Design Of Space Structures Research Articles

A simplified strategy for force finding analysis of suspendomes

The suspendome has been widely used as the structural roof system of sports buildings in recent years. It is a kind of hybrid space structure composed of an upper rigid single-layer latticed shell and a lower flexible tensegrity (cable–strut) system. The prestress level in the lower cable–strut system is of great significance for the suspendome structure because it has no initial geometric stiffness (for a rib–ring type) before prestress is introduced into the lower tensegrity system. The traditional solution for calculating the self-internal-force mode and the prestress force level (force finding) is somewhat complicated; in general it is based on the Equilibrium Matrix Theory. In the present paper, a simplified computational strategy for the determination of the self-internal-force mode based on the nodal equilibrium is presented for the tensegrity system in a suspendome which is grounded on a newly developed method: the Local Analysis Method. Two types of cable–strut arrangement, the Levy system and the Geiger system, are addressed, and the characteristic of each type is expounded. An analytical solution for the self-internal-force mode of the lower cable–strut system is put forward together with the equivalent nodal force acting on the upper single-layer dome for the two types of cable–strut arrangement. The determination of the prestress level of the lower tensegrity system is then elucidated on the ground of the initial architectural configuration, the counterbalance of the bearing reaction, the equivalent nodal force, and the wind-induced slackening effect. An illustrative example is appended in the end to validate the efficiency of this simplified method. It is shown that force finding, at the viewpoint of structural design, based on this method is of great accuracy and efficiency. The prestress in the outermost ring generally has the highest level among the cable–strut system, and has the most influence on the structural performance of the suspendome. The results from the studies can be referred to not only for direct design use in practical engineering, but also for the design of similar hybrid space structures.

Optimum Shape Design of Space Structures by Genetic Algorithm

Space structures are usually highly indeterminate and therefore have a large number of redundant members. It is important to choose the appropriate number of elements and joints for the structure under consideration. Optimum shape design of space structures is the aim of the present work and to achieve an optimal configuration, parameters such as number of joints, number of members, support conditions and the overall shape of the structures are considered. To attain a practical configuration, the presence of the joints of the structures and the locations of the columns are taken as the shape design variables as well as the cross-sectional area of the elements of the structures under considerations. The resulting configurations are very interesting after the removal of unnecessary joints and columns. It was also observed that a part of sphere might not be appropriate for the dome structures as usually chosen by the designers. For different static loading conditions that presented in this research, second or third order polynomial would be more suitable for the shape of these structures. In this study, optimum shape design of space structures is performed using a modified genetic algorithm (MGA).

柔軟宇宙構造物のセンサ・アクチュエータ配置問題：逐次LMIによる線形化拘束条件

In this paper, we address simultaneous structure/controller design of flexible space structures. In particular, we consider optimal placement of sensors and actuators together with control design. Even though the original problem is non-convex, we transform it into a convex one via a novel approach. In particular, nonlinear parameter relationship is described as a bound of a convex region in a parameter space. Approximating the region from the inside by a set of successive LMIs, we seek optimal solutions that approach the bound of the region.

An augmented Lagrangian optimization method for inflatable structures analysis problems

This paper describes the development of an augmented Lagrangian optimization method for the numerical simulation of the inflation process in the design of inflatable space structures. Although the Newton–Raphson scheme was proven to be efficient for solving many nonlinear problems, it can lead to lack of convergence when it is applied to the simulation of the inflation process. As a result, it is recommended to use an optimization algorithm to find the minimum energy configuration that satisfies the equilibrium equations characterizing the final shape of the inflated structure subject to an internal pressure. On top of that, given that some degrees of freedom may be linked, the optimum may be constrained, and specific optimization methods for constrained problems must be considered. The paper presents the formulation and the augmented Lagrangian method (ALM) developed in SAMCEF Mecano for inflatable structures analysis problems. The related quasi-unconstrained optimization problem is solved with a nonlinear conjugate gradient method. The Wolfe conditions are used in conjunction with a cubic interpolation for the line search. Equality constraints are considered and can be easily treated by the ALM formulation. Numerical applications present simulations of unconstrained and constrained inflation processes (i.e., where the motion of some nodes is ruled by a rigid body element restriction and/or problems including contact conditions).

