单层双曲椭圆抛物面网壳弹塑性稳定性能

基于通用有限元软件ANSYS及自编的前后处理程序,有计划地针对400余例单层双曲椭圆抛物面网壳结构进行双重非线性全过程分析,系统地考察了屈曲模态、塑性发展分布等特征响应,总结初始缺陷和荷载不对称分布以及考虑材料非线性等因素对网壳弹塑性稳定承载力的影响规律,对现有网壳规程中安全系数取值进行重新核定。结果表明:双曲扁网壳屈曲模态通常表现为局部结点的跳跃失稳,并主要发生在网壳角部支座或边缘跨中位置;有缺陷双曲扁网壳的极限承载力可按完整结构的74%取值,并且此类结构对于荷载不对称分布不敏感;同时建议双曲扁网壳稳定性验算中安全系数的取值应根据不同结构形式和几何参数确定,取值范围为4.67~5.16。     

单层球面网壳的弹塑性稳定性

为了解和掌握单层球面网壳在静力荷载作用下的弹塑性稳定性能,采用有限元软件ANSYS及自编的前后处理程序对典型单层球面网壳结构稳定性能进行对比分析,初步了解了球面网壳弹性与弹塑性稳定性能的主要差异。在此基础上进行了1000余例K8型单层球面网壳弹性、弹塑性全过程分析,同时考虑竖向均布荷载的不对称分布、初始几何缺陷等因素对球面网壳稳定性能的影响,掌握了以上因素变化对球面网壳弹塑性稳定性能的影响规律,并将其定量化。最后,通过对弹性、弹塑性稳定极限承载力的统计分析,提出适用于K8、K6型球面网壳的塑性折减系数,用以表示材料非线性对极限承载力的影响。这些成果的获得为进一步开展网壳结构的弹塑性稳定性能研究以及工程实践提供了理论依据和技术参考。     

Elasto-plastic instability of single-layer reticulated shells under dynamic actions

This paper addresses the issue on dynamic collapse mechanism of single-layer reticulated shells subjected to harmonic load, sudden load and seismic load. The method for failure mechanism has reviewed the relationship between the response of the reticulated shell and the peak acceleration of dynamic action. Besides, the steel damage accumulation is considered in the method by compiling a user subroutine based on the computing program ABAQUS. An example is introduced to describe dynamic instability collapse resulting from geometric nonlinearity of the shell and the other example is presented to describe strength failure resulting from excessive development of plastic deformation, for it is discovered that the structure is not only to be prone to instability collapse in dynamic action. According to the responses of the single-layer reticulated shell under dynamic loads, this study discusses the relationship between the failure model and the corresponding dynamic load parameters. Then, the method for distinguishing failure modes is proposed based on the fuzzy synthetic evaluation theory and the structural responses of sufficient samples at the failure state. The technique feasible to be used to distinguish different failure modes of single-layer reticulated shells under different dynamic loads is validated.     

Elasto-plastic stability of single-layer reticulated domes with initial curvature of members

Initial curvature of members is an inevitable geometrical imperfection for reticulated domes. To investigate the stability of single-layer domes with initial curvature of members, the multi-beam method was presented to simulate the initial curvature of members, and two modeling methods were adopted to introduce the initial curvature of members for reticulated domes by means of ANSYS. First, the random imperfection mode method was introduced according to the randomness of initial curvature of members. The example of a Kiewitt-8 dome was used to explain the method and investigate the influence of angle and amplitude random variables on the stability of reticulated domes. Second, the modified consistent imperfection mode method was obtained, which was an efficient method to evaluate the lowest buckling load of the structure with initial curvature of members. Based on this method, the Kiewitt-6 and Kiewitt-8 single-layer reticulated domes were taken as examples to analyze the stability of structures with initial curvature of members, and the influences of initial curvature of members on the ideal structure and the structure with nodes deviation were obtained quantitatively. The results show that, for the ideal structure and the structure with nodes deviation, initial curvature of members can decrease the buckling load of the structure obviously. Initial curvature of members can change the buckling mode and plasticity development of the structure. The influence of initial curvature of members on the elasto-plastic stability of single-layer reticulated domes cannot be neglected.     

