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Aluminum alloy doors and Windows, curtain walls since entering China, from the initial stage of surveying and mapping imitation to the subsequent rapid development and then to today is independent research and development has gone through more than 30 years. What is the curtain wall, what is the window? It seems like a simple question to industry insiders, and many do not think it should be a problem. In fact, through the experience of curtain wall technical consultation and curtain wall structural safety review in recent years, it has been found that quite a few people are not correct in the identification of curtain walls and Windows. This situation not only happens to young curtain wall designers, but even some old "curtain people" often confuse and misjudge curtain walls and Windows.

So, how to correctly determine whether a building perimeter protection system is a curtain wall or a window? To explain this problem, we must first understand the definition of curtain wall. Article 3.1 of "Building Curtain Wall" (GB/T21086-2007) defines: "Building curtain wall, composed of panel and supporting structure system (supporting device and supporting structure), can relative to the main structure has a certain displacement capacity or a certain deformation (the entry" deformation "is provided by the industry Wikipedia) ability, does not bear the role of the main structure of the building periphery wall." This definition is based on the English name Curtain Wall. From the meaning of the word, Curtain - Curtain, curtain, Wall - Wall, curtain wall - curtain wall. From the noun meaning, curtain wall is curtain wall. If it is a curtain, it is suspended and has a certain displacement ability with the main structure it is attached to. Therefore, the building curtain wall must be installed on the main structure through the hanging point. This is just like the winter in the north, we usually see large public places with thick cotton curtains hanging on the entrances and exits to protect them from the cold wind, with the upper end fixed and the lower end swinging freely. If the cotton curtain is fixed on the door, as the door opens, it is no longer a door curtain, and can only be called a thermal door (Figure 1). The difference between curtain walls and Windows is similar.

Figure 1

Now, we briefly analyze several common viewpoints according to the definition of curtain wall.

Viewpoint 1: The curtain wall is installed on the outside of the structure.

This statement can not be said to be wrong, because most of the curtain walls we usually see are installed on the outside of the main structure, but not all curtain walls are so. The location of the curtain wall installation is either outside the side beam or under the beam, which is determined according to the architectural design needs (Figure 2).

Figure 2

From the perspective of installation, the curtain wall is connected through the column and the main structure, and the window is fixed on the solid wall of the main structure by four borders or connecting pieces (fixed pieces) on the border, and is continuously connected through the gap between the window frame and the structure. Therefore, whether it is installed outside the main structure or under the structural beam, as long as it is connected to the main structure by hanging through the column, it is the curtain wall system (Figure 3). We often see that the window is also installed across the layers, because the installation method is fixed on the structure with the surrounding frame, there is no displacement ability relative to the main structure, so the window is not a curtain wall.

View 2: The curtain wall is suspended on the structure, and the window is supported in the structure.

Figure 3 Curtain wall installation connection

According to this statement, the window must be supported in the structure, and the curtain wall must be suspended on the structure. It is correct from the noun meaning of the curtain wall and the definition in GB20186, but this is only one of the ways of curtain wall installation. This point can be more clearly understood in the Shanghai "Building curtain wall engineering Technical Regulations" (DGJ08-56-2012), which defines the building curtain wall is "composed of a panel and supporting structure, relative to the main structure has a certain displacement capacity, in addition to the main structure to transfer its own load (the entry" load "provided by the industry encyclopedia). The external protection system of the building does not assume the role of the main structure." This statement is more clear, whether installed outside the structure or installed in the structure, the curtain wall relative to the main structure must have a certain displacement capacity; Article 5.5.3 of the "Technical Specifications for Glass Curtain Wall Engineering" (JGJ102-2003) states that "the column supporting the glass curtain wall should be suspended on the main structure", and does not mandate that it must be suspended, which is also based on this reason. Therefore, whether it is suspended or supported, the curtain wall does not withstand the role of the main structure, and under the premise of eccentric compression of the column without losing stability, it is still a curtain wall. The window frame is continuously fixed on the structure, and has no displacement ability relative to the main structure. Therefore, curtain wall and window can be distinguished from the connection mode.

From the point of view of force transmission ways, different connection ways determine the difference between the two force transmission ways. The self-weight and load of the curtain wall are transferred to the main structure through the way of panel → frame (cross frame - mullion)→ mullion → connecting parts → embedded parts through the anchor connector in a point way; The self-weight and load of the window are continuously transmitted to the main structure through the fixed pieces on the window frame. Simply and graphically, the force transfer of the curtain wall is a point, and the force transfer of the window is a line (Figure 4).

Figure 4 Installation of doors and Windows

Because the building vertical window is to be installed across layers, it is also to be installed on the outside of the structural beam, but the installation form is fixed on the structure with the surrounding border, and the force transmission mode is continuous. Therefore, it is necessary to determine whether the maintenance structure is a curtain wall, not to see the installation location, but to see how it is connected to the main structure.

View 3: The curtain wall profile (the entry "profile" is provided by the industry encyclopedia) is produced by the curtain wall.

