Computers & Structures最新文献

This paper presents a new multi-spring finite element formulation called P2PE that simulates the cyclic behavior of panel-to-panel Cross-Laminated Timber (CLT) connections. The formulation comprises five types of uncoupled linear/nonlinear springs representing the fasteners and contact between panels. For instance, the in-plane fastener behavior is simulated with a co-rotational spring and the Modified Richard–Abbott (MRA) model, which is adapted to account for the asymmetry, pinching, degradation, and low-cycle fatigue of timber connections. The model was implemented into ANSYS through user-element/materials, including all computer implementation steps, and can be freely downloaded. The model's response and sensitivity were studied in three demonstrative CLT diaphragms, and it was validated at the connection and assembly stage with benchmark tests. In the first stage, the fastener model was verified with four cyclic CLT connections, while in the second stage, the model was validated with three medium-to-large scale CLT assemblies. The model accurately predicts the stiffness, strength, deformation, slip, and failure mechanisms of both stages. Finally, a parametric analysis of in-plane bending CLT diaphragms was assessed by varying their panel dimensions. This analysis demonstrated that diaphragms with slender panels have larger capacities, fastener energy dissipation, and shear slips but lower ductilities than shorter ones.

The purpose of this paper is to investigate the performance of a certain family of low-order quadrilateral finite elements in the solution of the stationary Navier-Stokes equations governing incompressible fluid flows. These finite elements are derived from the ‘overlapping finite elements’, first developed for the solution of problems in solid mechanics [5,9,48] and incorporate features of both meshfree and traditional finite element methods. One of their most remarkable properties is the insensitivity to mesh distortions. Also, since the Shepard functions are replaced by a suitable interpolation, the resulting basis functions are entirely polynomial, which allows the numerical integration of the weak forms to be performed with few integration points [6,49]. We also discuss the theoretical reasons for the stability of the solutions, that is, the absence of spurious pressure modes, and show that the proposed discretization scheme passes the relevant inf-sup test.

This paper presents a method for detecting the location of spalling and assessing the severity level of the spalling in concrete surfaces. The proposed method is constructed based on deep learning architectures and multi-class semantic segmentation. The proposed method can detect each pixel as a non-spalling, a deep-spalling, or a shallow-spalling. The proposed method consists of three different deep learning architectures with several encoders as backbone networks. Both qualitative and quantitative analyses show that the deep learning architecture with a certain encoder network can detect spalling with different severity levels very well. Additionally, the paper proposes a method to analyze the deep spalling areas of concrete to show their severity levels. The performance analysis shows that this approach provides very convincing results with respect to the actual affected spalling areas. The results convey that this paper achieved a higher level of performance for detecting spalling and assessing the severity of the spalling.

This paper presents for the first time a top-down procedure for calculating the multi contact responses from the response of a multi DOF vehicle (containing two bogies and four wheelsets), which can be measured or simulated. Two key steps are involved. First, the nodal distribution method was devised for distributing the vehicle’s responses to those of the four wheelsets. Then by treating the wheelset as a single-DOF system, the contact response is calculated exactly by the enhanced integration algorithm for each time step. Two scenarios are studied. In Scenario 1, the vehicle is kept stationary on the rails, but excited differently via the contact points, by which the transmission of vibration from the wheelsets up to the vehicle components and down again by the present method is validated. In Scenario 2, the vehicle is set to move over a simple bridge, by which the contact responses are shown to outperform the vehicle’s responses in extracting the bridge frequencies, due to the fact that the vehicle’s frequencies were totally eliminated. In addition, the present method has been demonstrated to be of excellent accuracy, efficiency and robustness in each application.

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

Cracking behavior investigation is very important in solid mechanics. In this study, a non-uniform discretization bond-based peridynamic (NUD-BBPD) method is proposed to investigate the cracking behavior, in which the new volume correction method for regenerative family material points is proposed based on Monte Carlo statistical approach. When computational domain non-uniform discretization (NUD) is employed, the proposed method eliminates the need to use the variational horizon, and naturally solves the issue of unbalanced force in NUD. Additionally, the force loading condition is revised based on the energy conservation in the proposed method. This revision eliminates the need for fictitious material points when the displacement loading condition is used in simulation, and the drawback of the conventional force loading condition, in which the force is constrained, is also solved. The proposed method is then used to analyze the static and dynamic fractures of solids. The effects of the material points arrangement on the cracking behavior are obtained via a comprehensive comparison, and the numerical results obtained by the proposed method are in good agreement with those obtained by the conventional uniform discretizational peridynamics. Moreover, NUD peridynamics with constant horizon has higher computational efficiency than traditional peridynamics.

