Glass curtain wall is a new type of wall. It originates from the idea of free facade of modern architecture theory. After World War II, it has been widely used in public buildings. Glass curtain wall applies large area of glass to the building facade to illustrate the modern style and make the building appear unique. Glass curtain wall is a novel and beautiful wall decoration, and is also a distinctive feature of modern high-rise buildings. Most people who have been to New York will be amazed by the prosperous face of the metropolis, the magnificent skyscrapers and glass curtain wall, blue sky and floating white clouds to add a more brilliant color. 1983, the glass curtain wall was first applied to the Great Wall construction project in Beijing, China.

1.1 Definition and development

Glass curtain wall refers to the support structure system and glass composed of a certain displacement capacity of the external enclosure or decorative structure, does not share the main structure of the force. Single and double-layer glass curtain wall can be selected.
Glass curtain wall originated from the idea of free facade in modern architectural theory. After World War I, due to the requirements of large-scale reconstruction, architects began to promote standard and industrial buildings. Large continuous horizontal windows replaced the thick facades and various narrow windows of traditional buildings. Facades were no longer constrained by traditional design, and exterior views were introduced into the interior with unprecedented visibility.
It was not until the end of World War L that glass curtain walls were commonly used in large office buildings. The architects represented by Mies van der Rohe advocated simple, standard, industrialized design. They created a number of public buildings with glass curtain walls, such as the Seagram Building, using a minimalist architectural vocabulary, new steel structures and glass, exquisite and reasonable connection design and precise industrialized standard components. By the beginning of the 21st century, China’s glass curtain wall area exceeded 2 billion square meters, close to 85% of the total glass curtain wall area in the world, and China has become the largest producer and user of glass curtain walls.

1.2 Advantages and shortcomings of glass curtain wall

Curtain wall has many advantages such as light and beautiful, not easy to be polluted, energy saving, etc.

Generally speaking, the weight of curtain wall is about 50kg/m², which is 1/12-1/10 of brick wall and 1/7 of precast concrete slab wall, which is conducive to reduce the self-weight of high-rise buildings, both Reduce the cost of the foundation and the main structure, but also to improve the reliability and safety of the main structure.

Glass has a unique feature – transparent. Glass can transmit natural light and provide sufficient lighting for the interior, thus reducing the need for artificial lighting during the day and achieving energy saving. Heat-absorbing glass can reduce solar radiation by 20-30% for the interior, while also acting as a heat insulator.

However, glass curtain walls also have some shortcomings.

· First, the large amount of glass used, especially coated glass, can produce glare in the sunlight, affecting pedestrians, drivers and residents and causing serious light pollution.
· Secondly, if not regularly inspected and replaced in time, the hidden dangers of glass curtain walls will increase.
· Finally, curtain walls have limited sound insulation capacity. In curtain wall design, sometimes single-layer tempered glass with thickness of 8mm, 10mm or 12mm is used, which cannot achieve the desired sound insulation effect. However, insulating glass, especially vacuum glass which is commonly used nowadays, can greatly reduce noise and is helpful for energy saving and environmental protection.

Of course, with the development of society and the progress of science, these shortcomings are gradually overcome. Glass curtain wall has a broad development prospect in the construction industry.

1.3 Bare frame glass curtain wall classification and composition

Exposed frame (Bright- frame) glass curtain wall is the exposed metal frame components of the glass curtain wall. The frame is made of aluminum alloy with special cross-section and has a groove for the glass panel to embed. Generally, LD31 aluminum alloy extruded profiles, extruded at high temperature, quick cooling, oxidation treatment (RCS form) molding, for curtain walls.
Bare frame glass curtain wall is the most commonly used curtain wall with stable and reliable performance, which is easy to accept and install because it is derived from glass windows.
In open-frame glass curtain wall systems, not only glass but also aluminum alloys transfer heat between the exterior and interior. In the curtain wall unit, the area of the glass is much larger than the frame, so the thermal performance of the glass plays a dominant role in the open frame curtain wall.

Hidden frame glass curtain wall

Hidden frame glass curtain wall, as the name implies, the metal frame is hidden behind the glass and cannot be seen from the outside. This glass curtain wall can be divided into two kinds of glass curtain walls: full hidden frame glass curtain wall and semi-hidden frame glass curtain wall, the latter of which can be horizontal or vertical hidden frame half frame.

Hidden frame glass curtain wall is characterized by: the glass is bonded with silicone structural sealant on the outside of the aluminum frame, which bears most of the load of the curtain wall.

Point-supported glass curtain wall

Point-supported glass curtain wall is a fixed device through the metal claw structure, combined with the brushed curtain wall to achieve a completely transparent and simple appearance. There are three types of this curtain wall support steel claws: secondary glass type, metal structure type and cable structure type.

Unit glass curtain wall

Unit glass curtain wall is a glass panel and metal frame (beam, column) in the factory assembly, on-site installation of the frame support curtain wall.

The advantages of unit glass curtain wall is easy to install and shorten the construction period. Disadvantages are inconvenient transportation and recovery, high requirements for lifting process during installation, to avoid damage.

All-glass curtain wall

All-glass curtain wall is composed of glass ribs and glass panels. With the development of glass production technology and the diversification of glass products, this type of curtain wall allows architects to create unique, transparent and sparkling buildings. All-glass curtain walls can be divided into three types: floor-to-ceiling (glass supported by a subframe), suspended (suspended by a suspension device) and back-supported (glass ribs supporting glass panels behind).
The all-glass curtain wall is commonly used in the lower two floors of public buildings. It can have a fairly large split size with few gaps in the vertical and horizontal directions. The overall appearance is smooth and transparent.

1.4 Glass curtain wall design in architecture

Glass curtain wall design should echo with the overall style of the building, and choose the appropriate curtain wall system, glass type and façade division method.

Selection of glass curtain wall system

Curtain wall system can influence the function and style of the building. For example, exposed curtain wall improves the texture of the building; hidden frame curtain wall appears smooth and simple; point-supported curtain wall enhances the transparency; unit curtain wall highlights the integrity; all-glass curtain wall strengthens the connection between interior and exterior. Architects can choose different types of curtain walls according to specific building parts and combine them with other materials.

The division of glass curtain wall and color

The division of the curtain wall should consider the style of the building and the specifications of the glass panels. In addition, the division of height should also correspond to the structural beams, ceiling height and the fire partition between the layers. The setting of movable windows should consider the human scale or install mechanical control devices.
The glass used in the early days was mainly transparent. With the emergence of various new glass products, color has become an important means of decoration. In the glass curtain wall, color can be increased by the following methods. Using colored glass: add color in glass production, with relatively few choices; add colored film on the back of a single piece of glass: simple and practical, with a variety of choices; add a variety of printed colors and patterns through colored glazes: this method can achieve a variety of effects; choose transparent glass, with colored roller blinds or blinds: this is the most commonly used.