Double-layer Space Research Articles

Comparative Study of Optimal Flat Double-Layer Space Structures with Diverse Geometries through Genetic Algorithm

This paper investigates the structural performance of flat double-layer grids with various constitutive units, addressing a notable gap in the literature on diverse geometries. Six common types of flat double-layer grids are selected to provide a comprehensive comparison to understand their structural performance. Parametric models are built using Rhino and Grasshopper plugins. Single- and multi-objective optimization processes are conducted on the considered models to evaluate structural mass and maximum deflection. The number of constitutive units, the structural depth, and the cross-section diameter of the members are selected as design variables. The analysis reveals that the semi-octahedron upon square-grid configuration excels in minimizing structural mass and deflection. Furthermore, models lacking a full pyramid form exhibit higher deflections. Sensitivity analyses disclose the critical influence of the design variables, particularly highlighting the sensitivity of structural mass to the number of constitutive units and cross-section diameter. These findings offer valuable insights and practical design considerations for optimizing double-layer grid space structures.

Experimental and Numerical Analysis for Eccentricity Solution in Double-Layer Space Truss

This paper shows an extensive study on the Typical Connections used in Double-Layer Space Truss. For this structural system, the ends of the bars are flattened to connect the bars. However, the flattening process results in a highly plastic stamping zone susceptible to warping with the appearance of two eccentricities, one of which causes rotation of the connection, with the presence of a bending moment with local rupture resulting in progressive collapse of the entire coverage system, as already evidenced in several countries. Therefore, eccentricity in this paper is studied and an analytical solution to the problem is presented through the use of a new device called a spacer. Furthermore, a preliminary study with complex numerical simulation was carried out with nonlinear analysis in ABAQUS were evaluated. For this study, nine space trusses were experimentally tested with reinforcement spacer in reduced trusses. After confirming the efficiency of the spacer proposal, another six space trusses were tested in the laboratory, this time, on a full-scale. In this study, two types of spacers were evaluated, one made of USI SAC 350 steel and another cheaper one made from recycled tires from heavy vehicles with multiple filaments of steel and nylon wires in the rubber layers. The two devices presented very close resistance capacity values, with a resistance gain of approximately 30% in relation to connections without reinforcement, with structural failure characterized by buckling of the bars. Finally, a numerical study of space trusses with spacers was developed. In practical design terms, from these FE simulations it was possible to determine the normal stresses for different spacers applied in the different modeled spans.

Progressive collapse demolition of double-layer space truss under different demolition load conditions

Two double-layer space trusses (DLSTs) under different demolition load conditions were tested for progressive collapse demolition. The primary load-carrying members of the tested DLSTs were removed one by one according to a pre-designed demolition process. The global structural responses, including the strains of the members on the main force transmission paths and the vertical displacements of representative joints, were measured. The structures' internal force redistributions and load-carrying mechanisms were investigated based on the experimental results and the corresponding FE analysis. The results show that both the tested DLSTs achieved progressive collapse demolition as expected. The two tested DLSTs under different demolition load conditions followed the same internal force redistribution patterns and exhibited three identical mechanical characteristics: arch action, catenary action, and beam action. The removal of specific members will change the load-carrying mechanism of the DLST and lead to local or global collapse.

PhloVer: A Modular and Integrated Tracking Photovoltaic Shading Device for Sustainable Large Urban Spaces—Preliminary Study and Prototyping

In this work, a flower-shaped shading system with integrated tracking photovoltaic, suitable for sustainable extensive urban coverages, is designed. Detailed photovoltaic energy yield simulations with a single-diode model approach are performed to disclose the potential of the proposed tracking photovoltaic shading device (PVSD). Simulations are performed with reference to a case study. A double-layer space truss is used to house the innovative modular photovoltaic tracking system, and the first application is envisaged for the coverage of a public market area of a sunny municipality in Southern Italy. By comparing it with the traditional photovoltaic fixed system, the results of the simulations show a steadier energy generation of the new PVSD, and it also provides better coverage with renewable energy during the hours of the day when the traditional system produces low electric energy. Lastly, an early interactive prototype of the PVSD system is presented. The tracking mechanism is carefully designed, 3D-printed at a small scale and tested with a motorized dynamic system controlled by a microcontroller board. The realization of the physical prototype and the engineering of the movement mechanism confirmed the feasibility and the correct functioning of the conceived system opening to real-scale applications.

