What is a glass curtain wall? The secret of its popularity?

1. What is a glass curtain wall?

1. Classification of glass curtain wall frame systems

The exposed frame glass curtain wall is the most traditional form, with the metal frame completely exposed on the outside of the glass, forming a distinct grid-like appearance. This structure is stable and reliable, easy to install and maintain, and is widely used in various types of buildings. The hidden frame glass curtain wall uses a special structure to hide the metal frame inside the glass or at the joints. From the outside, it is almost all glass, and the visual effect is more concise and unified. The semi-hidden frame glass curtain wall combines the characteristics of both. Usually, one side of the frame is hidden horizontally or vertically, and the other side is exposed, achieving a balance between structural safety and aesthetic effects.

2. Classification by construction method

Unitized glass curtain wall is the mainstream choice for high-rise buildings today. It prefabricates the entire curtain wall unit (including frame, glass, sealing materials, etc.) in the factory, and then transports it to the site for direct hoisting. This construction method is quality-controlled and efficient, but it requires extremely high precision in production and installation. The component-type glass curtain wall is to transport each component to the site and then gradually assemble it. It has strong adaptability and is suitable for buildings with complex shapes, but the construction period is long. The point-supported glass curtain wall directly fixes the four corners of the glass through metal connectors, eliminates the traditional frame, and achieves maximum transparency. It is commonly seen in the atriums and canopies of large public buildings.

2. Material composition and technical points of glass curtain walls

1. Glass materials

Glass panels are the core materials of curtain wall systems. Ordinary float glass is processed into a variety of functional products. Tempered glass is 4-5 times stronger through heat treatment. After breaking, it is small particles without sharp edges and corners, which is highly safe. Laminated glass adds PVB film between two pieces of glass, so that even if it breaks, the fragments will not fly away, and it has explosion-proof and anti-theft characteristics. Hollow glass consists of two or more pieces of glass to form a sealed space, which is filled with dry air or inert gas to significantly improve the heat insulation and sound insulation performance. The surface of coated glass is covered with metal or metal oxide film, which can be divided into different types such as heat-reflective glass and low-emissivity glass (Low-E), which effectively regulates solar radiation heat.

2. Metal frame

Aluminum alloy is the main material for curtain wall frames due to its light weight, corrosion resistance and easy processing. The surface is treated by anodizing, powder coating or fluorocarbon spraying. Steel structure curtain walls are protected by hot-dip galvanizing or anti-corrosion coatings, which are suitable for large spans. Stainless steel components are mostly used in highly corrosive environments or high-demand connection parts. Modern curtain wall systems also use metal materials such as titanium zinc plates and copper plates as decorative elements to enhance the texture of the building.

3. Sealing and connection system

Silicone structural sealant is a key material to ensure the water tightness and air tightness of the curtain wall. It must have excellent weather resistance, anti-aging performance and bonding strength. Ethylene propylene diene monomer (EPDM) rubber strips are used for joint sealing and have good elasticity and durability. The connection between the curtain wall and the main body of the building usually adopts a special support that can be adjusted in three dimensions, allowing structural deformation and facilitating installation and correction. The lightning protection system incorporates the curtain wall metal frame into the overall lightning protection network of the building through the grounding conductor to ensure safety.

3. Design principles and engineering considerations of glass curtain walls

1. Structural safety design

The design of curtain walls needs to consider multiple factors such as wind load, earthquake action, and temperature deformation. In high-rise buildings, wind pressure is the main control load, and it is particularly important in coastal typhoon areas. Structural calculations include glass strength verification, frame deflection verification, and connector bearing capacity analysis. Earthquake-resistant design follows the principle of “small earthquakes are not damaged, medium earthquakes can be repaired, and large earthquakes do not collapse”, and absorbs earthquake energy through flexible connections. Thermal stress calculations consider the temperature deformation difference between glass and metal frames to avoid cracking due to stress concentration.

2. Physical performance optimization

Modern curtain walls pursue excellent thermal performance, and reduce the U value to below 1.0W/(㎡·K) through low-emissivity coating, warm edge spacers, argon filling and other technologies. Sound insulation design uses unequal thickness glass combinations or special sandwich structures to effectively block traffic noise. Lighting design needs to balance the introduction of natural light and glare control, and use light simulation software to optimize glass selection and grid size. Anti-condensation analysis ensures that the indoor surface temperature is not lower than the dew point in extreme climates to avoid condensation.

3. Integration of aesthetics and function

The design of curtain wall grids must take into account the building facade effect and material economy. Common modular design improves processing efficiency. Color matching considers the coordination and unification of glass reflectivity, transmittance and frame color. Special-shaped curtain walls such as curved, tilted, twisted and other forms require BIM technology to assist in design and prefabrication. Functional requirements such as identification systems and lighting effects should be considered in the curtain wall design to avoid destructive modifications in the later stage.

V. Construction technology and quality control of glass curtain walls

1. Construction preparation stage

Before the curtain wall construction, special design review and construction plan demonstration must be completed, focusing on the interface issues between structure and architecture. High-precision instruments such as total stations are used for measurement and layout to establish a three-dimensional control network. The installation of embedded parts is carried out simultaneously with the construction of the main structure, and the position deviation must be controlled within the allowable range. Strict acceptance of materials entering the site, and 100% appearance inspection of glass is required.

2. Installation and construction process

Unit curtain wall installation usually adopts track hoisting system, which is carried out from bottom to top, first in the middle and then on both sides. After each unit is installed, preliminary adjustment is made immediately to ensure uniform joints. The component curtain wall first installs the main keel, and then installs the secondary keel and glass panel after multiple leveling. Point-supported curtain walls need to pay special attention to the positioning accuracy of the claws and the quality of glass drilling. Waterproof sealing treatment is carried out simultaneously during the construction process to prevent rainwater from seeping in.

3. Acceptance and maintenance

The acceptance of curtain wall projects includes material re-inspection, node concealment acceptance, and four-property testing (airtightness, watertightness, wind pressure resistance, and plane deformation). After completion, a detailed use and maintenance manual should be provided to guide daily cleaning and regular inspections. Common maintenance items include sealant aging inspection, hardware lubrication, and drainage hole dredging. High-rise curtain wall cleaning requires professional team operation, equipped with window cleaning machines and safety protection equipment.

As an important feature of modern architecture, glass curtain walls have evolved from simple enclosure structures to intelligent building surfaces that integrate functionality, aesthetics, and ecology. With the advancement of material science and digital technology, glass curtain walls will become more intelligent, personalized, and ecological in the future, adding more artistic charm to urban landscapes while ensuring building performance. Only by correctly understanding the advantages and disadvantages of glass curtain walls, scientifically designing, carefully constructing, and standardizing maintenance can their value be fully utilized to create a beautiful and sustainable building environment.