Decreasing the Displacements of a Composite Saddle-Shaped Cable Roof

The structural possibilities of decreasing the compliance of a composite saddle-shaped cable roof having a compliant support contour are investigated. The use of a supporting contour consisting of cables joined together with tie-bars is considered as a structural method enabling one to decrease the compliance of the roof. Each cable of the support has its own initial flexure. The method is most efficient from the viewpoint of material consumption per unit of covered area relative to the increasing rigidity and prestress level of the cable net.The efficiency of the method was evaluated by a numerical experiment, which was carried out for a composite saddle-shaped cable roof 50 × 50 m in the plan. The roof was formed by two orthogonal cable groups joined with a compliant supporting contour. A hybrid composite cable based on a carbon-fiber-reinforced plastic, a glass-fiber-reinforced plastic, and steel was considered as a material for the cable net in combination with steel. The material consumption and the maximum vertical displacement of the cable net in relation to the initial geometrical characteristics of the supporting contour were obtained. A possibility of decreasing the maximum vertical displacements of the roof by 8% was established.     

Utilization of Composite Materials in Saddle-Shaped Cable Roofs

A saddle-shaped cable roof formed by two orthogonal groups of cables joined with a compliant support contour is considered. The kinematic invariability of the roof obtained by prestabilizing the cables makes it possible to avoid heavy slabs of reinforced concrete in the construction of roofs and to use light composite materials. The main geometric characteristics for a cable roof with CFRP load-carrying and contour cables and steel stabilizing cables are determined by a numerical experiment.     

Dynamic modelling of a multi-cable driven parallel platform with guiding devices

ABSTRACT

In this paper, a mathematical model is presented to numerically simulate the dynamical responses in a multi-cable suspension platform taking into account the slack cables and guiding devices. The state change of the cable (slack versus tensioned) is considered and is described mathematically by a complementary condition equation, and the interactions between the guiding wheels and the shaft wall are described by the Heaviside step function. The Lagrange’s equation with constraints is used to derive the dynamic equations of the system, and a non-smooth generalized-α algorithm for non-smooth phenomena of multibody dynamics is applied to numerically solve the equations. The simulation results have shown the dynamic responses of the platform and the cable tension characters when different cables are excited by different longitudinal excitations. Moreover, the results have illustrated how the cable tension differences may affect the pressure on the shaft wall applied by the guiding devices.     

Dynamic analysis of cable-driven parallel manipulators with time-varying cable lengths

In conventional researches, cables of cable-driven parallel manipulators are treated as simple linear elements that can only work in tension. This results in the fact that the effect of cable dynamics on the positioning precision of the end-effector is not adequately taken into account. To overcome this shortcoming, a dynamic model for cable-driven parallel manipulators with cables of slowly time-varying length is presented in this paper. The partial differential equation characterizing the dynamics of a cable with varying-length is deduced, and converted into ordinary differential equations through spatial discretization by finite difference approximation. Then, the dynamic model for cable-driven parallel manipulators is achieved considering the relationship between the motion of the end-effector and the cable end force, in which the degrees of freedom of cables and the end-effector are all involved. Two numerical examples are demonstrated to validate the dynamic model, and also show that it is necessary to take into consideration the cable dynamics for manipulators of long-span cables.     

Mathematical Modelling of Cable Stayed Bridges: Existence, Uniqueness, Continuous Dependence on Data, Homogenization of Cable Systems

A model of a cable stayed bridge is proposed. This model describes the behaviour of the center span, the part between pylons, hung on one row of cable stays. The existence, the uniqueness of a solution of a time independent problem and the continuous dependence on data are proved. The existence and the uniqueness of a solution of a linearized dynamic problem are proved. A homogenizing procedure making it possible to replace cables by a continuous system is proposed. A nonlinear dynamic problem connected with the homogenizing procedure is proposed and the existence and uniqueness of a solution are proved.     