Research on stability of single-layer inverted catenary cylindrical reticulated shells

The structural configuration and method of analysis of the single-layer inverted catenary cylindrical reticulated shell are introduced in this paper, and the elastic as well as elastic–plastic stability of this kind of reticulated shell is then investigated. The stability of the structures with different types of grid patterns is compared, and the reasonable grid pattern is hence recommended. The structural buckling mode and ultimate load-carrying capacity are studied in detail by parametric analysis. Influence of various factors on structural ultimate load is investigated, and the fitting formula of ultimate load is thus presented. Comparison analysis between the inverted catenary and circular cylindrical reticulated shells is also carried out. The work will provide guidance in theory for practical applications of this kind of structure.     

半刚性节点单层球面网壳整体稳定性分析

上海国际会议中心单层球面网壳采用的贯通式节点属于半刚性节点,这种节点的弯矩一转角关系可以采用分段等效剐度的方法来考虑。本文采用一致模态法分析了考虑节点刚度和不考虑节点刚度时的网壳在两种荷载工况下的整体稳定性,并研究了节点刚度对网壳整体稳定性的影响。     

非对称荷载作用下K6型单层球面网壳结构的动力稳定性

为了研究非对称荷载作用下K6型单层球面网壳结构的动力失稳机理,采用数值模拟和试验方法,依据结构峰值加速度和节点最大位移曲线将失稳过程分为3个阶段:线性阶段、非线性阶段和失稳阶段,定义了两个关键点:临界点和失稳点.研究表明,K6型网壳结构峰值加速度-节点最大位移曲线能够很好地描述结构整体的动力失稳过程,提出用临界点作为判定结构动力失稳的依据更为保守,增大结构刚度能明显提高网壳结构的稳定性;网壳结构危险点的分布位置受荷载的作用形式、荷载的大小以及输入地震波的频谱特性等因素影响,结构在线性阶段危险点点位是相对确定的,而在非线性阶段危险点点位是不确定的.数值模拟分析结果和地震振动台实验结果能够较好地吻合,验证了数值模拟计算的正确性.     

节点刚度对凯威特型单层球面网壳稳定性的影响

稳定性是单层球面网壳理论与设计中的突出问题，影响稳定性的因素众多．本主要就节点刚度，引入一种节点模型，采用ANSYS软件，通过常见的凯威特型单层球面网壳，分析这一因素对整体稳定性的影响，得出一些有意义的结论。     

屋面系统对单层球面网壳稳定性及地震响应的影响研究

单层球面网壳的静力稳定性及抗震性能已经取得较为系统的研究成果,但在传统的研究方法中,学者们只考虑结构部分,忽略了屋面板、吊顶、隔墙等非结构构件的影响;其中,屋面系统作为一类非结构构件,其平面刚度较大、在动力荷载下的阻尼也较大的特点会在一定程度上影响结构的受力特性。因此,选取考虑屋面系统的单层球面网壳作为研究对象,开展屋面系统对于单层球面网壳弹塑性稳定性及抗震性能的影响研究。采用有限元分析软件ABAQUS分别建立带屋面系统单层球面网壳和传统单层球壳的数值模型;通过弧长法分别对两种模型进行均布荷载作用下的非线性数值模拟,对比分析屋面系统对单层球面网壳弹塑性稳定承载力的影响;对考虑屋面系统的网壳结构进行不同地震荷载作用下的时程动力分析,采用基于响应的分析方法,考察屋面系统对于网壳结构抗震性能的影响,得到屋面系统会显著提高网壳整体刚度、增强结构抗震能力的结论;本研究可为以后网壳结构的理论研究及工程实践提供一定的参考。     

