Global Structural Stability Research Articles

Optimal bracing system design for funicular twin arches against out-of-plane buckling

Twin arch bridges are often designed with a bracing member system that can significantly enhance the out-of-plane stability. This study presents an exact matrix stiffness method (MSM) for the out-of-plane buckling analysis of funicular twin arch bridges and investigates the optimal bracing system design. A novel 14 × 14 s-order element stiffness matrix of three-dimensional beam–columns was used in the MSM and the out-of-plane buckling analysis was performed after assembling the exact global structural stability stiffness matrix. The influences of the bracing location, number, length, and flexural rigidity of both the transverse bracing and X-bracing systems on the buckling capacity of the twin arch system were investigated. The in-plane stiffness of the bracing system (i.e., the horizontal flexural rigidity in a transverse bracing system) was found to be the critical factor in suppressing the out-of-plane buckling of the twin arch system. In addition, the twin arch system achieved the maximum out-of-plane buckling capacity with the bracing location at S/4, where S is the total arc length. For optimal bracing system design of funicular twin arches, it is recommended that one uses the more economical X-bracing system or a transverse bracing system with adequately rigid bracing members.

Exploring the conformational dynamics and thermodynamics of EGFR S768I and G719X + S768I mutations in non-small cell lung cancer: An in silico approaches.

Non-small cell lung cancer (NSCLC) is often driven by mutations in the epidermal growth factor receptor (EGFR) gene. However, rare mutations such as G719X and S768I lack standard anti-EGFR targeted therapies. Understanding the structural differences between wild-type EGFR and these rare mutants is crucial for developing EGFR-targeted drugs. We performed a systematic analysis using molecular dynamics simulations, essential dynamics (ED), molecular mechanics Poisson-Boltzmann surface area, and free energy calculation methods to compare the kinetic properties, molecular motion, and free energy distribution between wild-type EGFR and the rare mutants' structures G719X-EGFR, S768I-EGFR, and G719X + S768I-EGFR. Our results showed that S768I-EGFR and G719X + S768I-EGFR have higher global and local conformational flexibility and lower thermal and global structural stability than WT-EGFR. ED analysis revealed different molecular motion patterns between S768I-EGFR, G719X + S768I-EGFR, and WT-EGFR. The A-loop and αC-helix, crucial structural elements related to the active state, showed a tendency toward active state development, providing a molecular mechanism explanation for NSCLC caused by EGFR S768I and EGFR G719C + S768I mutations. The present study may be helpful in the development of new EGFR-targeted drugs based on the structure of rare mutations. Our findings may aid in developing new targeted treatments for patients with EGFR S768I and EGFR G719X + S768I mutations.

Newtonian Limits and Global Stability of Shock Solutions for Piston Problem to the Relativistic Full Euler System

We are concerned with a one-dimensional piston problem to the compressible relativistic full Euler system when the piston is drawn forward relatively. Given some small perturbations of the piston speed and the initial state, we establish the global structural stability of large shock solutions to the piston problem and also study Newtonian limits as the ratio between the speeds of the flow and the light goes to zero. Furthermore, the long time behavior of shock solutions has been investigated.

Exact Matrix Stiffness Method for Out-of-Plane Buckling Analysis of Funicular Arches Considering Warping Deformations

