Two-dimensional modeling of material failure in reinforced concrete by means of a continuum strong discontinuity approach

The paper presents a new methodology to model material failure, in two-dimensional reinforced concrete members, using the Continuum Strong Discontinuity Approach (CSDA). The mixture theory is used as the methodological approach to model reinforced concrete as a composite material, constituted by a plain concrete matrix reinforced with two embedded orthogonal long fiber bundles (rebars). Matrix failure is modeled on the basis of a continuum damage model, equipped with strain softening, whereas the rebars effects are modeled by means of phenomenological constitutive models devised to reproduce the axial non-linear behavior, as well as the bond-slip and dowel effects. The proposed methodology extends the fundamental ingredients of the standard Strong Discontinuity Approach, and the embedded discontinuity finite element formulations, in homogeneous materials, to matrix/fiber composite materials, as reinforced concrete. The specific aspects of the material failure modeling for those composites are also addressed. A number of available experimental tests are reproduced in order to illustrate the feasibility of the proposed methodology.     

Surrogate measures to optimize structures for robust and predictable progressive failure

Optimizing complex structures for robust and predictable progressive failure using probabilistic approaches is computationally expensive. In this paper we investigate the progressive failure characteristics of structures subjected to random variability and deduce patterns to identify surrogate measures that correlate with robustness and predictability of the design’s progressive failure. The procedure is demonstrated for the optimization of robustness and predictability in progressive failure of truss structures. Deterministic optimization of trusses was used to generate candidate designs to compare and contrast robustness and predictability. The stochastic analyses of the candidate designs are then used to identify surrogate features that correlate to robustness and predictability of progressive failure response. These features are converted to numerical surrogate objectives or constraints and used in optimization to demonstrate their effectiveness and computational efficiency. The example shows that surrogate measures can be developed for robustness and predictability optimization, and that such measures are computationally efficient compared to robustness optimization using sampling based methods.     

Stability and robustness issues in numerical modeling of material failure with the strong discontinuity approach

Robustness and stability of the Continuum Strong Discontinuity Approach (CSDA) to material failure are addressed. After identification of lack of symmetry of the finite element formulation and material softening in the constitutive model as possible causes of loss of robustness, two remedies are proposed: (1) the use of an specific symmetric version of the elementary enriched (E-FEM) finite element with embedded discontinuities and (2) a new implicit-explicit integration of the internal variable, in the constitutive model, which renders the tangent constitutive algorithmic operator positive definite and constant. The combination of both developments leads to finite element formulations with constant, in the time step, and non-singular tangent structural stiffness, allowing dramatic improvements in terms of robustness and computational costs. After assessing the convergence and stability properties of the new strategies, three-dimensional numerical simulations of failure problems illustrate the performance of the proposed procedures.     

Probabilistic fiber element modeling of reinforced concrete structures

A computational model based on a stochastic fiber element model is developed in this study. This model can be utilized for probabilistic evaluation of reinforced concrete (RC) members. The stochastic fiber element model is developed by combining the conventional fiber element formulation and the midpoint method for random field representation, to account for spatial variability of material and geometrical properties within a structural member. Three verification examples show the capability of the developed model in estimating the nonlinear structural behavior including softening. As an application of the developed computational model, a probabilistic strength analysis of a RC column is conducted in terms of the axial load-bending moment interaction. An approach of evaluating RC structural systems using the developed probabilistic computational model is also presented.     

Constitutive ply damage modeling, FEM implementation, and analyses of laminated structures

The present work is concerned with the modeling of progressive damage in fiber reinforced polymer laminates and its implementation into a finite element code as constitutive material law. The objective is to predict damage evolution and material degradation due to matrix dominated failure modes (“matrix cracking”). In a previous work, a ply-level continuum damage model based on ply failure mechanisms postulated by Puck has been presented. This model predicts the evolution of the complete tensor of elasticity for the damaged material and is able to capture the effects of stiffness recovery and slanted cracking under transverse compression. In the current work, this damage model is adapted for arbitrary loading paths and implemented within the finite element method in order to analyze complex structures and study their damage behavior including load redistribution due to damage. To demonstrate some key features and the application of the damage model in structural analysis, it is applied in a single element analysis as well as in the simulation of Open Hole Compression tests for which results are compared to experimental data from the literature.     

