Effect of joint stiffness on the stability of cable-braced grid shells

Bolted joints used in cable-braced grid shells are typically semi-rigid joints, and the joint stiffness has a significant effect on the stability of cable-braced grid shells. The effect of joint stiffness on the stability of cable-braced grid shells is studied in this paper. Based on the experimental results of improved bolted joints, finite element models of elliptic paraboloid cable-braced grid shells with bolted joints are established, and spring elements are used to simulate the joint stiffness. The effect of the joint stiffness on the nonlinear buckling load is studied by changing the joint stiffness. The main conclusions are as follows. First, the joint rotational stiffness has a significant effect on the failure mode. When the joint rotational stiffness is small to a certain extent, the failure mode of cable-braced grid shells changes from overall buckling to local buckling. Second, the nonlinear failure mode is similar to the first-order eigenvalue buckling mode and the maximal compression stress distribution. The structural integrity is weakened, and the maximal steel tube compression stress decreases with the decrease of the joint rotational stiffness. The smaller the joint rotational stiffness, the lower the utilization rate of steel strength. The results suggest that the joint stiffness of elliptic paraboloid cable-braced grid shells should not be less than 20% of the rigid joint stiffness.     

基于B样条的自由曲面结构形态创构方法研究

在B样条曲面上设定关键点并引入参考平面,利用所设定的关键点形成B样条曲面与参考平面上参数化B样条曲线确定的内外边界,采用Delaunay网格划分技术进行三角划分,生成能够适应复杂边界的自由曲面初始结构。利用关键点坐标的变化与自由曲面应变能的关系,推导了应变能对关键点的敏感度,建立了结构应变能最小化的自由曲面结构形态创构的方法,解决了以节点为优化变量计算效率低且优化后曲面不光滑需要二次加工的问题。研究结果表明,所提出的方法可以解决在实际工程应用中具有复杂边界的自由曲面形态创构问题,可以创构出自由、灵活的多种合理自由曲面结构,由此获得的曲面结构具有刚度大、承载力高,同时最大限度地抑制了弯矩的产生,且具有初始缺陷对结构受力性能影响减小的特点。     

球面网壳非规则网格划分方法研究

非规则网格球面网壳是一种用于特殊领域的新型结构,目前国内还没有这种结构理论方面的研究.基于多面体网壳拓扑关系及构型特征,提出了通过球面五边形旋转实现非规则网格构型的理论和基本技术,根据一个基本单元内三角形个数及划分方法确定五边形边长.推导了三角形多面体网壳的基本计算公式,实现了非规则三角形网格多面体网壳的计算机可视化建模,说明本文的构型理论和计算公式是合理的、可行的.     

Hybrid optimization of hierarchical stiffened shells based on smeared stiffener method and finite element method

In this study, Smeared Stiffener Method (SSM) of hierarchical stiffened shells is derived to release the prediction burden of buckling loads. Then, a minimum-weight optimization formulation for hierarchical stiffened shells is developed based on SSM, attempting to demonstrate the higher lightweight potential of hierarchical stiffened shells compared to the traditional ones. Further, the main aim of this paper is to present a hybrid optimization framework of hierarchical stiffened shells including imperfection sensitivity, combining the efficiency of SSM with the accuracy of FEM, since there are currently no closed-form solutions to take imperfections into account accurately. The illustrative example demonstrates that the proposed framework has a higher optimization efficiency and global optimization capability compared to the conventional methods.     

Shape optimization of aluminium alloy spherical reticulated shells considering nonlinearities

This study proposes a shape optimization method for K6 aluminum alloy spherical reticulated shells with gusset joints, considering geometric, material, and joint stiffness nonlinearities. The optimization procedure adopts a genetic algorithm in which the elastoplastic non-linear buckling load is selected as the objective function to be maximized. By confinement of the adjustment range of the controlling points, optimization results have enabled a path toward achieving a larger elastoplastic non-linear buckling load without changing the macroscopic shape of the structure. A numerical example is provided to demonstrate the effectiveness of the proposed method. In addition, the variation in structural performance during optimization is illustrated. Through parametric analysis, practical design tables containing the parameters of the optimized shape are obtained for aluminum alloy spherical shells with common geometric parameters. To explore the effect of material nonlinearity, the optimal shapes obtained based on considering and not considering material non-linear objective functions, the elastoplastic and elastic non-linear buckling loads, are compared.     

