shape. A phase diagram for different bifurcation types is characterized as well. Our numerical model is validated by three-dimensional numerical simulations. It is expected that the results in this paper will offer useful insight into pattern formation in anisotropic soft materials. • The wrinkling responses of anisotropic parameters and fiber orientation are analyzed. • Stretch-induced wrinkling could be an N-shaped pitchfork bifurcation. • A phase diagram for different bifurcation types is provided. • The numerical model is validated by 3D numerical simulations. [ABSTRACT FROM AUTHOR]

• A series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • The observed failure modes are flexural, flexural-torsional and local-global interaction buckling failure modes. • The experimental results are compared with predictions by current Australian/New Zealand, North American and European design specifications. Cold-rolled aluminium alloy sections have been recently introduced in Australia as newly developed thin-walled products. To fabricate these sections, the roll-forming process used in cold-formed steel production has been employed, which has proven to be more cost-effective than the conventional extrusion process. This paper describes a series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy 5052-36 channel columns. Twenty-eight specimens of three commercially available sections (C10030, C25025 and C40030) were tested at the University of Sydney. Two configurations of end boundary conditions were specially designed to capture flexural, flexural-torsional and local-global interaction buckling failure modes. Prior to testing, initial geometric imperfections were measured using a laser scanning method, and flat/corner coupons were tested to determine compressive and tensile strengths of the aluminium alloy material. The experimental results are compared with ultimate column strength predictions by current Australian/New Zealand, North American and European design specifications for aluminium structures. Additionally, the test results provide data for calibration of finite element models of cold-rolled aluminium structural members for use in parametric and similar studies. A companion paper describes such parametric study and the derivation of new design guidelines for member buckling of cold-rolled aluminium channel columns based on the numerical parametric data and the experimental data presented herein. [ABSTRACT FROM AUTHOR]

• Experiments on the member buckling and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • Non-linear FE models are developed using ABAQUS to simulate laboratory experiments and calibrated against the test results. • A parametric study based on FE models is performed to extend the data by varying cross-section dimensions and member lengths. • Experimental and numerical results are ued to calibrate the new design equations for cold-rolled aluminium alloy columns. The paper first presents the development of detailed finite element (FE) models for investigating the member capacity of cold-rolled aluminium alloy 5052-36 channel columns. The numerical non-linear FE models are developed using the commercial FE software package ABAQUS to simulate laboratory experiments and calibrated against the test results. The experimental program was performed by the authors at the University of Sydney and the detailed test results are fully described in a companion paper. The calibrated numerical FE models with actual mechanical properties and measured geometric imperfections in analyses accurately predict the experimental results and behaviours, including flexural and flexural-torsional buckling as well as local-global interaction buckling failure modes. A parametric study is subsequently performed to extend the data range by varying cross-section dimensions and member lengths. The effects of loading eccentricity positions and initial geometric imperfections are also considered in the parametric study. The experimental and numerical results are compared with design strength predictions from current Australian/New Zealand, American and European specifications for aluminium structures in the companion paper. In this paper, the Direct Strength Method (DSM) for the design of compression members as per the Australian/New Zealand standard AS/NZS 4600 for cold-formed steel structures is adopted for comparison. The DSM design rules for cold-formed steel compression members are found to provide more accurate predictions than those of current specifications for aluminium structures and therefore used to propose improved design equations for cold-rolled aluminium alloy columns. Finally, a reliability analysis is performed to evaluate the safety level of current design specifications and the proposed design rules. [ABSTRACT FROM AUTHOR]

The paper is devoted to the analysis of the influence of ambient temperature on the linear free and non-linear harmonic vibrations of laminate plates with viscoelastic layers. The Zener fractional material model is adopted. The plate kinematics is described using the refined zig-zag theory. The formulation of vibrations of the plate is based on the physical law with the separation of deviatoric and volumetric deformation. The temperature influence is included using the frequency-temperature superposition principle. The shift factor applied to modify the damping properties of the viscoelastic material is computed using the Willams-Landel-Ferry formula. The paper contains the results of several analyses of laminate plates with various viscoelastic materials for which the material data were available in the literature. In particular, the analyses focus on determination of the properties characteristic for the plates with Zener fractional model under the influence of the ambient temperature. • Frequency-temperature superposition for temperature influence on plates vibrations • Refined zig-zag theory applied to define the plate kinematics • Fractional Zener material with separated volumetric and deviatoric deformation • Numerous analyses of various viscoelastic materials • Explanation of non-monotonous character of temperature effects on damping [ABSTRACT FROM AUTHOR]

• Phononic crystals, elastic metamaterials, ABHs and elastic metasurfaces are considered. • The principles of suppressing vibration and sound radiation by these artificial structures are introduced. • The advances in suppressing vibration and sound radiation by wave manipulation are reviewed. • The further works of suppressing vibration and sound radiation by wave manipulation are prospected. The newly generated artificial structures, including phononic crystals, elastic metamaterials, acoustic black holes (ABHs) and elastic metasurfaces, can abnormally control wave propagations. In this paper, focusing on plate structures and from the perspective of the suppression of vibration and especially sound radiation by manipulating flexural waves, we give a thorough review of the advances of above-mentioned artificial structures, involving their extraordinary characteristics, corresponding mechanisms of vibration and sound radiation suppression, design methods of phase-gradient elastic metasurfaces, and some representative works on suppressing vibration and sound radiation of plates by flexural wave manipulations. Additionally, we compare the advantages and disadvantages of these artificial structures in vibration and sound radiation suppression. Finally, we look forward to the prospects on vibration and sound radiation suppression of plates based on wave manipulations. This paper will provide a timely and practical assistance to academic and technical researchers in the field of vibration and noise reduction. [ABSTRACT FROM AUTHOR]

• Twelve rack-to-spine-bracing shear connections were experimentally investigated. • Comprehensive test data were generated using digital image correlation technique. • A component-based analytical model is established for the shear connections. • Three-dimensional behavior of individual components are analytically determined. • Design and construction recommendations for the shear connections are provided. High-rise steel storage racks are cold-formed thin-walled steel frames, which achieve their lateral strength and stiffness by the use of a spine bracing system in the down-aisle direction commonly located at a short horizontal distance away from the main rack frames. The shear connections between the main rack frame and the spine bracing system play a dominant role in the effectiveness of the spine bracing system. This paper experimentally investigates the behavior of the shear connections used in industrial practice between a steel storage rack and the spine bracing system with posts using four groups of three nominally identical connection specimens. By employing a digital image correlation (DIC) system, the tests generate comprehensive data and establish the real-time deformation fields of individual components of such shear connections. Based on the component-based approach, a linear-elastic analytical model is developed for the type of shear connections under consideration. The proposed analytical model explicitly captures the behavior of the individual connection components, including the three-dimensional flexural bending of endplates, as well as the distortions of the open sections of the upright and the bracing post. Based on the proposed model, this paper quantifies the contribution of each component towards the total deformation of the shear connections. The investigation establishes that the cross-sectional distortion of the bracing post and the out-of-plane bending of the upright web are the most flexible components of such shear connections. Recommendations associated with the shear connections under consideration are proposed for the rack designers and manufacturers. [ABSTRACT FROM AUTHOR]