Controlling failure using structural fuses for predictable progressive failure of composite laminates

Structural fuses have been used to bias and control failures in structural applications where predictability of the progressive failure or collapse response is important. Tailoring structural fuses by trial and error in large structures that have numerous possible load and failure paths is not possible because the optimum failure sequence is not known a priori. Using nondeterministic methods to tailor structural fuses is computationally expensive. A procedure for developing deterministic measures to optimize structural fuses is presented here. The progressive failure of composite laminates is used for demonstration. Structural fuses are optimized using a reliability optimization. The failure response characteristics of the laminate with optimum structural fuses are used to identify deterministic measures that correlate with high progressive failure predictability. The deterministic measures are validated by using them as surrogate design criteria in a deterministic optimization to optimize structural fuses that control failure and improve progressive failure predictability. The improvement in predictability of the deterministic optimum design achieved by using optimized structural fuses is better than that obtained by optimizing the ply angles of the laminate explicitly for predictability.     

Fast accessing Web3D contents using lightweight progressive meshes

Accessing Web3D contents is relatively slow through Internet under limited bandwidth. Preprocessing of 3D models can certainly alleviate the problem, such as 3D compression and progressive meshes (PM). But none of them considers the similarity between components of a 3D model, so that we could take advantage of this to further improve the efficiency. This paper proposes a similarity‐aware data reduction method together with PM, called lightweight progressive meshes (LPM). LPM aims to excavate similar components in a 3D model, generates PM representation of each component left after removing redundant components, and organizes all the processed data using a structure called lightweight scene graph. The proposed LPM possesses four significant advantages. First, it can minimize the file size of 3D model dramatically without almost any precision loss. Because of this, minimal data is delivered. Second, PM enables the delivery to be progressive, so called streaming. Third, when rendering at client side, due to lightweight scene graph, decompression is not necessary and instanced rendering is fully exerted. Fourth, it is extremely efficient and effective under very limited bandwidth, especially when delivering large 3D scenes. Performance on real data justifies the effectiveness of our LPM, which improves the state‐of‐the‐art in accessing Web3D contents. Copyright © 2015 John Wiley & Sons, Ltd.     

Nonlinear finite element analysis of concrete structures using new constitutive models

Nonlinear finite element analysis was applied to various types of reinforced concrete structures using a new set of constitutive models established in the fixed-angle softened-truss model (FA-STM). A computer code FEAPRC was developed specifically for application to reinforced concrete structures by modifying the general-purpose program FEAP. FEAPRC can take care of the four important characteristics of cracked reinforced concrete: (1) the softening effect of concrete in compression, (2) the tension-stiffening effect by concrete in tension, (3) the average (or smeared) stress–strain curve of steel bars embedded in concrete, and (4) the new, rational shear modulus of concrete. The predictions made by FEAPRC are in good agreement with the experimental results of beams, panels, and framed shear walls.     

Damage analysis and numerical simulation for failure process of a reinforced concrete arch structure

This work focuses on the implementation of damage mechanics model to explain and understand failure mechanisms of the concrete structures. A tensorial damage theory and an isotropic application to the arch ribs of a real bridge are presented. Two reinforced concrete arch ribs of a 28 year old bridge has been removed from the field to the laboratory. They were loaded up to failure in order to study the remaining strength of the structure. The damage model involves three independent parameters for simulating the damage behaviors of the concrete material. The damage theory—additional load—finite element method is developed to simulate numerically the failure process of the RC structures based on the proposed damage model. The predicted displacements, strains and failure mode of the RC arch are good agreement with the experimental results. The values of the three material parameters that describe the damage characteristics of concrete were obtained. The numerical calculations revealed the interested behaviors of concrete in a damaging process. The proposed damage model can be used effectively to describe the damage and fracture behaviors of concrete.     