The out-of-plane buckling behavior of arches is closely related to the element torsional behavior. The traditional 12-degree-of-freedom second-order element stiffness matrix which uses a simplified element torsional stiffness GJ/[Formula: see text] (where [Formula: see text] is the shear modulus, [Formula: see text] the St. Venant torsion constant, [Formula: see text] the element length) may significantly underestimate the out-of-plane buckling loads of funicular arches. This paper presents a simple and effective exact matrix stiffness method (MSM) for the out-of-plane buckling analysis of funicular arches. The developed MSM uses a 14-degree-of-freedom second-order element stiffness matrix of three-dimensional beam-columns considering both torsion and warping deformations. The out-of-plane buckling analysis of funicular arches is performed by using the global structural stability stiffness matrix, which combines the transformed second-order element stiffness matrices. The proposed MSM with the exact 14-degree-of-freedom second-order element stiffness matrix for the out-of-plane buckling analysis is verified by comparing with some classical solutions of funicular circular and parabolic arches with box sections and I-sections. Further discussions show that the 14-degree-of-freedom second-order element stiffness matrix may be reduced to a simplified 12-degree-of-freedom form only by deriving the exact element torsional stiffnesses, which could be significantly larger than GJ/[Formula: see text] for members with large cross-sectional torsional stiffness parameters (especially open cross-sections).

Global structural stability and the role of cooperation in mutualistic systems.

Dynamical systems on graphs allow to describe multiple phenomena from different areas of Science. In particular, many complex systems in Ecology are studied by this approach. In this paper we analize the mathematical framework for the study of the structural stability of each stationary point, feasible or not, introducing a generalization for this concept, defined as Global Structural Stability. This approach would fit with the proper mathematical concept of structural stability, in which we find a full description of the complex dynamics on the phase space due to nonlinear dynamics. This fact can be analyzed as an informational field grounded in a global attractor whose structure can be completely characterized. These attractors are stable under perturbation and suppose the minimal structurally stable sets. We also study in detail, mathematically and computationally, the zones characterizing different levels of biodiversity in bipartite graphs describing mutualistic antagonistic systems of population dynamics. In particular, we investigate the dependence of the region of maximal biodiversity of a system on its connectivity matrix. On the other hand, as the network topology does not completely determine the robustness of the dynamics of a complex network, we study the correlation between structural stability and several graph measures. A systematic study on synthetic and biological graphs is presented, including 10 mutualistic networks of plants and seed-dispersal and 1000 random synthetic networks. We compare the role of centrality measures and modularity, concluding the importance of just cooperation strength among nodes when describing areas of maximal biodiversity. Indeed, we show that cooperation parameters are the central role for biodiversity while other measures act as secondary supporting functions.

Large scale fire test: The development of a travelling fire in open ventilation conditions and its influence on the surrounding steel structure

In the frame of the European RFCS-TRAFIR project, natural fire tests in large compartment were conducted by Ulster University, involving steel structure and aiming at understanding the conditions in which a travelling fire develops, how it behaves and impacts the surrounding structure. During the experimental programme, the path and geometry of the travelling fire was studied and temperatures, heat fluxes and spread rates were measured. The experimental data is presented in terms of gas temperatures recorded in the test compartment at different positions and levels. The influence of the travelling fire on the surround structure is presented in terms of the temperatures recorded in the selected steel columns and beams. The temperatures in the test compartment were dependent on the positioning of the travelling fire band as well as the height from the floor level. The non-uniform temperatures in the compartment lead to transient heating of the nearby structural steel elements, resulting in a reduction of their resistance which may influence the global structural stability. The results obtained will help to understand the behaviour of travelling fires and their influence on the structural members. This knowledge will help to reduce the travelling fire associated risks in future.

Stability of Attached Transonic Shocks in Steady Potential Flow past Three-Dimensional Wedges

We develop a new approach and employ it to establish the global existence and nonlinear structural stability of attached weak transonic shocks in steady potential flow past three-dimensional wedges; in particular, the restriction that the perturbation is away from the wedge edge in the previous results is removed. One of the key ingredients is to identify a "good" direction of the boundary operator of a boundary condition of the shock along the wedge edge, based on the non-obliqueness of the boundary condition for the weak shock on the edge. With the identification of this direction, an additional boundary condition on the wedge edge can be assigned to make sure that the shock is attached on the edge and linearly stable under small perturbation. Based on the linear stability, we introduce an iteration scheme and prove that there exists a unique fixed point of the iteration scheme, which leads to the global existence and nonlinear structural stability of the attached weak transonic shock. This approach is based on neither the hodograph transformation nor the spectrum analysis, and should be useful for other problems with similar difficulties.

