空腹混凝土网架有限元计算——挠度分析

以新三亚火车站预应力混凝土空腹网架结构为例,应用有限元软件ANSYS进行相应的理论分析,用空间梁单元模拟该混凝土空腹网架,详细了解混凝土空腹网架结构随着荷载的增加其挠度大小及发展。从结构挠度方面,掌握该结构的安全储备,对该混凝土空腹网架结构的经济性做客观评述。     

地震作用下空间网架结构考虑损伤累积效应的弹塑性分析

考虑钢材的损伤累积效应和应变强化效应,应用塑性应变和能量耗损理论建立了钢材的损伤力学模型;在此模型基础上,推导了网架结构考虑损伤累积效应的单元弹塑性刚度矩阵和结构动力平衡微分方程,编制了相应的有限元分析计算程序,并对一空间网架结构算例进行了数值仿真分析。结果表明,考虑损伤累积效应对空间网架结构的弹塑性地震反应有着显著的影响,其中有损伤杆件的应力减小、应变增大;无损伤杆件的应力、应变均增大;在不同方向组合地震的作用下,考虑与不考虑损伤累积效应,网架结构的内力和变形趋势相同;不同的地震作用,考虑损伤累积效应时对网架结构的内力和变形的影响也较大。     

工业厂房屋面球节网架施工质量监督控制

近些年来,我国的经济发展迅速,屋面球节网架结构在建筑领域中的应用,其性能能够满足建筑结构需求,现已经开始广泛应用于大型工业厂房及公共建筑领域。网架施工质量会直接对工程整体质量以及结构安全造成影响,因此如何控制好网架施工质量开始成为业内人士的重点关注内容。目前应用的网架结构类型有多种,其中焊接球节网架施工技术操作较为便捷且施工质量易于控制,因此在工业厂房的施工过程中得到了应用。本文在焊接球节网架施工技术特点的基础上对如何做好施工中的质量控制进行了分析阐述。     

浅析配电网网架结构优化及其对供电影响

配电系统供电可靠性直接反映配电系统对用户供电能力,是配电系统可靠性管理的基础。文章分析了配电网网架结构的优化原则和内容,指出配电网网架结构对供电可靠性的影响是最为主要的,然后对配电网网架结构应用及评估进行了分析,指出了未来网架优化规划问题应是我们关注和研究的方向。     

板锥网架结构的理论分析与试验研究

空间板锥网架结构是一种新型的组合网架结构，它是以一系列板锥代替网架结构中的钢腹杆以形成型式新颖，结构暴露，可集承重与围护为一体结构形式，可以达到一定的建筑效果。本文对这类结构形成进行了讨论，并用有限元法对这类结构进行了线弹性及几何非线性分析，编制了相应的计算程序，同时还进行了模型试验，分析及试验表明，这类结构受力性能良好，制作方便，安装简便，能扩大一些板材在空间结构中的应用范围，值得进一步研究及推     

某综合体育馆网架悬臂扩展拼装施工技术研究

中国海洋大学综合体育馆屋面结构为双曲抛物面结构,该体育馆为承办第十一届全运会篮球的比赛场馆,是青岛市的重点建设项目之一。结合该工程结构特点和现场施工条件提出了一种新的网架施工方法——运用条形支撑悬臂扩展拼装技术,避免了布置满堂脚手架而影响下部施工,利用ANSYS软件对起步单元稳定性条件、扩展拼装顺序、悬臂拼装网格的大小进行了系统的分析,针对该网架提出了采用该施工方法起步单元的稳定性条件、拼装顺序以及拼装网格的个数。     

网架结构损伤检测的一种方法

从网架结构单元刚度矩阵的分解出发,导出单元刚度联系向量,由各单元刚度联系向量和损伤前后振型变化向量之间的点积来判别可能的损伤单元,利用频率灵敏度法来计算损伤程度.以一个网架结构为例对所提方法作了验证.结果表明:所提方法计算简单,在测量数据有误差的情况下也能较好地识别出损伤位置和程度.     