强震下单层柱面网壳损伤及失效机理研究

基于结构损伤理论,对单层柱面网壳在强震下的失效机理进行研究。单层柱面网壳在强震下不仅会发生动力失稳,也可能由于过度塑性发展导致动力强度破坏的模式。对于动力强度失效的研究,应当在分析中考虑材料损伤累积以及断裂效应的影响。为在有限元分析中包含这一影响因素,编制了基于通用有限元软件ABAQUS的用户材料子程序,具有较高的计算精度和较好的收敛性。应用其对单层柱面网壳在强震下的响应进行参数研究,并与基于理想弹塑性材料时的响应对比,讨论考虑材料损伤对网壳失效特征的影响。将单层柱面网壳在强震下失效时刻的多项特征响应进行统计分析,拟合了能够表征网壳损伤程度的损伤模型,建立单层柱面网壳在强震下的失效判别准则。针对实际工程抗震设计中采用损伤累积本构模型计算的困难,提出网壳结构失效极限的简化判别方法。     

正交正放单层鞍型网壳在强震下的失效研究

对跨度40m正交正放单层鞍型网壳在强震作用下的失效机理进行研究。通过典型算例探讨结构在强震作用下的响应特征,考察结构的节点位移、不同屈服程度杆件比例、不同失效程度杆件等多项结构响应随荷载强度递增的变化规律;可认为单层鞍型网壳在强震下发生明显的动力强度破坏,综合结构的典型响应提出一种失效极限荷载的确定方法。在系统参数分析的基础上,讨论高跨比、屋面质量、初始缺陷等因素对结构失效极限荷载的影响规律,并讨论考虑下部支承结构刚度因素对上部鞍型网壳强震失效极限荷载、失效模式的影响规律。     

节点刚度对四边支承单层柱面网壳稳定性的影响

利用ANSYS有限元软件建立了半刚性节点单元模型,对四边支承单层柱面网壳进行了几何非线性全过程分析,主要考察考虑初始几何缺陷和荷载不对称分布情况下,节点刚度变化对柱面网壳稳定性的影响规律.研究结果表明,四边支承单层柱面网壳当缺陷相同时,刚度减弱,极限荷载下降,且抗弯刚度的影响较强;缺陷增大,扭转刚度对四边支承柱面网壳的影响增强;同一刚度下,随着缺陷的扩大,极限荷载呈下降趋势,随着刚度的减小,缺陷对网壳极限荷载的影响程度减弱;荷载不对称分布导致四边支承柱面网壳结构极限荷载降低至对称荷载作用情况的80％左右,缺陷变化使得节点刚度对极限荷载的影响程度有所改变,但对承载力终值影响不大.     

Wind loading and its effects on single-layer reticulated cylindrical shells

In this paper, the wind load distribution as well as its effects on single-layer reticulated cylindrical shells, which are widely used in practice, is investigated. At first, wind pressure distributions on three rigid cylindrical shell models considering different shape ratios are measured simultaneously in a wind tunnel. Some special characteristics of the measured wind pressure, especially its fluctuating component, are discussed. Then, considering the special structural mechanical behaviors, the effects of wind load, especially the fluctuating component, on the limit load-carrying capacity and the stability of the shells are investigated by both equivalent static analysis and dynamic analysis. Suitable methods to get a reasonable estimation of wind load effects in estimating the equivalent static wind load distribution for such shells are investigated. Finally, with comparison analyses using different methods mentioned in this paper, the efficiency of the method in estimating the effective wind load distribution presented by the authors previously for single-layer reticulated spherical shells is demonstrated, and some advices for estimating the wind load distribution on single-layer reticulated cylindrical shells is given for wind-resistant design in practice.     

六种网格形式的单层球面网壳的风振响应

分析六种网格形式的单层球面网壳的风振响应，在频域内直接求解网壳风振响应（位移、内力、加速度）的统计值，研究不同网格形式及不同矢跨比对单层球面网壳风振响应的影响。     

单层网壳结构动力稳定性分析方法

本文系统分析了单层网壳结构动力稳定性的研究方法。论证了对于在复杂荷载作用下非线性、多自由度复杂结构的动力稳定性问题,基于严格数学定义的Lyapunov运动稳定性理论目前尚不能提供有效的判别准则。通过理论分析和计算指出“刚度矩阵的正定与负定”不足以判定结构是否动力失稳。提出了动力响应全过程曲线的概念,并以此曲线为基础结合结构的时程响应曲线来判定网壳结构的动力稳定性。通过对不同类型荷载、不同计算条件下的网壳结构的弹性和弹塑性动力稳定性的分析,验证了本文所提判别方法的合理性。     

