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Axial compression tests were conducted on short rhombic tubes of different cross-sectional shapes. The deformation modes of the rhombic short tubes were obtained. To induce a finite element model with deformation modes consistent with the actual working conditions, buckling modes are introduced into the model as the initial imperfections of the structure. However, the buckling modes resulting from finite element buckling analyses often do not meet the needs of actual crushing modes. A coefficient superposition method of solution is proposed to derive modal characteristics consistent with the actual deformation modes by linear superposition of the buckling modes. Through the study of three aspects of theory, test, and simulation, and the comparison and verification of this method with the simulation results of related literature, the results show that the indexes derived from this method are closer to the actual circumstances and are more expandable, which provides a reference for the project. [ABSTRACT FROM AUTHOR]

A bimetallic steel bar (BSB) consisting of stainless-steel cladding and carbon steel substrate exhibits excellent corrosion resistance and good mechanical properties. The bimetallic structure of BSBs may affect their low-cycle fatigue performance, and current investigations on the above issue are limited. In this study, the low-cycle fatigue properties of bimetallic steel bars (BSBs) with inelastic buckling were investigated. Experiments and numerical studies were conducted to investigate the low-cycle fatigue capacity for BSBs, considering buckling. The buckling mode of BSBs is discussed. The hysteretic loops and energy properties of BSBs with various slenderness ratios (L/D) and fatigue strain amplitudes (εa) are investigated. With increases in the L/D and εa, the original symmetry for hysteresis loops disappears gradually, which is caused by the buckling. A predictive equation revealing the relation between the εa and fatigue life is suggested, which considers the effects of the L/D. A numerical modelling method is suggested to predict the hysteretic curves of BSBs. The effect of buckling on the stress and energy properties of BSBs is discussed through the numerical analysis of 44 models including the effects of the L/D, εa, and cladding ratios. The numerical analysis results illustrate that the hysteresis loops of BSBs with various εa values exhibit similar shapes. The increase in the cladding ratio reduces the peak stress and the dissipated energy properties of BSBs. The hysteresis loop energy density decreases by about 3% with an increase of 0.1 in the cladding ratio. It is recommended that the proportion of stainless steel inBSBs should be minimized once the corrosion resistance requirements are met. [ABSTRACT FROM AUTHOR]

Prestressed stayed steel columns (PSSCs) are structural components notable for their exceptional stability and load capacity. However, their behavior under eccentric compression remains poorly understood compared to their performance under axial compression. This study conducted tests and finite element analysis (FEA) to investigate the stability of PSSCs under eccentric compression loading. The study focused on examining the overall stability, buckling modes, and ultimate load capacity of PSSCs under various scenarios. The findings revealed that PSSCs exhibit significantly higher stability and load capacity than conventional columns. However, when subjected to eccentric compression, they experience a substantial decrease in stability. The results of the linear and nonlinear buckling analyses suggest that interactive buckling may occur under certain conditions, thereby influencing the buckling load. These findings clarify the correlation between stability and eccentric compression, offering valuable insights for future research and practical engineering applications. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of friction on the buckling behavior of a thin, shallow, elastic spherical shell under uniform external pressure based on an axisymmetric model of the finite element method. The study examines a combination of different geometric parameters with three different types of boundary conditions: clamped, hinged, and frictional ends with a wide range of friction coefficients. Friction has a significant influence on the buckling response of the spherical shell for all geometric parameters. In general, the critical pressure decreases as the friction coefficient or geometric parameter decreases. The buckling behavior of the frictional end with small friction coefficients presents an obvious difference compared to the results of high coefficients. For certain geometric parameters, the buckling mode of the spherical shell is transited because of changing the friction coefficient. A buckling map that describes the dependence of critical pressure on both friction coefficient and geometric parameter combined with buckling mode is generated. This map can be applied to the design of the spherical shell against buckling.

Axial compression tests were conducted on short rhombic tubes of different cross-sectional shapes. The deformation modes of the rhombic short tubes were obtained. To induce a finite element model with deformation modes consistent with the actual working conditions, buckling modes are introduced into the model as the initial imperfections of the structure. However, the buckling modes resulting from finite element buckling analyses often do not meet the needs of actual crushing modes. A coefficient superposition method of solution is proposed to derive modal characteristics consistent with the actual deformation modes by linear superposition of the buckling modes. Through the study of three aspects of theory, test, and simulation, and the comparison and verification of this method with the simulation results of related literature, the results show that the indexes derived from this method are closer to the actual circumstances and are more expandable, which provides a reference for the project.

The Three Gorges Reservoir area presents a complex geological environment, where the deterioration of rock masses in the riparian zone of karst bank slopes is expedited by the fluctuating reservoir water levels of the reservoir, thereby hastening the evolution of the bank slopes towards instability. This study focuses on the Huangyanwo dangerous rock mass in the Three Gorges Reservoir area. A comprehensive filed investigation was conducted to scrutinize the deterioration phenomenon of rock masses within the water–level fluctuation zone, and a numerical analysis was performed to assess the long–term stability of the dangerous rock mass. The findings reveal the presence of a vertical karst zone and a bottom seepage zone in the Huangyanwo dangerous rock mass. The bottom seepage zone is situated within the water–level–fluctuation zone, characterized by areas of weakness and rock mass deterioration. Considering the influence of reservoir water levels and rainfall events, the stability coefficient of karst water pressure on the bank slope is calculated to be 1.69, indicating that the dangerous rock mass remains stable. Nevertheless, due to the progressive deterioration of rock mass parameters within the weak area at the bottom, the stability coefficient experiences an annual decline of approximately 0.01. It is predicted that the Huangyanwo dangerous rock mass will transition to an unstable state after approximately 57 cycles of periodic water level variations, and the instability failure will occur after 62 cycles. The failure mode of the dangerous rock mass involves a compound failure mechanism of toppling and sliding subsequent to the connection of the weak zone at the bottom, aligning closely with the qualitative understanding grained from field investigations. The research results hold significant instructive implications for the early warning and prevention strategies concerning analogous geological disasters in reservoir areas.