Study on progressive collapse demolition method of double-layer space truss

This paper conducted a demolition test of a double-layer space truss (DLST) to investigate more efficient, safe and environmentally friendly demolition methods of truss systems. The high-speed 3D displacements of representative joints and the global dynamic strain response of the structure were well collected. The internal force redistribution and load-carrying mechanisms of DLST structures during demolition were explored. The results indicate that new equilibrium states were sought in the DLST through local and global internal force redistribution. When the main force transmission members were removed, the load-carrying mechanism of the DLST underwent sudden changed, which resulted in a snap-through in the structural load-carrying capacity. The test DLST exhibited three load-carrying mechanisms in time sequence during the proposed demolition: arch action, catenary action, and beam action. The theoretical vertical load-carrying capacity provided by each load-carrying mechanism was investigated separately. Finally, a progressive collapse demolition method was presented for the engineering DLST structures subjected to certain demolition external loads.

Buckling-Controlled Member for Improving the Ductile Behavior of Double-Layer Latticed Space Structures

In this paper, a new buckling-controlled member (BCM) is introduced for use in space structures. This member is composed of four components; namely: the encasing, joints, core, and adjustable nuts. The core is intended to act as a structural element to resist the axial loads by its yielding under compression loading. The steel encasing is supposed to confine the steel core. Adjustable steel nuts on the steel core act as lateral bracings and are responsible for lateral load transmission between the encasing and core. The joints at the two ends of the supports of the member. Six experimental tests have been performed under compression load to show the efficiency of the new member. The test results reveal that the proposed member can provide the needed ductility and can delay the brittle buckling of the members. Also, the BCM is capable of considering buckling modes and controlling the plastic range. The experimental and numerical results have also been compared. Additional numerical evaluations have been carried out using finite element models, in which the effects of different parameters of the member have been investigated. The obtained results showed that the arrangement of inner elements is the main factor affecting ductility and postponing the buckling of the members. In the end, the effects of the BCMs on the overall behavior of four double-layer space structures have been studied. The obtained results of analyses indicated that the BCMs can enhance the strength and ductility of space structures, thereby reducing the risk of collapse. Also, the seismic collapse of the space structure was postponed.

Nonlinear technique of prestressing spatial structures

One of the crucial aspects of the design of structural space systems is the degree of prestressing since it is involved in the load transferring, deformability and charges. The prestress state can be reached via required member alteration. This paper presents an efficient nonlinear numerical approach based on the force method for prestressing the spatial nonlinear structures to the desired level through computing nonlinear actuation as a function of external nodal displacements. Two equations are derived for indicating the required amount of member alteration eo and prestressing level by using Taylor's series and Pade approximation methods. This technique can be applied to both rigid and flexible spatial structures. The present technique is validated based on three numerical examples, and the computational findings are in well agreement with the compared methods. The results show that the new approach requires less effort and makes greater economic sense. Moreover, the member forces with concern to nonlinear eo of double-layer space grid structure by imposing lack of fit of some members successfully obtained.

Estructura espacial con elementos a cortante desarrollables

En este artículo se revisita la clásica cercha espacial de doble pared reemplazando las diagonales por módulos poliédricos curvos de paredes delgadas. Las mejoras esperadas son tanto tecnológicas como mecánicas. Los nodos complejos de 8 ramas se dividen en una conexión de dos miembros continuos superpuestos y una conexión lineal entre las barras y los bordes del poliedro. La curvatura en las caras y bordes de los módulos introduce resistencia por forma y estabiliza los miembros frente al pandeo. La optimización global de la estructura se realiza mediante un proceso de búsqueda de forma basado en la parametrización individual de los módulos.Finalmente, se lleva a cabo una validación experimental mediante la fabricación y prueba de un prototipo a escala real (de 6 x 6 m aproximadamente).