包带连接建模与非线性动力学特性分析

在航天工程中,包带连接机构是应用最为广泛的星箭连接分离机构,其主要由两个半圆形钢带(包带)和若干V形截面的卡块组成。为研究包带连接的力学特性,首先分析了包带连接中各个部件之间的接触力以及接触力之间的关系。然后通过将接触力等效为有限单元节点载荷的方法,把包带连接加入到整体结构的有限元模型当中。对于包含包带连接的结构,其动力学方程为非线性微分方程,方程的求解采用了Newm ark直接积分法。最后,采用所提出的建模方法对一个标准接口的包带连接进行了计算,分析了包带连接的非线性动力学特性以及预紧力的影响。     

基于连接特性识别的子结构综合法

子结构综合法因其分块计算的特性,适用于由多单元组成的系统动特性的计算,但是对结构间连接的处理尚缺乏系统的分析和处理,而实际应用中,由于子结构之间的连接较为复杂,导致传统的机械导纳法计算结果准确性较低。考虑子结构综合法中连接单元特性对综合计算带来的影响,引入虚阻抗的概念,在结构综合计算中将连接单元对结构特性的影响以阻抗阵的形式引入进来,而连接单元的特性则根据整体单元及各个子单元的频响特性逆向推导所得,通过离散单元及弹性连续体单元模型验证考虑连接特性的综合方法在计算上的准确性,并将方法引入到铣刀动特性的预测中,通过设计实验验证了方法的可靠性。     

基于110KV电网网架结构优化研究

电网网架是整个电力系统的重要组成部分,也是电网电源的主体。分析了电网网架结构要求与省内现有主要的110kV网架接线形式,结合实例分析,对110kV电网网架的优化建设提出了建设性的探讨。     

A solid‐like shell element allowing for arbitrary delaminations

In this contribution a new finite element is presented for the simulation of delamination growth in thin‐layered composite structures. The element is based on a solid‐like shell element: a volume element that can be used for very thin applications due to a higher‐order displacement field in the thickness direction. The delamination crack can occur at arbitrary locations and is incorporated in the element as a jump in the displacement field by using the partition of unity property of finite element shape functions. The kinematics of the element as well as the finite element formulation are described. The performance of the element is demonstrated by means of two examples. Copyright © 2003 John Wiley & Sons, Ltd.     

A singular element for three-dimensional fracture mechanics analysis

In this article, a singular boundary element for three-dimensional fracture mechanics analysis is presented. It is a nine-node quadratic element with plane geometry. These nodes are located at one quarter of the distance between two opposite sides of the element. Shape functions with a 11/√r singularity at the crack front are used to represent the tractions. The Stress Intensity Factors are computed as system unknowns appearing (except for a constant) as traction nodal values. Special attention is paid to the development of a simple and accurate integration approach for this singular element. The accuracy of the results obtained with the proposed element is demonstrated by solving several crack problems including edge and embedded cracks with different geometries. The element can be easily implemented and incorporated into existing quadratic boundary element codes. In a companion paper the element is formulated and used for fracture mechanics problems in transversely isotropic materials. Extension to other fields for which boundary element formulations exist, is quite simple.     

A two-dimensional damaged finite element for fracture applications

A novel finite element was developed for fatigue and fracture applications. The new element is two-dimensional with an embedded edge crack. The crack is not physically modeled within the element, but instead, its influence on the local flexibility of the structure is accounted for by the reduction of the element stiffness as a function of the crack length. The components of the stiffness matrix for the cracked element are determined from the Castigliano’s first principle. The element was implemented in the commercial finite element code ABAQUS as a user element (UEL) subroutine. Models using the UEL are shown to produce accurate results when compared with results from traditional models using physical modeling of the crack. The newly developed element is useful for studies focused on the global response of a structure, and does not allow evaluation of the local stress singularity near the crack tip. An advantage of the developed UEL is that the singularity at the crack tip does not need to be captured accurately with a significant number of elements.     

Numerical solution of axisymmetric nonlinear elastic problems including shells using the theory of a Cosserat point

Starting with a recently developed three-dimensional eight node brick Cosserat element for nonlinear elastic materials, a simplified Cosserat element is developed for torsionless axisymmetric motions. The equations are developed within the context of the theory of a Cosserat point and the resulting theory is hyperelastic and is valid for dynamics of nonlinear elastic materials. The axisymmetric Cosserat element has four nodes with a total of eight degrees of freedom. As in the more general element, the constitutive equations are algebraic expressions determined by derivatives of a strain energy function and no integration is needed throughout the element region. Examples of large deformations of a nearly incompressible circular cylindrical tube and large deflections of a compressible clamped circular plate are considered to test the accuracy of the element.     

Thermal deformation vector for a bilinear temperature distribution in an anisotropic quadrilateral membrane element

This paper presents a thermal-structural deformation vector for an anisotropic quadrilateral membrane element. The elastic properties of the element are based on linear stress assumptions and were developed by Robinson¹. A general bilinear temperature field within the element is chosen in order to obtain a thermal deformation capability for the element commensurate with its elastic capability. A pseudo shear term is developed to account for part of the thermal deformation. The element is suitable for finite element analysis of advanced aircraft structures under elevated temperature environments and is particularly well suited for analysis of regions with severe temperature gradients such as occur in the vicinity of local heat sources and sinks. An example problem is included to demonstrate the behaviour of the element.     