This paper investigates the effect of friction on the buckling behavior of a thin, shallow, elastic spherical shell under uniform external pressure based on an axisymmetric model of the finite element method. The study examines a combination of different geometric parameters with three different types of boundary conditions: clamped, hinged, and frictional ends with a wide range of friction coefficients. Friction has a significant influence on the buckling response of the spherical shell for all geometric parameters. In general, the critical pressure decreases as the friction coefficient or geometric parameter decreases. The buckling behavior of the frictional end with small friction coefficients presents an obvious difference compared to the results of high coefficients. For certain geometric parameters, the buckling mode of the spherical shell is transited because of changing the friction coefficient. A buckling map that describes the dependence of critical pressure on both friction coefficient and geometric parameter combined with buckling mode is generated. This map can be applied to the design of the spherical shell against buckling. [ABSTRACT FROM AUTHOR]

This study investigates the influence of friction on the buckling behavior of thin, elastic, spherical shells under uniform external pressure. The study spans a range of geometric parameters, from shallow shells to hemispheres. Three different end-edge boundary conditions - clamped, hinged, and frictional ends - are considered across a wide range of friction coefficients using an axisymmetric model and nonlinear buckling analysis. The spherical shell becomes increasingly susceptible to buckling when the friction coefficient falls below the converged friction coefficient. A formula is developed to estimate this converged friction coefficient for each geometric parameter. Furthermore, a boundary separating the effects of friction on critical pressure into distinct regions is established, and equations predicting critical pressure within each region are provided. The study also finds that friction influences the buckling mode transition in the shells. Due to significant changes in the theta angle of the no-bending point with increasing geometric parameter and friction coefficient, buckling mode transitions occur at lower friction coefficients in wider spherical shells. These findings provide valuable insights into the intricate interplay between geometric parameter, friction, and buckling behavior in shells. In practical applications, this study can be used to assess and enhance the safety and reliability of spherical shells. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Geological Hazard & Control is the property of China Institute of Geological Environmental Monitoring (CIGEM) Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Designing thin‐walled structural members is a complex process due to the possibility of multiple instabilities. This study aimed to develop machine learning algorithms to predict the buckling behavior of thin‐walled channel elements under axial compression or bending. The algorithms were trained using feed‐forward multi‐layer Artificial Neural Networks (ANNs), with the input variables including the cross‐sectional dimensions, the thickness, the presence and location of intermediate stiffeners, and the element length. The output data included the elastic critical buckling load or moment, as well as a modal decomposition of the buckled shape into the pure buckling mode categories: local, distortional and global buckling. The Finite Strip Method (FSM) and the Equivalent Nodal Force Method (ENFM) were used to prepare the sample output for training. To ensure the accuracy of the developed algorithms, the ANN models were subjected to a K‐fold cross‐validation technique and featured optimized hyperparameters. The results showed that the trained algorithms had a remarkable accuracy of 98% in predicting the elastic critical buckling loads and modal decomposition of the critical buckled shapes. [ABSTRACT FROM AUTHOR]

Because non-buried submarine pipelines under cyclic thermal loading are prone to global buckling, sleepers are commonly laid along the pipeline route to induce a series of relatively small and controllable lateral buckling. A finite element model which can simulate the transformation of pipeline laid on a sleeper from vertical buckling to lateral buckling is established in this work. The parameters of sleeper affecting pipeline buckling modes are analysed, and a new kind of sleeper is proposed aimed at avoiding antisymmetric buckling. Results show that the lateral trigger force can avoid antisymmetric lateral buckling when acting between 1°C and 13°C before the critical buckling temperature. The range increases slightly with increasing trigger force. Compared with an ordinary sleeper, the proposed new sleeper with slider can reduce the critical buckling temperature by 25%, which significantly improves the success rate of sleepers. [ABSTRACT FROM AUTHOR]

The buckling failure of the afterburner cylinder is a serious safety concern for aero-engines. To tackle this issue, the buckling simulation analysis of the afterburner cylinder was carried out by using finite element method (FEM) software to obtain the buckling mode and critical buckling loads. It was found that the afterburner cylinder was susceptible to buckling when subjected to differential pressure or the compressive force of the rear flange. Buckling would occur when the differential pressure reached 0.4 times the atmospheric pressure or when the axial compressive force on the rear flange reached 222.8 kN. Buckling was also found at the front of the cylinder under the auxiliary mount load. Additionally, under various loads on the rear flange, buckling occurred in the rear section, with the buckling mode being closely related to the load characteristics. Based on the simulation results and structural design requirements, two structural improvements were proposed, including the wall-thickening scheme and the grid reinforcement scheme. FEM simulation analysis results showed that both schemes would improve the rigidity and stability of the afterburner cylinder. For the 0.3 mm increase in the wall thickness scheme, the critical buckling load increased by 17.86% to 66.4%; for the grid reinforcement scheme, the critical buckling load increased by 169% to 619%. Therefore, the grid reinforcement scheme had a stronger anti-buckling ability and was deemed the optimal solution. The findings of this paper could provide technical support for the structural design of large-sized and thin-walled components of aero-engines. [ABSTRACT FROM AUTHOR]

