What are the advantages and disadvantages of glass curtain walls?

1、 About Glass Curtain Wall

The glass curtain wall in modern architecture adopts a combination of mirrored glass and ordinary glass, with insulated glass filled with dry air or inert gas in the partition. Hollow glass can be divided into two layers and three layers. Two layers of hollow glass are composed of two layers of glass and a sealed frame, forming a sandwich space; Three layer glass is composed of three layers of glass to form two interlayer spaces. Hollow glass has the advantages of sound insulation, heat insulation, frost prevention, moisture resistance, increased lighting, and high wind pressure resistance. However, there are also issues such as light pollution and high energy consumption.

1. Advantages and disadvantages analysis

(1) Advantages

Glass curtain wall is a new type of wall in contemporary times, which endows buildings with the greatest feature of organically unifying factors such as architectural aesthetics, building functions, building energy efficiency, and building structure. Buildings present different color tones from different angles, giving people dynamic beauty with changes in sunlight, moonlight, and lighting.

Reflective insulating glass with a thickness of 6mm and a wall weight of approximately 50kg/㎡ has the advantages of being lightweight, aesthetically pleasing, less prone to pollution, and energy-efficient. Adding trace metal elements to the composition of float glass and tempering it to make color transparent plate-shaped glass can absorb infrared radiation, reduce solar radiation entering the room, and lower indoor temperature. It can reflect light like a mirror and pass through light like glass. The inner side of the outer glass of the curtain wall is coated with colored metal coating. From the appearance, the entire exterior wall looks like a mirror. Under the reflection of light, the interior is not exposed to strong light, and the vision is soft.

(2) Disadvantages

Glass curtain walls also have some limitations, such as light pollution and high energy consumption. Coated glass or coated glass is used on the curtain wall of the building. When direct sunlight and sky light shine on the surface of the glass, glare is generated due to the mirror reflection (i.e., normal reflection) of the glass. But with the development of glass curtain wall technology and the continuous emergence of new material technology, the materials used in glass curtain walls in buildings can now effectively solve the problems of light pollution and energy consumption.

2、 Basic classification

1. Clear frame glass curtain wall

Clear frame glass curtain wall is a glass curtain wall with metal frame components exposed on the outer surface. It is framed with aluminum alloy profiles with special cross-sections, and the glass panels are fully embedded in the grooves of the profiles. Its characteristic is that the aluminum alloy profile itself has a dual function of skeleton structure and fixing glass. Clear frame glass curtain wall is the most traditional form, widely used, and reliable in terms of performance. Compared to hidden frame glass curtain walls, it is easier to meet the requirements of construction technology level.

2. Hidden frame glass curtain wall

The metal frame of the hidden frame glass curtain wall is concealed on the back of the glass and cannot be seen outdoors. Hidden frame glass curtain walls can be divided into two types: fully hidden frame glass curtain walls and semi hidden frame glass curtain walls. Semi hidden frame glass curtain walls can be horizontally visible and vertically hidden, or vertically visible and horizontally hidden. The structural feature of the hidden frame glass curtain wall is that the glass is placed on the outside of the aluminum frame and bonded to the aluminum frame with silicone structural sealant. The load on the curtain wall is mainly borne by the sealant.

3. Point type glass curtain wall (metal supported structure point type glass curtain wall)

Point type glass curtain wall is a glass curtain wall composed of glass panels, point support devices, and support structures. The point type glass curtain wall has the stability of steel structure, the lightness of glass, and the precision of machinery.

The glass of a point type glass curtain wall is reliably fixed by stainless steel claws passing through pre drilled holes on the glass. Generally, glass curtain walls are bonded and fixed to the frame with structural adhesive. After punching holes in the corners of the glass, it is connected to the supporting structure of the full glass curtain wall with metal connectors. However, general glass curtain walls are mostly flat frame and vertical rod load-bearing systems. Compared to general glass curtain walls, point type glass curtain walls have a load-bearing system that is not in the frame, but in the supporting system.

The glass panels on the point type glass curtain wall are only connected to the supporting structure through a few points, almost unobstructed, and the field of view is maximized. The transparency of the glass is applied to the extreme. Therefore, when using glass, white glass, ultra white glass, and low radiation glass that do not cause light pollution are often chosen, especially when using insulated glass, which has a more obvious energy-saving effect. But this type of glass curtain wall has no opening fan.

3、 Technical requirements

1. Sealing material

Weather resistant silicone adhesive is used to seal between glass and metal structures, and structural silicone adhesive is used to bond between glass and metal structures. In the construction point glass technology, sealant only plays a sealing role and does not require strength calculation. Before use, a compatibility test must be conducted between the adhesive and the contact material, and the performance test must be qualified. The adhesive must be used within its validity period, and the operating procedures must be strictly followed to ensure construction quality.

2. Glass

Glass curtain walls should use curtain wall glass with a reflectivity of no more than 0.30. For glass curtain walls with lighting requirements, the lighting reduction factor should not be lower than 0.20. The frame supported glass curtain wall should use safety glass (laminated glass, tempered glass, laminated glass, etc.); The panel glass of the point supported glass curtain wall should be made of tempered glass.

3. Metal

The surface of steel should undergo anti-corrosion treatment. When hot-dip galvanizing is used, the film thickness should be greater than 45 μ m; When using electrostatic spraying, the film thickness should be greater than 40 μ m. Insulation measures should be taken between different metal materials to prevent electrochemical corrosion between heterogeneous metals.

4、 Problems that glass curtain walls are prone to

1. Poor fire prevention capability

Glass curtain walls are non combustible materials, but they can melt or soften in the face of intense fire. Glass breakage can occur in a short period of time during a fire, so the fire protection requirements of the building should be fully considered in architectural design.

2. Structural adhesive failure

Due to long-term adverse factors of the natural environment, the structural adhesive of the curtain wall is prone to aging and failure, causing the glass curtain wall to fall. So in the design, it is advisable to use visible or semi hidden frame glass curtain walls as much as possible, because even if the structural adhesive fails, the probability of glass falling will be greatly reduced due to the support and constraints of the frame.

3. Glass breakage caused by thermal stress

Glass will expand when heated, and if heated unevenly, tensile stress will be generated inside the glass. When there are small cracks at the edges of the glass, these small defects are easily affected by thermal stress, ultimately leading to glass damage. Therefore, when installing glass, the edges of the glass should be finely processed to reduce the occurrence of cracks.

4. Water seepage

There are many reasons for water seepage in glass curtain walls, but the main one is related to the construction and sealing materials. Therefore, it is necessary to choose a construction party with excellent technology and materials that meet national standards. To minimize water seepage to the greatest extent possible.