• A novel general semi-analytical dynamic model for the bolted composite flanged cylindrical-cylindrical shell structure under arbitrary connection conditions is established. • The free vibration characteristics of locally loose structures are emphatically studied. • A spring surface model for the bolted joint and the corresponding parameter determination method based on fractal contact theory is developed. • Plenty of comparisons with the modal test results of the structure under different working conditions fully prove the accuracy of the model. • The influence of the number and degree of loosening bolts on the free vibration characteristics of the structure and the coupling phenomenon between different modes are discussed. The bolted composite coupled cylindrical shell is a common substructure in modern engineering, which may encounter the issue of local loosening conditions during service. Meanwhile, the influence of flanges on the structural vibration characteristics is often overlooked in dynamic numerical analysis. In this paper, a semi-analytical dynamic model for the bolted composite flanged cylindrical-cylindrical shell structure under arbitrary connection conditions is established, and the free vibration characteristics of locally loose structures are emphatically studied. In the model, the annular plate modeling method is developed to achieve the simulation of the flange part. To fully reflect the connection characteristics of the bolted joint, a spring surface model and the corresponding parameter determination method based on fractal contact theory are developed. The equations of motion of the structure are obtained utilizing the Lagrange equations. The accuracy of the model and its predictive ability for the vibration characteristics of the bolted composite flanged cylindrical-cylindrical shell under local loosening conditions are fully demonstrated through numerous comparisons with experimental results from other literature and modal test results obtained under various working conditions. Furthermore, the influence of the number and degree of loosening bolts on the free vibration characteristics of the structure and the coupling phenomenon between different modes are discussed. The research in this paper is expected to provide references for the design of bolted composite flanged cylindrical shell structures and the monitoring of bolt connection defects. [ABSTRACT FROM AUTHOR]

• Experimental tests of CFDSST columns is presented in detail in this paper. • Using ABAQUS, 3D finite element CFFSST column models under axial compression are developed. • The fundamental behaviour of the CFDSST columns is discussed in detail. • The feasibility of current design codes to design the CFDSST columns is evaluated. • The proposed design model is shown to predict well the strengths of CFDSST columns. This paper explores the performance of concrete-filled double-skin (square stiffened hollow sections (SHS) outer and circular hollow sections (CHS) inner) steel tubular (CFDSST) stub columns under axial compression through experimental research and finite element analysis. The static axial compression experiments of six concrete-filled stiffened steel tubular (CFST) stub columns and fifteen CFDSST stub columns were conducted. The test method, process, phenomena and results are introduced in detail. The results indicated that compared with conventional CFST stub columns, CFDSST stub columns with reasonable hollow ratio can maintain load-carrying capacity, increase ductility and reduce self-weight. Increasing the strength of concrete is the most effective way to increase the load-carrying capacities of specimens when other variables remain constant. Finite element (FE) software was then utilised to generate the models of current specimens. The simulation results showed reasonableness and accuracy compared to the experimental results. Based on the validated models, parameter analysis was performed to reveal the influence of concrete strength, width-to-thickness ratio of the outer steel tube, stiffener depth, hollow ratio and yield strength of the outer steel tube on the ultimate strengths of the specimens. In addition, compared with test and FE strengths, the ultimate strengths predicted by available international codes were found to be quite conservative. Consequently, a formula was proposed to predict the load-carrying capacity of CFDSST stub columns considering the effective cross-sectional areas of the outer steel tubes and the strength of the confined concrete. The formula has been shown to provide the best prediction with acceptable reliability. [ABSTRACT FROM AUTHOR]

• The paper deals with ultimate of thin-walled, open cross section PC beams. • An approach to determine the interaction diagrams for axial force, bending and torsion is suggested. • The limits of this method are described. • Some examples show the effectiveness of this approach. Thin-walled, open cross section PC (prestressed concrete) beams are widely used in precast structures. Nevertheless, the analytical computation of their load carrying capacity under bending and torsion is still an unsolved problem. This is because of the markedly non-linear behaviour of both steel and concrete and of the asymmetry of the behaviour of concrete in tension and compression. This involves a search for the correct solution from a physical point of view (among those mathematically admissible) based on trial-and-error methods of numerical analysis. This paper suggests a method to evaluate the interaction diagrams under bending and torsion. According to this method the solving system is made by two equilibrium plus two compatibility equations. Some examples show the outcomes of this approach. [ABSTRACT FROM AUTHOR]

• A vertically oriented double corrugated steel plate shear wall is proposed. • The elastic buckling behavior of the wall is affected by the bolt spacing. • The compressive and shear stability coefficients are established. • The stability of the wall affects the correlation curve of N/N u - V / V u. As a novel structural component, the Double Corrugated Steel Plate Shear Wall (DCSPSW) is formed by interlocking two corrugated steel plates using high-strength bolts. This paper investigates the global stability design methods for DCSPSWs under combined shear and compression loads. Firstly, this paper examines the elastic buckling performance of DCSPSWs under horizontal shear loads and vertical compression loads separately. A bolt spacing factor (η) is introduced to reflect the influence of bolt spacing on the elastic buckling stress of DCSPSWs. Then, based on extensive finite element analysis (FEA), this paper investigates the elastoplastic buckling behavior of DCSPSWs under shear loads and compression loads and establishes the corresponding stability curves to predict ultimate load-bearing capacity. It is found that the stability coefficients (φ s and φ c) are closely related to the normalized slenderness ratios (λ ns and λ nc). A smaller bolt spacing allows the DCSPSWs to exhibit improved elastic and elastoplastic stability. Finally, this study investigates the load-bearing performance of DCSPSWs under combined shear and compression loads and proposes the design formulas. The results show that the correlation curve of N / N u - V / V u can provide a conservative and accurate design. The research findings of this paper are advantageous for promoting the application of the innovative DCSPSWs. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel combined rivet structure, including a conventional tubular outer rivet and an inner rivet with an outer flange, is proposed. • The effect of new rivet structure on strength improvement and its underlying mechanism is studied. • The joint failure behavior and failure modes of in DSSPR process using the combined rivets are analyzed. Double-sided self-pierce riveting (DSSPR) has great application potential in joining the same or dissimilar sheets due to its simplified die structure, high joining efficiency, and smooth joint surface. Previous studies have shown that changing rivet parameters, such as chamfered angle position, can improve joining strength, but the improvement effect is still relatively limited. In this paper, to significantly enhance the joining strength, a novel combined rivet structure was proposed and used in the DSSPR process of Al5052 sheets, and its effect on strength improvement and the underlying mechanism were investigated. Morphological change, strain, and stress distribution of the combined rivets during the joining process were investigated through experiments and numerical simulations. Tensile shear tests were conducted to compare the shear strength of the combined rivets and conventional rivets. Moreover, the failure behaviors of joints including macroscopic failure mode and microscopic surface morphology were analyzed, and the mechanism for combined rivets to enhance the joining strength was illustrated. Results showed that adopting the new combined rivets can significantly improve joint strength. Compared with a single conventional tubular rivet, the tensile shear strength and energy absorption of combined rivets can increase by up to 91% and 261%, respectively. Two types of failure modes were discovered according to the failure behaviors of sheets, which were characterized by the detachment of rivets and the tearing characteristics of the sheet. This paper provides a new approach for the rivet design and joining strength improvement strategy for the DSSPR process. [Display omitted] [ABSTRACT FROM AUTHOR]

