The Evolution of Curtain Wall Systems in Architecture
19/06/2025 No Comments
The Evolution of Curtain Wall Systems in Architecture Introduction The curtain wall is not only a carrier of the building’s appearance, but also the crystallization
Prefabricated Construction Techniques for Stick Curtain Walls
Prefabrication is an clear trend in the development of the curtain wall industry. However, due to the cost-effectiveness of stick curtain walls, they still hold a prominent share of the market. These two characters have brought about a new approach: making traditional stick curtain walls into prefabricated systems. In this way, it can retain the economic advantages of stick systems while also incorporating the stable quality and high installation efficiency typical of unitized curtain walls. In this article, let’s explore a new construction concept for prefabricated stick curtain walls from the perspectives of design, fabrication, and installation methods.
In recent years, industrialized construction has emerged as a new development direction for the building industry. China’s Ministry of Housing and Urban-Rural Development (MOHURD), has emphasized the importance on promoting prefabricated buildings in its 14th Five-Year Plan for the construction sector. As a result, the market share of unitized curtain wall systems has become bigger and bigger.
But for the buildings around 100 meters high, the benefits of unitized curtain walls are not so prominent. This is mainly due to the relatively low utilization rate of lifting equipment and the high cost of related construction measures. And all of these make the stick curtain walls still enjoy a stable market presence. However, issues related to installation quality and efficiency in stick systems still remain. And these issues also have posed growing concerns for developers, especially amid the significant downturn facing the construction industry.
At the time, the idea of “unitizing stick curtain walls” has gained more and more attention. At the very beginning, this concept was developed just to solve the difficulties in installing intricate components like stone trim or shaped aluminum panels. But over time, it became clear that unitization of stick curtain walls not only improved structural aspects but also had far-reaching implications for production and construction management. Then, new construction methods have emerged.
The principle of “unitization of stick curtain wall” is very simple, that is, without changing the basic structure of the curtain wall system, individual components are assembled into modular units on the ground through precise positioning and constraints, and then installed as a whole. Under the guidance of this idea, various special components such as lines and shapes can be easily “unitized”, such as aluminum cornices and formed panels.
After the successful unitization of stick curtain wall, the vision began to expand to its fabrication processes and installation methods. Then this technology was systematically organized, and the ideas of stick curtain wall prefabrication were initially formed:
☛ Through unit division, meet the requirements of on-site assembly and hoisting.
☛ By solving the positioning and constraints of the components of the stickcurtain wall before installation, the assembly quality meets the installation requirements.
☛ By taking auxiliary measures, ensure that the assembled units can maintain shape and position accuracy and withstand installation loads during the hoisting and installation process.
☛ By adopting the “segment construction” method, reduce the requirements for construction facilities and other conditions.
“Division of curtain wall units” mainly refers to the division of curtain wall units in an appropriate way to meet the requirements of on-site unit assembly and hoisting. In terms of the principle of unit division, the following methods are generally used:
This type of curtain wall is usually regularly distributed with decorative lines or modeling elements. It can be simply divided by lines or modeling elements with the entire curtain wall divided into appropriate units. In this approach, since these decorative elements are relatively independent from the main curtain wall system, the unitization work is relatively simple. Generally speaking, line units and curtain wall units can maintain their own construction methods and form independent units by themselves. The focus is on solving the design problem of integrated supports. It is to ensure that the two different unit panels can maintain accurate spatial positions and can be easily connected during installation.
This type of application scenario is mainly aimed at complex modeling elements on the curtain wall, solving the problems of complex on-site assembly and difficult construction. In the specific construction, the most difficult processes on the facade will be carried out on the ground, while taking into account the on-site hoisting conditions. Then a complex shape will be decomposed into several assembleable units. The focus of this type of unitized transformation is to decompose the scale of the unit and reduce the number of splicing times as much as possible within the permitted range.
This method is typically applied to conventional curtain walls with relatively fragmented grids and a large workload on site. This type of curtain wall can be very flexible in the unit division and can adopt a “continuous unitization” approach. That is, all panels are grouped into their respective units. But this method often requires special treatment at the joints between units, like using “semi-unit auxiliary frame structures” or interlocking mullion systems similar to those used in unitized curtain walls. Another approach is “intermittent unitization”. In this case, some panels are deliberately excluded from unit formation, and the associated horizontal mullions are also left out. After the adjacent units have been hoisted and installed, the horizontal mullions and panels in the skipped sections are then added on site.