Novel soft members in double-layer space trusses

Progressive collapse of space structures has received much attention in recent years due to the recent failure of a double-layer space truss (DLST) stadium in Terengganu, Malaysia which collapse twice in Year 2009 and 2013. There is a considerable interest in understanding the collapse behaviour of space structures and possibility of improving its collapse behaviour. This phenomenon was demonstrated by earlier researchers, such as Collins (1981) and Parke (1988) which investigated the collapse behaviour both theoretically and experimentally. In their study a carefully designed DLST structure may possess reserve of strength in excess of their elastic capacity. Although DLST have a high degree of statically degree of statically indeterminacy, not all of them are robust, as it has been found a loss of one critical member could trigger the collapse of the entire structure. Usually the collapse of the DLST is influenced by the ductility behaviour of the compression members. The aim of this study was to investigate the use of novel soft member to reduce the catastrophic progressive collapse behaviour of DLSTs. A novel soft member was constructed to measure its behaviour under tensile and compressive loads. The term novel soft member used in this study is referred to a combination of three circular tubes which is made into one component and is used to support compressive load. It was found that using a blend of three circular tubes significantly increase the ductility behaviour of the member. These test illustrates that while the inner and outer tube experience compressive forces, the middle tube will continue to increase linearly. This indicates that there is a possibility of improving the collapse behaviour of DLST by incorporating the novel soft member.

Assessment of the Progressive Collapse Resistance of Double-Layer Grid Space Structures Using Implicit and Explicit Methods

A double-layer grid space structure is a conventional long span structure used where large column-free areas are required. Due to its’ large indeterminacy and the redundancy of its structural configuration, it is normally considered in design practice, that progressive collapse will not be triggered when the loss of an individual member occurs. However, research and several prior accidents have shown that progressive collapse could occur following the loss of some critical members when the structures are subject to abnormal loading such as heavy snow. To investigate the structural behavior of this type of structure, a 3D finite element model of a double-layer space structure grid was built by the authors, several collapse scenarios have been investigated using an implicit method which follows the alternative path method defined in GSA. In addition, case studies have been made using the explicit method which is to simulate the whole process of the structural collapse. In the analysis, different members failure or support collapses were studied. The response of the structure was investigated and the correspondent potential of progressive collapse was discussed in detail. Methods to mitigate the progressive collapse of this type of space structure have also been recommended.

Stable boron nitride nanocomposites based membranes for high-efficiency proton conduction

Proton conduction is a not only a universal and fundamental process in nature but also have been widely used in energy- and environment-related applications. Achieving high-efficiency proton conduction is very important in these areas. Herein, stable and selective membranes with novel ionic nanochannels based on functionalized two-dimensional boron nitride nanocomposites (NBN) are successfully fabricated. The proton conductivity of Nafion-sNBNM at 80 °C - 95 %RH is as high as 0.44 S cm−1. At the same time, NBN-sNBNM shows impressing stability at high-humidity conditions and in redox environments. The high proton conductivity could be attributed to the favorable microphysical and microchemical environments of the nanochannels in the membranes. On one side, the double-layer space among the closely assembled NBN propels the local surface-charge enhanced proton conduction. On the other side, the formation of connected long-range ionic nanochannels and quasi-isotropic architecture facilitate the long-range proton conduction. Benefiting from the excellent stability of NBN, the proton conductivity of Nafion-sNBNM at high-temperature and low-humidity conditions could be conveniently increased by H3PO4 adsorption. Furthermore, Nafion-sNBNM also shows low methanol permeability and high membrane selectivity. These outstanding properties of Nafion-sNBNM demonstrate great application potential in many areas.

Reliability Analysis of Space Structures Using Monte-Carlo Simulation Method

The existence of initial imperfections in manufacturing or assemblage of real structures is inevitable. Many of these imperfections in double-layer space structures, such as the curvature and length imperfections, are random in nature. In this paper, the effect of initial curvature imperfection in the load carrying capacity of double-layer space structures is investigated. For this purpose, three different types of supports are considered. The curvature imperfection is considered as a random number by gamma distribution. The probabilistic model is used to distribute random imperfections among all members of the structure. Collapse behavior and the ultimate capacity of the structures are determined using nonlinear analysis and this procedure is repeated by Monte Carlo simulation method. The results show that the collapse behavior of double-layer grid space structures is sensitive to the random distribution of initial imperfections.