This study presents a comprehensive exploration of Peridynamic (PD) theory, with a specific focus on its theoretical foundations and practical implementations, including various PD formulations and PD operators. The objective is to highlight the unique attributes of each PD formulation and assess their suitability in the framework of material failure simulations by providing an extensive literature review. The research focuses on the bond-based (BB), ordinary state-based (OSB), and non-ordinary state-based (NOSB) PD formulations, offering a thorough understanding of their distinctive characteristics. Moreover, this study presents the importance of the PD operators on the solution of the differential equations. Numerical implementation is a central aspect of this research, providing a detailed flow chart of the computer codes for PD and PD operator models. In order to demonstrate the robustness of the PD formulations, this study presents numerical results, showcasing predictions generated by computer codes that can be accessed online.

This work aims to establish a numerical framework for mesostructure characterization and diffusivity estimation of concrete with non-convex aggregates. Firstly, a new two-dimensional (2D) non-convex aggregate model is proposed by applying contraction deformation to the contour of an ellipse. Then, a 2D three-phase mesostructure of concrete is constructed, which includes simulating a random packing model of non-convex aggregates by the discrete element method (DEM) and forming interfacial transition zones (ITZs) surrounding aggregates based on the hard core-soft shell (HCSS) model. Subsequently, the ITZ area fraction of the 2D three-phase concrete mesostructure is numerically estimated through a Monte Carlo random point sampling method. In addition, a theoretical model of ITZ area fraction incorporating aggregate properties is derived. Lastly, the effective diffusivity of the concrete mesostructure is evaluated by a developed Dual-probability-Brownian motion (DP-BM) scheme. The results show that the effective diffusivity of concrete depends on the competition of the decreasing effect by more tortuous diffusion paths and the increasing effect by a higher ITZ fraction, which can be resulted from a higher packing fraction, a smaller sphericity, and a finer gradation of aggregates. This work has the potential to serve as a foundation for estimating and optimizing the properties of concrete.

This paper presents a new numerical method called the zonal free element method (ZFREM) for the free and forced vibration analysis of elastodynamic problems. In this approach, a complex computational domain is divided into some simple zones and generates a series of regularly arranged nodes in each zone, which can improve the accuracy during the analysis of complex models. The distinguishing feature of the ZFREM is that an independent isoparametric element is formed by only one freely chosen surrounding node at each configuration node. In this method, the mass term exists only in the internal nodes, which can accelerate the assembly of the final system equations. Building upon this foundation, the present study developed the Krylov reduced dimensional iterative method, which approximates the solution of the equation system by constructing a lower-dimensional subspace. This approach avoids the complex equation transformations involved in traditional algorithms for solving eigenvalue problems, thereby further enhancing computational efficiency. Moreover, to tackle damped vibration problems encountered in engineering applications, the proposed method is further extended to solve the non-linear forced vibration problems. The accuracy and effectiveness of the method are verified by numerical examples of free and forced vibration problems.

This paper addresses the automatic calibration of constitutive parameters of the Discrete Element Method (DEM) models of masonry structures. Three swarm intelligence algorithms were applied, which are efficient in problems characterised by the small number of unknown parameters but high computational demand for the evaluation of the target function. Trust-Based Particle Swarm Optimisation (TBPSO) was chosen due to its excellent convergence rate. It was already tested that TBPSO converged faster than the original Genetic Algorithm and Particle Swarm Optimisation Methods. Therefore, TBPSO was compared with two recent and promising methods, the Marine Predator Algorithm (MPA) and the Golden Eagle Optimiser (GEO). The paper also presents a novel two-step approach, which enhances the performance of the tested optimisation strategies. The methodology is capable to account for and precisely find the mode of failure using Convolutional Neural Networks (CNN). The three optimisation methods and the two-step approach were applied on the DEM model of a quasi-static masonry arch collapse experiment from the literature. Performance of the three algorithms in identifying the appropriate constitutive parameters values of the DEM model were compared. Clear evidence on the advantage of the two-step approach with TBPSO is demonstrated. Remarks about different modelling issues are also included.