• This paper presents an innovation theoretical framework based on ML technology for predicting the load capacity and buckling modes of CFS built-up I-sections. • The proposed theoretical framework offers significant advantages in engineering applications. Engineers can seamlessly integrate our ML method into their familiar DSM design process. • The overall framework design of the machine learning model, the construction of the dataset, the algorithm selection, the tuning of the hyperparameters and the impact of these factors on the output results were described in detail. • To improve the explainability of the ML model, the physical information-enhanced features based on the knowledge of the direct strength method were adopted instead of directly using the parameters of geometric dimensions and material properties as the input features. • With the help of the developed model, an in-depth study was conducted on why there is a conflict conclusion between the existing methods in literature, giving a deeper understanding for design such section columns. This paper presents a regression-classification ensemble machine learning (ML) model for loading capacity and, in particular, buckling mode prediction with respect to cold-formed steel (CFS) I-section columns. The ML model comprises two sub-models, including the regression sub-model for load capacity prediction and the classification sub-model for buckling mode prediction. A total of 541 experimental and numerical data for CFS built-up I-section columns with varies geometric dimensions, material properties and buckling modes were collected from the literature to construct a dataset. To improve the accuracy and the explainability of the ML model on relative small-scale dataset, physical information-enhanced features based on the knowledge of the direct strength method were adopted as the input features of the ML model, including the yield strength, the elastic local buckling load, the elastic distortional buckling load and the elastic global buckling load, instead of directly using the parameters of geometric dimensions and material properties as the input features. The appropriateness of seven classical machine learning algorithms was compared, namely Decision Tree (DT), Random Forest (RF), Support Vector Machine (SVM), K-Nearest Neighbour (KNN), Adaptive Boosting (ADA), Extreme Gradient Boosting (XG), and Categorical Boosting (CB). The statistical analysis showed that the XG algorithm had the highest level of accuracy for both loading capacity and buckling mode prediction. In addition, the explainability analysis indicated that the developed ML model successfully learned the mechanical characteristic of CFS built-up I-section columns. Finally, the developed ML model was further compared with the existing codified method in the literature. The comparison results indicated that the developed ML model can significantly improve the level of accuracy for loading capacity and buckling mode prediction, which provides a promising alternative choice for the design of CFS built-up I-section columns [ABSTRACT FROM AUTHOR]

An innovative type of steel-concrete composite column, named the prestressed stayed circular concrete-filled double skin steel tubular (PS-CCFDSST) column, is introduced in this study, aiming to achieve both structural efficiency and economic advantages. Numerical simulation and theoretical analysis on the axial compressive behaviour of PS-CCFDSST columns were carried out, to understand and reveal their fundamental working mechanisms. Nonlinear finite element analysis (FEA) utilising ABAQUS was performed and validated against collected test data of CCFDSST columns and PS columns. Properly designed PS-CCFDSST columns could gain cost savings of over 30 % while maintaining identical load-bearing capacity as prestressed stayed hollow steel tube (PS-HST) columns with the same steel usage. The effects of initial pretension, nominal steel ratio, hollow ratio, column's slenderness ratio, relative length of struts, column diameter, strut diameter and cable area on the buckling mode and buckling capacity of PS-CCFDSST columns were evaluated via parametric studies. The stiffness ratio β could be used as an index to comprehensively assess the structural efficiency of PS-CCFDSST columns, and a critical threshold of β = 2 corresponds to the transition between symmetric and anti-symmetric buckling modes. Linear calculation formulae for the theoretical buckling capacity and optimal initial pretension of PS-CCFDSST columns were derived. Finally, practical design equations for predicting the column's buckling capacity were developed, and recommended values for the actual optimal initial pretension and other primary parameters were provided for PS-CCFDSST columns under axial compression. This study, for the first time, provides the fundamental mechanical behaviour, identification of the critical stiffness ratio for buckling mode transition, and design framework for buckling capacity of the PS-CCFDSST column, which is useful for advancing theoretical exploration and informing engineering practices for this new column type. • A new type of steel-concrete composite column named PS-CCFDSST was introduced. • FEA modelling yielded good predictions for axial behaviour of PS-CCFDSST columns. • Structural efficiency and economic benefits of PS-CCFDSST columns were evaluated. • Parametric studies on compressive performance of PS-CCFDSST columns were conducted. • Design recommendations for buckling capacity and optimal pretension were given. [ABSTRACT FROM AUTHOR]