Information modeling of earthquake-damaged reinforced concrete structures

Accurate and reliable information about buildings can greatly improve post-earthquake responses, such as search and rescue, repair and recovery. Building Information Modeling (BIM), rapid scanning and other assessment technologies offer the opportunity not only to retrieve as-built information but also to compile as-damaged models. This research proposes an information model to facilitate the data flow for post-earthquake assessment of reinforced concrete structures. The schema development was based on typical damage modes and the existing Industry Foundation Class (IFC) schema. Two examples of damaged structures from recent earthquake events, compiled using an experimental damage modeling software, illustrate the use of the data model. The model introduces two new classes, one to represent segments of building elements and the other to model the relationships between segments and cracks. A unique feature is the ability to model the process of damage with a binary tree structure. Methods for exporting as-damaged instance models using IFC are also discussed.     

Exploiting the structural reserve of textile composite structures by progressive failure analysis using a new orthotropic failure criterion

In this paper, a novel orthotropic layer based failure criterion for modelling progressive failure of non-crimp fabrics is presented. The strength parameters and stiffnesses needed for this failure criterion are obtained from virtual material tests. Therefore, a finite element multiscale algorithm is used to model the effect of lower scale inhomogeneities on macroscale material behavior. With this multiscale approach it is possible to make predictions for one single layer within a textile preform solely from the knowledge of the mechanical behavior of the constituents fiber and matrix and from the textile fiber architecture. The obtained stiffnesses and strengthes for one textile layer are used as input data for the novel orthotropic failure criterion presented in this paper. In order to show the workability of this failure criterion, finite element simulations of coupon tests and of a three-point bending test of a textile composite are shown and compared to experimental data.     

Protective Structures with Waiting Links and Their Damage Evolution

The paper is concerned with simulation of the damage spread in protective structures with waiting links. These highly nonlinear structures switch their elastic properties whenever the elongation of a link exceeds a critical value; they are stable against dynamic impacts due to their morphology. Waiting link structures are able to spread partial damage through a large region, thereby dissipating the energy of the impact. We simulate various structures with waiting links and compare their characteristics with conventional designs. The figures show the damage propagation in several two-dimensional structures.     

巴西圆盘劈裂破坏的近场动力学建模与分析

基于非局部近场动力学（Peridynamics,PD）理论,对含预置裂纹的混凝土巴西圆盘劈裂破坏问题进行建模分析.将结构离散为包含混凝土材料信息的粒子,引入动态松弛、分级加载和失衡力守恒等粒子系统数值算法,构建可以自然模拟脆性裂纹扩展的PD算法体系.对含不同角度单预置中心裂纹巴西圆盘的裂纹扩展过程进行数值模拟,所得结果与试验结果吻合较好,验证所提出的模型和算法正确.进一步采用该方法模拟双预置裂纹巴西圆盘劈裂破坏过程中的裂纹扩展、交汇、贯通过程,通过将所得模拟结果与试验结果进行比较分析,探究该方法处理多裂纹扩展问题的可行性.     

Damage localization in irregular shape structures using intelligent FE model updating approach with a new hybrid objective function and social swarm algorithm

Health monitoring of structures and damage diagnosis are important research disciplines under investigation worldwide. Soft computing techniques are usually used to solve the uncertain complex inverse problem of revealing structural damage. In the current research, FE model updating (FEMU) paradigm is embraced for solving the damage tracking problem in three dimensional irregular shape structures. By taking into account the complexity of problem, the pivotal point is to efficiently educe damage through well-evolved objective function. Therefore, a novel objective function merging the modal characteristics of modal strain energy (MSTEN) and mode shape curvature (MSC) is established. Posteriorly, to solve the FEMU problem, a hybrid algorithm combining the particle swarm optimization with a new social version of the sine–cosine optimization algorithm (SPSOSCA) is proposed. The SPSOSCA is considered to take advantage of two enhanced search mechanisms to overcome the overall problem complexity. The proposed paradigm is evaluated using many damage scenarios even under noise conditions and the total outcome reveals outstanding performance with fair computational time.     

Self-healing routing: failure,modeling and analysis

Network failures occur frequently, and self-healing ability of existing routing protocols cannot guarantee fast route convergence under these failures without impacting packet forwarding. During routing convergence, network routes may be incorrect and even routing black holes and loops occur, which will result in extensive packet loss and thus influence network performance. To solve this problem, several improved routing solutions have been proposed. In this paper, we propose the concept and model of self-h...     