• The low-restraint GLARE is taken as a research object and its deformation characteristics and failure mode are studied using uniaxial tensile, bending experiments and numerical simulation in this paper. • Based on experimental observations, it is found that the low-restraint GLARE produces the phenomenon of interlayer slip, and the interlaminar residual stress is much smaller than the cured laminate, whereas the deformation limit and performance are improved. • The results of bending experiments revealed that the load variation of low-restraint laminate is significantly different from the cured laminate during bending. • The low-restraint GLARE does not obviously delaminate and fracture during bending due to the low interlayer residual stress and a certain degree of interlayer slipping, exhibiting a significant improvement in the bending forming limit. • This paper provides theoretical bases for the in-depth analysis of deformation properties and forming laws of low-restraint GLARE, guiding further applications of laminates. Fiber metal laminates (FMLs) possess a better weight reduction effect than traditional metal materials due to the coupling properties of heterogeneous materials, showing promise in the areas of aviation and aerospace. At present, the research on FMLs mainly focuses on the deformation properties after curing while the mechanical properties in the low-restraint state, i.e. the laminates are temporarily not cured and are formed under lower constraint stresses, are not studied in detail. Herein, the low-restraint GLARE is taken as a research object and its deformation characteristics and failure mode are studied using uniaxial tensile, bending experiments and numerical simulation in this paper. Moreover, the influence of key parameters, such as temperature, laminate structure and span length, is investigated, as well as the tensile and bending deformation behavior of GLARE in a low-restraint state is obtained. In addition, based on experimental observations, it is found that the low-restraint GLARE produces the phenomenon of interlayer slip, and the interlaminar residual stress is much smaller than the cured laminate, whereas the deformation limit and performance are improved. This paper provides theoretical bases for the in-depth analysis of deformation properties and forming laws of low-restraint GLARE, guiding further applications of laminates. [ABSTRACT FROM AUTHOR]

• Contact explosion tests were conducted on the corrugated steel-plain concrete plates. • Compared the dynamic response of corrugated steel-plain concrete composite structures under varying TNT charges. • The blast resistance of corrugated reinforced concrete slabs with different shear connectors arrangements was analyzed. • An engineering collapse coefficient Kz was established to predict the failure level of the CSPC composite slabs. This paper investigates the dynamic response and blast resistance of corrugated steel-plain concrete (CSPC) composite structures subjected to contact blast. A series of explosive tests were conducted to investigate the acceleration, deformation, and damage patterns of CSPC plates under varying blast loads and arrangements of shear connectors, and these findings were compared with reinforced concrete (RC) plates. The results suggested that CSPC plates exhibited superior ductility and blast resistance, and effectively mitigated concrete collapse. The CSPC slab primarily underwent elastic deformation when the TNT charge was small, with the rebound deformation of the concrete and steel plates acting as a significant mode of energy dissipation. As for larger TNT charges, the maximum deformation of the plate progressively increased, especially when exceeding 0.3 kg, the deformation rebound ratio decreased significantly, and the plastic deformation increased. For further increased explosive loads, the concrete and steel plates exhibited a pronounced strain rate effect with a slowed growth rate of deformation. By examining different configurations of shear connectors, it was discovered that the adhesive strength between concrete and steel plates was closely related to the energy dissipation mode, and the elastic recovery capability and deformation resistance of the CSPC structure significantly deteriorated when the shear connectors were shorter, sparser or thinner. A numerical model based on LS-DYNA was designed to further analyze the blast resistance characteristics of CSPC plates. An engineering collapse coefficient Kz was established to predict the failure level of the CSPC plates. This paper provides useful insights for the optimal design and damage assessment of CSPC composite structures. [ABSTRACT FROM AUTHOR]

• The results of more than 4 000 non-linear shell F.E. computations are presented, detailed and analysed. • Prior to the numerical parametric studies, the numerical models were validated against test data on full-scale specimens, as detailed in the companion paper. • Various parameters such as the base cross-section profile, the bending moment distribution, the size and position of the openings, the steel grade and member slenderness have been studied. • Besides, a dedicated design model is presented. Systematic comparisons with the results of software ACB+, which is by far the most highly used tool in design practice, are described. • A significantly improved performance of the proposed design approach in terms of accuracy, consistency and reliability is demonstrated. The present paper investigates the lateral torsional buckling resistance of cellular steel beams numerically. Such beams are quite sensitive to lateral instability owing to a substantial increase in depth of the cross-section with respect to the base profile. While a companion paper was dedicated to (i) characterising experimentally the behaviour of cellular and Angelina beams and to (ii) validating dedicated non-linear shell F.E. models, this paper details the results of extensive numerical studies. Several key parameters in the structural response are investigated, such as the base cross-section profile, bending moment distribution, size and position of the openings, steel grade and member slenderness. The results have further been used to assess an original design proposal for the lateral torsional buckling resistance of such girders. The improved design rules are shown to provide accurate yet safe ultimate load predictions. Also, in comparison with existing and available design rules, the proposal is seen to allow for substantially higher design loads – still safe-sided –, potentially leading to significant material savings. [ABSTRACT FROM AUTHOR]

• This paper studies the overall topology and the arrangements of the cables and struts for the conical cable dome in detailed. • This paper gives a simplified method for calculating feasible prestress of the components. • This paper introduces prestress and energy uniformity index to evaluate the structural mechanical properties. • The single-criterion and multi-criterion optimization based on the genetic algorithm is used to enhance the uniformity of the feasible prestress and the load-bearing capacity. The conical cable dome with a rotating cone and zero Gaussian curvature is a new type of cable dome with the generatrix that follows a straight line. The paper studies the prestress design and mechanical properties of such cable domes. First, on the basis of the section and vertical diagrams of the proposed cone, a simplified method is developed to calculate feasible prestresses of cables and struts using the principle of nodal balance. Second, prestress distribution, load-bearing capacity, and prestress of the conical cable domes with 15 different combinations of rise-span ratio and inner triangular slope under both prestress and load states are studied. Additionally, the paper proposes five load conditions to assess the performance of the conical cable domes. Finally, the total strain energy, basic frequency, radial reaction, and gravity are optimized through single-criterion and multi-criterion based on the combination of a genetic algorithm and the Newton iteration method. To keep the outer appearance of the conical cable dome, the work selects the strut length as the optimization variable. An optimized conical cable dome is recommended with a low prestress uniformity index and high uniformity index. The results indicate that the conical cable dome is sensitive to the asymmetrical loads, especially the wind loads. For the single-criterion optimization, the structure with the basic frequency under loads as the objective function has the best load-bearing capacity. After optimization, the maximum nodal displacement is 32% and 43% of the original one under LC4 and LC5. Besides, to get a synthetic optimization result, a multi-criterion optimization is suggested. [ABSTRACT FROM AUTHOR]

• This paper reviews investigations on energy absorption and dynamic response of sandwich structures over the past few decades. • The impact loading includes low-velocity impact, explosive loading as well as ballistic impact. • Core configurations of sandwich structures include metal foam and polymer foam, ungraded and graded honeycomb, auxetic honeycomb and foam inserted honeycomb, corrugated core and foam inserted corrugated core, truss core, undrilled and drilled I-core, and Y-shaped core. • The excellent characteristics concerning load resistance and energy absorption of sandwich structures can guide their application in engineering practice. With the swift advancement of aerospace, shipbuilding and engineering, the significance of sandwich structures with cellular cores is becoming increasingly prominent due to their multi-functional and lightweight attributes. In addition, impact loadings are very common in the engineering practice and may potentially cause significant adverse impact on products and equipment. Emerging manufacturing technologies facilitate the fabrication of high quality sandwich plates with improved stiffness and strength to withstand impact loadings. Therefore, extensive investigations have been conducted on sandwich structures under various impact loadings. This paper provides a comprehensive review of the valuable experimental, analytical, and numerical investigations conducted on the dynamic response of sandwich structures spanning several decades. The paper aims to reveal the underlying deformation mechanisms governing the response of sandwich structures subject to impact loadings. The focus is primarily on popular sandwich structures, such as beams, plates, and curved plates, under low-velocity impact, blast loading, and ballistic impact. Various core configurations of sandwich structures are explored, including metal and polymer foams, uniform and graded honeycombs, auxetic honeycombs, foam inserted honeycombs, corrugated core and foam inserted corrugated core, truss core, undrilled and drilled I-core, chiral core, star-shaped core and Y-shaped core. Current challenges and recommendations for future work have also been articulated. [ABSTRACT FROM AUTHOR]