自由形态空间网格结构建模技术研究综述

自由形态空间网格结构是指结构整体几何形态不能用解析函数精确表达或拟合,并能以任何方式自由变化的空间网格结构,具有形式多样化和自由化的特点,但其网格划分存在一定的难度.本文总结以往的研究成果,将其归纳和汇总为三种自由形态空间网格结构建模的思路,然后总结并分析比较了用于自由形态网格生成的典型方法的特点、性能及其应用,总结了网格质量的衡量指标及网格优化方法,同时对曲面造型方法及曲面优化方法进行介绍,最后对自由形态空间网格结构建模技术的发展做出展望.     

基于鲁棒性的索穹顶结构形状优化设计

针对索穹顶结构缺乏有效的鲁棒性分析方法及基于结构鲁棒性能的优化设计现状,首先构建该类结构鲁棒性评价方法,然后结合实际工程案例分析Geiger型、Levy型和Geiger-Levy组合型3类索穹顶结构鲁棒性随结构榀数、环索圈数及矢跨比等形状参数的影响.在此基础上,采用遗传算法,进一步探索基于结构整体鲁棒性能的结构形状优化...     

基于节点应变能灵敏度的拱轴线形状优化

结合两个算例,研究了基于节点应变能灵敏度拱轴线选择的方法,指出根据节点应变能灵敏度进行结构形状优化,降低了结构应变能,改善了结构的综合性能,达到了更加合理的结构形态。     

Computational generation of free-form shells in architectural design and civil engineering

This study develops a computational model of free-form shell generation in the design of roof structures that rely on the optimized behavior of the membrane theory of thin shells. For architects and engineers, the model offers a low cost, fast, and relatively easy design solution. A computational model for structural free-form shell generation is presented to simulate physical models of shell optimization. This method of designing optimized structures is based on mathematical programming combined with the finite element technique, and is inspired by the laws of nature and, in particular, by the Heinz Isler methods of designing shells using physical models. A flexible membrane is simulated automatically, initially in the horizontal plane surface, with any shape and boundary conditions, and able to carry several specified loads. The membrane under the action of these loads is deformed until reaching one of its equilibrium configurations, which defines the middle surface of the shell to be built. By the principle of minimum total potential energy, the positions of steady equilibrium of the membrane correspond to the local minimum points of the total potential energy function. When the total potential energy function does not exist, it is advisable to use an incremental Newton–Raphson-type method to find the solutions for the nonlinear system of equations given by the equilibrium equations of the membrane in the space. Structural analysis of thin concrete shells with the final shapes of the optimized membranes demonstrates which displacements and principal stresses are optimal. The computational method presented in this paper could be integrated, for example, with Contour Crafting (CC), a layered fabrication technology that offers the potential to construct full-scale buildings directly from three-dimensional computer-aided design models (3D CAD). Structural behavior is in accordance with the membrane theory of thin shells and aesthetic appeal is a natural consequence of the forms generated for applications in architectural design and civil engineering.     

基于可靠度的单层网壳稳定设计方法

基于可靠度的钢结构稳定设计理论,提出了通过抗力分项系数验算网壳结构稳定性的方法。在确定分项系数时,分别考虑了材料、几何初始缺陷和计算模式的不确定性,使用基于响应面函数的蒙特卡罗模拟方法对结构进行二阶弹塑性分析。首先对两个网壳试验模型的试验结果做了数值分析对比,验证了本文有限元模型的有效性。然后选择应用最广的K8作为重点对象,使用基于响应面函数的蒙特卡罗模拟方法对结构进行考虑初始缺陷的二阶弹塑性分析,得出了抗力分项系数。     

基于方格网法对工程土方量精度计算的研究

对建设项目土方量计算中使用最常用的方格网法进行研究与分析,总结出影响土方量计算精度的主要因素,通过建立计算精度模型解决了不同条件下方格网法计算偏差的控制问题。     

基于动网格技术的阻力型风机气动性能数值模拟

以一种新型阻力型叶片为研究对象,利用动网格技术的数值模拟方法,对叶片在多个转速下进行数值模拟,得到叶片的输出扭矩、输出功率和风能利用系数,结果表明,转速在30 r/min时叶片气动性能效果最佳。     