Based on the negative Poisson ’s ratio effect of the re-entrant honeycomb, the finite element simulation of its buckling mechanical properties was carried out, and 2 buckling modes other than those of the traditional hexagonal honeycomb structures were obtained. The beam-column theory was applied to analyze the buckling strength and mechanism of the 2 buckling modes, where the equilibrium equations including the beam end bending moments and rotation angles were established. The stability equation was built through application of the buckling critical condition, and then the analytical expression of the buckling strength was obtained. The re-entrant honeycomb specimen was printed with the additive manufacturing technology, and its buckling performance was verified by experiments. The results show that, the buckling modes vary significantly under different biaxial loading conditions; the re-entrant honeycomb would buckle under biaxial tension due to the auxetic effect, being quite different from the traditional honeycomb structure; the typical buckling bifurcation phenomenon emerges in the analysis of the buckling failure surfaces under biaxial stress states. This research provides a significant guide for the study on the failure of re-entrant honeycomb structures due to instability, and the active application of this instability to achieve special mechanical properties. [ABSTRACT FROM AUTHOR]

This research addresses the nonlinear analysis of flat bottom clinker silos that are typically used to store granular materials. Most of silos' failure is due to the inefficiency to resist seismic forces. One of the silo failure reasons is that filled granular material is usually treated as a water pressure which is not realistic. Water pressure is linearly distributed, while granular material has a nonlinear distribution along silo height. The main investigated variables were silo width, height, reinforcement ratio, and the existence of opening in the bottom part of the silo wall. Effects of these variables on silos' dynamic properties - modal periods and mode shapes - as well as seismic response, base shear, base overturning moment, and the least number of modes needed to satisfy mass participation of 90%, were examined. Extensive numerical analyses were conducted to examine these parameters using different types of analyses such as free vibration, response spectrum, and pushover analysis. It was found that increasing height has a great effect on time-period when compared to the effect of diameter increase. Reinforcement ratio in silo without openings has a minor effect in small diameters while it has a major effect in case of silos with large diameters. [ABSTRACT FROM AUTHOR]

The structural instability of multi-walled carbon nanotubes (MWCNTs) has captured extensive attention due to the unique characteristic of extremely thin hollow cylinder structure. The previous studies usually focus on the buckling behavior without considering the effects of the wall number and initial pressure. In this paper, the axial buckling behavior of MWCNTs with the length-to-outermost radius ratio less than 20 is investigated within the framework of the Donnell shell theory. The governing equations for the infinitesimal buckling of MWCNTs are established, accounting for the van der Waals (vdW) interaction between layers. The effects of the wall number, initial pressure prior to buckling, and aspect ratio on the critical buckling mode, buckling load, and buckling strain are discussed, respectively. Specially, the four-walled and twenty-walled CNTs are studied in detail, indicating the fact that the buckling instability may occur in other layers besides the outermost layer. The obtained results extend the buckling analysis of the continuum-based model, and provide theoretical support for the application of CNTs. [ABSTRACT FROM AUTHOR]

The three-dimensional linearized theory of stability and the piecewise homogeneous medium model are used to analyze the near-surface buckling of a layered composite material in an inhomogeneous subcritical state associated with the edge effect in the vicinity of the surface load. The case of imperfect contact between layers modeled by a periodic system of interlayer cracks in the form of a mathematical cut with stress-free edges is considered. The effect of the crack size on the stress decay length, critical loads, and buckling modes is studied. A mesh-based method based on a modified variational-difference approach is used for numerical solution of the problem. The computational experiment uses the sequential and parallel algorithms of the Cholesky method to solve the system of linear algebraic equations and the subspace iteration method to solve the generalized eigenvalue problem. [ABSTRACT FROM AUTHOR]

This research addresses the nonlinear analysis of flat bottom clinker silos that are typically used to store granular materials. Most of silos’ failure is due to the inefficiency to resist seismic forces. One of the silo failure reasons is that filled granular material is usually treated as a water pressure which is not realistic. Water pressure is linearly distributed, while granular material has a nonlinear distribution along silo height. The main investigated variables were silo width, height, reinforcement ratio, and the existence of opening in the bottom part of the silo wall. Effects of these variables on silos’ dynamic properties - modal periods and mode shapes - as well as seismic response, base shear, base overturning moment, and the least number of modes needed to satisfy mass participation of 90%, were examined. Extensive numerical analyses were conducted to examine these parameters using different types of analyses such as free vibration, response spectrum, and pushover analysis. It was found that increasing height on time-period has a great effect when compared to the effect of diameter increase. Reinforcement ratio in silo without openings has a minor effect in small diameters while it has a major effect in case of silos with large diameters.

The instability of the pipe jacking has threatened the safe construction of the project seriously during the jacking process. The research was based on the Shiyanbei sewage diversion steel pipe jacking project, which was undertaken by the Fourth Engineering Co., Ltd. of China Communications Second Highway Bureau. Based on the buckling theory of thin-walled cylindrical shells, the stress, buckling mode and buckling load was analyzed by changing the influencing factors such as slenderness ratio, diameter-thickness ratio and buried depth. The research results show that the stability of steel pipe jacking decreases with the increase of slenderness ratio (the ratio about the length of the jacking pipe to the outer diameter of the pipe). When the slenderness ratio <30 (short jacking pipe), local buckling failure is prone to occur. However when the slenderness ratio >30 (long jacking pipe), the overall instability failure is prone to occur. Under distributed confining pressure, the buckling mode of steel pipe jacking is dominated by local buckling, and its stability decreases with the increase of the diameter-to-thickness ratio. The actual stability coefficient is determined by the pressure around the pipe and the elliptical deformation, which varies with the buried depth. Based on the above analysis results, an empirical formula was proposed about the stability coefficient of large-diameter steel pipe jacking. It has been verified by engineering examples and has good guiding significance. [ABSTRACT FROM AUTHOR]