• A new analysis model of the cylindrical shell with dynamic vibration absorbers has been established in the current research. • Fast convergence, high accuracy and reliability of the model presented in the current research have been proved. • The efficiency of equivalent mass solution is greatly improved through the mathematical model proposed in the current research. • Cylindrical shell and dynamic vibration absorbers with different parameters can be achieved only by changing geometry parameters in self-made program, which does not need reconstructing the model. • We discover that when the antinodes of different vibration modes of the cylindrical shell coincide, multiple resonance peaks can be controlled simultaneously by placing a single dynamic vibration absorption at the coinciding point. Dynamic vibration absorber is efficient in controlling low frequency vibration of cylindrical shell, which is meaningful for engineering practice. However, the efficiency of designing dynamic vibration absorber using traditional method is low. This paper demonstrates a semi-analytical method for designing dynamic vibration absorber of cylindrical shell. The convergence analysis presented in the research proves the accuracy of the current method when handling different edge constraints through limited truncation numbers. Additionaly, forced vibration and control of multi-line spectrum vibration of cylindrical shell have also been studied. The comparison between FEM and current method shows a significant improvement when handling equivalent mass, which is a key process when designing dynamic vibration absorbers. Finally, an intriguing relationship is discovered when controlling multiple resonance peaks through a single dynamic vibration absorber. The semi-analytical method described in this paper may be beneficial when controlling the vibration of cylindrical shell structures in the further research. [ABSTRACT FROM AUTHOR]

• Proposed an innovative active hydroforming & curing hybrid method to manufacture complex thin-walled FML structures. • The new method enhances the formability of thin-walled FMLs and enable the forming and curing in a single step. • The new method increases the ultimate stress by 10 % and reduces the curing deformation from 3.1 mm to 1.3 mm. • Four typical defects during forming of thin-walled FMLs have been characterized and analyzed. • Influence of key parameters on forming accuracy has been discussed. Fiber Metal Laminates (FMLs) are preferable thin-walled structures in several fields for their exceptional mechanical properties. However, how to manufacture thin-walled FMLs structures with complex shapes and guarantee the high mechanical properties is still a challenge. To address these, this paper proposes an innovative hybrid forming method, referred to as active warm hydroforming and curing, to enhance the formability and performance of FMLs in GLARE form by combining the forming and curing process into a single step. The hybrid method was verified on a box-shaped part as a proof-of-concept to assess the feasibility and parameter influence. Online curing was utilized to enhance efficiency and quality. The outcomes revealed that the new method increases the ultimate tensile stress by 12.1 % and reduces curing deformation from 3.1 mm to 1.3 mm compared to the vacuum bagging method. Furthermore, the critical parameters in forming of thin-walled structures, including blank holder force (BHF), pressure rate (PR), maximum pressure (MP), and forming temperature (FT), were identified using experimental, mathematical, and numerical approaches. Four defects in the formed thin-walled structures were observed and successfully eliminated through the control of these parameters. The method and results presented in this paper also provide direct guidance for optimizing the process parameters of FMLs warm hydroforming. [ABSTRACT FROM AUTHOR]

• Effect of thermal cycling on the mechanical properties of carbon fiber/epoxy laminated composites was investigated. • The residual tensile and in-plane shear moduli decrease rapidly during the initial thermal cycles. • The reduction ratio of the residual in-plane shear modulus is larger than that of the residual tensile modulus. • Different fiber materials affect the residual tensile and in-plane shear moduli of the laminates exposed to thermal cycling. Carbon fiber reinforced polymer (CFRP) composites are commonly used for reflectors of artificial satellites operating in low earth orbit (LEO). The decay of the modulus of the CFRP composite varies under different thermal cycling environments, which can lead to a reduction in the accuracy of the reflector panels, affecting the transmission of signals. This paper investigates the impact of different thermal cycling conditions on the mechanical behavior of carbon fiber/epoxy laminated composites experimentally. Three kinds of thermal cycling conditions involving continuous temperature changes are employed to explore the influence of temperature range on the residual tensile and in-plane shear moduli of the laminates. Test results indicate that the upper temperature limit and the temperature span of the thermal cycling conditions jointly affect the mechanical properties of CFRP composite laminates, but the responses of the residual tensile and in-plane shear moduli are different under the variation of each temperature parameter alone. The residual tensile and in-plane shear moduli of the laminates under thermal cycling decrease with an expansion of the temperature span having the same upper limit. If the temperature span remains constant, an increase in the upper temperature limit leads to an increase in the residual tensile modulus, but a decrease in the residual in-plane shear modulus. The main damages causing the decay of residual tensile and in-plane shear moduli of unidirectional laminates were investigated by scanning electron microscopy (SEM) technology. Observations of the microscopic fracture of the material show that the post-curing reaction factor predominantly influences the residual tensile modulus of unidirectional laminates, while the fiber/matrix interface damage factor dominates the residual in-plane shear modulus of the unidirectional laminates. Furthermore, an increase in the fiber tensile modulus decreases both residual tensile and residual in-plane shear moduli. Notably, the residual in-plane shear modulus exhibits greater sensitivity to thermal cycling compared to the residual tensile modulus. The findings reported in this paper would provide valuable insights and guidance for the design and application of carbon fiber/epoxy composites subjected to thermal cycling conditions. [ABSTRACT FROM AUTHOR]

• The seismic damage assessment model for DSCWs was developed based on 37 experimental specimens using the modeified Park&Ang model. • The formulation for the combination coefficient β for DSCWs was proposed. • A comparative analysis on the feasibility of directly applying the representative value β m was conducted. • The damage characteristics and repair methods of DSCWs were summarised into specific damage states. • The probabilistic and quantitative relationships between damage states and damage index are established. The damage indices are widely used to evaluate the performance level and damage state of structural elements in buildings subjected to seismic actions. Despite the widespread promotion of double-skin composite walls (DSCWs) in global construction practices, the research related to the seismic damage assessment of DSCW members is still limited. In order to establish a seismic damage assessment procedure for DSCW members, an experimental database that includes 37 test results of DSCW specimens subjected to cyclic loads was built in this paper. Based on an existing modified Park-Ang model, an empirical expression of the combination coefficient is introduced. The damage state levels of DSCWs are determined as follows: Basically intact (DS 0), Slight damage (DS 1), Mild damage (DS 2), Moderate damage (DS 3), Relatively severe damage (DS 4), Severe damage (DS 5), and Critical collapse (DS 6). The typical damage characteristics and repair methods are introduced and discussed. Subsequently, a comprehensive statistical analysis is conducted to study the probabilistic correlation between these damage states and the corresponding index specific to DSCW members. Fragility functions for each damage state associated with the damage index have been developed. The threshold values of the damage index corresponding to the damage states are also provided. This paper intends to provide a theoretical foundation for performance-based seismic design and post-earthquake damage assessment of DSCW structures. [ABSTRACT FROM AUTHOR]

