The design of membrane structure mainly includes four major problems: body shape design, initial equilibrium shape analysis, load analysis and cutting analysis. Through the shape design, the shape, size, three-dimensional shape and clearance volume of the building are determined, the coordinates and structure of each control point are determined, and the membrane material and construction scheme are selected. The initial equilibrium shape analysis is the so-called shape-finding analysis.
Since the membrane material itself has no compressive and flexural rigidity, the shear strength is poor, so its stiffness and stability need to be improved by the curvature of the membrane surface and the prestressing thereof. For the membrane structure, it does not exist at any time. There is no stress state, so the film surface shape must finally meet the mechanical balance under certain boundary conditions and certain prestress conditions, and use this as a benchmark for load analysis and cutting analysis.
At present, the methods for shape-finding analysis of membrane structures mainly include dynamic relaxation method, force density method and finite element method. The loads considered for the membrane structure are generally wind and snow loads. The deformation of the membrane material is large under load, and the load distribution changes with the change of shape. Therefore, the geometrical nonlinear method should be used to accurately calculate the deformation and stress of the structure. Another purpose of the load analysis is to determine the initial pretension in the cable and membrane.
Under the external load, the stress in one direction increases and the stress in the other direction decreases. This requires that the initial tensile stress be applied to such an extent that the stress does not decrease to zero under the most unfavorable load, that is, no wrinkles occur. Because the membrane material is relatively soft, the natural vibration frequency is very low, and the wind vibration is easily generated under the wind load, which causes the membrane material to be destroyed. If the initial prestressing is applied too high, the coating of the membrane is increased, the aging is easy, and the strength reserve is small. The strength requirements of the stressed members are also high, which increases the difficulty of construction and installation. Therefore, the determination of the initial prestress is determined by the load calculation. The touch structure formed by the shape-finding analysis is usually a three-dimensional non-expandable space surface. How to form the required three-dimensional space surface by the cutting of the two-dimensional material is the most critical problem in the whole membrane structure engineering. The main content of the cropping analysis.
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