The buckling failure of the afterburner cylinder is a serious safety concern for aero-engines. To tackle this issue, the buckling simulation analysis of the afterburner cylinder was carried out by using finite element method (FEM) software to obtain the buckling mode and critical buckling loads. It was found that the afterburner cylinder was susceptible to buckling when subjected to differential pressure or the compressive force of the rear flange. Buckling would occur when the differential pressure reached 0.4 times the atmospheric pressure or when the axial compressive force on the rear flange reached 222.8 kN. Buckling was also found at the front of the cylinder under the auxiliary mount load. Additionally, under various loads on the rear flange, buckling occurred in the rear section, with the buckling mode being closely related to the load characteristics. Based on the simulation results and structural design requirements, two structural improvements were proposed, including the wall-thickening scheme and the grid reinforcement scheme. FEM simulation analysis results showed that both schemes would improve the rigidity and stability of the afterburner cylinder. For the 0.3 mm increase in the wall thickness scheme, the critical buckling load increased by 17.86% to 66.4%; for the grid reinforcement scheme, the critical buckling load increased by 169% to 619%. Therefore, the grid reinforcement scheme had a stronger anti-buckling ability and was deemed the optimal solution. The findings of this paper could provide technical support for the structural design of large-sized and thin-walled components of aero-engines.

Regarding the buckling resistance design of thin-walled structures, the conventional iterative optimization approaches pose significant challenges for engineering professionals and create a high barrier for structural designers. This study introduces a novel approach for the anti-buckling design of stiffening ribs, which is based on the solved linear buckling modes rather than on the buckling load factors (BLFs) as in traditional iterative optimization methods. Specifically, the design process begins with a linear buckling analysis of the pre-stiffened part to extract the first-order eigenmode shape. Subsequently, normal vectors are calculated for both the pre-buckling geometric model and the buckled mode shape. By analyzing the normal deflection angle, a group of characteristic points is identified, and these points would be used to serve as guidelines for determining the layout of the stiffening ribs. We validate the effectiveness and efficiency of the proposed protocol through numerical examples spanning from 2D to 3D space considering different loading conditions. Our approach eliminates the need for tedious parametric modeling and high computational cost associated with conventional optimization-based methods. It is particularly well-suited for engineering applications that solely require linear buckling analysis. • Establish a Mapping between buckling modes and ribs layout. • No need for parametric modeling and optimization iterations. • Analysis starts with 2D Euler beams and concludes with spacecraft module. • Nonlinear buckling analysis is used for performance verification. [ABSTRACT FROM AUTHOR]

In this study, we use a large-scale parameter analysis and linear regression method to characterize the static stability of Kiewitt-sunflower-type single-layer reticulated spherical shell. Based on more than 15,000 numerical cases of elastic–plastic load–displacement process, and the investigations on the influence of buckling and instability mode, rise-span and ring-numbers ratio, efficiency of the structure, load distribution, support conditions, size of the initial geometric imperfection and distribution patterns are proceeded. We summarize the key effect for stable performance of structure, and develop the formulation to calculate the ultimate capacity of stability. The results show that Kiewitt-sunflower type single-layer reticulated spherical shell is sensitive to defect, and different distribution patterns of geometry defect lead to different structural buckling. The ultimate stability bearing capacity can be improved by increasing the rise-span and ring-numbers ratio. The asymmetrical load distribution has little effect on the stability. The most unfavorable eigenmode is arbitrary, and it is generally not the lowest order. We summarize the key effect for stable performance of structure, and develop the formulation to calculate the ultimate capacity of stability. [ABSTRACT FROM AUTHOR]

This paper presents experimental tests, numerical simulations, and design methods on steel equal-leg angles subjected to compression. In the experimental programme, a total of 30 steel angles, with different depths of local defects produced at the mid-height, were loaded by a compression force on one leg. Two slendernesses of steel angles were selected in the design of specimens, and the location of local defects were placed at the inner face of the loaded leg and the inner and outer faces of the unloaded leg. The applied compression force and the associated deflections at the mid-height of steel angles were measured during testing. Besides, longitudinal strains of sections at the mid-height, top and bottom ends of steel angles were also measured to gain insight into the development of failure pattern. Comparisons were made among steel angles in terms of the ultimate load and the associated deflection to investigate the effects of slenderness, the location and depth of local defects. Numerical models are also developed for steel equal-leg angles in compression, in which residual stresses and initial geometric imperfections are considered. The validated numerical model is then used to conduct parametric studies on slenderness and local defect on the load capacity of steel angles. Based on the results of the parametric study, a design equation to calculate the ultimate load-carrying capacity of corroded steel angle is proposed. Comparisons with experimental results show that the design equation can calculate the ultimate load-carrying capacity of steel angle with local defects with good accuracy. • Ten groups of steel angles with local defects at the mid-height were tested under compression on one leg. • Numerical models are developed for steel angles in which residual stresses and initial geometric imperfections are considered. • Design equations are developed to calculate the load capacity of steel angles. [ABSTRACT FROM AUTHOR]