• The physical explosion of high-pressure natural gas pipeline could be divided into impact expansion stage and stable injection stage, and the energy of harmful effect came from the expansion work of high-pressure gas in the pipeline in the impact expansion stage. There was a linear relationship between the duration of the impact expansion stage and the explosion equivalent, that is, in the impact expansion stage, the output power of the gas expansion was basically constant. • Taking the pipeline used in the experiment as an example, (OD1422-13.3MPa-X80, depth 1.2 m), the duration of the physical explosion impact expansion stage was about 0.11 s. The TNT equivalent of explosion is about 177 kg. The explosion equivalent varies with the depth, and there are extreme points. • The type of medium around the pipeline has a great influence on the explosion equivalent and damage degree of the pipeline. The pipe wall deformation of overhead pipeline was the largest, the buried pipeline finally presented a U-shaped section due to the compaction of soil, and the pipe wall damage of shallow water pipeline was the smallest due to the resistance of water. And its explosive equivalent is also the smallest. However, the scope of personal injury caused by the shock wave generated by shallow water pipeline was far beyond that of overhead pipelines. High pressure natural gas pipelines are prone to material failure and explosion due to various reasons. Over the years, scholars have done in-depth research on the process of chemical explosion. In this paper, the energy components of high-pressure trunk natural gas pipeline under normal operation state were derived. Based on the assumption of adiabatic non isentropic, the pressure distribution in the pipeline within a period of time after the pipeline cracks was derived, and the energy released by the physical explosion of the pipeline was further derived. To verify the theoretical results, an original size pipe explosion experiment was organized, and the pressure distribution obtained from the experiment was found to be in good agreement with the theoretical calculation results. Through the crack propagation time and the duration of ground motion obtained from the experiment, the range of the duration of the pipeline burst crack impact was obtained, and the equivalent range of the pipeline explosion was further calculated. At the same time, through the regression analysis of ground motion, the equivalent of the pipe explosion in this experiment was about 177 kg TNT, which was consistent with the theoretical results. Further, the theoretical model and experimental results were verified by numerical simulation, and deeply studied the influence factors of buried depth on the explosion equivalent, as well as the relationship between the environment of the pipeline and the explosion damage mode and hazard range of the pipeline. The research results of this paper give the calculation method and magnitude range of physical explosion equivalent of high-pressure trunk natural gas pipeline. It provides a reference for the formulation of safety standards for high-pressure trunk natural gas pipelines and inert gas pressure vessels. [ABSTRACT FROM AUTHOR]

• The paper presents a novel approach for calculating the elastic critical moment of corrugated web girders. • The results obtained with the new proposal significantly enhance the outcomes of previous methods. • The new proposal is based on closed-form formulas to determine equivalent section properties. Using corrugated web girders offers several advantages, including increased resistance to lateral-torsional buckling. Researchers have proposed various methods for determining the critical moment value as a function of the cross-sectional geometry. Previous studies have suggested that the enhanced critical moment is attributable to a larger warping constant. In this paper, we present the results of a systematic numerical study using finite element analysis on girders with various corrugated web shapes. Bending along the weak axis demonstrates that corrugated web girders possess a higher moment of inertia. Furthermore, our torsion linear analysis indicates that the increase in the critical moment is primarily due to a larger torsional constant. We compare the elastic critical moment values obtained using finite element linear buckling analysis to those derived from theoretical expressions that introduce equivalent section properties. Our results illustrate that the equivalent section properties method provides values that closely resemble those obtained using finite elements. Finally, we provide closed-form expressions that can be used to estimate equivalent section properties for any girder with a corrugated web. Our findings suggest that employing these expressions to calculate the critical moment yields results that are satisfactory when compared to those obtained through finite element linear buckling analysis. [ABSTRACT FROM AUTHOR]

• A series of 3 full-scale bending tests on cellular and Angelina girders is reported. • 4-pt bending arrangements of beam from 7.5 m to 11 m span were chosen so as to maximize the occurrence of lateral torsional buckling. • Careful measurements on material properties (tensile tests) and geometrical imperfections are reported. • Besides, dedicated non-linear shell F.E. models were developed and validated against the experimental data. • As excellent agreement between experimental and numerical sources is evidenced, the numerical models are found fit to be used in extensive numerical parametric studies aimed at characterizing in detail the structural response of cellular beams. This paper deals with the response of so-called "cellular members" against lateral torsional buckling. These beams comprising regularly-spaced circular web openings are especially used for their high resistance-to-weight ratio, the possibility to integrate service pipes within their height, and for aesthetics. Such profiles usually exhibit a complex behaviour and many potential failure modes, including interactional local/global instability modes. Regarding global instability, the members are usually designed by means of approximate design rules, which often lead to an unduly conservative solution, with beams sometimes showing up to 150 % resistance reserves. The present research works aim at improving this situation, through the development of adequate design formulae. In this respect, the present paper reports on investigations led towards improved solutions for cellular members at the experimental and numerical levels. This first paper focuses on experimental activities and on the development and validation of dedicated shell F.E. models. The results of three bending tests on members spanning from 7.5 m to 11 m are reported. Cross-sectional dimensions, material properties and accurate initial geometrical imperfections were measured for each specimen and further introduced in the corresponding F.E. models, which are shown to provide predictions in close agreement with the experimental results. The companion paper [1] further makes use of the F.E. models within extensive parametric studies and proposes a new set of design rules that could be proposed for integration in Eurocode 3. [ABSTRACT FROM AUTHOR]

• Recent trends and challenges in metal faced sandwich composites. • Influence of Core geometries on mechanical performance of sandwich panels. • Impact, flexural, blast & fire resistance of metal sandwich panels. • Importance of core design for optimal performance of metal sandwich panels. This review paper discusses the challenges in improving the mechanical and structural performance of metal-faced sandwich composite panels while reducing weight and cost. It focuses on the core and facesheet structural trends of metal-faced sandwich panels, highlighting innovative design concepts and mechanical performance with respect to failure modes. The paper categorizes recent core geometries used in metal-faced sandwich structures into three types: cellular foam cores, two-dimensional periodic cores, and three-dimensional periodic cores, each with unique characteristics and advantages. The performance of metal sandwich panels with different core structures in response to various mechanical tests is also summarized, including high and low-velocity impact, flexural, and blast and fire resistance. The review emphasizes that the core geometry, facesheet thickness, and core-face interfacial bonding of sandwich composites play a critical role in determining their structural performance and potential applications. Overall, this review paper provides valuable insights into the challenges of improving the mechanical and structural performance of metal-faced sandwich composite panels and highlights the importance of innovative design concepts for achieving optimal performance. [ABSTRACT FROM AUTHOR]

• Inclined stiffened panels of the fuselage tail were tested under shear load. • The simulation model was established to predict the buckling, post-buckling, and failure modes of inclined stiffened composite panels. • The non-linear relationship between the debonding of the stiffeners and the skin was quantitatively analyzed. • The concept of equivalent skin thickness was introduced to analyze the influence of stringer configuration on panel buckling and post-buckling. The purpose of this paper is to investigate the buckling and post-buckling behavior of inclined stiffened composite panels under shear load. Two types of stiffened composite panels were manufactured and tested. The buckling load, ultimate load and other required structural properties of the inclined stiffened composite panels were obtained. The test results show that the failure load of the two types of panels are 5.79 times and 11.2 times of the buckling load, respectively, indicating that such inclined stiffened panels have a large post-buckling capacity. The damage modes of the panel are tearing around the skin near the clamps and debonding of the stringers from the skin. The combination of Hashin failure criterion, Cohesive model and nonlinear connection of clamp was used to conduct finite element modeling, which effectively predicts the buckling, post-buckling and damage modes of the structure. The buckling and post-buckling behavior of stiffened panels with different stinger configurations were discussed based on finite element analysis. The results show that when the initial buckling occurs between the stringers, the buckling and failure load of the stiffened panel become larger as the equivalent skin thickness between the stringers become larger. The research in this paper can provide reference for aircraft structural design. [ABSTRACT FROM AUTHOR]