Space Structures for Low-stress Environments

This paper examines the criteria for the architectural design of space structures in low-stress environments, where stress-carrying ability is no longer a relevant consideration in the design of the space structure. In such environments, ergonomics and minimum surface criteria can lead to the most efficient design of the space structure. Based on these two criteria, the paper then considers the architectural design of a space tunnel and an interchange station. In direction-controlled artificial gravity environments, the nesting of ergonomic shapes, for minimum surface area, can lead to even more cost-effective design. 3–D computer graphics are used to display the results of this research.

Nonlinear spectral dynamic analysis of guyed towers. Part I: Theory

One of the important parameters in the analysis and design of large space structures is to account for the dynamic forces induced by wind and the subsequent progressive collapse. During the past two decades, problems of extreme loading conditions have been considered by some authors, and special attention has been devoted to the collapse modes. Nonlinear time history dynamic analysis, involving the post-buckling characteristics of the space structures, may be analyzed using the conventional finite element method. However, to guarantee stability and accuracy of the solution, the number of elements used to model the structure may be very large. In this respect, the nonlinear spectral element method (SEM) is developed for analyzing dynamic problems in large space structures. Through use of a computer program, the proposed method has been used to obtain the nonlinear dynamic response of guyed power transmission towers under severe wind loading condition. Key words: nonlinear dynamic analysis, space structures, guyed towers, spectral element method.

On using genetic algorithms for optimum damper placement in space trusses

Although similar in some ways to the design of aircraft and other lightweight structures, the optimal design of space structures has several unique challenges. A flexible optimization system allowing for multiple analysis techniques and including continuous and discrete design variables is desired. Although not as computationally efficient as traditional optimization techniques, genetic algorithms meet this requirement.

Design of Large Space Structures with Imperfection Using ANN-Based Simulator

Based on the advanced computational plasticity and an artificial neural network (ANN) simulator, a new design strategy has been presented for large space structures with imperfections. Nonlinear system identification approach has also been greatly spread among the researchers and engineers in the past few years. The neural network simulators as a non-parametric system identification approach present a robust and efficient way to simulate the nonlinear behaviour of engineering systems. In the paper herein an artificial neural network (ANN) simulator, a general back error propagating perceptron, is use to simulate random imperfection for nonlinear dynamic analysis of large space structures. It is also desirable to search for a procedure for wind pressure calculation with accuracy and reliability. In this respect, attention is paid to the advanced computational fluid dynamics (CFD). The use of the advanced CFD analysis can help engineers to estimate the wind pressure for the design of large space structures with complex geometries. The characteristics of the new design method have been shown graphically using a full documented numerical example, which highlights the efficiency of the new simulation method. The purpose of this paper is to present a new design method, which takes into account the effects of imperfection on the resulting dynamic responses of large space structures under gravity, temperature and wind loadings.

Simulation of Impact Effects on Large Space Structures Using Advanced SE Method

One of the important parameters in analysis and design of large space structures is to account for the possible forces induced by flying object impact and the subsequent progressive collapse. Conventional finite element methods have been used successfully in linear and nonlinear dynamic analyses of large space structures. During the past three decades, problems of contact mechanics have also been considered by some authors, and special attention has been devoted to high speed impact. Impact wave propagation in space structures may be analyzed using the conventional finite element method. However, in order to guarantee stability and accuracy of the solution, the number of elements used to model the structure may be very large indeed; more precisely, accurate results can be obtained only after a substantial computational effort. In this respect, the spectral element method (SEM) is developed for analyzing the wave propagation problems in large space structures. Using a computer program, the proposed formulation has been used to derive the impact global dynamic responses of a large dome structure.