The instability behavior of a compressive bilayer on a soft substrate is of significance for epidermal electronics adhered to human skin. Conventionally, two different wrinkling modes dependent of the modulus of intermediate layer were proposed to evolve from flat feature. Here, we uncover a new periodic pattern of secondary wrinkling feature with further compression in the case of a moderate-modulus intermediate layer. FEM simulation results illustrate a linear relationship between this wavelength of secondary wrinkling and the modulus of intermediate layer. An analytical model based on Timoshenko beam theory is utilized to predict the wavelength and critical strain of this secondary wrinkling, which agrees well with that in FEM simulations. Further, a phase diagram of instability feature in the system of bilayer/soft substrate is proposed. The secondary wrinkling feature with such large wavelength has broad applications in tunable surface morphologies for smart glasses, color controlling and manipulation of water droplets. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper aims to investigate the buckling behavior of circular hollow section (CHS) T-joints in retrofitted and non-retrofitted states under axial brace compressive loading. For this purpose, two types of analysis are carried out. The first one is evaluating the critical buckling load in various tubular joints, and the other one is investigating the post-buckling behavior after each buckling mode. More than 180 CHS T-joints with various normalized geometric properties were numerically modeled in non-retrofitted state to compute their governing buckling mode, i.e., chord ovalization, brace local, or global buckling. Then three joints with different buckling modes were selected to be retrofitted by fiber-reinforced polymer (FRP) patches to illustrate the improving effect of the FRP wrapping on the post-buckling performance of the retrofitted joints. In addition, FRP composite failures were investigated. The results indicate that the FRP retrofitting is able to prevent the brace local buckling, and that matrix failure is the most common composite failure in the retrofitted joints. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bistable compliant elements offer excellent advantages in many applications ranging from high precision sensing to energy harvesting. The essential nonlinear mechanics of such elements are strongly coupled with their buckling mode, geometric parameters, and loading conditions. The force-displacement plot of bistable curved beams could contain a displacement limit point, which cannot be well modeled by the commonly used smooth cubic function and would cause operational problems due to incorrect predictions of the bistability. In this technical brief, the nonlinear bistable mechanics of a compliant curved beam with both ends fixed is analyzed based on the large deflection finite element theory. By using the multistep displacement loading method, the deformation behaviors and their transition from symmetric to asymmetric modes are numerically studied, which provides insights into the force-displacement curve and the multiple snapping pathways. Furthermore, the influences of the structure parameters on bistable mechanics are analyzed, and a quality factor for identifying the occurrence of displacement limit points is introduced for different loading conditions. Finally, a method for achieving a single smooth snapping pathway is proposed, providing a theoretical basis to the design and control of the bistable compliant structures. [ABSTRACT FROM AUTHOR]

The load-carrying component of wind turbine blades is a composite box beam that often consists of two spar caps and two shear webs. Local buckling of such beams usually leads to failure of spar caps and/or shear webs. As the failure modes change with cross-sectional geometries and load conditions, it is of interest to develop a method for efficient structural failure evaluation. As a correlation exists between linear buckling response and the potential structural failure, this study presents comprehensive numerical studies on the box beams with different external shapes and layer thicknesses to establish buckling mode maps that can be useful for the preliminary structural design. The results show that the changes of cross-sectional aspect ratio affect the buckling strength more than the change of the weight or the material usage when the spar cap buckling dominates the failure. Larger curvature of spar caps can significantly improve the buckling strength due to better resistance to the cross-sectional flattening. The evaluation method only uses the modeling techniques readily available in common commercial FE software, and no in-house user subroutines is needed, thus allowing the failure evaluation to be performed efficiently in the early design of the load-carrying box beams in wind turbine blades. [ABSTRACT FROM AUTHOR]

Abstract The protective shield of PMT (photon multiplier tubes) is a typical spherical-cylindrical thin-walled shell structure which works in the environment of deep water pressure with the material of plexiglass and character of low Young's Modulus. Therefore, it is significant to analyze the stability of the structure. The validity of eigenvalue buckling prediction and arc length method was verified by classic buckling theory of rotation shell firstly. Then the stability of plexiglass shield was researched by these two methods and a general calculation formula of shallow shell was fitted. The results show that the critical stress of plexiglass shield decreases with the reduction of section roundness; if the height of cylindrical shell is less than 0.3 R , there is no influence on sphere-cylindrical shell structure, but when the height is more than 0.3 R , the structure stability decreases with the increasing of cylindrical shell height. If the influence of exhaust orifice is considered, the geometry of shell is the main factor for the stability of shell when the orifice radius is less than 0.3 times of orifice spacing. Otherwise, orifice is the main factor for the stability of shell. There is a significant influence of initial imperfection on the critical stress of the protective shield and the critical stress decreases with the increasing of initial deformation. The research of this paper can provide useful guidance for the design of PMT plexiglass shield. Highlights • A simplified stability calculation formula of shallow shell under uniformly distributed pressure is fitted. • The critical stress of plexiglass shield decreases with the reduction of section roundness. • If the influence of exhaust orifice is considered, the geometry of shell is the main factor for the stability of shell, when the orifice radius is less than 0.3 times of orifice spacing. Otherwise, orifice is the main factor. • If initial deformation is considered, there is a little reduction of shield critical stress, and the critical stress decreases with the increasing of initial deformation factor. [ABSTRACT FROM AUTHOR]