短程线型单层球面网壳的自振特性分析

采用LANCZOS方法系统地分析了短程线型单层球壳的自振特性,考虑了不同矢跨比、不同跨度、不同屋面荷载、不同的杆件截面面积和不同支座条件等参数的影响,得出了短程线型单层球面网壳结构的自振规律。     

预应力局部单双层扁网壳的参数分析与近似优化

预应力局部单、双层扁网壳具有较好的室内视觉效果和良好的经济性。其结构参数的确定属多级别优化问题,实施困难。为满足初步设计的需要,提出采用均匀设计法进行结构的参数分析与近似优化。它可利用现有软件来实现。作为算例,对一个柱支承预应力扁网壳进行了参数分析,得到了网壳用钢量、变形和极限荷载系数与三个主要设计参数(单层部分材料设计应力折减系数、单层部分范围和预应力值)之间的近似函数关系,并找出了满足规范要求的各参数之间的较理想的最优水平组合。设计检验说明了分析结果的可靠性。该方法可为解决类似优化问题提供参考。     

单层K6型球面胶合木网壳结构受力性能试验研究

为分析不同节点刚度、矢跨比对单层K6型木网壳结构受力性能的影响,设计了4个跨度为4m,矢跨比分别为1/10、1/5,连接节点分别为单列、双列螺栓的缩尺比1∶10网壳试件,进行了全跨、半跨以及破坏荷载作用下的试验。研究结果表明：在不同加载阶段,试件节点位移基本呈顶点位移最大,1环其次,2环最小的趋势,矢跨比对试件的初始刚度影响较大;半跨加载阶段,矢跨比对试件刚度的影响比全跨加载阶段更明显;破坏荷载作用阶段,矢跨比对提高试件跨中挠度达到l/400（l为跨度）时的加载值的影响更大,节点刚度对提高杆件出现第2条裂缝时的加载值的影响更大;矢跨比越大,试件由于节点处应力集中而易发生开裂,节点刚度提高有利于抑制第2条裂缝的发生,并减缓试件刚度的退化;矢跨比大的试件易发生承载力破坏,矢跨比较小的试件易发生失稳破坏。     

单层柱面铝合金网壳结构强震失效机理及地震易损性

通过有限元分析软件ABAQUS建立了单层柱面铝合金网壳结构的有限元分析模型,利用增量动力分析方法（IDA）对网壳结构进行强震作用下动力响应全过程分析,获得了单层柱面铝合金网壳结构强震失效模式。基于模糊数学理论提出单层柱面铝合金网壳结构强震失效判别方法,结合结构损伤理论拟合网壳结构强震损伤因子,通过大规模参数分析定义适用于铝合金网壳结构的损伤程度分级,对铝合金网壳结构不同损伤状态进行划分。通过随机抽样选取一定数量的结构-地震样本,对铝合金网壳结构开展地震易损性分析,通过回归分析建立地震易损性函数,获得单层柱面铝合金网壳结构的概率地震易损性曲线。结果表明：通过结构地震易损性分析可以看出铝合金网壳结构具有良好的抗震性能,在强震作用下保持基本完好或仅有轻微破坏的概率较大。     

基于杆系离散单元法的单层网壳结构屈曲行为研究

离散单元法因适合处理大位移、非线性和非连续等问题而逐渐被应用于结构工程中,但采用离散单元法进行结构屈曲全过程分析还有待研究。为此,基于杆系离散单元法的基本理论和计算方法,提出离散元力控制法及离散元位移控制法,研究上述方法在结构弹性屈曲全过程分析中的特点及适用性,同时给出离散元位移控制法（力控制法不需要单独处理）对不同荷载工况的处理方法及离散元法在进行结构弹性屈曲分析时的计算流程。采用Fortran语言自编程序,对典型算例进行弹性屈曲全过程分析,与传统方法相比,该方法无需组集刚度矩阵,对几何非线性问题不需特殊处理即可模拟结构的屈曲行为,更具优越性,并通过结果对比,验证了离散单元法在单层网壳结构弹性失稳全过程分析中的有效性。