带人工雨线的拉索在风激励下的响应

通过在风洞中对一具有可调动力特性、雨线位置和风向角的带人工雨线的拉索模型进行了试验,研究了拉索的风雨激振特性.试验结果和其他研究人员的结果进行了仔细对比,得到了一些新的结论,澄清了过去的一些模糊认识.结果表明,带人工雨线的水平索在风向为零时的响应可以用Den Hartog驰振机制来解释,而风向不为零时,拉索表现为限速振动或限速和驰振的混合型振动.     

索结构的静力分析

根据柔索应变与位移的非线性几何关系以及自重作用与温度影响下的平衡方程,采用Euler描述的坐标系统精确地求得了各点的位移和张力的一般解．由索结构静力问题建立的非线性代数方程组应用改进的Powell混合算法编制的高精度DNEQNF程序直接进行求解A·D2在例题中计算了由3根索被一竖直弹簧支撑在一起的索结构,并与其他学者用不同方法得到的结果进行对比．     

带斜拉索的索结构的特征频率分析

计算了带斜拉索的索结构在面内振动的近似特征频率，该索结构的不同位置还带有质点．发现经典传递矩阵法已不足以解决此问题，因此采用较大的外矩阵来确定特征频率方程．然后在对外矩阵渐近估计的基础上，确定一般索结构的动力学性能．     

斜拉桥拉索-阻尼器系统非线性瞬态响应分析

考虑索的抗弯刚度、垂度及几何非线性的影响,得出了索-阻尼器系统的空间非线性振动偏微分方程,用中心差分法将偏微分方程在空间内离散,导出了系统的非线性振动常微分方程组．结合Newmark法及虚拟力法提出了一种用于求解非线性振动瞬态响应的杂交分析算法．并以典型的斜拉桥拉索为研究对象,给出了数值算例,并与Runge-Kutta直接积分法进行了比较,说明了杂交算法的准确性及有效性．为大跨斜拉桥拉索的振动控制研究提供了一种简便、有效、快速的时程分析方法．     

一类四阶变系数振动问题的复合解

以一类斜拉索模型为背景,讨论了一类四阶变系数振动问题.用匹配法导出了方程的复合解,从而较简捷地得出了一类斜拉索的振幅的渐近表达式,并为解决相关类型的变系数问题提供了一种有效的方法.     

Dynamic response of cable-stayed bridges to moving vehicles using the structural impedance method

The importance of dynamic interactions between cable-stayed bridges and heavy moving vehicles, such as trucks and locomotives, has been recognised by bridge engineers for a long time. A structural impedance algorithm is developed for analysing the dynamic response of cable-stayed bridges subjected to traversing vehicles. The bridge deck is modelled as an elastic plate, and the cables are idealised as springs for simplicity. The vehicles are modelled as a series of masses with suspension systems moving with different speeds and accelerations. A comprehensive computer program, CABLESIM, is developed for the static and dynamic analyses of a cable-stayed bridge. The accuracy of the numerical procedure and its computer implementation is verified with the available analytical and experimental results. A parametric study is conducted to investigate the effects of vehicle velocity, girder depth, different types of cable arrangements, and traffic load on the dynamic response of the deck. The numerical results are expected to be important in assessing the dynamics of cable-stayed bridge components and in determining the safety and allowable traffic conditions.     

Static and dynamic behavior of a selected cable-stayed footbridge with respect to change of the cable tension

The paper presents the theoretical analysis of the possibilities of using the authors' own method of actively reducing resonant vibration in cable-stayed footbridges. The method of actively reducing vibration was earlier tested on a laboratory model of a steel footbridge, [1]. The method relies on changing the static tension in chosen cables. The term “active” refers to the fact that the tension changes would only be introduced when resonant vibration of the structure occurred. A change in the cable tensions should cause a change of the natural frequencies for which resonant vibration amplification appeared earlier. Eigenproblem sensitivity analysis, formulated for the structure according to the second order theory, is the basis for choosing the cables in which the tension should change. Apart from analyzing the effectiveness of the active method for reducing resonant vibration, the influence of cable tension change on other values was also studied. These values included the changes in vibration amplitudes, as well as changes of cross-section forces, tensions, and static bend of the structure elements that are most sensitive to tension change. It was also established whether the tension changes in chosen cables, which were large enough to cause a practically significant reduction of resonant vibration, cause exceeding the levels of Serviceability Limit State (SLS) and Ultimate Limit State (ULS) for the structure as a whole or for some of its elements. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Instability of Oscillations in Cable-Stayed Bridges

