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What Is Membrane Structure Shape-Finding?

May. 13, 2020

Whether or landscape membrane structure, membrane structure stands now that chose to Commercial Membrane Structure this kind of building Structure, so the shape is one of the features of the relative, the shape of the membrane structure is to not only beautiful but also to ensure the stability of the membrane structure architecture firm, so find a shape when the design is very important, membrane structure manufacturers will introduce membrane structure for skills and common shape of Membrane Structure.

I. principle of shape finding of membrane structure

1. Importance of shape finding of membrane structure

The shape finding of membrane structure is the initial step of membrane structure design. In this process, it is necessary to comprehensively consider the plane, elevation requirements and building functions of the building, as well as the supporting conditions of the lower part to determine the curved surface that meets the boundary conditions and the requirements of mechanical balance. In fact, the design of the membrane structure breaks the traditional "building first, structure later" design method, requiring architects and structural division in the proposal phase will be closer together, jointly determine the shape of the building.

From the point of view of mechanics, the shape-finding problem of membrane structure can be reduced to solving the initial equilibrium problem of the space surface. This problem involves the following important parameters:

(1) topological relation of structure;

(2) physical strength and facial strength;

(3) structure geometry;

(4) geometric boundary conditions;

(5) the size and distribution of the initial pre-tension.

Among them, structural topological relation refers to the connection between different structural components, which can also be understood as the connection between structural units in the computer finite element model. Physical force and surface force refer to the dead weight and external load of the structure, and the external load is usually zero in the shape-finding stage. The structural geometry is the solution required in the shape-finding phase and generally belongs to the unknown quantity. The geometric boundary conditions and the initial pre-tension are usually determined by the structural engineer according to the building conditions and construction conditions, which are the main independent variables in the shape-finding stage. It can be said that looking for shape is to seek the balance of the above factors.

2. Matters needing attention for shape finding of membrane structure

(1) the bending of the surface should be reciprocal in two directions, that is, it should be a negative gaussian surface. The tension membrane structure is affected by wind pressure and wind suction, and the surface with reciprocal directions can make the membrane surface restrict each other in two directions and effectively transfer the external load.

(2) avoid large flat areas. Large flat areas appear on the surface, which means the natural stiffness of the surface is low, the ability to bear a vertical load is weak, and it is easy to accumulate water or snow. In order to increase the stiffness of the surface in the flat region, a very large amount of prestressing needs to be applied to the surface, which will result in a very large force acting on the boundary member, or even impossible to implement.

(3) the ups and downs on the surface should be gentle, to avoid "sharp Angle".A too drastic change of curvature will lead to stress concentration.

(4) reasonably determine the position of the supporting point to ensure that the film surface has a large curvature. The ratio of arch height to chord length along the main curvature direction of the membrane should be greater than 1:20.

(5) when conditions permit, flexible edge members (cables) and movable connection methods (such as floating cap ring at the top of the mast and articulated connection structure at the joints) should be preferred to adapt to deformation, ensure the stress in the film is as uniform as possible, and avoid stress concentration or folding of the film under the action of load;

(6) for the more important membrane structure, an appropriate number of additional garages should be arranged outside the membrane material to fix the main supporting members, so as to ensure that the structure will not collapse due to the damage of the membrane material;

(7) the layout of the supporting structure should also consider the specific construction process, secondary tension, and membrane material replacement;

(8) the span of the single film should not exceed 15 meters, and the coverage area should not exceed 400 meters; If the limit is exceeded, additional reinforcement cables should be added appropriately.

(9) the size of the pre-tension needs to be determined by the expected shape and design load. Under the action of the design load, the tensile stress value which can maintain the shape of the curved surface should be guaranteed inside the structure. If the pretension is too small, the structure will vibrate under the wind load. Too much pretension will bring difficulties to the design and construction of supporting structures (including foundation). Generally, for PVC Membrane materials, the pre-tension level is 1 ~ 3kN/m, and for PTFE Membrane for roofing system, the pre-tension level is 3 ~ 6kN/m.

PTFE Membrane For Roofing System

PTFE Membrane For Roofing System

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