Studies on failures of castellated beams have identified instability as a critical one. After reviewing the existing investigations, the buckling modes of castellated beams could be summarized into three categories ： lateraltorsional buckling, web post buckling and distortional buckling. Based on the studies on the stability of castellated beams published in recent 30 years, the main factors that influence the stability of castellated beams were investigated. The probability distribution and sensitivity of the influencing factors of simply supported castellated beams subjected to pure bending were obtained by using the Monte Carlo method. Furthermore, part of the representative test results were compared with the European code EN 1993-1-1 predictions. Based on the partial safety factor for resistance in Chinese specification GB 50068--2001 ' Unified standard for reliability design of building structures ' ， a calculation of reliability index of castellated beams experiencing lateral-torsional buckling under various loading conditions was conducted, which formed basis on the development of domestic specification on castellated beams. Finally, this paper summarized the shortcomings of the current research on the stability of castellated beams，and further research direction was pointed out. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the buckling behavior of circular hollow section (CHS) T-joints in retrofitted and non-retrofitted states under axial brace compressive loading. For this purpose, two types of analysis are carried out. The first one is evaluating the critical buckling load in various tubular joints, and the other one is investigating the post-buckling behavior after each buckling mode. More than 180 CHS T-joints with various normalized geometric properties were numerically modeled in non-retrofitted state to compute their governing buckling mode, i.e., chord ovalization, brace local, or global buckling. Then three joints with different buckling modes were selected to be retrofitted by fiber-reinforced polymer (FRP) patches to illustrate the improving effect of the FRP wrapping on the post-buckling performance of the retrofitted joints. In addition, FRP composite failures were investigated. The results indicate that the FRP retrofitting is able to prevent the brace local buckling, and that matrix failure is the most common composite failure in the retrofitted joints.

The axial compressive experiment was conducted on the domestic advanced composite stiffened panel, and its buckling and post-buckling performance was analyzed by monitoring strain and out-of-plane displacement of typical positions. The initial buckling load and buckling mode of panels were calculated by engineering methods to direct the follow-up axial compressive experiment. The experimental results show that the buckling patterns are mainly local buckling of panels between stiffeners, the second buckling of few positions of panels and cylindrical buckling of all 4 stiffeners successively; after local buckling of panels, part of load bearded by panels before is transferred to stiffeners and then stiffeners become the main bearing part; after fracture failure of stiffeners, the specimen is destroyed rapidly; the average value of failure load is 482.67 kN, which is 2.37 times of 204 kN of the average value of buckling load; the composite stiffened panel can bear more load after buckling.

There are currently three design methods to verify the in-plane buckling of an arched structure: substitute member method, the method of equivalent imperfection with recommendations for arched bridges, and the equivalent unique global and local initial imperfection method (EUGLI), which uses the critical elastic buckling mode as an imperfection. The latter method is included in the EN 1993-1-1 cl. 5.3.2 (11) since 2002; however, to this day it is neither utilized in the design practice nor is it incorporated in ordinary structural analysis software. The main purpose of this article is to show the application of the proposed methods in a step-by-step manner to the numerical example considered and to compare these design methods for various arched structures. Verification of the in-plane buckling of an arch is explained in detail.

This research studies a bending test of cold-formed steel box beams with large crosssections. Torsional rigidity of an open single C-section is weak since a cold-formed steel cross-section usually consists of thin elements. With this lack of thickness, buckling in the compression elements is introduced including local, distortional, and lateral-torsional buckling. To improve torsional rigidity and extend further investigation, flexural tests on a built-up box beam assembled with 2 C-sections were conducted in this study. C30024 was selected as the large cross-section, and stiffening plates and self-drilling screws were used as fasteners on both the top and bottom flanges of each C-section. A 4-point bending test and simply supported condition were employed as specimens to achieve a series of bending tests under pure moment. In addition, the influence of the connection spacing on the flexural behavior was investigated at L/2, L/3, L/4, and L/6. The maximum loads and failure modes are examined and presented, and it was observed that there was no failure of the stiffening plates and self-drilling screws. [ABSTRACT FROM AUTHOR]

Abstract Metallic circular tube with external uniform grooves has excellent behaviors on axial crashworthiness during axial compression because it can generate stable responses. In the present research, three novel energy absorbers are proposed based on uniform grooved tube (UGT), namely, depth gradient grooved tube (D-GGT), thickness gradient grooved tube (T-GGT) and coupling gradient grooved tube (C-GGT). A theoretical model considering both the depth and thickness gradients and an efficient numerical model based on axisymmetric assumption are put forward. Meanwhile, some quasi-static compression experiments are performed to validate the theoretical and numerical models. The results conclude that the deformation of gradient grooved tubes (GGTs) under axial buckling can be classified into two modes, namely, random asymptotic buckling (RAB) and sequential asymptotic buckling (SAB). Compared with UGT, the D-GGT has a slight improvement on the axial energy performance even though the sum of depth of thin-walled sections is constant; for T-GGT, a force-displacement curve with upward trend and an obvious improvement of energy absorption are observed; specially, the energy absorption characteristics of D-GGT and T-GGT will occur simultaneously when C-GGT is subjected to axial loading. Graphical abstract fx1 Highlights • A novel theory of gradient grooved tube (GGT) under axial compression is obtained. • An axisymmetric numerical modeling method for GGT is proposed. • The axial buckling modes of GGT are defined. • GGT has better axial crashworthiness compared with uniform grooved tube (UGT). [ABSTRACT FROM AUTHOR]