In this paper the stability of two basic types of cable stayed bridges, suspended by one or two rows of cables, is studied. Two linearized models of the center span describing the vertical and torsional oscillations are investigated. After the analysis of these models, a stability criterion is formulated. The criterion expresses a relation between the eigenvalues of the vertical and torsional oscillations of the center span. The continuous dependence of the eigenvalues on some data is studied and a stability problem for the center span is formulated. The existence of a solution to the stability problem is proved. Some other qualitative results concerning the stability/instability of oscillations are studied as well. This work was supported by Grant ASCR K1019101.     

Flatness‐Based Trajectory Tracking Control of an Underconstrained Cable Suspension Manipulator

Cable suspension manipulators support a payload platform in space by several spatially arranged cables with computercontrolled winches. The winches are mounted either fixed or on movable trolleys. Compared to conventional cranes, it is possible to control not only the translational motion of the payload but also its orientation in order to perform, for example, assembly tasks. By this, cable suspension manipulators combine the ability of cranes to support heavy payloads in a large workspace with the dexterity of robot manipulators. The present contribution treats nonlinear trajectory tracking control of cable suspension manipulators that are kinematically undetermined and statically determined. In particular, the cable suspension manipulator Cablev [4] is considered that has been developed at University of Rostock (Fig. 1). Its payload platform is supported by three cables with winches mounted on trolleys that move themselves on a gantry. Thus, the payload platform may perform sway motions with three degrees of freedom while the cable lengths are kept fixed. Applications are, for example, precise handling and assembling large and heavy components on construction sites or on shipyards. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Approximating connected facility location with buy-at-bulk edge costs via random sampling

In the connected facility location problem with buy-at-bulk edge costs we are given a set of clients with positive demands and a set of potential facilities with opening costs in an undirected graph with edge lengths obeying the triangle inequality. Moreover, we are given a set of access cable types, each with a cost per unit length and a capacity such that the cost per capacity decreases from small to large cables, and a core cable type of infinite capacity. The task is to open some facilities and to connect them by a Steiner tree using core cables, and to build a forest network using access cables such that the edge capacities suffice to simultaneously route all client demands unsplit to the open facilities. The objective is to minimize the total cost of opening facilities, building the core Steiner tree, and installing the access cables. In this paper, we devise a constant-factor approximation algorithm for this problem based on a random sampling technique.     

小垂度粘弹性索非线性响应及振动主动控制

研究具有初始应力的小垂度粘弹性索的非线性动态响应及振动主动控制。在假定索材料的本构关系为一般微分本构类型的基础上,建立小垂度粘弹性索的运动微分方程;应用Galerkin方法将其转化为可用Runge-Kutta数值积分方法求解的一系列三阶非线性常微分方程。在仅考虑面内的横向振动及忽略非线性的情况下得到了连续状态空间中的状态方程,将状态方程离散为差分方程形式,并用矩阵指数来逐步近似状态转移矩阵;基于二次性能指标的最小化得到了最优的控制力与状态向量。最后通过数值仿真研究说明了粘性参数对索动态响应的影响。     