• A modified force density method utilizing the concept of relation matrix was proposed in this paper. The modified method realized the establishment of a clear correspondence between members and nodes of cable net structures. • The modified force density method was used in the single-layer spoke cable net structures, and the effect of pretension on form-finding was analyzed. • The surface equation of circular single-layer crossed cable net structure without inner ring was derived. Combined with the modified force density method, the form-finding process of this type of structure is achieved. Form-finding is crucial for the design of typical cable net structures. Based on the original basic force density method, a modified force density method utilizing the concept of relation matrix is proposed in this paper. The modified method realizes the establishment of a clear correspondence between members and nodes of cable net structures. On the basis of the relation matrix, the find function is introduced, and the calculation formula of the modified branch-node matrix is derived. Meanwhile, the corresponding analysis steps and calculation process are given. The modified method is verified by the analysis of representative structural forms. The results show that for the saddle-shaped orthogonal cable net structure, the outcomes obtained from the modified force density method highly agree with the theoretical values, providing preliminary verification of the method's effectiveness. For single-layer spoke cable net structures, the relative error between the results calculated by the modified force density method and the numerical solution is approximately 5 %. The results of both methods are relatively consistent, and the relative error varies in relation to the ratio of inner ring cable force density to radial cable force density. For circular single-layer crossed cable net structure without inner ring, the results of the modified force density method are very close to the numerical solution. The maximum relative error between the two is 6.95 %, and the accuracy is higher than that of the nonlinear finite element method. The outcome of this research demonstrates the accuracy of the modified force density method and its effective application in the form-finding of actual cable net structures. [ABSTRACT FROM AUTHOR]

• Reddy's third-order shear deformation theory is used to analyze the thermal vibrations of FG-GPLRC plates and shells partially resting on the Kerr foundation. • Kerr foundation is distributed centrally or along the edges of the plates and shells. • Two typical boundary conditions are considered for the FG-GPLRC structures. • In-depth analysis of the effects of Kerr foundation distributions and sizes, geometrical parameters, material properties, and thermal environment on dynamic behaviors of structures. In this paper, we present a novel analytical approach for investigating the influence of non-homogeneous Kerr elastic foundations on the nonlinear dynamical characteristics of functionally graded graphene platelets reinforced composite (FG-GPLRC) doubly curved shells. A new aspect of this study is the investigation of various distributions of the Kerr foundation, either centrally within or along the edges of the nanocomposite shells, a model not previously explored. Three distinct distributions of graphene nanoplatelets reinforcement are examined, utilizing the rule of mixtures and the Halpin-Tsai micromechanical model. The theoretical framework is based on Reddy's third-order shear deformation theory. The equations of motion, formulated as partial differential equations, are efficiently resolved through the application of Galerkin's method. The effectiveness of this approach resides in its utilization of integration to tackle the distribution issue of the elastic foundation, all without the need for deploying intricate algorithms. The validity of our proposed method is established through meticulous comparisons with findings from prior literature. Furthermore, this paper delves into the effect of material properties, thermal conditions, boundary conditions, geometrical parameters, and four configurations of the shells on the vibrational responses. Of notable significance is our thorough investigation of the impact of variations in the distributions, stiffness, and geometrical parameters of the elastic foundation on natural frequencies and the nonlinear transient response of these shells, all of which hold great importance in structural design. We present the obtained results systematically in various formats, including tables, 2D and 3D graphs, and contour plots, providing a comprehensive overview of the research outcomes. These findings have profound implications for the field of engineering, contributing to advancements in novel structural designs and their diverse applications. [ABSTRACT FROM AUTHOR]

• A semi-analytical model of variable stiffness plates with curvilinear fiber paths described by higher order polynomials is established. • The frequency veering and modal interaction of variable stiffness plates caused by curvilinear fiber paths are studied. • The variation rule of modal coupling vibration for variable stiffness plates at veering regions is analyzed. • The combined effects of material nonlinearity and modal interaction on variable stiffness plates are studied. The coupling forced vibration behaviors of a variable stiffness plate with curvilinear fiber paths at mode veering regions caused by variations of fiber angle have been rarely found in previous papers, especially in the presence of considering the complex material nonlinearity of composite materials. In this paper, the variable stiffness plate of carbon fiber reinforced composites (CFRC) with curvilinear fiber paths is taken as the research object, and the influence of curvilinear fiber paths on its natural characteristics and vibration responses are studied in detail on the basis of considering the material nonlinearity of CFRC. Firstly, it is found that the variations of curvilinear fiber paths can cause complex frequency veering behavior of the variable stiffness plate, and lead to the appearance of irregular modal shapes formed by modal interaction. Then, the forced vibration response of the variable stiffness plate in the frequency veering region is analyzed methodically, and the variation rules of the vibration response under modal interaction is obtained. After analyzing the nonlinear vibration response of the variable stiffness plate under the combined influence of modal interaction and CFRC material nonlinearity, the mechanism of complex nonlinear dynamic behavior of variable stiffness plate in frequency veering region is further investigated. [Display omitted] [ABSTRACT FROM AUTHOR]

• The symmetric and anti-symmetric distortion modes are introduced for I-sections. • All the nine DOFs of the connected elements at a common joint can be straightforwardly transformed to the global coordinates for stiffness assembly. • The warping-distortion compatibility problem in frames and curved beams can be naturally resolved. • The results obtained by the present beam element agree excellently with those by the shell element. Warping-distortion coupling is common in frames and curved beams made of I-sections, which tends to decrease significantly the lateral and torsional resistance of structures. Traditionally, it has been difficult to consider such effects in structural analysis, because the warping and distortional degrees of freedom (DOFs) of two connected elements at a common joint cannot be easily transformed to a common coordinate system for global stiffness assembly. The purpose of this paper is to conquer such a problem. By introducing the symmetric and anti-symmetric distortion modes, in addition to the warping and conventional six DOFs, this paper develops a new theory that consists of nine DOFs per node for the two-node I-beam element. The three deformational DOFs of the cross-section, i.e., the symmetric distortion, anti-symmetric distortion and warping, can be regarded as three mechanical couples relating to the twisting, shearing and bending , respectively, of the two flanges in the opposite sense. This allows all the DOFs of the connected elements at a common joint to be easily transformed to the global coordinates for stiffness assembly. As a result, the warping-distortion compatibility problem that occurs in frames and curved beams is resolved. In the exemplar studies, the present beam element has been demonstrated to be capable of producing results that are in excellent agreement with those of the shell element for the lateral deformation of angled frames with unstiffened and stiffened joints and of curved beams with various boundary conditions. It is also observed that the cross-sectional distortion effect becomes more manifest in curved I-beams of high curvature or of high flange-to-web rigidity ratio. [ABSTRACT FROM AUTHOR]