Nonlinear elastoplastic dynamic analysis of single-layer reticulated shells subjected to earthquake excitation

A nonlinear dynamic finite element technique is developed to analyze the elastoplastic dynamic response of single-layer reticulated shells under strong earthquake excitation, in which the nonlinear three-dimensional beam elements are employed. An elastoplastic tangent stiffness matrix of three-dimensional beam element is derived by using the updated Lagrangian formulation, in which the isotropic hardening model, the Von-Mises yield criterion and the Prandtl–Reuss flow relations are applied to this study. This procedure considers both geometric and material nonlinearities. In this paper, several condensation and reduction techniques in matrices and degrees of freedom are used to simplify the analysis. An incremental-iterative technique based on the Newmark direct integration method and the modified Newton–Raphson method is employed for obtaining the solutions of the nonlinear dynamic equilibrium equations. Moreover, an accurate method is developed to compute the large rotations of space structures. As a numerical example, the elastoplastic dynamic response of a single-layer reticulated shell under strong seismic excitation is investigated. It is shown through the numerical example that the method developed in this paper is efficient for the nonlinear dynamic response analysis and plastic design of space structures.

Studying form – Innovation in Structural Engineering Education

This paper summarises the authors' experience in the design and implementation of an innovative course in structural engineering education. A course on structural form and behaviour of “non-conventional” or space structures, which primarily focuses on form-finding through physical modelling, is described, although, where appropriate, computer modelling is also encouraged. Several case studies of student work are presented and the insights acquired by the students are discussed. It is concluded that the design of space structures, based on qualitative assessment of their functionality and performance, should be given more prominence within the civil and structural engineering curriculum.

Optimum design of cold-formed steel space structures using neural dynamics model

Optimization of space structures made of cold-formed steel is complicated because an effective reduced area must be calculated for members in compression to take into account the non-uniform distribution of stresses in thin cold-formed members due to torsional/flexural buckling. The effective area varies not only with the level of the applied compressive stress but also with its width-to-thickness ratio. For statically indeterminate structures a new effective area has to be calculated for each member in every iteration of the optimization process. As such, the constraints are implicit, non-smooth, and discontinuous functions of design variables. The patented robust neural dynamics model of Adeli And Park (U.S. patent 5,815,394 issued on September 29, 1998) has been adapted for optimum design of space trusses made of commercially available cold-formed shapes in accordance with AISI specification. A CPN network was developed to learn the relationship between the cross-sectional area and dimensions of cold-formed channels. The model has been used to find the minimum weight design for several space trusses commonly used as roof structures in long-span commercial buildings and canopies, including a large structure with 1548 members with excellent convergence results.

Passive Vibration Suppression of Flexible Space Structures via Optimal Geometric Redesign

Acomputationalframework is presented for the design of large flexible space structures with nonperiodicgeometries to achieve passive vibration suppression. The present system combines an approximationmodel management framework (AMMF) developed for evolutionary optimization algorithms (EAs) with reduced basis approximate dynamic reanalysis techniques. A coevolutionary genetic search strategy is employed to ensure that design changes during the optimization iterations lead to low-rank perturbations of the structural system matrices, for which thereduced basis methods give high-quality approximations. The k-means algorithm is employed for cluster analysis of the population of designs to determine design points at which exact analysis should be carried out. The fitness of the designs in an EA generation is then approximated using reduced basis models constructed around the points where exact analysis is carried out. Results are presented for the optimal design of a two-dimensional cantilevered space structure to achieve passive vibration suppression. It is shown that significant vibration isolation of the order of 50 dB over a 100-Hz bandwidth can be achieved. Further, it is demonstrated that the AMMF can potentially arrive at a better design compared to conventional approaches when a constraint is imposed on the computational budget available for optimization.

Practical aspects of numerical simulations of dynamic events: effects of meshing

The use of finite-difference and finite-element computer codes to solve problems involving fast, transient loading is commonplace. A large number of commercial codes exist and are applied to problems ranging from fairly low to extremely high damage levels (e.g., design of containment structures to mitigate effects of industrial accidents; protection of buildings and people from blast and impact loading; foreign object impact damage; and design of space structures to withstand impacts of small particles moving at hypervelocity, a case where the pressures generated exceed material strength by an order of magnitude). But, what happens if code predictions do not correspond with reality? This paper discusses various factors related to the computational mesh that can lead to disagreement between computations and experience. Subsequent papers focus on problems associated with contact surfaces and material transport algorithms, constitutive models, and the use of material data at strain rates appropriate to the problem. It is limited to problems involving fast, transient loading, which can be addressed by commercial finite-difference and finite-element computer codes.