Structure analysis, fatigue testing, and lifetime prediction of composite steels

Composite steels prepared by technology of powder metallurgy are widely used as low cost parts with good resistance to wear, fracture, and corrosion. The development of powder composite steels is directly related to strength under vibration, fatigue stabilizing, and accurate lifetime prediction for actual composite topology. The fatigue behavior of powder steels was studied by experimental and numerical methods of composite mechanics and materials sciences. The chemical composition of composite steel is a pure iron powder as the base material and a handful of carbon, chromium, nickel, or phosphorus powders. The powder multi-component mixture is compacted by cold isostatic pressing to a rectangular form. The compactants are sintered in protective atmosphere. The microscale examination of the composite structure included an METAM-RV-21 metallographic optic microscope with a high-resolution ScanNexIIc scanner and an image processing package on the PC platform. The phase composition of powder steels has complex disordered topology with irregular ferrite/austenite grains, iron carbide inclusions, and pores. The microstructure images are treated according to the theory of stochastic processes as ergodic probability functions; statistical moments and a structural covariance function of the composite steels are given. The microscale stress-strain state of the composite steel is analyzed by finite element methods. The stiffness matrix of the composite steel is also presented together with stiffness matrices of ferrite/austenite grains, iron carbide inclusions, and pores as zero matrices. Endurance limits of the microstructural components are described by the Basquin or Coffin-Manson laws, respectively, as high and low cycle fatigue; cumulative microdamage in loading with a variable amplitude is taken from the Palmgren-Miner rule. Planar specimens were tested by console bending. Symmetric fatigue cycling was performed at a stable frequency of 20 Hz with endurance limits up to 5·10⁶ cycles. The probabilistic S-N curves were studied for various types of the composite steels. The fatigue properties of the structural components such as ferrite/austenite grains and carbide particles were defined by the microscale stress-strain modeling. Structural impact on the fatigue lifetime was computed; the probabilistic fatigue curves of the composite steels of various phase compositions are given. The prediction of cyclic lifetime and fatigue testing show good agreement for the powder composite steels studied.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Perm' State Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 371–382, May–June, 1998.     

社会演进中钢未来使用规律预测及政策分析

运用国际上新兴的动态物质流分析方法,对2014~2100年中国钢使用规律进行预测。研究发现,2014年至21世纪30年代,中国人均钢存量迅速增长,并于2035年以后达到饱和。在联合国中等方差人口增长情景下,2014年以后中国钢总存量出现了先迅速上升、后逐步下降的态势。中国未来钢消费量将于2015年左右达到峰值。2035年以后,钢退役量将超过钢消费量,并于消费峰值出现的30年后达到最大值。根据上述钢未来使用规律,中国应根据消费峰值出现的时间和数量合理安排钢的生产量,并于消费峰值出现之前做好减产准备;提高退役钢的处理能力,加强循环技术研究,实现资源解耦;开拓国际钢铁市场,与初级工业化国家进行产业联合,释放过剩产能。     

Vibration elimination in cable-stayed footbridges and bridges

In this paper, the problems of eliminating vibration in cable stayed footbridges and bridges by dynamically steering the tension in cables during construction vibration are considered. A physical and a mathematical model of cable stayed footbridges and bridges has been formulated. A damping model has been selected on the basis of an analysis of vibrations due to periodic excitation. Standard computer software and the author's own program, both leaning on Finite Element Method (FEM), have been used to analyze the eigenproblem and the forced vibration of bridges. On the basis of the formulated theory an efficient algorithm of forced vibration reduction analysis was established. The reduction is achieved by dynamically steering the tension in cables. A sensitivity analysis has been used. An example has been provided. The theory presented takes into account the new method in the elimination of vibration in cable stayed bridges and footbridges. It can therefore be applied to dynamic analysis of modern cable stayed bridges with typical structure systems. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interdisciplinary design optimization: A search method

The design of architectural structures frequently involves interdisciplinary aspects and aesthetic considerations which, being of subjective nature, are difficult to quantify. The computer-aided design optimization model presented here, therefore, is an attempt to optimize, in an interdisciplinary context, quantifiable parameters only. The objective function is graphically illustrated to give the designer a means to evaluate the impact of esoteric design decisions on performance variables, such as costs. A search method is used, i.e., evaluation of a discrete number of designs and nonlinear interpolation. The model's system of computer programs is demonstrated on the sample of an anticlastic cable roof structure.This paper contains excerpts from Refs. 1–2.