Do You Understand Membrane Structure Design?

Nowadays, the membrane structure is more and more widely used. As the most important and indispensable part of the project, how much do you know about membrane structure design? Below is the fabric roof manufacturer for your analysis.

The membrane structure design is mainly divided into the following four parts:

1. Composition and classification of membrane materials

Second, the shape of the membrane structure is determined

3. Load analysis of membrane structure

4. Cutting analysis of membrane structure

1. Composition and classification of membrane materials

In layman's terms, the membrane material is a film material in which the surface coating of the fluoroplastic is bonded to the fabric base according to a specific process. Commonly used fluorine material coatings are PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PVC (polyvinyl chloride), etc. There are two main types of fabric fabrics, polyester filament (polyester PES), and glass fiber.

Membrane Construction Design

According to the difference between surface coating (Coating) and fabric substrate (Layer), membrane materials are divided into three categories:

(1) Class A membrane material is coated with polytetrafluoroethylene resin (PTFE) on the glass fiber cloth base. The chemical property of this membrane material is extremely stable. The open-air service life is more than 25 years. It is a non-combustible material (passed A-level fire test) .

(2) The B-type membrane material is a silicone coating on the glass fiber cloth base. Due to the poor performance of the membrane material, it is basically no longer used.

(3) Type C membrane material is coated with polyvinyl chloride resin (PVC) on polyester filament cloth base. This membrane material is greatly affected by natural conditions such as sunlight and rain, and the general service life is 10 to 15 years , Is a flame retardant material.

2. Classification of membrane materials

As the fifth-generation building structural material after wood, masonry, metal, and concrete, the membrane has remarkable characteristics. The first-generation wood and the third-generation steel have good tensile and compression properties, the second-generation masonry and the fourth-generation concrete only have the good compressive capacity, and the fifth-generation membrane material can only be tensioned, without compression and The ability to resist bending is the most essential feature of the film. Specifically, the main features of the membrane are as follows:

(1) Tensile properties

The tensile properties of the membrane include tensile strength (TensionnStrength), tensile modulus (Modulus of Elasticity), and Poisson's ratio (Poisson ‘station) three mechanical indicators. The membrane itself cannot be compressed or flexed but has high tensile strength, so to make the membrane structure work properly, it must introduce pre-tension and form a reciprocal curved surface. Usually the tensile strength of the membrane material can reach more than 100MPa.

(2) Tear strength

The membrane is a tensile structure material, and its tearing damage is much more serious than the tensile damage, so the tear strength and tear resistance are very important. The PVC-coated polyester filament fabric has medium tear strength, and the PTFE-coated glass fiber material has higher tear strength.

(3) Orthotropic

The curved surface of the tensile membrane structure needs the reverse curvature of the warp and weft directions to ensure that the curvature in one direction is concave downward and the other direction must be convex upward. The traditional membrane base material is woven by warp and weft yarns, so it exhibits strong orthotropic properties, and the warp and weft deformation ability differs by as much as 3-5 times.

(4) Creep and relaxation

Creep and relaxation is another important characteristic of the film, and it is also an important cause of film wrinkling and failure. This factor needs to be considered during cutting analysis and processing. Polyester filament fabrics lose 50% of the pretension in the first ten years of use due to creep. On the contrary, glass fiber fabrics are much more stable.

(5) Non-mechanical properties: safety properties, such as durability, fire performance, lightning protection performance, etc.; non-safety properties, such as sound insulation or sound performance, self-cleaning performance, etc.

3. Load analysis of Membrane construction design

The load analysis of the membrane structure is based on the shape and initial stress distribution obtained from the shape analysis, and the process of checking whether the strength and stiffness of the structure under various load combinations meets the predetermined requirements.

There are different theoretical methods to find the shape of the membrane structure, but the load analysis basically uses a nonlinear finite element method, that is, the structure is discretized into elements and nodes. The elements are connected to the elements through the nodes, and the external load acts on the nodes. Establish the equilibrium equation of the node and obtain the solution.

Since the cable-membrane structure is a large deformation problem, when deducing the finite element equation, the influence of the higher-order displacement term on the strain must be considered, that is, geometric nonlinearity. Of course, the membrane itself is also nonlinear, and in engineering applications, the nonlinearity of the material is generally not considered.

1. Wind load

The two distinguishing characteristics of the membrane structure from the traditional structure are lightness and flexibility. Light means that the structure's own weight and inertial force are small, its own weight is not the main load, the seismic force is negligible, and the wind is the main load; soft means that the structure has no bending stiffness, and the structure's resistance to external loads is achieved by changing the shape, Showing geometrically nonlinear characteristics. The characteristics of the membrane structure determine that the membrane structure is a wind-sensitive structure, and the wind resistance design plays a major role in the membrane structure design.

The obvious characteristics of the membrane structure are light, soft, and floating, which determines that the wind resistance calculation of the membrane structure also has its own characteristics.

2. Film wrinkle problem

The structural wrinkle refers to the wrinkling phenomenon that the membrane surface yields due to the compressive stress of the membrane surface in one direction, and the structural relaxation refers to the membrane surface presenting a tension-free state in both directions, so the relaxed membrane surface cannot Bear any load.

4. Cutting analysis of membrane structure

As mentioned above, the analysis of the membrane structure includes three major aspects, namely shape determination, load analysis and cutting analysis. Clipping analysis is to convert the space curved surface obtained by shape finding and verified by load analysis into an unstressed flat blanking diagram.