In steel plate girder railway bridges with open deck system, damage caused by local corrosion of the upper flanges under sleepers is well-known. This damage reduces ultimate strength of the main girders significantly (e.g., in the case of 50%-corroded upper flanges, approximately 30 percent reduction in bending strength). This paper presented a simple evaluation method for estimating the remaining strength of the plate girders that have local corrosion damage under sleepers. Remaining strength of the damaged plate girders can be calculated by taking into account both the remaining strength for local load (hereinafter referred to as "patch load") that acts directly on the upper flanges under the sleepers, and the remaining strength for bending load that acts on the main beam itself. This new evaluation method using the equations proposed in this paper, is based on the idea that the remaining strength under pure bending load can be obtained as the minimum value of strengths calculated in light of the various buckling modes of the compression flange, while taking the thickness reduction due to corrosion into account. Thereafter, the remaining strength under patch load only can be calculated by using an equation which is further simplified based on Takimoto's original equation. Finally, the remaining strength of the plate girder as a whole is obtained from the strength interaction curve between patch and bending loads. In addition, by comparing the estimated remaining strengths obtained through this method with those obtained from nonlinear Finite Element Method (FEM) analyses using full-scale beam models, it could be concluded that the simple evaluation method by using both new and original equations can estimate the remaining strength of plate girders with corroded flanges under sleepers with around 95 percent accuracy. [ABSTRACT FROM AUTHOR]

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This paper presents an experimental investigation and a finite element analysis on web-stiffened cold-formed lipped channel columns with batten sheets connected between the column's two lips at reasonable space. Initially, the paper presents the static compressive test results on 18 specimens under pinned-end restraint conditions with different column length and load eccentricities considered. It is shown that the batten sheets exert significant influence on both the buckling modes and the ultimate strength of the specimens under positive eccentric loading and/or axial loading conditions, while they just have few impacts on that of the specimens under negative eccentric compression. Strengthened by the batten sheets, the columns performed obviously higher ultimate strength under axial and positive eccentric compression compared with the ones without batten sheets and the strengthening effect increase with the increase of column length. Furthermore, the tested specimens were also numerically investigated by finite element program of ANSYS. Geometric and material nonlinearities were both included in the finite element models and it is demonstrated that the numerical analysis can closely predict the ultimate strength and the buckling behavior of the tested columns. Finally, a parametric study was conducted by using program of ANSYS, in which effect of the increasing lip stiffener width and varying batten sheet space were all investigated and it is concluded that the contribution of the batten sheets to the columns’ strength decreased notably with the increasing lip width or batten sheets’ space for axial and/or positive compressed columns. The best choice of the distance between batten sheets (d≤λ/3) for axial compressed lipped channel columns must also be a reasonable choice for positive compressed columns. [ABSTRACT FROM AUTHOR]

Due to the reduction in the financial plans in recent years, innovative bridge girders with corrugated webs have been widely studied and used to reduce the construction costs. Additionally, flat flanges have in some cases been replaced by hollow tubular flanges. These two innovative solutions have been found separately to provide girders with superior load carrying capacities. This paper, however, tries to combine the advantages of the corrugated webs and the hollow tubular flanges into one structural bridge girder. Accordingly, bridge girders with corrugated webs and hollow tubular flanges (BGCWTFs), which have seldom been considered in literature, are investigated here under constant shear loading. This is done by using Abaqus software on large-scale girders, with the main aim of examining the influence of using hollow tubular flanges on the strength and behaviour of these BGCWTFs. Opposite to what was previously found in literature, the results show the great effect of adding upper and lower tubular flanges to the strength and stiffness of the girders compared with the case of flat flange girders, though using tubular flanges with small depth-to-width ratios is found insignificant. The fundamental behaviour of the BGCWTFs has been addressed and the shear strengths are compared with available design model for the first author. Overall, the current results show the importance of considering the shear contribution from the flange with large depth-to-width ratios. [ABSTRACT FROM AUTHOR]

Lateral brace is an effective way to increase the out-of-plane stability of steel arches, and the certain bracing stiffness achieving full restraining effect is concerned. Unlike braced columns and beams, the buckling of steel arches with discrete lateral braces and the effect of bracing stiffness are not well explored. This paper deals with the bracing stiffness effect of equally-spaced lateral translational braces and rotational braces in steel circular arches pertaining to elastic out-of-plane flexural-torsional buckling. Firstly, for arches with discrete lateral translational braces in uniform compression, an analytical solution for the threshold bracing stiffness is derived by the Rayleigh–Ritz method, ensuring full restraint of the displacement at the bracing points. Then for arches with discrete rotational braces in uniform compression, the flexural-torsional buckling modes are explored using the finite element analysis (FEA), then improved predictions to the buckling load related to the bracing stiffness are obtained theoretically by assuming proper buckling shapes. Compared with the FEA results, it is found that the analytical solutions of threshold stiffness proposed for arches in uniform compression are reasonably accurate and can be used in other loading cases for arches under combined compression and bending moment conservatively. [ABSTRACT FROM AUTHOR]