Theoretical exploration of global minima, magnetism, structural stability and growth pattern of holmium‐doped silicon HoSin0/− (n = 10–18) nanoclusters

AbstractThe structural growth pattern of medium‐sized holmium‐doped silicon nanoclusters HoSin0/− (n = 10–18) was systematically probed by means of unbiased structure searches and double‐hybrid density functionals. The identified global minima of the nanoclusters have been confirmed by comparing the calculated spectral properties such as photoelectron spectroscopy, adiabatic electron affinities and vertical detachment energies with the experimental data. The structural evolution reveals Ho‐linked configuration for neutral and anionic nanoclusters (starting from n = 10 and 12, respectively). In this configuration, the linker Ho atom connects two small silicon sub‐clusters. The nanoclusters starting from n = 16 prefer the configuration in which Ho atoms reside in the center of Si‐cluster. The natural population analysis interprets the involvement of 4f electron of Ho atom in bonding. The participation in bonding has been traced by a transition of an electron from 4f to 5d orbital. This also results in larger magnetic moments (4 and 5 μB) than that of an isolated Ho atom. The HoSi16− nanocluster has good thermodynamic and moderate chemical stabilities as corroborated by average bond energy analysis, highest occupied molecular orbital‐lowest unoccupied molecular orbital gap, and chemical bonding, thus suggesting it the most appropriate building block for new functional nanomaterials.

Advanced Structural Analysis of Innovative Steel–Glass Structures with Respect to the Architectural Design

This paper provides a comprehensive analysis of a steel–glass spindle torus structure based on the prototype of the Jewel Changi Airport, Singapore. Instead of studying a common cuboid building, the research in this paper focuses on a spindle torus shape structure which incorporates tremendous, curved members. Hence, the advanced modeling and structural analysis of this structure provides valuable information about an irregularly shaped building. Meanwhile, the modeling and analysis process of this innovative structure also gives rise to some practical design recommendations for both architects and engineers. In this paper, both global structure stability and local member buckling behavior were studied. With the use of commercial finite element software, Strand7 (R2.4.6) and ABAQUS (6.14), a series of numerical simulations were conducted. In terms of the behavior of the global structure, both numerical spindle torus models incorporating straight and curved steel members were tested under different load combinations specified in Australian building standards. A significant difference was observed between the results of the two models; therefore, research on the individual curved members was undertaken. Regarding the local member buckling behavior, the effective length factor for curved members with braced and sway boundaries conditions was investigated in Strand7. Moreover, the interaction curves of curved beams with different L/R ratios were compared with perfectly straight members in Australian building standards. ABAQUS can provide more precise predictions of local buckling behavior; therefore, the elastic local buckling behavior of the perimeter beams on different levels was investigated using ABAQUS. Additionally, the impacts of boundary conditions and L/R ratios on the beam buckling behavior are discussed.

A Remote Sensing Image Registration Algorithm Based on Multiple Constraints and a Variational Bayesian Framework

ABSTRACT Aiming at complicated remote sensing image registration problem, we proposed a multi-constraint registration algorithm based on variational inference. Gaussian mixture model is used to construct the entire Bayesian network, which facilitates the estimation of heteroscedasticity noise in mapping function regression, and distribution of outliers in scene point density estimation. We use a variational parameter proxy to approximate complex posterior distribution. In addition, while maintaining the stability of global structure, similarity of local structure is restricted. In order to limit the cost of image conversion, we added constraints on spatial curvature for image. Accuracy and smoothness of the spatial transformation can be maintained by minimizing the curvature in horizontal and vertical directions. Experimental results show that compared with other point set matching algorithms, this method can achieve better results in robustness and matching accuracy.