Optimum Design of Double-layer Barrel Vaults by Lion Pride Optimization Algorithm and a Comparative Study

In this article, the newly developed optimization method, so-called the Lion Pride Optimization Algorithm (LPOA), is applied to optimal design of double-layer space barrel vaults. In order to demonstrate the performance of the LPOA, three large-scale benchmark optimization design problems of double-layer barrel vaults are optimized and the results are compared with those of some metaheuristics from literature. The second aim of this article is to solve these examples using three other robust metaheuristic algorithms, namely Artificial Bee Colony (ABC), Cuckoo Search (CS), and Particle Swarm Optimization (PSO). A comparative study of these algorithms shows the suitability of the LPOA for solving real-world practical spatial truss structures.

Field-measured Performance of Lightweight Roof Chimney Integrated with DC fans

This paper present the results of an experimental comparative research investigation of the thermal performance and heat gain reduction between two houses built with light roof. The first one is installed with a lightweight roof chimney (LRC) integrated with a DC fan while the one is a house installed with a simple lightweight roof (SLR). The south facing roofs of the two houses were made of clear polycarbonate sheets with the same dimensions. The LRC with DC fan configuration consists of double-layer space with a small air gap and two openings located at the bottom (interior side) and at the top where an exhaust fan is installed (exterior side). This design is aimed to induce natural ventilation and indoor air circulation. The 12V-0.40A DC fans are employed to increase ventilation to remove polluted indoor air to the outside environment. The outer roofs and the inner roofs (ceiling) are made of polycarbonate sheets and gypsum boards respectively. The experiment revealed that indoor air temperature of the house with LRC and DC fans appears to be significantly lower than that of the house with SLR. As a result, this LRC integrated with DC fans can become a tool not only for reducing the attic and indoor temperatures but also inducing natural ventilation, saving energy and promoting solar energy integration in buildings and houses such that protecting the environment.

Probing the Probabilistic Effects of Imperfections on the Load Carrying Capacity of Flat Double-Layer Space Structures

Load carrying capacity of flat double-layer space structures majorly depends on the structures' imperfections. Imperfections in initial curvature, length, and residual stress of members are all innately random and can affect the load-bearing capacity of the members and consequently that of the structure. The double-layer space trusses are susceptible to progressive collapse due to sudden buckling of compression members. Progressive collapse is a chain of local failures leading to the collapse of either the entire or a part of the structure. In this paper, the effects of the probabilistic distribution of initial curvature and length imperfections on the bearing capacity of flat double layer grid space structures for different member’s length and support conditions have been studied. First, equal to the number of the members of the structure, two sets of random numbers have been generated using the Gamma and Gaussian distributions to account for the initial curvature and the length imperfections, respectively. Thereupon, the amount of the imperfection randomly varies from one member to another. Afterward, based on the Push-Down analysis, the ultimate load-bearing capacity of the structure was determined through nonlinear analyzes performed through the OpenSees software and this procedure for certainty was repeated numerous times. Finally, based on the Monte Carlo simulation method, the structure’s reliability diagrams and tables were procured. The acquired results indicate that the behavior of flat double-layer space grids are sensitive to and can be affected by the random distribution of initial imperfections.

Improving double-layer space trusses collapse behavior by strengthening compression layer and weakening tension layer members

Progressive collapse is a chain of local failures leading to the collapse of either the entire or a part of the structure. The double-layer space trusses are susceptible to progressive collapse due to sudden buckling of compression members. The method of strengthening the compression layer members along with weakening the tension layer members is an effective method for retrofitting the double-layer space truss behavior against progressive collapse. In this study, the method is applied on offset double-layer space truss models with different support conditions, members’ geometrical imperfections, height, and shapes, and the effectiveness in increasing the structure’s ductility and load-bearing capacity is demonstrated. The results show that the method converted the sudden collapse of the structures into a beneficial gradual (progressive) collapse. More specifically, for double-layer space trusses comprising members with similar geometrical imperfection, strengthening the compression layer chords along with weakening the tension layer chords within 30%–40% will significantly improve the ductility and load-bearing capacity. In addition, the results show that the method can decrease the weight of the structures and consequently provide more economical structures.