The so-called “semi-unit auxiliary frame structure” is actually to use the “auxiliary frame unit” to solve the empty space between two adjacent main units. A grid is left between the two main units. After the main unit is installed in place, the “auxiliary frame unit” is fixed onto the mullions of the neighboring main units. Since the auxiliary frame unit is only responsible for integrating the panel materials together, it is light and easy to install. When it is fixed to the two main units, the main unit’ mullions can be used for structural support. This approach is very suitable for curtain wall structures where the window sashes are flush with the columns. And its unitized transformation can be easily achieved. In addition, it is also widely used in curtain wall and ceiling systems that are hoisted in pieces.
Generally, it is not recommended to imitate the method of interlocking vertical-horizontal mullion that is usually used in unitized curtain walls. This is mainly because this approach will cause a higher material cost. And once an interlocking structure is adopted, it reduces the flexibility of installing panels in any order, which can negatively impact construction scheduling and organization. However, the interlocking approach has a large degree of freedom for unit division and is a simple and easy unitized transformation solution. Both this method and the semi-unit auxiliary frame approach have their own advantages and disadvantages. The choice is mainly depended on the specific requirements and conditions of the project.
The first problem prefabrication of stick curtain walls faces is the processing and assembly. Since the assembly unit is completed in the factory or on the ground, there is an opportunity to use various auxiliary positioning fixtures to improve the assembly accuracy and efficiency. Especially for more complex shapes, special molds can be used to accurately position the mullions and panel at one time. And that can greatly improve the assembly accuracy and efficiency.
When it comes to the situation where there are multiple connection points between the unit body and the main structure with some of the connection points concealed by the plate, it is necessary to set up auxiliary positioning and guiding structures. These measures can ensure that the concealed connection points can be properly aligned and connected to the main structure during hoisting. It is the key to whether the curtain wall unit plate with multiple grids can be hoisted smoothly.
Another issue that needs attention is that, unlike the conventional unitized curtain wall, the horizontal mullions in stick systems generally have smaller cross-sections, resulting in low overall in-plane stiffness after frame assembly. If the cross-sectional size is not increased, local reinforcement is usually required. Generally, the in-plane stiffness of the unit is improved by setting supports in non-visible areas. In addition, the lifting plan must take into account the influence of factors such as construction sequence, force mode and force location, and perform simulation calculations, and use appropriate lifting points and lifting equipment to avoid deformation of the unit during lifting.
The conventional unitized curtain wall panels are interlocking structures both horizontally and vertically. Therefore, the unit panels must be installed in sequence. After each floor’s unit installed in sequence and water-tightness tests completed, the unit panels of the next floor can be installed.
However, for the curtain wall system that has undergone unitization, since its waterproofing principle is different from that of the unitized curtain wall, it does not need to be strictly constructed in sequence. As a result, installation does not need to follow a strict sequence and construction can be carried out at multiple points at the same time. This is very helpful to increase the construction speed.
Based on this feature, the most suitable method is “section construction”. This method is based on the principle of flow operation: a construction section is divided into several workflow segments horizontally. During installation, the panels in each segment are hoisted from bottom to top before the next segment is operated. The segment that has completed the hoisting operation can start the glue sealing on the outdoor side and the fire blocking on the indoor side. In this way, the hoisting, glue application, and fire blocking operations can form a flow. And so there will be no obstruction due to the cross construction in the vertical direction.
There are many benefits to doing this:
The prefabricated construction technology of stick curtain walls is an innovative practice to seek a balance between the current trend of building industrialization and market reality. It not only continues the advantages of low cost and wide application of stick curtain wall, but also significantly improves the construction quality and efficiency through the unitization idea, assembly process and section construction method. With the gradual improvement of relevant technical systems, this “transitional” curtain wall system between stick type and unitized type is expected to be applied in more projects and bring profound changes to the traditional curtain wall construction method. In the future, how to further optimize between standardization and flexibility will be a key issue in the development of prefabrication of stick curtain walls.
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