Behaviour of a joint between a U-shaped steel-concrete beam and a concrete-filled steel tubular column

A new type of U-shaped steel-concrete beams (USCB) using L-angle shear connectors was recently proposed as an alternative solution for long-span structures. In a specific portal frame configuration used in a recent building, the USCB is connected to concrete-filled steel tubular columns by welded steel-concrete joints. The behaviour of these joints plays a crucial role in the global structural stability of the frame as much as that of the whole building. Due to the composite steel-concrete action within the joint, its design is not explicit nor available in design provisions. This paper has the objective to investigate the behaviour of this complex joint and propose a design model of the joint for practical engineers. An experimental campaign of two full-scale tests was carried out in order to determine the moment resisting capacity, the deformation capacity, the cracking patterns, and the failure mode of the joint. A finite element model of the test was also developed and validated against the experimental results to investigate more closely the load transfer mechanism and the propagation of plastification in the components of the joint. The stress map obtained from the FE model was afterwards used to define the geometry of the design model of the joint. This model was proposed based on the strut-and-tie method for the concrete part and the shear panel model for the steel part of the joint. The interesting feature of the design model is the inclusion of the load transfer mechanism of the forces between the steel and the concrete parts of the joint. Finally, a parametric study on the influence of steel detailing inside the joint using the FE model was carried out. It was found out that the initial solution can be simplified and optimised.

Canine SOD1 harboring E40K or T18S mutations promotes protein aggregation without reducing the global structural stability.

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease associated with aggregation of superoxide dismutase 1 (SOD1) protein. More than 160 mutations in human SOD1 have been identified in familial ALS and extensively characterized in previous studies. Here, we investigated the effects of T18S and E40K mutations on protein aggregation of canine SOD1. These two mutations are exclusively found in canine degenerative myelopathy (an ALS-like neurodegenerative disease in dogs), whose phenotype is unknown at the level of protein folding. Interestingly, the T18S and E40K mutations did not alter far-UV CD spectrum, enzymatic activity, or global structural stability of canine SOD1. However, thioflavin-T assay and transmission electron microscopy analysis revealed that these mutations promote formation of fibrous aggregates, in particular in the Cu2+/Zn2+-unbound state. These evidence suggested that the T18S and E40K mutations promote protein aggregation through a unique mechanism, possibly involving destabilization of the local structure, reduction of net negative charge, or production of disulfide-linked oligomers.

Static properties and stability of segmentally prestressed cylindrical reticulated mega-structures

A new type of segmentally prestressed cylindrical reticulated mega-structure is proposed. The mechanism and detailed layout of the segmental cable-strut system are presented. The static properties and stability of the structure are analyzed and compared with those of the structure without cable-strut system. The reasonable ranges of key arrangement parameters for the segmental cable-strut system are obtained, including the rise-to-span ratio, length and distribution of the strut, and pretension degree and distribution of the cable. In addition, the effects of member buckling on the global stability of the structure and its propagation rule are investigated. On this basis, the substitution of buckling-resistant members for buckling members is proposed, and the improvement effect on the global structural stability is further discussed. The results indicate that the introduction of the segmental cable-strut system can effectively improve the static properties and stability of the reticulated mega-structure. Member buckling has a significant adverse effect on the global structural stability, and thus their interaction should be considered in the stability analysis of the structure. Member buckling initially occurs in the lower chord members near the supports in the middle of the structure, and subsequently propagates to both ends of the structure along the longitudinal direction and toward the supports along the transverse direction at the same time. Additionally, substituting buckling-resistant members for the lower chord members within about 1/6 of the arc length of each latticed arch close to supports is an effective measure for improving global stability.