This statement is only judging the curtain wall and window from the form, which is obviously inaccurate. In the 1980s, when the domestic curtain wall was still in its infancy, there was no more mature curtain wall system. Many curtain walls are made of aluminum square tubes and glass inserts, which we called "simple curtain wall" at that time. The reason why it is called simple curtain wall is that this structure does not have good air tightness (the entry "air tightness" is provided by the industry encyclopedia), watertight performance and thermal insulation performance, but as far as its installation is concerned, it is connected to the main structure through the way of "pillar - connector - embedded part". The load on the plate is transferred to the main structure in the form of points through the connection of the connector and the anchor plate. The system itself does not bear the role of the main structure, and has a certain displacement and deformation ability relative to the main structure, so even if it is simple, it belongs to the curtain wall system. On the contrary, in the case that some holes are large and ordinary window profiles cannot meet the load requirements and effect requirements, the use of curtain wall profiles is also a common method in actual projects. At this time, the installation method is to fix the system on the structure with the form of equal spacing connection of the window peripheral frame, and the system has no displacement ability relative to the main structure. From the connection method and force transfer form, it is a window and not a curtain wall (which is usually said in the industry curtain wall window).

View 4: The curtain wall is a continuous peripheral protection system suspended outside the main structure, while the window is a discontinuous peripheral protection system supported within the main structure.

The premise of this view has its acceptable aspects, but it is one-sided. The curtain wall should be suspended, but it is not necessarily hanging outside the structure, nor is it necessarily continuous; The window is supported in the structural opening, but it can also be continuous, which is what is called "row window" or "strip window" in our industry. Many building curtain walls are separated by structural columns, and each column is a curtain wall, similar to the separation of the window, although it is not a continuous large area, but it is still a curtain wall. Many buildings are designed with long corridors or open office Spaces, and the outer window is a row of Windows. One or several faces are combined into a continuous row of Windows by various forms of Windows such as open Windows and fixed Windows. It is continuous, but it is not a curtain wall.

View 5: The decorative frame (plate) installed on the outside of the solid wall is also a curtain wall.

One reason for this statement is that we lack a correct understanding of the terms and concepts of the curtain wall, and another reason is that the concept of the curtain wall is not strictly described in the relevant specifications.

As mentioned above, in the "building curtain wall" (GB/T20186-2007), the definition of the building curtain wall is "composed of the panel and the supporting structure system (supporting device and supporting structure), which can have a certain displacement capacity or a certain deformation capacity relative to the main structure, and does not bear the role of the main structure." In the "Glass curtain wall engineering Technical Specifications" (JGJ102-2003) description is "by the support structure system and panel composition, relative to the main structure has a certain displacement capacity or a certain deformation capacity, do not share the main structure by the role of the building envelope and decorative structure." The description of JGJ102 is more specific, it illustrates that the building curtain wall includes two structural forms: one is the curtain wall with thermal insulation, thermal insulation, waterproof (the entry "waterproof" provided by the industry encyclopedia), sound insulation and other functions, we temporarily call it a functional curtain wall; There is also a building itself has an envelope structure, just for the architectural effect of the need to design the curtain wall, such as aluminum curtain wall (the entry "aluminum curtain wall" provided by the industry encyclopedia), stone curtain wall, and other open structure of the curtain wall, all belong to the decorative curtain wall. However, this should also be differentiated according to the specific architectural design requirements, if the aluminum curtain wall or stone curtain wall inside there is no design solid envelope structure, and the curtain wall structure itself needs to have waterproof, thermal insulation, sound insulation and other functions, then such aluminum and stone curtain wall is also a functional curtain wall. However, in the "Technical Specifications for Metal and Stone curtain wall Engineering" (JGJ133-2001), the definition of building curtain wall is "composed of metal frames and plates, and does not bear the load and function of the main structure of the building periphery." For this definition may be misunderstood as, a building peripheral protection system, regardless of whether it has displacement capacity relative to the main structure, as long as it does not bear the load and effect of the main structure is the curtain wall. This causes the confusion of curtain wall and doors and Windows, and also leads to the status quo of mixing decorative components as curtain walls.

To sum up, judging whether a building external maintenance system is a curtain wall or a window should be determined from the meaning of its name and the connection between the system and the main structure. The building curtain wall should have the following conditions: 1) a system composed of frames and panels independent of the main structure; 2) Connect with the main structure through the column; 3) Does not bear the load and action of the main structure; 4) Relative to the main structure has a certain displacement ability. According to these four characteristics and combined with the noun meaning of the curtain wall, it should be defined as follows: The building curtain wall is composed of a panel and supporting structure, connected with the main structure through the column, relative to the main structure has a certain displacement capacity or a certain deformation capacity, in addition to transferring its own load to the main structure, does not bear the load and effect of the main structure of the building perimeter structure and decorative structure. It should be emphasized here that the curtain wall must be connected to the main structure through the column, which is the key to distinguish the curtain wall and the window.