Constrained multi-objective optimization algorithms: Review and comparison with application in reinforced concrete structures

Engineering design problems are often multi-objective in nature, which means trade-offs are required between conflicting objectives. In this study, we examine the multi-objective algorithms for the optimal design of reinforced concrete structures. We begin with a review of multi-objective optimization approaches in general and then present a more focused review on multi-objective optimization of reinforced concrete structures. We note that the existing literature uses metaheuristic algorithms as the most common approaches to solve the multi-objective optimization problems. Other efficient approaches, such as derivative-free optimization and gradient-based methods, are often ignored in structural engineering discipline. This paper presents a multi-objective model for the optimal design of reinforced concrete beams where the optimal solution is interested in trade-off between cost and deflection. We then examine the efficiency of six established multi-objective optimization algorithms, including one method based on purely random point selection, on the design problem. Ranking and consistency of the result reveals a derivative-free optimization algorithm as the most efficient one.     

武器装备故障预测建模方法选择研究

针对武器装备故障预测方法选择需要考虑的实际问题, 从国际标准化组织对故障预测的定义出发, 明确预测建模需要考虑的因素, 在此基础上对故障预测定义作进一步扩展, 突出故障预测具有的显著特征; 结合装备的实际使用环境, 设计故障诊断和预测流程, 以及对应故障预测方法选择标准; 对具体的每一种故障预测方法划分其主要类别和优缺点, 总结每种预测模型在工程实际中的使用方式, 为具体案例选择合适预测方法提供依据。最后根据目前故障预测应用还存在的差距, 指出未来进一步研究的方向。     

Design optimization of 3D reinforced concrete structures having shear walls

This paper presents a computer-based method for the optimal design of three-dimensional Reinforced Concrete (RC) structures having beams subjected to shear force and bending moment, columns subjected to biaxial moments, biaxial shears and axial loads, and shear walls subjected to pure shear. Regarding the beams and columns, the design variables are the width, depth and area of longitudinal reinforcement of member sections. The design variables for the shear walls are the thickness of the wall, the area of vertical reinforcement, horizontal distance between the vertical stirrups, the area of horizontal reinforcement, vertical space between the horizontal stirrups, and the area of vertical flexural reinforcement. The Optimality Criteria (OC) method is applied to minimize the cost of the concrete, steel and formwork for the structure. ACI code [1] provisions concerning the strength and ductility of beams, columns and shear walls are taken as constraints. The constraints also impose upper and lower bounds on the dimensions of beams and columns, and on shear wall thickness, reinforcement area and the maximum and minimum vertical and horizontal spaces between the stirrups of the shear walls. Sensitivity analysis is conducted for both internal forces and the capacities of the sections of the beams, columns and shear walls. The features of the design method are illustrated by a solved example.     

冲击载荷作用下单层球面网壳结构的破坏和温度效应

基于材料的损伤和失效准则,考虑重物冲击和受火温度对钢材性能的影响,运用有限元软件Abaqus分析K8型单层球面网壳在不同温度范围受到冲击载荷时的失效模式.对693个网壳算例进行分析,根据网壳的竖向变形和塑性发展情况,总结K8型单层球面网壳在冲击载荷作用下的6种破坏类型和失效模式分布.研究结果表明:温度对网壳结构在冲击作用下的稳定性有较大影响;在冲击物质量和速度一定的前提下,当火灾温度达到某个限值时,网壳出现整体倒塌破坏;当火灾温度达到400℃时,结构的抗冲击能力明显降低;随着冲击物质量和速度的增加,网壳变形模式不再随着温度的升高发生明显变化,此时网壳失效类型以剪切破坏为主.     

旧混凝土路面共振破碎力学机理

采用有限元法建立旧混凝土路面的动力学模型,运用ANSYS进行模态分析和谐响应求解.基于混凝土破坏的莫尔-库仑准则判定使路面产生共振破坏的激振力的临界力幅.结果表明:考虑基层影响所得到的模型基频比单纯面层小;路面缺陷会使频率减小;在给定参数下,随着激振力的增大,在路面板中心处产生剪切破坏.