surface fitting approach for tensile membranes design - Tecnun

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It is important to have into account that using the formfinding method, the shape of the structure isobtained, as a collection of nodes and elements linking these nodes. We have to consider also, that themembrane is located into a scene with more objects around it, like trees, buildings, beams, persons, etc.So, a design tool in which the complete scene is shown while modifications are introduced, could be avery useful tool for the designers. Actually, there is a lack of design tools for covering this design stage,and actual formfinding tools solve it partially. The aim of this paper is to introduce a new approach fortensile membranes design, to cover the conception stage, in which the shape of the structure is defined.Requerimentsarchitectslack of design toolsConstruction, elevationConceptionMembrane cutting &manufacturingDetailingConstructors, othersCutting patterngenerationAnalysisFormFindingEngineers (Computer based tools)Figure 2. Tensile membrane design processOnce the conception stage has been completed, a static analysis of the structure is carried out. Materialproperties are assigned to the membrane and stress distribution is obtained under different loads andboundary conditions.The next step in the design process is called cutting pattern generation. This method allows us tocalculate the optimum way of cutting the membrane. Based on a geometrical process, flat strips areobtained, to comply with the desired shape.Many computer based tools covering static analysis and pattern generation can be found, butspecialized users are required to complete both tasks. In the majority of the existing software foranalysis and cutting pattern generation, many parameters need to be defined to complete the study, andthe interface with the user is not always as friendly as desired.Finally, detailing of the structure is carried out. Those details concerning foundation, structure supports,masts, connections, clamps, cable selection, drawings and many others are defined in this stage.After detailing is completed, membrane cutting is carried out, according to the previous cutting pattern.Once the strips are joined, the completed membrane is prepared for the construction of the structureand the elevation of the membrane.Figure 2 shows a diagram with the different stages of the membrane design process and the peopleinvolved in each of these stages. The following sections of this paper will cover the stage related withthe membrane shape conception.2 Design tools for tensile membranesMost of the existing software tools for membrane design and analysis are oriented to advanced users,and require a detailed knowledge of the analysis method. Even those tools focused on the form-findingprocess require specialized users, and many tasks need to be carried out to complete the analysis. It isvery common to come across with complex and non intuitive software for these tasks.There is clearly a lack of specialized tools to cover the initial design stage of the process, wheregeometric shapes are being defined according to several specifications. Many shapes are generated atthis stage, until the final shape is reached.
Figure 3 shows some pictures in which tensile membranes are combined with other shapes and objectsin the same scene. In this example, a space needs to be covered using tensile membranes structures.Two rectangular shapes represent the buildings. On the left side, a row of columns delimit the centralspace. This could be a usual statement of a project, and many layouts can be obtained until the finalshape is reached. One or more membranes could be used to cover the space. So, it is not only necessaryto calculate each of the shapes, but also to orient and place them in the appropriate position. The shapeof any membrane should be recalculated in real time, as the position of the vertex is modified by thedesigner. A flexible tool is required to achieve all these requirements, and a complete view of the sceneis needed to obtain an appropriate solution.In the left side of Figure 3, an initial sketch of the desired layout is drawn. In the right side, usingcomputer based techniques, a solution has been reached to comply with the initial requirements. Twopossible layouts are shown, with three (a) and four (b) membranes.(a)(b)Figure 3 Example of design tool scene for tensile membranes.(a) three membranes layout (b) four membranes layout.We will use this example to enumerate different features that a software tool should offer to thedesigner. The application should allow the designer the possibility of drag and drop any object of thescene, and obtain the new shape of the membrane in real-time. Each membrane has different materialproperties, boundary conditions and applied loads. In the same environment, many membranes shapesare evaluated in real-time and the complete scene offers the designer a whole integration of thestructure with the objects around it. So, formfinding is only a stage in the design process.Other features of interest could be: easy to use, flexible enough to modify any object in the scene,material library, predefined objects with various shapes and sizes, open to CAD systems (neutralformats like dxf, iges or step), and Windows based controls to obtain a user-friendly environment.These could be the requirements for most of the designers. In the next section, a computational methodis described, that would cover the described requirements for the design tool.3 Hybrid method for tensile membrane designAs described before, a combined method for membrane calculation has been performed. The methodcombines structural behavior (formfinding) and geometry (surface fitting) to offer a robust and fastmethod for tensile membrane design and analysis.Basically, the method consists in the representation of the membrane structure using a parametricsurface. This surface is based on the results of the previous structural analysis.The process diagram of the hybrid method proposed is shown in Figure 4.
Page 1: SURFACE FITTING APPROACH FOR TENSIL
Page 5 and 6: The analysis of tensile structures
Page 7 and 8: Computational times for Force Densi

surface fitting approach for tensile membranes design - Tecnun

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