Active Learning Accelerated Discovery of Stable Iridium Oxide Polymorphs for the Oxygen Evolution Reaction

The discovery of high-performing and stable materials for sustainable energy applications is a pressing goal in catalysis and materials science. Understanding the relationship between a material’s structure and functionality is an important step in the process, such that viable polymorphs for a given chemical composition need to be identified. Machine-learning-based surrogate models have the potential to accelerate the search for polymorphs that target specific applications. Herein, we report a readily generalizable active-learning (AL) accelerated algorithm for identification of electrochemically stable iridium oxide polymorphs of IrO2 and IrO3. The search is coupled to a subsequent analysis of the electrochemical stability of the discovered structures for the acidic oxygen evolution reaction (OER). Structural candidates are generated by identifying all 956 structurally unique AB2 and AB3 prototypes in existing materials databases (more than 38000). Next, using an active learning approach, we find 196 IrO2 polymorphs within the thermodynamic amorphous synthesizability limit and reaffirm the global stability of the rutile structure. We find 75 synthesizable IrO3 polymorphs and report a previously unknown FeF3-type structure as the most stable, termed α-IrO3. To test the algorithms performance, we compare to a random search of the candidate space and report at least a 2-fold increase in the rate of discovery. Additionally, the AL approach can acquire the most stable polymorphs of IrO2 and IrO3 with fewer than 30 density functional theory optimizations. Analysis of the structural properties of the discovered polymorphs reveals that octahedral local coordination environments are preferred for nearly all low-energy structures. Subsequent Pourbaix Ir–H2O analysis shows that α-IrO3 is the globally stable solid phase under acidic OER conditions and supersedes the stability of rutile IrO2. Calculation of theoretical OER surface activities reveal ideal weaker binding of the OER intermediates on α-IrO3 than on any other considered iridium oxide. We emphasize that the proposed AL algorithm can be easily generalized to search for any binary metal oxide structure with a defined stoichiometry.

Precast Concrete Tunnel Segments: A Review on Current Research

Tunnel lining design is an interactive problem, which is not merely about the strength, but on how much the tunnel allows to flexure to overcome the ground movement. When tunnel interacts with soil, stress from the ground is distributed into the structure. In the case of precast segmental bolted tunnel lining, it is critical to investigate the lining joint reaction, as this affects the overall flexural behaviour of the tunnel lining. Understanding the segmental behaviour is important to optimize the design of lining, leading to cost effective production and maintaining the good services during its design life. The objective of this paper is to present a short review on research works conducted in the past pertaining on the joint effect in longitudinal seam in tunnel lining. Review on numerical simulations and laboratory testing were carried out in order to understand the basis of the tunnel lining mechanical behaviour response. A series of flexural bending laboratory testing conducted by the authors was also presented to discuss the mechanics of segmental tunnel lining along the longitudinal joints. In conclusion, results indicate that the measured curvatures and deflections are nonlinearly changed with the increased of applied loads. Different support systems show that appropriate joints could help reduce the maximum moment but an excessive allowable joint movement could lead to high flexural moment which could endanger the global structure stability.

Global stability of buildings’ structural systems considering beam-wall connections

Abstract Several factors influence the stability of concrete structures, such as building height, structural components’ rigidity, bracing system, beam-wall connection rigidity, among others. Global structural stability is evaluated according to NBR 6118/2014 by the α e γz parameters. This article aims to evaluate the global structural stability concrete structures considering the eccentricity of the beam-wall connections. With the aid of software Abaqus© and TQS©, reticulated models were analyzed to evaluate the contribution of the eccentricity of the beam-wall connections on the global stability and the rigidity of the connections. The geometric nonlinear effects were disregarded in these analyses. The stability parameters from NBR6118/2014 were evaluated in the frame models, as well as the flexibilization criteria from the TQS© software, LEPMOL e REDMOL. The results of the displacement analysis show an increase of 26.45%, comparing the centered connection to the more eccentric connection.

