Membrane structures are a perfect combination of architecture and structure. They use high-strength flexible film materials combined with a supporting system to form a stable curved surface with a certain degree of rigidity that can withstand external loads. This spatial structural form has the advantages of free and light design, flame retardancy, easy production, fast installation, energy saving, and safety, making it widely used around the world. This type of structure is especially suitable for large sports venues, entrance corridors, small features, public leisure and entertainment squares, exhibition halls, shopping centers, and other fields.
### 1. Classification of Membrane Structures
From a structural perspective, membrane structures can be roughly divided into three forms: frame-supported, tensioned, and pneumatic membrane structures.
#### **1. Frame-Supported Membrane Structure (Frame Supported Structure)**
This involves constructing a roof skeleton using steel or integrated materials, then stretching the membrane material on top. The lower support structure is highly stable, with relatively simple roof shapes and unrestricted openings, as well as high economic benefits. It is widely applicable to spaces of any size, from small to large.
#### **2. Tensioned Membrane Structure (Tension Suspension Structure)**
This consists of membrane material, steel cables, and pillars, where tension is introduced into the membrane through steel cables and pillars to achieve stability. Besides enabling creative, innovative, and aesthetically pleasing designs, this is also the most representative form showcasing the essence of membrane structures. In recent years, large-span spaces have increasingly adopted the method of supporting the upper membrane with a steel cable network composed of steel cables and compressive materials. Due to its high construction precision requirements, strong structural performance, and rich expressiveness, the cost is slightly higher than that of the frame-supported membrane structure.
#### **3. Pneumatic Membrane Structure (Pneumatic Structure)**
The pneumatic membrane structure fixes the membrane material around the perimeter of the roof structure and uses a ventilation system to increase the indoor air pressure to a certain level, creating a pressure difference between the inside and outside of the roof to resist external forces. By utilizing air pressure for support and steel cables as auxiliary materials, no beams or columns are required, allowing for larger interior spaces and faster construction with high economic benefits. However, it requires continuous operation of the blower 24 hours a day, which increases the operational and maintenance costs.
### 2. Membrane Materials
The membrane material used in membrane structures is a thin film material with strength and good flexibility. It is made by weaving fibers into a fabric substrate, and then coating both sides of the substrate with resin. The central fabric substrate is divided into polyester fiber and glass fiber, while the resins used as coatings include polyvinyl chloride resin (PVC), silicone (silicon), and polytetrafluoroethylene resin (PTFE). In terms of mechanics, the fabric substrate and coating material respectively influence the following functional properties:
- Fabric Substrate: Tensile strength, tear strength, heat resistance, durability, fire resistance.
- Coating Material: Weather resistance, anti-pollution, processability, water resistance, light transmission, membrane structure installation.
### 3. Correct Selection of Membrane Materials
For membrane structures, membrane materials can generally be divided into PVC membranes and PTFE membranes based on the type of coating material. The correct selection should consider factors such as the scale, purpose, form, service life, and budget of the building comprehensively.
#### **PVC Membrane (PVC-Coated Polyester)**
PVC membrane materials are cheaper in both material and processing compared to PTFE membranes, and they have the advantage of being soft and easy to construct. However, they perform worse in terms of strength, durability, and fire resistance compared to PTFE membranes. PVC membranes are made by adding a PVC coating (polyvinyl chloride) to polyester fiber fabric. For general architectural membranes, an acrylic resin layer several microns thick is applied to the surface of the PVC coating to improve anti-pollution properties. However, after several years, discoloration, dirt accumulation, and degradation may occur. The typical service life of a PVC membrane is 5-8 years depending on the usage environment. To improve the weather resistance of PVC membranes, fluorine-based resins have been recently developed as coatings on the surface of PVC membranes to enhance their weather resistance and anti-pollution properties.
#### **PVDF Membrane**
PVDF stands for polyvinylidene fluoride. When PVDF resin is coated on the surface of a PVC membrane, the material is called a PVDF membrane. Compared to regular PVC membranes, the service life of PVDF membranes improves to approximately 7-10 years.
#### **PVF Membrane**
PVF is short for polyvinyl fluoride. PVF membranes involve applying a thin PVF resin film (laminate) on the surface of PVC membranes. This results in better durability and anti-soiling properties compared to PVDF membranes. However, due to poor processability, constructability, and fire resistance, its application scope is limited.
#### **PTFE Membrane (PTFE Coated Fiberglass)**
PTFE membranes are materials made by coating ultra-fine glass fiber fabrics with polytetrafluoroethylene resin. The most prominent feature of PTFE membranes is their excellent durability, fire resistance, and anti-pollution properties. Compared to PVC membranes, PTFE membranes are more expensive in terms of material and processing costs, and they are less flexible. During construction, specialized tools and techniques are required to prevent the glass fibers from breaking.
- **Durability**: The PTFE coating is very stable against acids, alkalis, and ultraviolet rays, resisting discoloration and cracking. Glass fibers do not experience strength degradation or tension reduction even after long-term use. The color of the membrane material is usually white, with high light transmittance and a service life exceeding 25 years.
- **Anti-Pollution**: Due to the low friction coefficient of the PTFE coating, it is not easily polluted and can be cleaned by rainwater.
- **Fire Resistance**: PTFE membranes meet the fire-resistant material test standards of nearly all countries and can be used as an alternative to other roofing materials for similar purposes.
### 4. Engineering Applications
- **Sports Facilities**: Sports arenas, fitness centers, etc.
- **Transportation Facilities**: Airports, train stations, bus stops, highway toll booths, gas stations, etc.
- **Cultural Facilities**: Exhibition/conference centers, theaters, museums, zoos, aquariums, etc.
- **Scenic Facilities**: Building entrances, swimming pool features, community corridors, outdoor plazas, parks, sculptures, landmark buildings, etc.
- **Commercial Facilities**: Shopping malls, restaurants, pedestrian streets, etc.
- **Industrial Facilities**: Factories, warehouses, sewage treatment centers, logistics centers, greenhouses, etc.