Practical aspects of numerical simulation of dynamic events: material interfaces

The use of finite-difference and finite-element computer codes to solve problems involving fast, transient loading is commonplace. A large number of commercial codes exist and are applied to problems ranging from fairly low to extremely high damage levels (e.g. design of containment structures to mitigate effects of industrial accidents; protection of buildings and people from blast and impact loading; foreign object impact damage; design of space structures to withstand impacts of small particles moving at hypervelocity, a case where pressures generated exceed the material strength by an order of magnitude). But, what happens if code predictions do not correspond with reality? This paper discusses various factors related to material interfaces in Lagrangian and Eulerian shock-wave-propagation codes (hydrocodes), which can lead to disagreement between computations and experience. Companion papers focus on problems associated with meshing and constitutive models and the use of material data at strain rates inappropriate to the problem. This paper is limited to problems involving fast, transient loading, which can be addressed by commercial finite-difference and finite-element codes.

Seismic Behaviour of Space Structures

Investigations show that the seismic behaviour of space structures may fundamentally differ from the conventional structures. This paper presents the results of dynamic analyses of double-layer barrel vaults with different configurations and support conditions subjected to a severe earthquake, and highlights some basic influential elements in seismic performance of the space structures. The effect of higher modes of vibration has been examined. The significance of the presence of snow loads on dynamic characteristics and seismic performance of space structures is emphasized. Various hysteresis models were used, and the effects of strength reduction and energy dissipation in compression struts were investigated. The results generally indicate that the induced seismic forces are enormously larger than the conventional seismic forces. The consequences of this finding on seismic design of space structures have been discussed, and remedial suggestions have been proposed.

Formex Configuration Processing I

This is the first paper in a series of papers that are intended to cover the present state of knowledge in the field of formex configuration processing. This field of knowledge has been developed during the last three decades and has now reached a level of maturity that makes it an ideal medium for configuration processing in many disciplines. In particular, it provides a rich assortment of concepts that are of great value to the engineers and architects involved in the design of space structures.

Optimal design of planar and space structures with genetic algorithms

One of the most important practical considerations in the optimization of steel structures is that structural members are generally to be selected from available steel profiles. Furthermore, the solutions produced according to the national specifications are undoubtedly valuable from the point of view of applicability in real-life practice. This paper reports the development of a computer-based systematic approach for discrete optimal design of planar and space structures composed of one-dimensional elements. The main characteristic of the solution methodology is the use of a genetic algorithm (GA) as the optimizer. Applications and experience on steel frame and truss structures are discussed. The results of comparative studies of the GA against other various discrete and continuous optimization algorithms for a class of representative structural design problems are reported to show the efficiency of the former. It is observed that a GA often finds the region of the search space containing the global optimum, but not the true optimum itself. Also, in this study an approach based on a proposed multilevel optimization is tested and proved to overcome this shortcoming.

New Structural Forms and New Technologies in the Development of Steel Space Structures in China

The last decades have seen major advances in the research, design and construction of steel space structures (space grid structures) in China. This paper provides a review of these developments, with particular attention to the new technologies and new structural forms employed in China. The following topics on new technologies and new structures are given emphasis: long-span and large-area grid structures; composite space trusses; composite reticulated shells; triple-layer space trusses; partial double-layer (single-layer) lattice shells; prestressed grid structures; cable-stayed grid structures; special grid structures; new types of joints; theoretical work and application research. Prospects for steel space structures in the 21st century are presented at the end of this paper.

Comparative Study of Backpropagation and Improved Counterpropagation Neural Nets in Structural Analysis and Optimization

The present paper, describes the applications of two artificial neural networks, namely the backpropagation neural net (BPN) and the improved counterpropagation neural net (CPN) to the analysis and design of large scale space structures. Different aspects of these nets and parameters affecting the performance of each net is investigated. Two examples are studied, both of which are oriented towards structural optimization. A comparison is made on the performance of these nets The improved CPN is trained faster than BPN, especially when large scale problems are involved. The responses of BPN and improved CPN are compared for the same input.