A comparative study on finite element methods for dynamic fracture

The performance of finite element methods for dynamic crack propagation in brittle materials is studied. Three methods are considered: the extended finite element method (XFEM), element deletion method and interelement crack method. The extended finite element method is a method for arbitrary crack propagation without remeshing. In element deletion methods, elements that meet a fracture criterion are deleted. In interelement crack methods, the crack is limited to element edges; the separation of these edges is governed by a cohesive law. We show that XFEM and interelement method show similar crack speeds and crack paths. However, both fail to predict a benchmark experiment without adjustment of the energy release rate. The element deletion method performs very poorly for the refinements studied, and is unable to predict crack branching.     

Uncertainty analysis of elastostatic problems incorporating a new hybrid stochastic-spectral finite element method

This article aims to present a combination of stochastic finite element and spectral finite element methods as a new numerical tool for uncertainty quantification. One of the well-established numerical methods for reliability analysis of engineering systems is the stochastic finite element method. In this article, a commonly used version of the stochastic finite element method is combined with the spectral finite element method. Furthermore, the spectral finite element method is a numerical method employing special orthogonal polynomials (e.g., Lobatto) and quadrature schemes (e.g., Gauss-Lobatto-Legendre), leading to suitable accuracy, and much less domain discretization with excellent convergence as well. The proposed method of this article is a hybrid method utilizing efficiencies of both methods for analysis of stochastically linear elastostatic problems. Moreover, a spectral finite element method is proposed for numerical solution of a Fredholm integral equation followed by the present method, to provide further efficiencies to accelerate stochastic computations. Numerical examples indicate the efficiency and accuracy of the proposed method.     

大射电望远镜FAST整体变形索网反射面仿真研究

针对大射电望远镜FAST的整体变形索网反射面方案的可行性问题,研制开发了一套专门的有限元计算软件,并提出了一个索网反射面拟合旋转抛物面的反馈控制算法。利用有限元计算软件,在索网反射面力学模型上,对反馈控制算法进行仿真实验,以论证该方案的可行性。采用有限元方法对索网进行力学建模和计算,推导了一种适于大范围空间运动的四节点索单元,利用动力松弛法进行三维索结构找形计算。     

An adhesively laminated plate element for PZT smart plates

An adhesively laminated element taking into consideration peel stress is developed for a piezoelectric smart plate. In this novel finite element analysis formulation, a four node piezoelectric element is firstly derived, and an adhesive element of finite thickness with both shear and peel stiffness is sandwiched between two collocated four node plate elements to form an adhesively laminated element for a piezoelectric smart plate. In this framework of finite element analysis, because the displacement filed in this adhesively laminated element is continuous and a plate element is derived based on the Reissner–Mindlin plate theory, and thus it can be accurately applied to a thin or moderately thick host plate with bonded or debonded piezoelectric actuators and sensors. The formulation is performed for an isotropic host plate and a fiber reinforced laminate plate. Numerical results are presented to compare with those of the exact solutions for smart beams, and validate with the experimental results of the isotropic and composite host plates available in the literature. Using the present finite element analysis formulation, energy transfer stresses in the adhesive and equivalent forces induced in the host plate are investigated. The present formulation is demonstrated to allow debondings of piezoelectric patches and the debonding detection.The authors are grateful to the support of the Australian Research Council via a Discovery Projects grant (grant No: DP0346419).     

Anomalous behavior of bilinear quadrilateral finite elements for modeling cohesive cracks with XFEM/GFEM

The performance of partition‐of‐unity based methods such as the generalized finite element method or the extended finite element method is studied for the simulation of cohesive cracking. The focus of investigation is on the performance of bilinear quadrilateral finite elements using these methods. In particular, the approximation of the displacement jump field, representing cohesive cracks, by extended finite element method/generalized finite element method and its effect on the overall behavior at element and structural level is investigated. A single element test is performed with two different integration schemes, namely the Newton‐Cotes/Lobatto and the Gauss integration schemes, for the cracked interface contribution. It was found that cohesive crack segments subjected to a nonuniform opening in unstructured meshes (or an inclined crack in a structured finite element mesh) result in an unrealistic crack opening. The reasons for such behavior and its effect on the response at element level are discussed. Furthermore, a mesh refinement study is performed to analyze the overall response of a cohesively cracked body in a finite element analysis. Copyright © 2013 John Wiley & Sons, Ltd.