• Developed a comprehensive approach that integrates theoretical analysis, finite element modeling, and experimental validation to achieve uniform deformation of forged rings and minimize defects. • Introduced the isothermal field method for designing ring preforms of irregular cross-section rings. • Employed a combination of isothermal field method, finite element simulation, and intelligent optimization algorithms to determine the reasonable size range of preforms. • Through comprehensive consideration of various forming preforms, rational ring preforms were obtained through redesign. One of the main challenges faced by the profiled ring rolling (PRR) process is to ensure the deformation uniformity of the ring, which is closely related to the design of the ring preform. The paper explores the application of the isothermal field method (IFM) in designing preforms for PRR processes, targeting the aerospace sector's high-end equipment manufacturing. Through the integration of advanced computational models and practical design principles, a comprehensive approach involving IFM, finite element simulation, support vector machine modeling, and genetic algorithm optimization is employed to determine the geometric dimensions of rational preforms. The material flow behavior during the PRR process is analyzed, and the effects of different isotherms combinations on strain, stress and temperature distribution are discussed. The findings demonstrate that adjusting the preform's shape during the section forming stage can optimize the uniformity of strain, stress, and temperature within the forging. The stable ring rolling process revealed no macroscopic or microscopic defects, validating the design method of ring preform based on IFM is reasonable. The research contributes to advancing near-net shape forming technologies, offering a novel approach to preform design that marries theoretical analysis with practical manufacturability considerations. [ABSTRACT FROM AUTHOR]

• High-strength CFS built-up beams comprising of four plain channels subjected to four-point bending were numerically investigated. • 240 FE analyses over a wide range of parametric variation (geometry, thickness, yield strength) were carried out. • The influence of aspect ratio, cross-section slenderness, flange and web slenderness on flexural strength was investigated. • A novel method to determine the elastic critical buckling stress of cold-formed HSS built-up beams was proposed. • Two modified design rules for high-strength CFS built-up beams based on DSM and CSM have been proposed and confirmed through a reliability analysis. The adoption of high-strength steel in the construction sector can provide potential advantages, such as supporting large-scale structures with small cross-sectional sizes leading to decreased self-weight and improved space availability. In this paper, detailed numerical investigations are presented to investigate the nonlinear behaviour of cold-formed high-strength steel (HSS) built-up beams subjected to in-plane flexure along with their bending moment capacities, deformed shapes, and moment-curvature curves. Finite element (FE) models incorporating the initial geometric imperfections of cold-formed sections and material nonlinearities were established and validated against the experiments presented in the literature by comparing the moment-curvature curves, deformed shape, and ultimate bending moment capacities. Following validation, the calibrated FE models were utilized to perform extensive parametric studies to generate further numerical data by varying three different parameters: cross-sectional yield strengths (S700, S900 and S1100), geometries (such that the local slenderness, λ l values varied from 1.07 to 4.65) and cold-formed steel (CFS) sheet thicknesses (1.0, 1.5, 2.0, and 2.5 mm). The specimens considered in the present study were restrained to inhibit lateral - torsional buckling and demonstrated failure owing to local buckling. The applicability of the design principles for predicting bending capabilities was assessed using numerical data in accordance with direct strength method (DSM) of AISI codal provisions and continuous strength method (CSM). The obtained numerical results demonstrated that the existing standards lack precise design procedures for cold-formed HSS built-up members and additional research is still required to provide accurate design procedures. Therefore, an improved rational extension of DSM of AISI codal provisions and CSM is recommended to predict the ultimate bending moment resistance. [ABSTRACT FROM AUTHOR]

• Buckling and vibration of AFG-nanobeam is studied with nonlocal integral models. • Finite element model with Lagrangian multiplier method is developed to obtain the numerical solution. • GDQM is developed to validate the efficiency and accuracy of finite element method. • The effect of AFG index on buckling and vibration of nonlocal nanobeam is studied. This paper presented an efficient finite element formulation for analysis of the buckling and free vibration of the axial functionally graded (AFG) Euler-Bernoulli nanobeam based on minimum total potential energy principle with linear constraints. The stress- and strain-driven two-phase local/nonlocal integral models are utilized to address small scale effects. The material properties of the AFG nanobeam vary exponentially along the axial direction. The nonlocal integral constitutive equation can be equivalently transformed into a differential equation with two constitutive boundary conditions. The governing equation and standard boundary conditions are derived via Hamilton's principle. The weak form associated with total potential energy is derived and the constitutive boundary conditions can be converted to external forces at the boundaries. By employing a numerical solution methodology on the basis of the finite element method (FEM) together with Lagrangian multiplier method (LMM), a unified finite element formulation based on stress- and strain-driven two-phase local/nonlocal elasticity is constructed to obtain the critical buckling load and vibration frequency. Meanwhile, the numerical results obtained through generalized differential quadrature method (GDQM) validate the efficiency and accuracy of the present results. The influence of gradient index, nonlocal parameter and local phase parameter on buckling and free vibration of AFG Euler-Bernoulli nanobeam is investigated in detail under different nonlocal models and boundary conditions. It is demonstrated that the gradient index has more effect on mode shapes than the buckling load and vibration frequency between the local stress- and strain-driven two-phase local/nonlocal models. [ABSTRACT FROM AUTHOR]

• Establish the vibration analysis model of a beam-plate system connected through multiple nonlinear single-degree-of-freedom systems. • Find that the transverse vibration of the vibration model established in this work can be validly predicted by the GTM. • Find that the introduction of nonlinear stiffness mainly influences the low-frequency responses of the beam-plate system and motivates nonlinear phenomena. • Find that adjusting the parameters belonging to nonlinear single-degree-of-freedom systems is good for controlling the transverse vibration of the beam-plate system. • The use of nonlinear single-degree-of-freedom systems presents the potential application in controlling the vibration of the beam-plate system. A beam-plate coupling system is widely used in the construction of different frameworks across industries according to engineering application requirements. In this paper, a nonlinear single-degree-of-freedom structure is introduced as a coupling element between the beam and the plate. Therefore, a coupling system connected through a plurality of the nonlinear single-degree-of-freedom structures is proposed with exposure of its operational mechanism and the dynamic behavior analysis as required. The nonlinear coupled governing equations of the beam-plate system with series nonlinear energy sinks are established according to the Hamilton principle and solvable by the Galerkin truncation method. Meanwhile, the nonlinear characteristics of transverse vibration of the coupling system are studied for discussing the effect of nonlinear stiffness on a low-frequency response of the beam-plate system. Further, the transverse vibration of the system may vary with changes in the nonlinear stiffness, the external viscous damping, and the motion mass of the nonlinear single-degree-of-freedom structures. Accordingly, the variations along with these factors are investigated. The results indicate that a reasonable nonlinear single-degree-of-freedom structure can have a significant influence on the transverse vibration characteristics of the beam-plate system. [ABSTRACT FROM AUTHOR]