异频法测试大型地网接地电阻技术的研究

针对用工频大电流法和三极法测量大型地网接地电阻时抗干扰能力不足,介绍了异频法测量接地电阻的原理、测试频率的选择方法及测试仪器的参数,结合测试实例,验证了异频法的有效性,并分析了测试频率和测试引线布线方式对测试结果的影响,以期解决地网干扰电流等问题。     

桁架形状优化的自适应协方差矩阵进化策略方法

自适应协方差矩阵进化策略(CMA-ES)是在进化策略算法(ES)基础上发展起来的一种新的全局优化算法,对于处理复杂非线性多峰值优化问题具有很好的适用性.结合有限元方法,提出一种桁架形状优化的自适应协方差矩阵进化策略方法.采用空间25杆桁架和平面37杆桥形桁架两个桁架形状优化的经典算例对方法的可行性和先进性进行验证,其中,空间25杆桁架分为不考虑局部稳定约束和考虑局部稳定约束两种情况进行计算.研究结果表明,该方法是可行的,与基于遗传算法、粒子群优化算法等现代全局优化算法的桁架形状优化方法相比较,具有寻优效率高、收敛速度快、全局优化能力强的优点,在获得相同精度最优解的条件下,调用有限元分析的次数明显较少,从而有效地减少了计算耗时.     

基于网架结构极限承载力的优化设计方法

对网架结构极限承载力的分析表明,是否考虑压杆稳定对于网架极限承载力有较大影响,因此需计入压杆失效效应.基于网架整体极限承载力由压杆屈曲失稳控制的理论,提出了加大压杆计算长度系数来提高网架结构承载力的方法.对多个网架结构算例进行了极限承载力分析,结果显示,加大压杆计算长度系数,可将40m至64m跨度内网架结构的极限承载力提高40%以上,同时对于其他跨度网架结构极限承载力的提高也较为有效.因此,通过适当提高压杆的计算长度系数,在用钢量增加不多的情况下,可大幅度提高网架结构的极限承载力,并可相应提高网架结构的抗连续倒塌能力.     

基于贴体同位网格法的空调气流组织数值模拟

针对建筑物复杂外形的结构特点,创建了贴体网格生成方法和基于同位网格的数值模拟算法。在通过与实验进行对比验证的基础上,数值模拟了不规则屋顶建筑物、大型体育馆等复杂外形建筑物内的气流组织分布。研究结果表明:所提出的基于贴体网格的同位布置算法及其计算程序具有较好的通用性,能用于各种不规则几何形状空调建筑内气流组织的数值模拟研究。     

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。     

基于振型加速度法的桁架结构拓扑优化设计

基于振型加速度法和全局收敛的移动渐近线法(GCMMA)求解结构动力响应及其灵敏度,建立了以结构材料用量最小为目标,指定自由度位移和杆件应力的均方差为约束的拓扑数学模型,最后以一桁架结构的优化算例验证了所提方法的有效性。     

基于改进双向渐进结构优化法的桁架结构拓扑优化

为了将双向渐进结构优化法应用于桁架结构优化设计中,结合能量原理和满应力设计准则,推导了以结构最小应变能为目标函数的优化计算公式,提出了可以应用于桁架结构优化的桁架-双向渐进结构优化(T-BESO)法.T-BESO法以杆件截面面积为设计变量,以结构应变能为目标函数,以应力约束和满应力设计准则为约束条件.在T-BESO法中...     

正方形边界悬垂织物自由形态的逆向实现

以正方形边界悬垂织物模型的逆向实验为例,研究自由形态的逆向实现技术,将正方形边界悬垂织物模型经三维扫描,得到表征自由形态特征的点云数据,基于逆向软件处理点云数据,得到重构曲面并生成初始网格,引进条带化旋转展开技术,进一步综合运用三维造型软件与三维打印技术,设计自由形态空间网格结构并可将其快速打印成型,验证了逆向实现技术的可行性。