An intelligent fuzzy theory for ocean structure system analysis

This paper deals with the problem of the global stabilization for a class of ocean structure systems. It is well known that, in general, the global asymptotic stability of the ocean structure subsystems does not imply the global asymptotic stability of the composite closed-loop system. The classical fuzzy inference methods cannot work to their full potential in such circumstances because given knowledge does not cover the entire problem domain. However, requirements of fuzzy systems may change over time and therefore, the use of a static rule base may affect the effectiveness of fuzzy rule interpolation due to the absence of the most concurrent (dynamic) rules. Designing a dynamic rule base yet needs additional information. In this paper, we demonstrate this proposed methodology is a flexible and general approach, with no theoretical restriction over the employment of any particular interpolation in performing interpolation nor in the computational mechanisms to implement fitness evaluation and rule promotion.

Ab Initio Prediction of Stable Crystal Structure of Procarbazine Molecule

The crystal structure of procarbazine molecule was predicted using first principles of quantum mechanics. The gas phase optimization was carried out by density functional theory and the resulted geometric coordinates were utilized for the search of hypothetical packings which reveals the possible stable conformers under a repulsion alone potential field with minimum cell volume. The thermodynamically favor structure was resulted from the lattice energy minimization of these hypothetical structures from the using the repulsion-dispersion potential field. The stability of global minimum structure was confirmed from the hydrogen bond interactions and second derivative properties.

On the global structure and asymptotic stability of low-stretch diffusion flame: Forced convection

The present work analyzes cylindrical diffusion flames (Tsuji burner) under low stretch condition, considering fuel injection also from the backward region of the burner. To highlight the fundamental aspects of this flame, some assumptions are imposed, like constant thermodynamic and transport coefficients, unitary Lewis number and no radiative heat loss. It is also considered potential flow model and incompressible Navier–Stokes model. Despite the simplicity of the former model, results from both models show good agreement. Also, an asymptotic analysis describing the problem far from the burner is able to capture the most important mechanisms controlling the flame, then the flame shape is determined and the dependence of the characteristic length scales on Peclet number (based on the burner properties), free stream velocity and stoichiometry is revealed. The results show that the flame width is proportional to the mass stoichiometric coefficient and reciprocal to the Peclet number the 1/4 power and free stream velocity the 3/4 power, and that the flame height is proportional to the square of the mass stoichiometric coefficient and to the square root of the ratio of Peclet number to free stream velocity. In addition, an asymptotic stability analysis reveals low-stretch flame extinction to be caused by reduction in fuel and oxidizer concentrations, which provides the range of the stoichiometric coefficient for stable regime, and at the same time the range of heat released.

Global stability analysis of spatial structures based on Eigen-stiffness and structural Eigen-curve

The global stability of a spatial structure is usually analysed via a nodal load-displacement curve (NLDC). However, the global mechanical properties of a structure can hardly be reflected comprehensively by specific NLDCs, and no criterion is available to select the representative node for getting the most reasonable NLDC. In this paper, a scalar parameter derived from the incremental equilibrium equation of nonlinear stability analysis, named Eigen-stiffness, is defined to characterize the global structural stiffness. The Structural Eigen-curve (SEC), based on Eigen-stiffness, is proposed to depict the equilibrium path. Two types of extreme points on SEC are defined to determine the critical state of the structure, including the structural limit state and the structural snap-back. Firstly, the stability of a hinge-supported planar arch is analysed to introduce the SEC concept. Then a K6 reticulated shell is designed to give further understanding. Subsequently, practical application of the SEC is illustrated in the stability analysis of a roof structure, namely, Shanghai International Conference Centre. In addition, a parametric study on a K6 reticulated shell is carried out, based on the Eigen-stiffness and the SEC, to investigate the effects of the rise to span ratio and the geometric imperfection amplitude on the structural stiffness and the structural load-carrying capacity. The results demonstrate that the ultimate load-carrying capacity obtained from the SEC is equal to that from NLDC. More importantly, unlike NLDC, the SEC — free from node selection — can efficiently capture the features of global structural behaviour and the evolution of structural stiffness.