• High-cycle fatigue of titanium-clad bimetallic steel butt-welded joints is tested. • Test S - N curves are compared to that of parent materials and other metals. • Test S - N curves are compared to that of butt-welded joints of other metals. • Test S - N curves are compared to the codified design curves. Titanium-clad (TC) bimetallic steel is a high-performance constructional material that yields promising application potential in future ocean and coastal civil engineering. However, the understanding on the mechanical behaviors of the corresponding weld joints is still limited. In this paper, a tensile-tensile fatigue experimental study was conducted on two types of butt-weld joints fabricated of hot-rolled TA2 +Q355B TC bimetallic steel. Based on the test results, the fatigue stress-life curves (S-N curve) of the two types of weld joints were obtained and subsequently compared with that of TC parent materials, other representative structural metals, that of butt-weld on other metals and the codified S-N curves provided by six structural/fatigue design standards. Most specimens of the two types of TC weld joints are initially cracked at the clad-to-cap weld. The bonding strength between clad and substrate layers exhibit a promising reliability under fatigue loadings. The fatigue resistance of the two types of TC weld joints is considerably less than the different TC parent materials studied. The fatigue lives of clad material (TA2) and substrate material (Q345/Q355B) are greater than that of TC weld joints. The S - N curves of two TC weld joints are considerably lower than that of high-strength steel series but higher than that of aluminum alloy 6061-T6. The design S-N curves of EC3 (Class 36) and IIW (Class 36) are too conservative for the two TC weld joints. [ABSTRACT FROM AUTHOR]

• This research achieves an enhancement of mechanical properties in CNT composite films through the incorporation of PA66 resin. • The quasi-static fracture strength and fracture energy absorption value increase by more than 286.5 % and 400 % respectively. • At a strain rate of 2900 s⁻¹, peak strength and EA values can reach 534 MPa and 107 MJ/m³, respectively. • The results of this study illustrate that the transition from simple tube bundle extraction fractures to more complex failure modes underscores the nuanced interplay between strain rate and fracture behavior. Carbon nanotube (CNT) has potential application in many fields owing to its excellent properties, but the weak Van der Waals forces between randomly arranged tube bundles limit their mechanical properties. In this paper, CNT films were prepared by floating catalyst chemical vapor deposition (FCCVD), whereas PA66 resin was introduced via impregnation and hot press curing in order to further improve the mechanical tensile properties and environmental resistance of the films. The results demonstrate that the tensile properties of PA66-impregnated CNT film are significantly improved. When the mass fraction of PA66 is 1 %, the composite film exhibits the best tensile properties under quasi-static conditions, with a tensile strength of 528 MPa and an energy absorption (EA) value of 109.5 MJ/m3. Plus, at the high strain rate of 2900 s −1, the strength and EA of CNT film/PA66 composite can reach 534 MPa and 107 MJ/m3, respectively. The results in present research can provide a feasible and effective strategy for the design of CNT composite film with high mechanical tolerance which will broaden the application field to a large extent. [ABSTRACT FROM AUTHOR]

• Numerical modelling was conducted to investigate the structural behaviour of CFST K-joints. • Effects of both geometric and material parameters were examined. • A shear stress distribution model for CFST K-joints was proposed. • Analysis-orientated and design-orientated equations for both the plastic and ultimate strengths of CFST K-joints were proposed. This paper presents a comprehensive investigation, numerically and theoretically, into the structural behaviour and design aspects of concrete-filled steel tubular (CFST) gapped K-joints under brace axial loading. Finite element (FE) models were developed and validated against test results from existing experimental programmes. Based on the validated FE models, influences of geometric parameters and steel material properties on the load-deformation curve, plastic strength, ultimate strength and punching shear stress distribution of CFST K-joints were systematically assessed. In general, the chord diameter-to-thickness ratio 2 γ , brace-to-chord diameter ratio β and steel material strength are crucial to the structural behaviour of CFST K-joints, whilst the brace-to-chord thickness ratio τ was found to have minimal influence. A shear stress distribution model was proposed as well to predict the shear stress distribution at ultimate load. To accurately account for the radial support of inner concrete, the classical ring model was modified accordingly. Based on the proposed shear stress distribution model and modified ring model, analysis-orientated and design-orientated equations were formulated to estimate both the plastic and ultimate strengths of CFST K-joints. The calculated plastic and ultimate strengths were compared against the experimental and numerical results, and the comparison demonstrates the ability of the proposed design methods to accurately and reliably determine the plastic and ultimate strengths of CFST K joints. [ABSTRACT FROM AUTHOR]

• A frame reinforced cell with superior and consistent bi-stable property is proposed and fabricated. • The proposed cell increases flexibility in designing geometric parameters that enable bi-stability. • The proposed metamaterial exhibits programmability with its mechanical response linearly correlating with the number of cells. • The cushioning performance is investigated through the analysis of peak force and energy trapping mechanism. Curved beams are a class of elements capable of bi-stability and can be used to construct multi-stable metamaterials. These materials leverage elastic snap-through in curved beams to transition between multiple stable states, effectively achieving energy absorption and trapping. The elastic deformation allows the structure to be used repetitively. However, the conventional curved beam unit cells design process omits the influence of supporting frames, resulting in inadequate constrains of the beam in the fabricated metamaterials. Its mechanical properties and number of stable states can be significantly diverged from theoretical predictions. This paper presents a novel multi-stable metamaterial with improved and consistent energy trapping ability based on frame reinforced curved beams. Comparative finite element analysis of three unit-cell types demonstrates the superior bi-stability of the proposed cell. Moreover, parametric analysis reveals the proposed cell has a wider range of parameters that can achieve bi-stability. The mechanical properties of the single cell and the 2 × 2 metamaterial are obtained by compression tests. The results validate the linear mechanical response that correlates with the number of unit cells which allows optimal programming of multi-stable metamaterials. Finally, plate impact test is conducted to investigate and analyze the cushioning performance of the multi-stable metamaterial. [ABSTRACT FROM AUTHOR]

• The mechanical behavior is studied on the FGM pipeline in geohazard area. • An S-shape profile is introduced to describe the deformation of the FGM pipeline. • Explicit expressions are obtained to predict the yield displacements and strains. • The present derivations are verified validly by the numerical results. • Material and geometric parameters are examined to evaluate the mechanics of the FGM pipeline. This paper focuses on the mechanical performances of the buried pipelines with functionally graded materials (FGM) subjected to strike-slip faults. A refined displacement function is introduced to derive the fault displacement and the strain distributions. The yield fault displacement is obtained by using the classical beam theory and the first yielding scheme. A finite element model is developed to verify the present derivations, and the verification indicates that the numerical results are in close agreement with the present analytical predictions characterized by the yield displacement and the strains, respectively. Finally, a parametric analysis is carried out to assess the factors that impact the performances of FGM pipelines, such as the diameter-to-thickness ratio of the pipeline, volume fraction exponent, fault inclination angles, the properties of the soil, and so on. [ABSTRACT FROM AUTHOR]

This paper proposes an effective numerical method for shape control of bi-directional functionally graded plates (2D-FGPs) with piezoelectric layers. Isogeometric analysis (IGA) based on non-uniform rational B-splines (NURBS) related to third-order shear deformation theory (TSDT) is employed for the static analysis of the 2D-FGPs with piezoelectric layers. The B-spline basis functions are utilized to represent the distribution of the ceramic volume fractions, where the control points placed along the plane corresponding to the ceramic volume fraction and the applied voltages are taken as the design variables. In addition, an improved moth flame optimization algorithm is utilized to solve the optimization problem of minimizing the static shape error, which effectively balances the exploratory and exploitative capabilities of the algorithm. Various numerical examples of square, skew, and dart-shaped 2D-FGPs are analyzed to validate the proposed method and demonstrated the superior mechanical performance of 2D-FGPs over 1D-FGPs. • The mechanical behavior of 2D-FGPs with piezoelectric layers is studied by IGA-TSDT. • Material layout and control voltages of 2D-FGPs with piezoelectric layers are optimized. • An improved moth flame optimization algorithm is employed as the optimization solver. • The effectiveness of the proposed method is demonstrated through numerical experiments. [ABSTRACT FROM AUTHOR]