Development of a new connector for double layer space grids

Summary Connection of the space grid elements by using connectors is one of the most common practices for construction of space structures. These connectors usually involve higher fabrication cost due to their complex geometry. To address this issue, in the present work, a new solid connector with simple geometry has been developed by truncating the corners of a cube, and is named as Truncated Hexahedron (THH). The experimental, theoretical and analytical studies have been carried out to obtain the stresses for THH connector. An instrumented axial loading test has been performed on actual THH connector, and the load-stress relationship has been obtained from load and strain measurement. A manual finite element analysis has also been carried out for theoretical computation of the stresses in the connector. Further, the THH connector has been modelled and analysed using ANSYS software and the obtained results have been compared with experimental and theoretically computed results. Subsequently, in order to assess the performance of THH connector in comparison to a standard connector (Spherical connector), a double layer grid has been analysed considering both Spherical and THH connectors at each joint of the grid separately, and it has been observed that the maximum principal stresses in both the connectors are mostly comparable. Hence, the newly developed THH connector can be considered to be as efficient as the Spherical connector. The study opens up a possibility of resorting to a new compatible connector for space grid structures, which can be easily manufactured due to its uncomplicated geometry, making it comparatively cheaper and quicker for fabrication.

An Experimental and Analytical Investigation on a Newly Developed Truncated Hexahedron Connector

Objective: The objective of thisresearch work is to investigate the performance of a newly developed Truncated Hexahedron (THH) connector by analytical and experimental studies, and assess its suitability for space grid structures. Method/Analysis: The newly developed THH connector has been modeled in Finite Element Analysis Software - ANSYS and analyzed under uniaxial tension. Experimental studies on a real scale THH connector has been conducted with strain gauges attached on faces of the connector in form of three-element rectangular rosette. The maximum principal stresses on the surface of the connector obtained from ANSYS analysis have been compared with the experimentally obtained maximum principal stresses. Findings: The present study evaluates the principal stresses of the THH connector subjected to axial tensile loading by conducting analytical (ANSYS software) and experimental studies.Further, tolerable resemblance was observed in values of analytically and experimentally obtained maximum principal stresses on the surface of the connector. Hence, this validates the ANSYS model for the THH connector, which may be useful for evaluating the allowable load on the connector. The analytical studies conducted for different magnitude of vertical loading in double layer grid indicates linear variation of maximum principal stresses with the increase in the magnitude of loading. The newly developed THH connector has advantage of less length of web members in double layer or multilayer space grids as compared to MERO connectors, which will reduce the total weight of space grids. Novelty/Improvement: This study opens up possibility of resorting to a new compatible connector for space grid structures, which can easily be manufactured due to simple geometry, making it comparatively cheaper.

Effect of Random Distribution of Member Length Imperfection on Collapse Behavior and Reliability of Flat Double-Layer Grid Space Structures

The existence of initial imperfections in manufacturing of double-layer space structures having thousands of members is inevitable. Many of the imperfections, such as member length imperfections, are all random in nature. In this paper, the probabilistic effect of member length imperfection in the load bearing capacity of double-layer grid space structures with different types of supports have been investigated. First, for the member length imperfection of each member, a random number is generated from a normal distribution. Then, the imperfections are randomly distributed amongst the members of the structure. Afterwards, the ultimate bearing capacity of the structure is determined by using nonlinear analysis and this procedure is frequently repeated using Monte Carlo simulation method. Ultimately, based on the maximum values of bearing capacity, structure's reliability diagrams are obtained. The results show the sensitivity of the collapse behavior of double-layer grid space structures to the random distribution of initial imperfections.

Random imperfection effect on reliability of space structures with different supports

The existence of initial imperfections in manufacturing or assembly of double-layer space structures having hundreds or thousands of members is inevitable. Many of the imperfections, such as the initial curvature of the members and residual stresses in members, are all random in nature. In this paper, the probabilistic effect of initial curvature imperfections in the load bearing capacity of double-layer grid space structures with different types of supports have been investigated. First, for the initial curvature imperfection of each member, a random number is generated from a gamma distribution. Then, by employing the same probabilistic model, the imperfections are randomly distributed amongst the members of the structure. Afterwards, the collapse behavior and the ultimate bearing capacity of the structure are determined by using nonlinear push down analysis and this procedure is frequently repeated. Ultimately, based on the maximum values of bearing capacity acquired from the analysis of different samples, structure's reliability is obtained by using Monte Carlo simulation method. The results show the sensitivity of the collapse behavior of double-layer grid space structures to the random distribution of initial imperfections and supports type.